Mundra Port to acquire biggest cutter suction dredger

Dec 25, 2011, 12:41PM EST

Mundra Port and Special Economic Zone Limited on a robust expansion of its dredging fleet

 Mundra Port and Special Economic Zone Limited (MPSEZ), India’s largest private port and special economic zone will acquire the biggest cutter suction dredger ever to be owned by any Indian company.  Under construction at the IHC Merwede shipyard in Sliedrecht, The Netherlands, the dredger was named Shanti Sagar XVI during its recent launch.

MPSEZ, which is part of the Adani Group, already has 13 dredgers in its fleet and has placed orders for three new building which includes Shanti Sagar. Two more dredgers are being built in India for MPSEZ. First being a water injection dredger and another self propelled hopper grab dredger. Both are scheduled to be delivered by the middle of next year.    

Giving details about the Shanti Sagar XVI being built at the IHC Merwede shipyard, Col. Vinod George, Head of Dredging Operations of MPSEZ informed that the dredger is a 13,000kW stationary cutter suction dredger and will be deployed for capital dredging at ports under MPSEZ.

“The dredger is under construction at the IHC Merwede shipyard,” Col. George said. “The contract for the design, construction and delivery of the vessel was signed in November 2010, and the keel was laid on 11 May 2011. The vessel will be delivered in the second quarter of 2012.”

The new cutter suction dredger is an IHC Beaver® 9029C, which is capable of dredging a wide range of materials. The vessel is equipped with three Cutter Special® dredge pumps, which are specially designed with a large sphere passage for cutter suction dredge operations. The anchor boom and spud-tilting installations allow the dredger to operate in remote areas with limited support equipment. The large fuel oil carrying capacity also allows for a high level of autonomy.”

“Dredging is critical to the development of Mundra Port and the work is managed by Mundra Port Special Economic Zone’s dredging fleet,” stated Bala K. Subramaniam, Director of Adani Shipping (India) Pvt. Ltd., and the Senior Advisor to Adani Shipping Singapore Ltd., the Adani Group and also the Mundra Port and Special Economic Zone Ltd., (MPSEZ) “In all we have 11 dredgers built at IHC Merwede shipyard and two from China. The SHANTI SAGAR XVI will be the largest vessel supplied by IHC Merwede to date.”

“At the moment our dredging activity has been concentrated exclusively for deepening and maintaining the draft at our own ports at Mundra and Hazira,” stated Col. George. “We have done some dredging for TATA’s but that has been incidental. We also have our other facilities at Dahej port, Goa, Vishakhapatnam and elsewhere. We have not undertaken any outside dredging contracts so far but in course of time we may consider taking up even international projects.”

Adani Group is a business behemoth based in India having a global footprint with interests in Infrastructure, Power, Global Trading, Logistics, Energy, Port & SEZ, Mining, Oil & Gas, Agri Business, FMCG products, Real Estate Development, Bunkering, et al. Founded in 1988, Adani Enterprises Ltd. (formerly known as Adani Exports Ltd.) is today the flagship company of the Adani conglomerate.

 

Fresh Water from Sea Water on Ships

When preparing for a voyage ships take on fresh water which is supplemented throughout the voyage by water making plants. Fresh water is used in motorships as an engine component cooling medium, but steamships use only the distilled water produced by the water-making plant for boiler feed make-up.

When I was a lad at sea many years ago, I sailed on motor and steamships as an Engineering Officer. In those days we had evaporators which used steam from the boilers or the main diesel cooling water as a heating medium to evaporate the seawater. As I gained experience and promotion, one of my duties as 4th Engineer was looking after the vaps, as we called them (among other things).
Nowadays, there are several very efficient types of evaporators still using the same heat sources, and of course we now use osmosis as well.
In the following sections we will examine the current evaporators in use, fresh water and condensate storage tanks, and condensate feed water testing. In this article we shall examine two categories of water evaporators, tube and flash, and have a look at how osmosis equipment operates to produce fresh water from seawater.
We begin with an examination of the types of evaporators used aboard ships.

Types of Fresh Water Evaporators

There are numerous types of evaporators and osmosis equipment used to produce fresh water from seawater on our ships today. Here we shall examine the following types:

• Multi-stage Flash Evaporator
• Tube or Coil Evaporator

Multi-stage Flash Evaporators
This type of evaporator uses a multi-stage process which has two components, the seawater heater and the flash drum, with these being two separate units.
The seawater can be heated using steam or the main engine cooling water, depending on the main propulsion unit.
The heated seawater is pumped into the flash drum, which has numerous sections all at a lower pressure than that of the water heater. Some of the hot seawater flashes of to steam in the first section, before going on through remaining sections, flashing as it moves through them. The steam rises up the flash drum through a demister, and upon contacting the condenser tubesis condensed and pumped via a salinometer to the fresh water or boiler water feed tanks. Should the salt content in the distillate rise to an unacceptable level, the salinometer alarm will be activated and the distillate diverted to bilges.
A sketch of a typical multi-stage evaporator is shown below:

                                                       Multi-Stage Seawater Evaporator

Coil or Tube Seawater Evaporator
This is a modern version of the type used when I was at sea in the 1960s. They used heating coils in those days as opposed to the pipe nest heaters of today. The coils used to become scaled in salt, with the attendant loss in output of distillate.
I was in charge of the vaps and I remember the old Chief coming down to the engine room on my watch and balling me out for the downturn in distillate. We were having problems with the boiler feed water purity (another article will cover the testing and treatment of boiler feed water), so I was blowing down the boiler regularly, which with the associated make-up requirement meant we needed more water pronto.
Anyway I took him up to the vaps and showed him the scaling on the heating coils, reminding him that I was pumping Foss chemicals into the beast to try and break this away.
He pushed me aside and shut off the seawater supply opening up the steam supply which rapidly dried the salt layer on the coils. He then opened the seawater inlet and hey presto – the salt scale cracked and fell of the coils. I used this system several times until I was up for Seconds ticket and examiner wasn’t too pleased to hear of this method, and called the old Chief several unprintable names!
Today we don’t have to resort to these measures as there is an innovative device which uses a material that emits oscillations counteracting the natural seawater oscillations, thereby altering its properties and preventing calcium carbonate scale. (See references section.)
A tube and coil evaporator consists of a steel vessel which has a nest of heating pipes near the bottom of the vessel being fed by steam or hot water from the main engine.
There is a tube condenser cooled by seawater installed near the top of the vessel. A vacuum is drawn in the vessel by air ejectors operated by steam or pressurised seawater.
Seawater is fed into the evaporator just covering the heating pipes. Heat is supplied to the pipes and, this combined with the vacuum conditions begins to boil the seawater producing steam. The steam rises up through a demister into the tube condenser where it is evaporated to distilled water. This is collected and pumped via the salinometer to the storage tanks.
A typical tube condenser is shown below.

Tube Evaporator Used Aboard Ships

Osmosis Equipment

Reverse Osmosis Process
Osmosis is a natural process which occurs due to osmotic pressure between two substances divided by a semi-permeable membrane. When the membrane divides two substances of different concentrations of solids, the solvent from the less concentrated solution will flow into the higher concentrated solution, with the membrane blocking the solids.
In an engine room, reverse osmosis takes place in a pressure vessel which contains a tank holding a quantity of seawater and freshwater separated by a semi-permeable membrane. In natural osmosis the freshwater would flow into the seawater, however when pressure is applied to the seawater side the process is reversed. This causes the seawater to flow into the freshwater side, the solids being stopped by the membrane.
A sketch of osmosis in action on ships blackwater is shown below. This can be applied to freshwater osmosis water-makers.

