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Pressure Vacuum (PV) ValveMay 1, 2014 1:05 pm | Leave a Comment | Frozee

Moderate pressures of 0.24 bar acting on large surfaces in liquid cargo tanks are sufficient to cause

damage and rupture. The pressure on each unit of area multiplied by the total area gives a large

loading on the underside of the top of a tank or other surface, which may then buckle or the metal

plate may be torn. Similarly, pressure drop within a tank can cause damage due to greater

atmospheric pressure on the outside.

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Scavenge Port Inspection onboard

Ships

Operation of Freshwater Generator with

Jacket Cooling Water

Shell and Tube Freshwater Generator

Testing of Water Mist Fire Fighting

System onboard Ships

Maintenance of Water Mist Fire Fighting

System

Water Mist Fire Fighting System

Alexa Rank

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Pressure / vacuum valves in the ventilation system will prevent either over or under pressure. They

are set usually so that tank pressure of about 0.14 bar will lift the main valve (The smaller valve will lift

along with it) and release excess pressure. The vapour passes to atmosphere through a gauze flame

trap. Drop in tank pressure compared with that of the outside atmosphere will make the small valve

open downwards to equalize internal pressure with that outside.

Pressure vacuum valves can relieve moderate changes in tank pressure due to variations in

temperature and vapour quantity. A drop towards vacuum conditions as the result of the

condensation of steam will also be handled by the valve. Rapid pressure rise due to an explosion

would not be relieved.

The fast rate at which a tank is filled while loading produces a very rapid expulsion of the previous

contents (vapour and inert gas). The pressure vacuum valve is not designed as a filling vent and

neither should the tank hatch be left open. The latter method of venting can cause an accumulation

of flammable vapours at deck level. Tanks should be vented while filling, through mast head vents or

through special high velocity vents.

References

General Engineering Knowledge by H.D. McGeorge

and ChecklistsGeneralEngineeringKnowledge HeatExchangers Hydraulics Inert Gas

System Instrumentation and

Control Lubricating Oil MarineElectrical TechnologyMEOExaminationStudy MaterialsMotor EngineeringKnowledge NavalArchitecture and ShipConstruction Pumps

Refrigeration Safety andEnvironmental ProtectionSewage Treatment Turbochargers

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Posted in: Inert Gas System | Tagged: inert gas system, marine engineering study materials, pressure vacuum

valve, pv valves

Soot BlowerMay 1, 2014 1:00 pm | Leave a Comment | Frozee

Between periodic boiler cleaning the gas surfaces of the boiler tubes should be kept as clean as

Apr

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practicable. To facilitate this, soot blowers, steam or air operated, are often fitted. They enable the

tube surfaces to be cleaned of loose sooty deposits rapidly without shut down of the boiler.

Figure below shows a typical soot blower arrangement fitted to a Scotch type boiler.

Working

With steam supplied to the blower and the steam supply line thoroughly drained. Rotation of the

blower hand wheel causes the supply tube and nozzle to move towards the combustion chamber.

Nozzle and tube are rotated as they move inwards by means of a scroll cut in the nut and a stationary



pin A in the body assembly that runs in the scroll. Ports in the tube communicate the steam supply

line with the nozzle.

The arrangement enables rotating, fine, high pressure jets of steam to be discharged to the tube

plate over a considerable area.

When not in use, the retractable nozzle of the blower is well within the housing tube and is therefore

protected from overheating, which could cause burning and distortion of the nozzle.

Too frequent use of the blower should be avoided as this could cause wastage of the tube plate. It is

advisable to operate the blower regularly even if the boiler tubes are clean (in this case without steam

supply to the blower) to ensure the blower unit is free and in operable order.

References

General Engineering Knowledge by H.D. McGeorge

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Posted in: Boilers | Tagged: boiler soot blower, marine engineering, marine engineering study materials, soot

blower

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