Temperature and volume changes play a critical role in flow testing. According to the ideal gas law (PV=nRT), pressure (P), volume (V), and temperature (T) are interrelated regardless of the volume flow or mass flow unit. 
Any change in temperature or volume will consequently affect the pressure within a closed system.
The effects of volume or temperature variation on flow testing are:
- Volume variation: An increase in volume reduces pressure and hence reduces the flow rate. A decrease in volume or volume compression increases the flow rate.
- Temperature variation: An increase in the temperature in the test part increases the pressure, which affects the flow testing measurement.
- Viscosity: An increase in temperature reduces fluid viscosity allowing the fluid to flow freely. This can result in a higher flow rate.