Reverse Osmosis Applied to Seawater Distillation

Role Of Compressed Air In Engine Starting

Do you know how diesel engines are started in ships? Equivalent in size to a four-story building, the main propulsion engine is started with the help of compressed air at a pressure of 30 bar. Learn more about how a ship gets its compressed air supply from.

Why compressed air?

We discussed diesel engine starting problems in our previous article and saw how various methods are used to overcome this problem. We also saw how a marine engine is different due to its size and location, and that compressed air is the solution to starting the diesel engine.
As you know that a ship is a mobile power plant or a moving mini-city. It has all facilities, sometimes better than what we find ashore. These moving giants have a pre-designed and erected compressed air system, which facilitates many activities onboard a ship. There are mostly 4 to 8 and sometimes 10 air compressors found onboard. These Air compressors take suction from the engine room atmosphere which is already under a slight positive pressure. These air compressors compress the air in stages and fill up the huge air bottles, which acts as accumulator. The air compressors compress usually upto 30 bar and keep the air bottles filled up all the time. The number of air bottles and its volume(capacity) depends on the power (size) of the main propulsion engine. These Air compressors are of varying capacity and used as per the requirement onboard.

Role of compressed air on a ship

The role of compressed air onboard is of a very vast nature. Every Ship will be having a "DEAD-START" or "The FIRST START" arrangement. This is nothing but when the ship is totally "Dead" i.e, with out any power and no machineries running and no compressed air in the air bottle to start the generator engine(auxiliary diesel engine), then a provision is given for every ship to get the air bottle filled up to bring back the ship to safe, normal, working condition. This is provided either by a "Emergency Air Compressor" driven by a small diesel engine or electric motor getting its power supply from "Emergency Generator". The various uses of compressed air onboard ship are listed below: 1. To start main propulsion engine
2. To start Auxiliary diesel engine(power generation)
3. To blow ship's whistle
4. For Engine Room general service and cleaning.
5. For the operation of pneumatic tools
6. For deck services, to carry out chipping.
7. For Automation & Instrumentation of various machineries,
8. For fresh & sea water hydrophores,
9. Fire alarms & operation of Quick closing Valves,
10. For Soot Blowing Exhaust Gas Economizer etc and many more...!!

Compressed Air System Layout

The compressed air system onboard typically has a set of 4 to 6 compressors, out of which 3 will be main are compressors, 2 service air compressors & one topping up air compressor. The Emergency air compressor is not to be counted as a normally used machinery.

Main air compressors: These are used only when a ship enters or leaves a port, mostly during maneuvering only. They are of higher capacity of all. During maneuvering, these compressors when put in use, fills up the air bottle faster than other compressors, thus enabling the ship to berth herself in the port. Topping-Up air compressors: These are comparatively of lesser capacity than the main air compressors. They are just used when the ship is sailing in the mid-seas where the consumption of air is very less (only for engine & deck services).
Service Air compressors: These are general service air compressors, which are used either for engine or deck service. They are of lesser capacity and their are designed for their pure strict oil free air quality. These compressors are used for pressing up the control air bottle and thus the control air of high purity is used for various automation purposes in the engine room and the pump room for oil tankers.
There may be set of main air bottles, service air bottle and a control air bottle for their respective purposes. The system also incorporates many pressure reducing valves and driers(de-humidifiers) to get rid of the moisture present in the compressed air.

Starting of an Auxiliary Diesel Engine

The auxiliary diesel engine is mostly started with the help of compressed air,depending upon the size of the engine. Other means of starting includes Electric start(battery) and air motor(engaged in the flywheel). The most common method is the use of compressed air. The lay out for starting the auxiliary engine is given below.

Before starting the auxiliary engine, the following safety checks must be carried out:
1. Turning gear disengaged(if available).
2. Lubricating oil sump level normal
3. Turbocharger oil level( both turbine & blower)side normal
4. Lubricating oil priming pump running.
5. Fuel oil/diesel oil booster pump running.
6. lube oil, cooling fresh water, fuel oil pressure normal.
7. Rocker arm tank level normal.
8. All valves in compressed air line open to the engine.
Referring to the above starting diagram of an auxiliary engine, the" main air" from the main air bottle arrives at the air starting valve. There is a tapping from the main air starting line, "pilot air" going to the starting air distributor. When the engine rotates, the camshaft also rotates which in turn rotates "the starting air distributor cam". This cam is designed as per the firing order of the engine such that, the distributor rotates and lets the pilot air to the particular unit. The pilot air reaches on top of the air starting valve, opening it, in turn making the long awaited main air to let inside the combustion chamber. The main air which is at 30 bar, pushes the piston down making the crankshaft to rotate. This leads to continuous rotation of the crankshaft making the engine to achieve the minimum r.p.m at which firing of the injected fuel takes place. When the engine picks up on fuel, the air is cut off and drained. Thus the auxiliary diesel engine is started with the help of compressed air.
In the next article, we will take up the study of the various valves mentioned in the starting air systems namely master air starting valve, cylinder valves and so forth.

Starting & Reversing Problems in Marine Engines

There are a number of reasons for starting and reversing problems in marine engines. This malfunction is one of the most frightening and dangerous situations to encounter when maneuvering a ships main diesel engine, but it can be avoided through regular maintenance of the air start components.

A ship’s main marine diesel engine is started on compressed air that is controlled by various components of the air start system. It is a well-tried and tested reliable system, but it can go wrong if not properly maintained.
The following sections examine a typical air start system, with the first section providing an overview of the system.

Overview of System

The air start system looks rather complicated, but it is quite simple when you examine it without the safeguards. These are put in place to prevent such occurrences as starting the engine without having a signal from the engine room telegraph, trying to start the engine with the turning gear engaged, or trying to start ahead when the telegraph asks for astern. There are also safety systems incorporated such as a bursting disk and numerous non-return valves in the event of a leaking air start valve.
The next section lists some of the problems that can be encountered when maneuvering.

Problems in Air Start Systems

We shall look at two common problems encountered when maneuvering the main engine: not starting and starting in the wrong direction (reversing instead of starting ahead).

• Not Starting

As we have seen, there are various interlocks in place to prevent the engine being started until certain criteria are met. If the engine won’t turn over on air, the bridge should be informed then the following checks should be carried out.

1. Check air start supply valves from air receivers are open and that the pressure is 30 bar.
2. Check that the turning gear is disengaged
3. Check that the turning gear and telegraph solenoid valves have actuated. This will supply air to the automatic valve, air distributer, the air manifold, and air start valve.

These are the initial checks that can be quickly carried out. If these are all satisfactory, then the problem lies in the controls ahead/astern solenoids. The air distributer or the air start valve itself may be stuck in the closed position. The ship will need to anchor or be towed alongside for these checks to be carried out.
Engine starts in wrong direction
If the engine starts in the astern instead of ahead direction, the following checks should be carried out.

1. Ensure the air start control moves to reverse mode at the control station. This is a visual check and can be observed when the telegraph rings from ahead to stop then astern. If this does not happen, the solenoid valve may be stuck.
2. The oil and air supply to and from the reversing valve should be checked. A blockage of either will stop the reversing servo motor operating and allowing change over from the astern to ahead position.

This again will take further investigation, so the ship should anchor or remain tied up to the quay.
As this ahead/astern changeover is controlled by lube oil and compressed air and is interlocked with the fuel pumps. These are the usual culprits and the starting point of a thorough investigation. I have experienced this situation only once and fortunately we were leaving port and still tied to quay by stern spring. Once the bridge was informed, a rope from the fo’c’sle was thrown ashore and made fast. This gave us the chance to check for the fault, which turned out to be the oil supply from the crosshead oil supply pipe being blocked.
As I have said before, the maintenance of the air start system components is paramount to the operation of the system.

