reciprocating air compressor

A great answer!

To elaborate further on your question, provide compressor make and size.

compressor model - TBTD RM

MAKE- KIRLOSKAR BROTHERS LTD

AND ALSO PLEASE TELL ME WHY A GAP IS MAINTAIN IN PISTON RINGS

Piston rings are normally made up of wear resisting materials like gray cast iron, carbon filled Teflon and like. These materials have relatively higher coefficient of expansion compared to cylinder/liner in which they reciprocate. More over the cylinder is cooled by air or water as to remove the heat so they are subjected to lesser expansion.

The expansion of the piston ring is to be accommodated. The ring expands in all directions, more so circumferentially and this piston ring gap accommodates this expansion. If no or less gap exists, the ends of ring butts soon and further expansion leads to excess friction which would leads to accelerated wear.

If this gap is excess, the air/gas may not be retained well during compression stroke. Ideally the gap should be just enough to get filled on working (heating). This will be very difficult to achieve since they wear and end up in excess gaps. To take care of this happening many arrangements are in use as shown in the figure.