# Calculation Methods - PD Pump or Compressor

The volumetric flow delivered by a positive displacement pump is given by the expression: Q = S DR Ecorr or in descriptive terms, operating speed x displacement volume x a volumetric efficiency factor. The volumetric efficiency factor, by default is 1 unless an entry has been made in the pump database. Volumetric efficiency can be a complex function of operating speed. If Adiabatic compression is selected as the heat loss model then FluidFlow estimates the output temperature from the expression T2 = T1(P2/P1)n where pressures and temperatures refer to absolute static conditions and n is the (Cp/Cv-1)/(Cp/Cv) ratio.