Main Components of the System

Air supply system

• Two air compressors
• Two air start vessels
• Numerous non-return valves
• Numerous drain valves

Control system

• Turning gear out sol v/v
• Telegraph signal sol v/v
• Automatic valve
• Ahead and astern change-over
• Air distributer
• Air start valve

Anti-explosion components

• Air supply to manifold from air vessels non-return valve- this prevents hot gasses from returning to air receivers.
• Air manifold pressure relief valve – this operates if pressure rises due to heat from gasses.
• Air supply to air start valve bursting disk – this disk ruptures under increased pressure caused an air start valve leaking back.

Mandatory Safety Precautions

Before we get into the operation of the system in the next section, this is an opportune moment to make a closer examination of the precaution against explosion, which is a very real threat even in today’s modern engines that incorporate the latest in engine management systems.

• Compressors

The compressor air inlet filters should be positioned in an oil-free zone, i.e. no oil fumes should be present.
The compressed air supply lines to the air receivers must be protected by non-return valves.

• The air receivers

There are two air receivers, linked by a common discharge pipe to the system. The air from the compressors will contain oil and water (there is no way around this). This mixture ends up in the air vessels as a mist, eventually settling to the bottom of the vessel. It is imperative, and I cannot overstress this, that the mixture be drained from the vessels after every charge, and regularly when maneuvering. The oil also coats the internal of the supply pipes; this too can be reduced by draining the air vessels.
These actions, as well as checking by hand for heat in the air supply pipe between the air start valve and the air manifold, form part of the watch keeper’s duties. Any excess heat here, and the fuel and air to that particular cylinder should be isolated, and the bridge made aware of the situation.
Before we leave the precautions there are many examples of air start system explosions. One of worst ones occurred on the MV Capetown Castle, killing seven engineers. Lloyd’s register recorded 11 such explosions between 1987 and 1998; all down to oil gathering in the receivers and piping and ignited by exhaust gasses. One a year speaks for itself: drain the air vessels regularily and maintain the system.
A sketch showing an air start system where the air start valve is leaking is shown below. Note the pipe that should be checked by hand for overheating;

                                  Air Start System Depicting a Leaking Air Start Valve

The Operating Principles of Marine Engine Air Start Systems

I have sailed on quite a few marine diesel engines, including B&W, Sulzer, and Stork/Werkspoor. All had variations of the system I am about to describe, but the principles are much the same.
I drew a sketch from memory (45 years ago) but updated it from a very good website referenced at the end of the section. The sketch also appears at the end of the section and can be referred to during the reading of the notes.
We begin then with the bridge ringing down standby on the engine room telegraph. (We used to change over fuel from Heavy Fuel Oil to Modified Diesel Oil for maneuvering.)
1. If in port, ensure turning gear is not engaged.
2. Open both air receivers’ isolation valves and start up a compressor to fill receivers to maximum; drain oily water of reservoirs and also from dead leg on supply pipe work.
3. This allows the compressed air to flow as far as the turning gear solenoid valve. Provided the turning gear is disengaged, this will allow the supply of air at 30 bar to the automatic valve passing though the non-return valve and into the manifold. From here the air is piped to the air chamber in the air start valve. (This is the pipe that will get hot if you have a leaking air start valve.) The valve is held in the shut position by the spring tension.
4. When an ahead or astern movement is rung and answered on the engine room telegraph, the telegraph start signal sol v/v is activated allowing air to the ahead and astern solenoid valves mechanism.
5. The air is now directed to the starting air distributer that is fitted on the end of the camshaft. This enables it to select the appropriate cylinder(s) to supply air to. This will be the relevant cylinder that is just passed TDC and on the downward stroke.
6. The air from the starting air distributer is at 30 bar, and this is injected into the air start valve top piston. This overcomes the spring tension and forces the piston downwards thus opening the valve and introducing the air at 30 bar to the cylinder(s) having been supplied earlier to the air chamber.
7. Depending on the engine make and model, air can be supplied to several cylinders to assist starting. A "slow start" supply can be used if there has been a lapse of half an hour between movements when maneuvering.

                   Typical Air Start System for a Marine Engine Operating on Local Control

Maintenance of System Components

• Compressors

Regular inspection of filters, suction and discharge valves, as well as piston and ring checks should be performed at the manufacturer’s recommended periods. Intercooler tube nests should be cleaned ensuring optimum air flow.

• Air supply Manifold Relief Valve

This should be regularly inspected to ensure that the spring is operating correctly, with the complete overhaul being to manufacturer’s instructions.

• Air Start Valves

This is the most important component and if not maintained, will begin to stick due to a weak/badly adjusted spring or worn piston rings allowing hot combustion gasses into the compressed air piping.
The valve should be replaced regularly with an overhauled and tested spare, the spare then being stripped and spring, pistons, and rings inspected. The valve is ground into the seat using fine lapping paste before rebuild and bench pressure testing.

Managing Severe Injury and Medical Ailments aboard Ship

Working on a ship can involve a substantial amount of risk to a seafarer's life. Numerous hazardous agents on a ship can be risky and even life threatening. So what should be done in case of an injured or ill sailor onboard a ship that is far away from the shore... and the nearest hospital?

Getting injured or becoming chronically ill aboard a ship risks the life of the person it happens to. Facing either of these circumstances involves not only the suffering attached to the mishap, but also the burden of unreliable diagnosis and ineffective medical monitoring. A patient on a ship is fully dependent on the skills of the medical officer and the meager first aid tools available.
Earlier, in situations involving serious injuries or sickness, there was nothing more that could be done other than giving sedatives or treating the person with whatever resources were there on hand. However, times have changed now, and so have been the procedures for providing emergency medical aid on ship.

History of Emergency Medical Care for Merchant Marine

In the last few decades, many steps have been taken to reduce the risk to life onboard a ship. Qualified medical officers have been deployed to reduce the level of risk as much as possible. It is to note that none of these officers are doctors, but only certified first aid and emergency medical care providers. Thus, in case of extreme emergency, all that a medical officer will provide is basic emergency care and some type of medication or sedative to ease the patient’s pain until the ship reaches the next port.

Starting in the 1920s, ship’s radios were used to communicate with a physician located onshore to obtain the right kind of medical aid. However, because of the variability of radio propagation, this system often couldn’t be used beyond a certain range. If the ship was within 200 nautical miles, high speed "life boats” and helicopters were a viable option for saving the distressed sailor. However, in bad weather and beyond 200 nautical miles, even this option could not be used. Also, if a person’s life is in serious danger, there was always an option of diverting the ship, but then the decision would be a serious blow to the company from a financial perspective.
With the advent of satellite communication, ways of providing medical aid to patients onboard a ship also changed. A new term, telemedicine, came into being and started providing remote medical aid to seafarers using high technology such as emails and live video footage. Telemedicine has now become the new face of providing medical aid at sea.

1950s Cardiac Monitoring and Recording Device (EKG)

Wikipedia Commons by user Daderot placed in public domain by photographer

Telemedicine

Telemedicine is a technology that uses modern methods such as email, face-to-face video, and audio communication to treat a diseased or injured person on a ship. In the early days, telemedicine had serious problems such as inferior video quality, limited file transfer, and network restrictions. Moreover, only recorded video and audio files could be transferred and those, too, of only short lengths. Now because of the many new satellites launched, the potential of telemedicine has increased from a file transfer medium to a fully capable live video exchanging device.

How does Telemedicine Work?

