Q: 1 Explain the operation of a main engine Exhaust valve which is operated hydraulically?
A: A hydraulic pump, operated by the exhaust cam supplies the hydraulic oil to operate the valve. A small permanent vent ensures that air is excluded fro the system. This leak off of oil returned to the air spring cylinder for lubrication and is then drained away. The hydraulic pump is supplied with a make up supply via a non return valve and a relief valve.
As the cam rotates in time with the crankshaft it lifts the plunger on the hydraulic pump. Oil displaced by the pump plunger displaces the exhaust valve operating piston, moving it and the exhaust valve spindle downwards against the air spring pressure and opening the exhaust valve.
The exhaust gas passes over the spinner, rotating the exhaust valve spindle, this reduces distortion due to uneven temperatures and helps remove deposits as the valve closes .when the cam passes its peak, the pump plunger moves downwards and the compressed air in the air spring closes the valve. As the operating piston enters the damping pin, the closing is slowed, thus preventing hammering of the valve.
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