VALVE ROTATION

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•              gives more even seat and face temperatures.

•              reduces effect of small leakages as it prevents single area  overheating, this gives less  chance of concentrated corrosion and erosion.

•              minimises build up on sealing faces.

•              ideal for engines burning heavy oil

There are two main methods currently in use, either vane rotators or mechanical rotators.

Vane rotators

•              Simple method  with no moving parts.

•              May cause back pressure and turbulence in the gas duct.

•              Possibility of inducing vibration

Rotacaps (mechanical valve rotators)

 Operation of Rotacap

•              with valve in closed position bellville washer is loaded against body.

•              as valve opens washer is compressed and load is transferred to ball.

•              further increase in pressure and ball moves along ramp causing rotation.

•              as valve closes the washer bears against the body relieving the pressure on the balls and the ramp springs return them to original position.

 A typical profile gauge for checking  seat wear and valve flap burn down. The gauge normally clamps onto the valve stem for datum position.

Valve cooling

•              reduction in temperature especially advantageous with HFO.

•              reduces distortion.

•              reduces stem temperatures allowing smaller guide/stem clearance.

•              allows use of cheaper materials and reduces need for hardening.

•              more necessary on large valves than small since more heat to be removed even though temperatures are similar.