Telemedicine is a whole new way of communicating from the ship to the shore and vice-verse in times of medical emergencies. The working of telemedicine can be divided into three main stages:

1. The medical personnel onboard the ship
2. The medical advisor panel on shore
3. The monitoring device and satellite

Telemedicine makes the whole remote diagnostic process very realistic. The injured or diseased person on the ship is monitored using a special device that involves taking real time measurements of diagnostic conditions (signs and symptoms) like the patient’s pulse rate, blood pressure, and cardiac trace or electrocardiogram. The medical panel on shore analyzes the situation and parameters and provides the right aid to the patient. Telemedicine also facilitates providing timely advice for injuries involving open wounds through the taking and transmission of high resolution pictures of the injury.
Shipping companies have begun investing heavily in telemedicine facilities because of the several benefits it provides. They realize that in a mishap involving a human element, there is nothing more important than saving the life of the seafarer. Also, the right investment in telemedicine can also save a large amount of money later, which a ship diversion or other methods never will.

References

• Author's experience

The Charge Air Cooler in Diesel Engines

The charge air cooler is an important device fitted in all turbocharged diesel engines to reduce the temperature of the charged air before its entry to the engine in order to increase the efficiency of engine. This article deals with purpose, location, and maintenance of charge air coolers.

In this article we discuss the charge air cooler fitted between the turbocharger and the scavenge air manifold in all modern four stroke and two stroke engines. Readers will be able to understand the concept of charge air coolers, and their operation, construction, and maintenance. One can also find reasons for cooler fouling, its location on engine, and methods of cleaning the charge air cooler.

Purpose of Charge Air Cooler

The exhaust gas from the engine is utilized in the turbocharger for compressing fresh air to charge the engine with a positive pressure greater than ambient conditions. This compression causes the temperature of the air to increase, which thus cannot be fed directly into the engine as it is out of operating limits. Thus a cooler that bring the air temperature back to near-ambient conditions is fitted on the engine. When the air is hot, its density is less and thus the mass of air charged into the engine is less when compared to the mass when the air is cold. Thus the charge air cooler improves the charge air density and its temperature.

The compressed charged air at the outlet of charge air cooler will have a reduced temperature of about 40 to 50 degrees Celsius from a temperature of about 200 degrees Celsius. This reduced temperature of air will increase the density of the charge air at low temperature. Increased air density of the charge air will rise the scavenge efficiency and allow a greater mass of air to be compressed inside the engine cylinder so that more fuel can be burned inside the combustion chamber, giving an increase in power. Also the engine is maintained at a safe working temperature. The lower compression temperature reduces stress on the piston, piston rings, cylinder liner, and cylinder head. The charge air cooler has another advantage in that it reduces the exhaust gas temperature. It has been proven that every one degree Celsius drop in scavenge air temperature will reduce the exhaust temperature about five to ten degree Celsius. This does not mean that the air can be charged at cryogenic temperatures. If very cold air enters the cylinder liner, it would cause a sudden thermal shock, leading to cracking of liner.

Thus charge air coolers also serve as heaters when a ship enters cold climate areas. Let us assume that the charge air cooler is cooled by fresh water (LT) circuit. If the ambient air temperature is very low, the fresh water, which is usually at 30 degrees Celsius, will heat the charged air and make it comfortable for the engine.

Charge Air Cooler

Location of a Charge Air Cooler

Charge air coolers are located between the turbocharger compressor side outlet and the engine inlet manifold or scavenge manifold. A clear view of the location of a charge air cooler is shown in the diagram below. The location of the charge air cooler between turbocharger and entry to engine should be such that the temperature of the charge air at the outlet of charge air cooler should not be increased before its entry to the engine cylinder due to the heated condition of the engine room. To avoid this, the air cooler should be located as close to the engine cylinder as possible. Also, the air duct between the charge air cooler and the engine inlet manifold should be insulated to avoid increase in the temperature of the air.

Location of Cooler on Large Diesel Engine

Air Cooler Fouling and its Effect on the Engine

When the air cooler becomes fouled, less heat will be transferred from the air to the cooling water (usually fresh water). This is indicated by the changes in the air temperature and cooling water temperature and a pressure drop in the air passing through the air cooler. To measure this pressure drop, a manometer is connected between the charge air cooler inlet and outlet. The amount of pressure drop will depend upon the degree and nature of the fouling.
Indications of Air Side Fouling:

• Increase of air pressure drop across the charge air cooler.
• Decrease of air temperature difference across air cooler.
• Rise in scavenge air temperature.
• Rise in exhaust gas temperature from all cylinders.

Indications of cooling water side fouling:

• Rise in scavenge air temperature.
• Decrease in the difference of the air temperature across the air cooler.
• Decrease in the temperature of the cooling water across the cooler if fouling is on the tubes.
• Increase in exhaust gas temperature from all cylinders.
• Increase in the temperature of the cooling water due to fouling or chocking material in tubes that reduce the amount of cooling water flow.

Methods of air side cleaning:

• Fins in the air side can be cleaned by using compressed air at Low pressure.
• The air side can be cleaned by dipping the air cooler in a chemical bath for a certain period of time. This will remove all deposits on the air side.
• Another method of cleaning the air side is by using the jet of water at Low pressure.
• Note: Usage of very high pressure may lead to bending of fins and thus causing permanent damage to the air cooler.

Methods of Fresh water side cleaning:

• For soft deposits on the water side, dip the cooler in a chemical bath. After a certain period of time, take the cooler out and then clean with water at some temperature higher than ambient. It is always preferred to circulate water using wilden pump and drums.
• For hard deposits use a long drill bit to drill the hard deposits on the tubes. Note this requires a specialist to drill the hard deposits because small mistakes in drilling may damage the tubes.

Image Credits:
www.turbobygarrett.com/.../turbo_tech101.html
www.chevon.com.sg/prod_4_charged_aircoil.aspx
http://www.av-tekk.com/chargeairinfo.html
http://en.wikipedia.org/wiki/Charge_air_cooler

Centrifugal Oil Purifiers - Starting and Stopping Procedures

We have already discussed the basic principle of operation of purifiers. Lets learn how to start and stop purifiers, and about necessary safety precautions before starting, de-sludging procedures, and emergency stopping.

We all know that centrifuges are an important type of auxiliary equipment on board ships and that they are classified into two operating functions. One is a clarifier, which separates solids from liquids. The other type is a purifier, which separates liquids of different density. The Purifier operates on the principle of separation by centrifugal force. But in order to optimize the purification process, certain parameters should be adjusted before the purifier is started. Out of those parameters, very important parameters are:

1. Feed inlet oil temperature
2. Density of Oil
3. RPM of the rotating bowl
4. Back Pressure
5. Throughput of oil feed

Understanding the Parameters

1. Feed inlet oil temperature: Before entering the purifier, the dirty oil passes through the heater. This increases the temperature, thus reducing the viscosity of the oil to be purified. The lower the viscosity, the better will be the purification.
2. Density of Oil: As the dirty oil entering the purifier is heated to reduce the viscosity, the density also reduces. The lower the density, the better the separation.

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3. R.P.M of the rotating bowl: If the purifier has not achieved full RPM (revolutions per second), then the centrifugal force will not be sufficient enough to aid the separation.
4. Back Pressure: The back pressure should be adjusted after the purifier is started. The back pressure varies as the temperature, density, viscosity of feed oil inlet varies. The back pressure ensures that the oil paring disc is immersed in the clean oil on the way of pumping to the clean oil tank.
5. Throughput of oil feed: Throughput means the quantity of oil pumped into the purifier/hr. In order to optimize the purification, the throughput must be minimum.

Pre-checks before starting a Purifier

Before starting a Purifier, following checks are very essential:
1. If the Purifier is started after a overhaul, then check all fittings are fiited in right manner. The bowl frame hood locked with hinges.
2. Check the Oil level in the gear case. Ensure that it is exactly half in the sight glass. Also ensure the sight glass is in vertical position, as there is a common mistake of fixing it in horizontal position.
3. check the direction of rotation of the seperator, by just starting and stopping the purifier motor.
4. Check whether the brake is in released position.

