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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
Categories
Air Conditioning BoilersCompressors DieselEngines Fire DetectorsFire Fighting Forms
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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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5/1/2015 Marine Engineering Study Materials - Page 55 of 89 - www.marineengineeringonline.com
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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
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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
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