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Boiler Mountings - Safety Valves, Mam Steftm Stop Valve & Auxiliary Steam Stop Valve

Marine boiler is an apparatus used to produce steam, either for a ships main propulsion or for auxiliary machinery. A boiler is, in general, any closed liquid-containing vessel to which heat is applied. It is also called steam generator as it transforms water into steam. Boilers generally consist of metal shells (or bodies), headers and tubes that form the container of the steam and water under pressure and, in certain types, of the furnace and passages for the hot gases. Some boilers have additional drums called superheaters.

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Boilers fall into two categories: water-tube and fire-tube ones, according to which substance passes through the tube and which flows round the outside. They are used to provide steam for propulsion or for various ship services.

A boiler is used to heat feed water in order to produce steam. The energy released by the burning fuel in the boiler furnace is stored (as temperature and pressure) in the steam produced.

The use of boiler mountings - Safety valves, Mam steftm stop valve, Auxiliary steam stop valve etc.

Certain fittings are necessary on a boiler to ensure its safe operation. They are usually referred to as boiler mountings. The mountings usually found on a boiler are: safety valves, main steam stop valve, feed check valve, water level gauge, pressure gauge connection, air release cock, sampling connection, blow down valve, scum valve, etc.

Safety valves :These are mounted in pairs to protect the boiler against overpressure. Once the valve lifting pressure is set in the presence of a Surveyor it is locked and cannot be changed. The valve is arranged to open automatically at the pre-set blow-off pressure.

Mam steftm stop valve :This valve is fitted in the main steam supply line and is usually of the non-return type.

Auxiliary steam stop valve: This is a smaller valve fitted in the auxiliary steam supply line, and is usually of the non-return type.

Feed check or control valve :A pair of valves are fitted: one is the main valve, the other the auxiliary or standby. They are non-return valves and must give an indication of their open and closed position.

Water level gauge :Water level gauges or 'gauge glasses' are fitted in pairs, at opposite ends of the boiler. The construction of the level gauge depends upon the boiler pressure.

Pressure gauge connection :Where necessary on the boiler drum, superheater, etc., pressure gauges are fitted to provide pressure readings.

Air release cock :These are fitted in the headers, boiler drum, etc., to release air when filling the boiler or initially raising steam.

Auxiliary steam plant system

Fig:Auxiliary steam plant system

Sampling connection :A water outlet cock and cooling arrangement is provided for the sampling and analysis of feed water. A provision may also be made for injecting water treatment chemicals.

Blow down valve :This valve enables water to be blown down or emptied from the boiler. It may be used when partially or completely emptying the boiler.

Scum valve: A shallow dish positioned at the normal water level is connected to the scum valve. This enables the blowing down or removal of scum and impurities from the water surface.

Whistle stop valve:This is a small bore non-return valve which supplies the whistle with steam straight from the boiler drum.

Recirculating valve : The purpose of the recirculating valve fitted in a boiler fuel system is to enable the fuel oil to be brought up to the desired temperature quickly for combustion.


Boiler mountings (water-tube boilers)

Watertube boilers, because of their smaller water content in relation to their steam raising capacity, require certain additional mountings: Automatic feed water regulator. Fitted in the feed line prior to the main check valve, this device is essential to ensure the correct water level in.the boiler during all load conditions. Boilers with a high evaporation rate will use a multiple-element feed water control system .

Low level alarm. A device to provide audible warning of low water level conditions.

Superheater circulating valves. Acting also as air vents, these fittings ensure a flow of steam when initially warming through and raising steam in the boiler.

Sootblowers, Operated by steam or compressed air, they act to blow away soot and the products of combustion from the tube surfaces. Several are fitted in strategic places. The sootbiower lance is inserted, soot is blown and the lance is withdrawn.




Summarized below marine boiler detail Info pages:

  1. Requirement for various boiler types - water tube boilers and more
    2. The watertube boiler is employed for high-pressure, high-temperature, high-capacity steam applications, e.g. providing steam for main propulsion turbines or cargo pump turbines. Firetube boilers are used for auxiliary purposes to provide smaller quantities of low-pressure steam on diesel engine powered ships.....