Starting the Purifier

1. Ensure the lines are set and respective valves are open. Usually the lines are set from settling tank to service tank.
2. Start the purifier feed pump with the 3-way re-circulation valve in a position leading to settling tank.
3. Open the steam to the heater slightly ensuring the drains are open so that the condensate drains. close the drains once steam appears.
4. Start the Purifier.
5. Check for vibrations, check the gear case for noise and abnormal heating.
6. Note the current (amps) during starting. It goes high during starting and then when the purifier bowl picks-up speed and when it reaches the rated speed, the current drawn drops to normal value.
7. Ensure the feed inlet temperature has reached optimum temperature for separation as stated in the Bunker report and nomogram ( bunker delivery note gives the density of the fuel and using this we can get the separation temperature and gravity disc size from the nomogram)
8. Now check whether the bowl has reached the rated speed by looking at the revolution counter. The revolution counter gives the scaled down speed of the bowl. The ratio for calculation can be obtained from the manual.
9. Now, after the bowl reaching the rated RPM, check for the current attaining its normal value.

De-sludge Procedure

10. Open the bowl closing water/operating water, which closes the bowl. (Ensure sufficient water is present in the operating water tank)
11. Now after 10 seconds, open the sealing water to the bowl.
12. The sealing water should be kept open till the water comes out of the waste water outlet.
13. Once the water overflows through the waste water outlet, stop the sealing water.
14. Now open the de-sludge water/bowl opening water. (This is done to ensure the bowl has closed properly). During de-sludge we can hear a characteristic sound at the opening of the bowl.
15. Repeat the steps 10, 11 ,12 & 13.
16. Open the 3-way re-circulation valve such that the dirty oil feed is fed into the purifier.
17. Wait for the back pressure to build up.
18. Check for overflowing of dirty-oil through waste water outlet & sludge port.
19. Now adjust the throughput to a value specified in the manual. Correspondingly adjust the back pressure, too.
20. Now the purifier is put into operation. Change over the clean-oil filling valve to service tank.

After-Checks and Stopping the Purifier

Checks after starting the purifier during regular watches:
1. Adjust the throughput, back pressure, temperature of feed inlet if necessary
2. gear case oil level, motor amps, general leakages, vibration have to be monitored
3. De-sludge every 2 hours for heavy oil purifiers & every 4 hours for lubricating oil purifiers. (Rrefer to the manual or chief engineer instructions.)
Stopping of Purifiers:
1. De-sludge the purifier after stopping the feed inlet.
2. Shut down the steam inlet to the oil.
3. Stop the purifier after filling up the bowl with water.
4. Apply brakes and bring up the purifier to complete rest.
5. If any emergency, the purifiers has emergency stops, on pressing it, will stop the purifiers immediately shutting off the feed.
Thus we have seen in detail how to start the purifier after carrying out all safety checks and we have also seen how to stop it.

Overheated Piston Failure, Detection & Correction

The piston performs its work silently within the cylinder liner invisible from outside, but there might be problems inside which could make it overheated causing a knocking sound. Learn how to detect piston failure and how to correct the situation

Introduction

Despite the best of maintenance and care, faults and piston failure can occur in the engine room and in marine diesel engines. One of the main requirements of the job profile of a marine engineer at any rank is to act quickly and thoughtfully to handle any kind of situation. It is important for a marine engineer to know what to do when he hears diesel engine knocking. This diesel engine troubleshooting guide will show you what to do when a piston gets overheated.

Causes of Overheating

A piston is constantly in contact with the high temperature and high pressure region of the combustion chamber while it is performing its functions of pressure sealing and motion transmission to the crankshaft. It can get overheated due to any or several of the following reasons

• The obvious reason could be the failure of the piston cooling system to perform its function which leads to temperature rise
• If the piston rings have insufficient clearance or are broken down and get seized, this also will lead to heating of the piston
• If the cylinder jacket liner lubrication system fails, this would result in increase of heat due to friction
• Leakage of combustion gases past the piston due to ring fault or failure
• Bad combustion which could be due to valve timing problems and so forth

External Symptoms

Hence we see that there can be a number of reasons for piston overheating, but remember when this situation occurs you cannot peep inside to find out immediately. First you need to know the external indicators of an overheated piston and they are as follows.

• Engine RPM falls without any reasonable cause
• Knocking is heard from the cylinders
• Abnormal rise in piston cooling temperature
• Abnormal rise in exhaust temperature
• Abnormal smoke in exhaust form the funnel

Handling the Situation

So what should be your first reaction if you see or sense an overheated piston? Well the first instinct would be to run and shut down the engine but just take care to avoid this reflex action and this could lead to other problems.

• Slow down the engine to a very low speed but NOT complete shutdown. This results in considerable reduction of heat in the relevant piston.
• Since not all pistons would likely develop this fault simultaneously (unless you are totally out of luck that day) so first identify the particular cylinder in which the problem has occurred using parameters such as temperatures, sound etc.
• The fuel supply to the affected cylinder should be cut-down from the fuel pump
• Lubrication to that cylinder should be increased from the appropriate arrangement depending on the specific engine under consideration
• Only stop the engine when it is sufficiently cooled to avoid any thermal stresses. Even after stopping the turning gear should be used to keep it moving for some time while cooling and lubrication is continued.
• Finally the piston needs to be dismantled and checked and this is a detailed procedure which we might take up in future.

Centrifugal pumps for general marine duties

Centrifugal pump principles and working procedure

A pump is a machine used to raise liquids from a low point to a high point. In a centrifugal pump liquid enters the centre or eye of the impeller and flows radially out between the vanes, its velocity being increased by the impeller rotation. A diffuser or volute is then used to convert most of the kinetic energy in the liquid into pressure.

The arrangement of a centrifugal pump is shown diagrammatically in figure below



Fig: Centrifugal pumping operation


A vertical, single stage, single entry, centrifugal pump for general marine duties is shown in Figure here. The main frame and casing, together with a motor support bracket, house the pumping element assembly. The pumping element is made up of a top cover, a pump shaft, an impeller, a bearing bush and a sealing arrangement around the shaft. The sealing arrangement may be a packed gland or a mechanical seal and the bearing lubrication system will vary according to the type of seal. Replaceable wear rings are fitted to the impeller and the casing. The motor support bracket has two large apertures to provide access to the pumping element, and a coupling spacer is fitted between the motor and pump shaft to enable the removal of the pumping element without disturbing the motor.



Fig: Single entry centrifugal pump


A vertical multi-stage single-entry centrifugal pump used for deep-well cargo pumping is shown in Figure below. This can be considered as a series of centrifugal pumps arranged to supply one another in series and thus progressively increase the discharge pressure. The pump drive is located outside the tank and can be electric, hydraulic or any appropriate means suitable for the location.



Fig: Multi stage centrifugal pump


A diffuser is fitted to high-pressure centrifugal pumps. This is a ring fixed to the casing, around the impeller, in which there are passages formed by vanes. The passages widen out in the direction of liquid flow and act to convert the kinetic energy of the liquid into pressure energy. Hydraulic balance arrangements are also usual. Some of the high-pressure discharge liquid is directed against a drum or piston arrangement to balance the discharge liquid pressure on the impeller and thus maintain it in an equilibrium position.

Centrifugal pumps, while being suitable for most general marine duties, are not self priming and require some means of removing air from the suction pipeline and filling it with liquid. Where the liquid to be pumped is at a level higher than the pump, opening an air cock near the pump suction will enable the air to be forced out as the pipeline fills up under the action of gravity. If the pump is below sea water level, and sea water priming is permissible in the system, then opening a sea water injection valve and the air cock on the pump will effect priming.

