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Ordinary Spring-loaded Safety Valve and Improved High-lift Safety Valve for a Marine Boiler

A marine 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. 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.

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Spring-loaded valves are always fitted on board ship because of their positive action at any inclination. They are positioned on the boiler drum in the steam space.

The ordinary spring loaded safety valve is shown in Figure below. The valve is held closed by the helical spring whose pressure is set by the compression nut at the top.

The spring pressure, once set, is fixed and sealed by a Surveyor. When the steam exceeds this pressure the valve is opened and the spring compressed. The escaping steam is then led through a waste pipe up the funnel and out to atmosphere.

Boiler safety valve

Fig:Ordinary spring-loaded Boiler safety valve

The compression of the spring by the initial valve opening results in more pressure being necessary to compress the spring and open the valve further. To some extent this is countered by a lip arrangement on the valve lid which gives a greater area for the steam to act on once the valve is open. A manually operated easing gear enables the valve to be opened in an emergency. Various refinements to the ordinary spring-loaded safety valve have been designed to give a higher lift to the valve.

Boiler highlift safety valve

Fig:Boiler highlift safety valve

The use of improved high-lift safety valve

The improved high-lift safety valve has a modified arrangement around the lower spring carrier, as shown in Figure above. The lower spring carrier is arranged as a piston for the steam to act on its underside. A loose ring around the piston acts as a containing cylinder for the steam. Steam ports or access holes are provided in the guide plate. Waste steam released as the valve opens acts on the piston underside to give increased force against the spring, causing the valve to open further. Once the overpressure has been relieved, the spring force will quickly close the valve. The valve seats are usually shaped to trap some steam to 'cushion' the closing of the valve.

A drain pipe is fitted on the outlet side of the safety valve to remove any condensed steam which might otherwise collect above the valve and stop it opening at the correct pressure.



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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