The effect of the clearance in a reciprocating machine on piston force

Cylinder clearance is generally understood as the space or gap that exists in certain parts of the cylinder due to requirements related to the compressor’s structure, manufacturing, assembly, and operation; this space or gap is referred to as the clearance volume. The clearance volume is the space between the top of the piston and the cylinder head at the end of the compression stroke. The presence of clearance volume is detrimental to the compression process, as it reduces the amount of air drawn in by the compressor and lowers the utilization rate of the cylinder’s working volume. The clearance volume, also known as the \"harmful volume\" or \"harmful space\", and simply referred to as \"clearance\", is created to prevent collision between the piston face and the cylinder head, as well as to meet the practical requirements for installing intake and exhaust valves. ”On Baidu. After reading this, it should resolve your doubts :)

The clearance prevents the piston from colliding with the cylinder due to the thermal expansion of the piston rod; its presence reduces the amount of air drawn in during a working cycle, which in turn lowers the actual compression work. The function of the clearance in a reciprocating compressor is to prevent the piston rod from expanding due to heat and hitting the cylinder wall ； Prevent liquid hammer ； Inertial force of buffer piston ； Prevent debris from entering the cylinder

The bore diameter of the cylinder cannot be changed; what changes is the gap between the piston face and the end face of the cylinder head at the end of the exhaust process. This should not affect the piston force, as the piston force is a fixed value once the compressor is manufactured by the factory. The magnitude of this force depends on the rotational speed and the weight of the piston components； The combined piston force includes the piston force, gas force, and friction force; the theory of the combined piston force is less than the piston force. This is my personal understanding; please correct me if I’m wrong. Thank you! :)

The clearance affects the magnitude of the expansion process, thereby directly influencing the actual magnitude of the gas force, although the effect is relatively small.

Because the instantaneous pressure inside the cylinder has changed