Effect of Valve Pressure Drops:
For the flow of any fluid, the pressure ought to drop in the direction of flow. Both of suction & discharge valves will open just when there is a pressure drop across them. The influence of these pressure drops on the indicator diagram of the compressor is indicated in given fig. It is seen that as a result of throttling or pressure drop on the suction side the pressure inside the cylinder at the ending of the suction stroke is Ps whereas the pressure at the suction flange is P1. The pressures in the cylinder go up to the suction flange pressure Pt only after the piston has travelled a definite distance inward throughout which the volume of the fluid has decreased from (V p + Vc ) to V1.
Supposing the compression index to be n instead of ?, as the compression procedure is also polytropic because of heat exchange with cylinder walls and friction, we obtain
The expression for volumetric efficiency becomes like as
By considering the effect of pressure drop at the discharge valve as well, it may be indicated that the expression for volumetric efficiency is
Effect of Valve Pressure Drops