Alternatively an air pumping unit can be provided to individual pumps or as a central priming system connected to several pumps. The water ring or liquid ring primer can be arranged as an individual unit mounted on the pump and driven by it, or as a motor driven unit mounted separately and serving several pumps. The primer consists of an elliptical casing in which a vaned rotor revolves. The rotor may be separate from the hub and provide the air inlet and discharge ports as shown in Figure down. Alternatively another design has the rotor and hub as one piece with ports on the cover. The rotor vanes revolve and force a ring of liquid to take up the elliptical shape of the casing. The water ring, being elliptical, advances and recedes from the central hub, causing a pumping action to occur. The suction piping system is connected to the air inlet ports and the suction line is thus primed by the removal of air. The air removed from the system is discharged to atmosphere. A reservoir of water is provided to replenish the water ring when necessary.



Fig: Water-ring primer


When starting a centrifugal pump the suction valve is opened and the discharge valve left shut: then the motor is started and the priming unit will prime the suction line. Once the pump is primed the delivery valve can be slowly opened and the quantity of liquid can be regulated by opening or closing the delivery valve. When stopping the pump the delivery valve is closed and the motor stopped.

Regular maintenance on the machine will involve attention to lubrication of the shaft bearing and ensuring that the shaft seal or gland is not leaking liquid. Unsatisfactory operation or loss of performance may require minor or major overhauls. Common faults, such as no discharge, may be a result of valves in the system being shut, suction strainers blocked or other faults occurring in the priming system. Air leaks in the suction piping, a choked impeller or too tight a shaft gland can all lead to poor performance.

When dismantling the pump to remove the pumping element any priming pipes or cooling water supply pipes must be disconnected. Modern pumps have a coupling spacer which can be removed to enable the pumping element to be withdrawn without disturbing the motor: the impeller and shaft can then be readily separated for examination. The shaft bearing bush together with the casing and impeller wear rings should be examined for wear.




Section B -- Pump Application Data B-4A Sealing
The proper selection of a seal is critical to the success of every pump application. For maximum pump reliability, choices must be made between the type of seal and the seal environment. In addition, a sealless pump is an alternative, which would eliminate the need for a dynamic type seal entirely.
Sealing Basics
There are two basic kinds of seals: static and dynamic. Static seals are employed where no movement occurs at the Juncture to be sealed. Gaskets and O-rings are typical static seals.
Dynamic seals are used where surfaces move relative to one another. Dynamic seals are used, for example, where a rotating shaft transmits power through the wall of a tank (Fig. 1), through the casing of a pump (Fig. 2), or through the housing of other rotating equipment such as a filter or screen.


Fig. 1 Cross Section of Tank and Mixer

Fig. 2 Typical Centrifugal Pump A common application of sealing devices is to seal the rotating shaft of a centrifugal pump. To best understand how such a seal functions a quick review of pump fundamentals is in order.
In a centrifugal pump, the liquid enters the suction of the pump at the center (eye) of the rotating impeller (Figures 3 and 4).


Fig. 3 Centrifugal Pump, Liguid End

Fig. 4 Fluid Flow in Centrifugal Pump As the impeller vanes rotate, they transmit motion to the incoming product, which then leaves the impeller, collects in the pump casing, and leaves the pump under pressure through the pump discharge.
Discharge pressure will force some product down behind the impeller to the drive shaft, where it attempts to escape along the rotating drive shaft. Pump manufacturers use various design techniques to reduce the pressure of the product trying to escape. Such techniques include: 1) the addition of balance holes through the impeller to permit most of the pressure to escape into the suction side of the impeller, or 2) the addition of back pump-out vanes on the back side of the impeller.
However, as there is no way to eliminate this pressure completely, sealing devices are necessary to limit the escape of the product to the atmosphere. Such sealing devices are typically either compression packing or end-face mechanical seals.


B-4A Stuffing Box Packing
A typical packed stuffing box arrangement is shown in Fig. 5. It consists of: A) Five rings of packing, B) A lantern ring used for the injection of a lubricating and/or flushing liquid, and C) A gland to hold the packing and maintain the desired compression for a proper seal.


Fig. 5 Typical Stuffing Arrangement (description of parts) The function of packing is to control leakage and not to eliminate it completely. The packing must be lubricated, and a flow from 40 to 60 drops per minute out of the stuffing box must be maintained for proper lubrication.
The method of lubricating the packing depends on the nature of the liquid being pumped as well as on the pressure in the stuffing box. When the pump stuffing box pressure is above atmospheric pressure and the liquid is clean and nonabrasive, the pumped liquid itself will lubricate the packing (Fig. 6).


Fig. 6 Typical Stuffing Arrangement when Stuffing Box Pressure is Above Atmospheric Pressure When the stuffing box pressure is below atmospheric pressure, a lantern ring is employed and lubrication is injected into the stuffing box (Fig. 7). A bypass line from the pump discharge to the lantern ring connection is normally used providing the pumped liquid is dean.


Fig. 7 Typical Stuffing Box Arrangement when Stuffing Box Pressure is Below Atmospheric Pressure When pumping slurries or abrasive liquids, it is necessary to inject a dean lubricating liquid from an external source into the lantern ring (Fig. 8). A flow of from .2 to .5 gpm is desirable and a valve and flowmeter should be used for accurate control. The seal water pressure should be from 10 to 15 psi above the stuffing box pressure, and anything above this will only add to packing wear. The lantern ring Is normally located In the center of the stuffing box. However, for extremely thick slurries like paper stock, it is recommended that the lantern ring be located at the stuffing box throat to prevent stock from contaminating the packing.


Fig. 8 Typical Stuffing Box Arrangement when Pumping Slurries The gland shown in Figures 5 through 8 is a quench type gland. Water, oil, or other fluids can be injected into the gland to remove heat from the shaft, thus limiting heat transfer to the bearing frame. This permits the operating temperature of the pump to be higher than the limits of the bearing and lubricant design. The same quench gland can be used to prevent the escape of a toxic or volatile liquid into the air around the pump. This is called a smothering gland, with an external liquid simply flushing away the undesirable leakage to a sewer or waste receiver.
Today, however, stringent emission standards limit use of packing to non-hazardous water based liquids. This, plus a desire to reduce maintenance costs, has increased preference for mechanical seals.


Mechanical Seals
A mechanical seal is a sealing device which forms a running seal between rotating and stationary parts. They were developed to overcome the disadvantages of compression packing. Leakage can be reduced to a level meeting environmental standards of government regulating agencies and maintenance costs can be lower. Advantages of mechanical seals over conventional packing are as follows:

1. Zero or limited leakage of product (meet emission regulations.)
2. Reduced friction and power loss.
3. Elimination of shaft or sleeve wear.
4. Reduced maintenance costs.
5. Ability to seal higher pressures and more corrosive environments.
6. The wide variety of designs allows use of mechanical seals in almost all pump applications.

The Basic Mechanical Seal
All mechanical seals are constructed of three basic sets of parts as shown in Fig. 9:

1. A set of primary seal faces: one rotary and one stationary?shown in Fig. 9 as seal ring and insert.
2. A set of secondary seals known as shaft packings and insert mountings such as 0-rings, wedges and V-rings.
3. Mechanical seal hardware including gland rings, collars, compression rings, pins, springs and bellows.

