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

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

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Theory of Machine
Crowning on pulleys helps

For automatic adjustment of belt position so that belt runs centrally
In increasing velocity ratio
Increase belt and pulley life
In decreasing the slip of the belt

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