Resistance to air flow stated in inches of H2O or PSI or kg/cm2 or bar. Though, compressors pump air, they do not make pressure. The system creates the back pressure which the compressors must pump against to overcome.
- In case of Centrifugal Compressors, during very low flow conditions, the impeller cannot add enough energy to overcome the system resistance or backpressure. Due to which the flow reverses its direction and cause surge or stalling of the Compressor.
- Whereas in a piping system, if air velocity is too fast, then back pressure can occur, also resulting in pressure drops. In case of nozzles, the back pressure can cause due to clogged exhaust, restriction in exhaust thereby substantially affecting their performance. Such concerns can be offset by using larger diameter pipe, tube or hose connected to the amplifier outlet and minimizing bends and other possible restrictions.
- In case of pneumatic gauging, air is supplied at constant pressure through the orifice and the air escapes in the form of jets through a restricted space which exerts a back pressure. The variation in the back pressure is then used to find the dimensions of a component.