  2. Fire tube boilers working principle and operational procedure
    3. The firetube boiler is usually chosen for low-pressure steam production on vessels requiring steam for auxiliary purposes. Operation is simple and feedwater of medium quality may be employed. The name 'tank boiler is sometimes used for firetube boilers because of their large water capacity. The terms 'smoke tube' and 'donkey boiler are also in use....

  3. Exhaust Gas Boilers And Economisers working procedure
    4. The use of exhaust gases from diesel main propulsion engines to generate steam is a means of heat energy recovery and improved plant efficiency.The auxiliary steam installation provided in modern diesel powered tankers usually uses an exhaust gas heat exchanger at the base of the funnel and one or perhaps two watertube boilers .....

  4. The use of boiler mountings
    5. Watertube boilers, because of their smaller water content in relation to their steam raising capacity, require certain additional mountings: Automatic feed water regulator. Fitted in the feed line prior to the main check valve, this device is essential to ensure the correct water level in.the boiler during all load conditions. Boilers with a high evaporation rate will use a multiple-element feed water control system ....

  5. Purity of boiler feedwater
    6. Most 'pure' water will contain some dissolved salts which come out of solution on boiling. These salts then adhere to the heating surfaces as a scale and reduce heat transfer, which can result in local overheating and failure of the tubes. Other salts remain in solution and may produce acids which will attack the metal of the boiler. An excess of alkaline salts in a boiler, together with the effects of operating stresses, will produce a condition known as 'caustic cracking'. This is actual cracking of the metal which may lead to serious failure.....

  6. The steam-to-steam generator working principle and operational procedure
    7. Steam-to-steam generators produce low-pressure saturated steam for domestic and other services. They are used in conjunction with watertube boilers to provide a secondary steam circuit which avoids any possible contamination of the primary-circuit feedwater. The arrangement may be horizontal or vertical with coils within the shell which heat the feedwater.....

  7. How to control combustion in a marine boiler
    8. The essential requirement for a combustion control system is to correctly proportion the quantities of air and fuel being burnt. This will ensure complete combustion, a minimum of excess air and acceptable exhaust gases. The control system must therefore measure the flow rates of fuel oil and air in order to correctly regulate their proportions.....

  8. Safe boiler operation - Preparations & raising steam
    9. All boilers have a furnace or combustion chamber where fuel is burnt to release its energy. Air is supplied to the boiler furnace to enable combustion of the fuel to take place. A large surface area between the combustion chamber and the water enables the energy of combustion, in the form of heat, to be transferred to the water.....

  9. Fuel oil burning process - various design burners
    10. Marine boilers currently burn residual low-grade fuels. This fuel isstored in double-bottom tanks from which it is drawn by a transfer pump up to settling tanks. Here any water in the fuel may settle out and be drained away.

  10. Boiler arrangement - combustion process - supply of air
    11. Combustion is the burning of fuel in air in order to release heat energy. For complete and efficient combustion the correct quantities of fuel and air must be supplied to the furnace and ignited. About 14 times as much air as fuel is required for complete combustion....

  11. Ordinary spring-loaded safety valve and improved high-lift safety valve for a marine boiler
    12. Safety valves are fitted in pairs, usually on a single valve chest. Each valve must be able to release all the steam the boiler can produce without the pressure rising by more than 10% over a set period.....

  12. Correct working level for marine boilers - use of water level gauges
    13. The water level gauge provides a visible indication of the water level in the boiler in the region of the correct working level.

  13. How to maintain water level in a marine boiler ?
    14. A modern high-pressure, high-temperature watertube boiler holds a small quantity of water and produces large quantities of steam. Very careful control of the drum water level is therefore necessary. The reactions of steam and water in the drum are complicated and require a control system based on a number of measured elements......

  14. Safety precautions for working with marine boiler
    15. All boiler controls, regulators, alarms and trips must be tested regularly in accordance with the applicable Planned Maintenance System and maker’s recommendations. Each test is to be recorded with the signature of the Engineer Officer who conducted the test....



Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||



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