Cylinder Relief Valve: Construction, Working and Overhaul.

cylinder relief valve

A cylinder relief valve is provided for each cylinder of two and four stroke marine engine; which protects the cylinder head from the resulting combustion force. The valve operates as the cylinder pressure exceeds of its safe operating limit.

The valve opens to provide the excess pressure inside the combustion chamber to escape out. The Relief valve is designed in such a way that the cylinder pressure never reach more than of its 10% above the normal working pressure.

A spring keeps the relief valve under closed condition while the lifting pressure is adjusted by an appropriate packer thickness. Once operated it reliefs the pressure quickly out of the cylinder avoiding any damage.

The valve and the spindle are separated in such a way that the valve can be positioned correctly after opening.

Procedures for overhauling of Cylinder Relief Valve.

1) Remove the relief valve from cylinder head and clean externally
2) Hold the valve at bench vice and dismantle the parts.
3) Clean the parts in diesel and dry with lint free cloths.
4) Inspect valve and valve seat for pitting ? burning, carryout lapping to remove these and clean with diesel to remove the lapping paste.
5) Inspect spring for crankcase or wrapping. Measure free length repeal if necessary.
6) Assemble in reverse order.
7) Replace copper gasket after annealing.
8) Apply molyKot (Anti-Cleasing parts) on the thread.
9) Mount the valve on the test-rig and set light pressure as per manual.

Cylinder Relief Valve Assembly.

cylinder relief valve

Function : To release the excess pressure from the cylinder and warn the incorrect condition of the unit.


Lifting of safety valve relieves the dangerous pressure in cylinder and warns of the incorrect condition. The reason for this must be ascertained and corrective action must be taken. The high temperature gas frame expelled may damaged the valve seat.

Safety valve area is only designed to relive excess gas pressure and may be sufficient to prevent damaged in the event of cooling water or oil leaking into cylinder before starting ON engine for the first time it should always be tunned slowly with indicator cocks open to expel any leakage.

The cylinder valve relief the pressure when the pressure exceed 10% to 20% of maximum mean pressure. Small amount of lifting is only permitted and the escaping gases are directed toward a safe outlet. The spindle and valve are two different pieces, so that valve can correctly sits on seat.

The operation of cylinder relief valve is the indication of fault in the engine, which should be identified and corrected as soon as possible. The valve itself should be examined as earliest as possible.

Helical Valve Spring

The spring is made-up of vanadium /silicon-chrome mostly, spring wire is being tempered and hardened in oil to the appropriate standards. It is then mounted inside the housing which is held by the upper and lower spring carrier.

The Valve and Stem

The valve and the spindle is made-up of high grade stainless steel

Causes of Cylinder Relief valve lifting?

A normal lift of safety valve can occur in the following situations:
1) If the engineer supplies too much fuel during start of the engine.
2) If air is being used as break when stopping an engine for reversal or during a “rash stop” high compression pressure about top dead center may cause safety valve to lift momentarily.
3) It can also occur when the engine is run on full astern direction for a long period of time. under such condition the bridge must always be informed of the astern running at limit.
4) Over-loading of engine.

However, some situations can cause the relief valve pressure to rise when the engine operates under normal load conditions.
1)Badly leaking fuel injector, through loose nozzle or injecting hoses.
2) Fuel pump setting is low or high or incorrectly timed.
3) Water leaking into combustion chamber.
4) Scavenge fire.

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