TDC AND BDC is the important position of reciprocating engine or compressor, the clearance between TDC and top cover end, BDC and frame end must be adjusted with in limit for smooth operation of compressor.

RECIPROCATING COMPRESSOR -It has a piston and cylinder mechanism with automatic spring controlled inlet and exhaust valves. Delivery is usually to a receiver. The receiver is effectively a store of energy used to drive compressed air tools. The main advantages of reciprocating compressor are that it can achieve high pressure ratio.

TDC- Also called top dead center, it is top most position of piston in to the cylinder or we can say that the maximum distance covered by piston called TDC of reciprocating compressor.

Piston bumping clearance (clearance between TDC and outer end) should be maintained 2 mm.

BDC- This is also called bottom dead center , it is the bottom last position of piston in to the cylinder called BDC of reciprocating compressor.

Piston bumping clearance (clearance between BDC and frame end) should be maintained 1mm.

SWEPT VOLUME – It is the space between TDC and BDC and also called space covered by piston in to cylinder during operation called swept volume, it is measured in cubic inch or cubic centimetre.

FAD- it is called free air delivery and it measure the capacity of a compressor in term of the air flow it can handle. It is normally measured at standard see level (SSL).


In order to be practical there is a clearance between the piston crown and top of cylinder and also piston bottom and cylinder bottom. Clearances are providing in compressor to absorb shock which will otherwise occur due to piston striking the cylinder head.

 The air compressed to small clearance volume will expand to a large volume during suction stroke and thus reduce the intake of fresh air. This decreases the volumetric efficiency of the reciprocating compressor. For this reason clearance volume is kept as small as possible.


Assembly of head of four stroke engine explain the precaution that must be taken while assembly of head of engine and setting of tappet know more - click here


To know why we use temperature sensor in compressor outlet - click here 


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