Theory of Machine
The advantage of the piston valve over the slide valve is that in the former case

The pressure developed being high provides tight sealing
Both wear and power absorbed are low
Wear is less
Power absorbed is less

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Theory of Machine
Angle of action of cam is defined as the angle

Moved by the cam from beginning of ascent to the termination of descent
Of rotation of the cam for a definite displacement of the follower
Moved by the cam from the instant the follower begins to rise, till it reaches its highest position
Through which the cam rotates during the period in which the follower remains in the highest position

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