Spinner or valve rotator is fitted to exhaust valve stern to rotate the valve during operation particularly in diesels engines burning residual fuel oils containing elements like vanadium and sodium.
In case any hard materials logged at a particular point between the valve and the seat, it will get repeatedly hammered forming a deep dent and allowing combustion gases to leak, there will be intense local temp rise and further damage due to erosion by high speed gas. A valve rotator may be of advantages in braking up the deposit. Rotation of the valve results in even temperature distribution around sealing surface and reduces carbon build-up. Rotation of the valve has a polishing effect removing combustion deposit between the valve and seat.
In 2-stroke engine, the hydraulically operated exhaust valve is provided with winged part on the stem in way of the gas stream. the valve is rotated by the high speed exhaust gas flowing past it.
In 4-stroke engines rotocap is fitted to the exhaust valve operating mechanism for the same purpose.
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