Fig. 9 A Simple Mechcanical Seal How A Mechanical Seal Works
The primary seal is achieved by two very flat, lapped faces which create a difficult leakage path perpendicular to the shaft. Rubbing contact between these two flat mating surfaces minimizes leakage. As in all seals, one face is held stationary in a housing and the other face is fixed to, and rotates with, the shaft. One of the faces is usually a non-galling material such as carbon-graphite. The other is usually a relatively hard material like silicon-carbide. Dissimilar materials are usually used for the stationary insert and the rotating seal ring face in order to prevent adhesion of the two faces. The softer face usually has the smaller mating surface and is commonly called the wear nose.
There are four main sealing points within an end face mechanical seal (Fig. 10). The primary seal is at the seal face, Point A. The leakage path at Point B is blocked by either an 0-ring, a V-ring or a wedge. Leakage paths at Points C and D are blocked by gaskets or 0-rings.


Fig. 10 Sealing Points for Mechanical Seal The faces in a typical mechanical seal are lubricated with a boundary layer of gas or liquid between the faces. In designing seals for the desired leakage, seal life, and energy consumption, the designer must consider how the faces are to be lubricated and select from a number of modes of seal face lubrication.
To select the best seal design, it's necessary to know as much as possible about the operating conditions and the product to be sealed. Complete information about the product and environment will allow selection of the best seal for the application.

Mechanical Seal Types
Mechanical seals can be classified into several tvpes and arrangements:


PUSHER:
Incorporate secondary seals that move axially along a shaft or sleeve to maintain contact at the seal faces. This feature compensates for seal face wear and wobble due to misalignment. The pusher seals' advantage is that it's inexpensive and commercially available in a wide range of sizes and configurations. Its disadvantage is that ft's prone to secondary seal hang-up and fretting of the shaft or sleeve. Examples are Dura RO and Crane Type 9T.

UNBALANCED:
They are inexpensive, leak less, and are more stable when subjected to vibration, misalignment, and cavitation. The disadvantage is their relative low pressure limit. If the closing force exerted on the seal faces exceeds the pressure limit, the lubricating film between the faces is squeezed out and the highly loaded dry running seal fails. Examples are the Dura RO and Crane 9T.

CONVENTIONAL:
Examples are the Dura RO and Crane Type 1 which require setting and alignment of the seal (single, double, tandem) on the shaft or sleeve of the pump. Although setting a mechanical seal is relatively simple, today's emphasis on reducing maintenance costs has increased preference for cartridge seals.

NON-PUSHER:
The non-pusher or bellows seal does not have to move along the shaft or sleeve to maintain seal face contact, The main advantages are its ability to handle high and low temperature applications, and does not require a secondary seal (not prone to secondary seal hang-up). A disadvantage of this style seal is that its thin bellows cross sections must be upgraded for use in corrosive environments Examples are Dura CBR and Crane 215, and Sealol 680.

BALANCED:
Balancing a mechanical seal involves a simple design change, which reduces the hydraulic forces acting to close the seal faces. Balanced seals have higher-pressure limits, lower seal face loading, and generate less heat. This makes them well suited to handle liquids with poor lubricity and high vapor pressures such as light hydrocarbons. Examples are Dura CBR and PBR and Crane 98T and 215.

CARTRIDGE:
Examples are Dura P-SO and Crane 1100 which have the mechanical seal premounted on a sleeve including the gland and fit directly over the Model 3196 shaft or shaft sleeve (available single, double, tandem). The major benefit, of course is no requirement for the usual seal setting measurements for their installation. Cartridge seals lower maintenance costs and reduce seal setting errors  

Mechanical Seal Arrangements
SINGLE INSIDE:
This is the most common type of mechanical seal. These seals are easily modified to accommodate seal flush plans and can be balanced to withstand high seal environment pressures. Recommended for relatively clear non-corrosive and corrosive liquids with satisfactory' lubricating properties where cost of operation does not exceed that of a double seal. Examples are Dura RO and CBR and Crane 9T and 215. Reference Conventional Seal.
SINGLE OUTSIDE:
If an extremely corrosive liquid has good lubricating properties, an outside seal offers an economical alternative to the expensive metal required for an inside seal to resist corrosion. The disadvantage is that it is exposed outside of the pump which makes it vulnerable to damage from impact and hydraulic pressure works to open the seal faces so they have low pressure limits (balanced or unbalanced).


DOUBLE (DUAL PRESSURIZED):
This arrangement is recommended for liquids that are not compatible with a single mechanical seal (i.e. liquids that are toxic, hazardous [regulated by the EPA], have suspended abrasives, or corrosives which require costly materials). The advantages of the double seal are that it can have five times the life of a single seal in severe environments. Also, the metal inner seal parts are never exposed to the liquid product being pumped, so viscous, abrasive, or thermosetting liquids are easily sealed without a need for expensive metallurgy. In addition, recent testing has shown that double seal life is virtually unaffected by process upset conditions during pump operation. A significant advantage of using a double seal over a single seal. The final decision between choosing a double or single seal comes down to the initial cost to purchase the seal, cost of operation of the seal, and environmental and user plant emission standards for leakage from seals. Examples are Dura double RO and X-200 and Crane double 811T.


DOUBLE GAS BARRIER (PRESSURIZED DUAL GAS):
Very similar to cartridge double seals ... sealing involves an inert gas, like nitrogen, to act as a surface lubricant and coolant in place of a liquid barrier system or external flush required with conventional or cartridge double seals. This concept was developed because many barrier fluids commonly used with double seals can no longer be used due to new emission regulations. The gas barrier seal uses nitrogen or air as a harmless and inexpensive barrier fluid that helps prevent product emissions to the atmosphere and fully complies with emission regulations. The double gas barrier seal should be considered for use on toxic or hazardous liquids that are regulated or in situations where increased reliability is the required on an application. Examples are Dura GB2OO, GF2OO, and Crane 2800.

TANDEM (DUAL UNPRESSURIZED): Due to health, safety, and environmental considerations, tandem seals have been used for products such as vinyl chloride, carbon monoxide, light hydrocarbons, and a wide range of other volatile, toxic, carcinogenic, or hazardous liquids. 

Tandem seals eliminate icing and freezing of light hydrocarbons and other liquids which could fall below the atmospheric freezing point of water in air (32? F or 0? C). {Typical buffer liquids in these applications are ethylene glycol, methanol, and propanol.) A tandem also increases online reliability. If the primary seal fails, the outboard seal can take over and function until maintenance of the equipment can be scheduled. Examples are Dura TMB-73 and tandem PTO. 


Mechanical Seal Selection
The proper selection of a mechanical seal can be made only if the full operating conditions are known:

1. Liquid
2. Pressure
3. Temperature
4. Characteristics of Liquid
5. Reliability and Emission Concerns

1. Liquid: Identification of the exact liquid to be handled is the first step in seal selection. The metal parts must be corrosion resistant, usually steel, bronze, stainless steel, or Hastelloy. The mating faces must also resist corrosion and wear. Carbon, ceramic, silicon carbide or tungsten carbide may be considered. Stationary sealing members of Buna, EPR, Viton and Teflon are common.
2. Pressure: The proper type of seal, balanced or unbalanced, is based on the pressure on the seal and on the seal size.
3. Temperature: In part, determines the use of the sealing members. Materials must be selected to handle liquid temperature.
4. Characteristics of Liquid: Abrasive liquids create excessive wear and short seal life. Double seals or clear liquid flushing from an external source allow the use of mechanical seals on these difficult liquids. On light hydrocarbons balanced seals are often used for longer seal life even though pressures are low.
5. Reliability and Emission Concerns: The seal type and arrangement selected must meet the desired reliability and emission standards for the pump application. Double seals and double gas barrier seals are becoming the seals of choice.

Seal Environment
The number one cause of pump downtime is failure of the shaft seal. These failures are normally the result of an unfavorable seal environment such as improper heat dissipation (cooling), poor lubrication of seal faces, or seals operating in liquids containing solids, air or vapors. To achieve maximum reliability of a seal application, proper choices of seal housings (standard bore stuffing box, large bore, or large tapered bore seal chamber) and seal environmental controls (CPI and API seal flush plans) must be made. STANDARD BORE STUFFING BOX COVER
Designed thirty years ago specifically for packing. Also accommodates mechanical seals (clamped seat outside seals and conventional double seals.)


CONVENTIONAL LARGE BORE SEAL CHAMBER
Designed specifically for mechanical seals. Large bore provides Increased life of seals through improved lubrication and cooling of faces. Seal environment should be controlled through use of CPI or API flush plans. Often available with internal bypass to provide circulation of liquid to faces without using external flush. Ideal for conventional or cartridge single mechanical seals in conjunction with a flush and throat bushing in bottom of chamber. Also excellent for conventional or cartridge double or tandem seals.

LARGE BORE SEAL CHAMBERS
Introduced in the mid-8o's, enlarged bore seal chambers with increased radial clearance between the mechanical seal and seal chamber wall, provide better circulation of liquid to and from seal faces. Improved lubrication and heat removal (cooling) of seal faces extend seal life and lower maintenance costs.
BigBore^{TM Seal Chamber}
TaperBore^{TM Seal Chamber}

Large Tapered Bore Seal Chambers
Provide increased circulation of liquid at seal faces without use of external flush. Offers advantages of lower maintenance costs, elimination of tubing/piping, lower utility costs (associated with seal flushing) and extended seal reliability. The tapered bore seal chamber is commonly available with ANSI chemical pumps. API process pumps use conventional large bore seal chambers. Paper stock pumps use both conventional large bore and large tapered bore seal chambers. Only tapered bore seal chambers with flow modifiers provide expected reliability on services with or without solids, air or vapors.
Conventional Tapered Bore Seal Chamber:
Mechanical Seals Fall When Solids or Vapors Am Present in Liquid
Many users have applied the conventional tapered bore seal chamber to improve seal life on services containing solids or vapors. Seals in this environment failed prematurely due to entrapped solids and vapors. Severe erosion of seal and pump parts, damaged seal faces and dry running were the result.

Modified Tapered Bore Seal Chamber with Axial Ribs:
Good for Services Containing Air, Minimum Solids
This type of seal chamber will provide better seal life when air or vapors are present in the liquid. The axial ribs prevent entrapment of vapors through.improved flow in the chamber. Dry running failures are eliminated. In addition, solids less than 1% are not a problem.
The new flow pattern, however, still places the seal in the path of solids/liquid flow. The consequence on services with significant solids (greater than 1%) is solids packing the seal spring or bellows, solids impingement on seal faces and ultimate seal failure.

Goulds Standard TaperBoreTM PLUS Seal Chamber: The Best Solution for Services Containing Solids and Air or Vapors
To eliminate seal failures on services containing vapors as well as solids, the flow pattern must direct solids away from the mechanical seal, and purge air and vapors. Goulds Standard TaperBoreTM PLUS completely reconfigures the flow in the seal chamber with the result that seal failures due to solids are eliminated. Air and vapors are efficiently removed eliminating dry run failures. Extended seal and pump life with lower maintenance costs are the results.

Goulds TaperBore^TM Plus: How It Works
The unique flow path created by the Vane Particle Elector directs solids away from the mechanical seal, not at the seal as with other tapered bore designs. And the amount of solids entering the bore is minimized. Air and vapors are also efficiently removed. On services with or without solids, air or vapors, Goulds TaperBore^TM PLUS is the effective solution for extended seal and pump life and lower maintenance costs.

1. Solids/liquid mixture flows toward mechanical seal/seal chamber.
2. Turbulent zone. Some solids continue to flow toward shaft. Other solids are forced back out by centrifugal force (generated by back pump-out vanes).
3. Clean liquid continues to move toward mechanical seal faces. Solids, air, vapors flow away from seal.
4. Low pressure zone create by Vane Particle Ejector. Solids, air, vapor liquid mixture exit seal chamber bore.
5. Flow in TaperBore^TMPLUS seal chamber assures efficient heat removal (cooling) and lubrication. Seal face heat is dissipated. Seal faces are continuously flushed with clean liquid.

Stuffing Box Cover and Seal Chamber Guide
The selection guide on this page and the Seal Chamber Guide are designed to assist selection of the proper seal housing for a pump application.

JACKETED STUFFING BOX COVER
Designed to maintain proper temperature control (heating or cooling) of seal environment. (Jacketed covers do not help lower seal face temperatures to any significant degree). Good for high temperature services that require use of a conventional double seal or single seal with a flush and API or CPI plan 21.
JACKETED LARGE BORE SEAL CHAMBER
Maintains proper temperature control (heating or cooling) of sea environment with improved lubrication of seal faces. Ideal for controlling temperature for services such as molten sulfur and polymerizing liquids. Excellent for high temperature services that require use of conventional or cartridge single mechanical seals with flush and throat bushing in bottom of seal chamber. Also, great for conventional or cartridge double or tandem seals.
Stuffing Box and Seal Chamber Application Guide

Stuffing Box Cover/Seal Chamber	Application
Standard Bore Stuffing Box Cover	Use for soft packing. Outside mechanical seals. Double seals. Also, accommodates other mechanical seals.
Jacketed Stuffing Box Cover	Same as above but also need to control temperatures of liquid in seal area.
Conventional Large Bore	Use for all mechanical seal applications where the seal environment requires use of CPI or API seal flush pans. Cannot be used with outside type mechanical seals.
Jacketed Large Bore	Same as Large Bore but also need to control temperature of liquid in seal area.
Tapered Large Bore with Axial Ribs	Clean services that require use of single mechanical seals. Can also be used with cartridge double seals. Also, effective on services with light solids up to 1% by weight. Paper stock to 1% by weight.
Tapered Large Bore with Patented Vane Particle Ejector (Alloy Construction)	Services with light to moderate solids up to 10% by weight. Paper stock to 5% by weight. Ideal for single mechanical seals. No flush required. Also, accommodates double seals. Cannot be used with outside mechanical seals.

Environmental Controls
Environmental controls are necessary for reliable performance of a mechanical seal on many applications. Goulds Pumps and the seal vendors offer a variety of arrangements to combat these problems.

1. Corrosion 2. Temperature Control 3. Dirty or incompatible environments

CORROSION
Corrosion can be controlled by selecting seal materials that are not attacked by the pumpage. When this is difficult, external fluid injection of a non-corrosive chemical to lubricate the seal is possible. Single or double seals could be used, depending on if the customer can stand delusion of his product. TEMPERATURE CONTROL
As the seal rotates, the faces are in contact. This generates heat and if this heat is not removed, the temperature in the stuffing box or seal chamber can increase and cause sealing problems. A simple by-pass of product over the seal faces will remove the heat generated by the seal (Fig. 25). For higher temperature services, by-pass of product through a cooler may be required to cool the seal sufficiently (Fig. 26). External cooling fluid injection can also be used.

DIRTY or INCOMPATIBLE ENVIRONMENTS
Mechanical seals do not normally function well on liquids which contain solids or can solidify on contact with the atmosphere. Here, by-pass flush through a filter, a cyclone separator or a strainer are methods of providing a clean fluid to lubricate seal faces. Strainers are effective for particles larger than the openings on a 40 mesh screen. Cyclone separators are effective on solids 10 micron or more in diameter, if they have a specific gravity of 2.7 and the pump develops a differential pressure of 30-40 psi. Filters are available to remove solids 2 microns and larger.
If external flush with clean liquid is available, this is the most fail proof system. Lip seal or restricting bushings are available to control flow of injected fluid to flows as low as 1/8 GPM. Quench type glands are used on fluids which tend to crystallize on exposure to air. Water or steam is put through this gland to wash away any build up. Other systems are available as required by the service.