A positive displacement blower has no built-in compression ratio. It simply displaces a volume of air or gas from the inlet side to the discharge side and can operate against a back pressure of up to 1 bar (14.5 psig). Back pressure is a function of process resistance to flow, and the blower forces the air or gas through the downstream system.

When working against higher back pressures, it is inherently more efficient to internally compress the air or gas - this is where we recommend our screw compressors suitable for pressures above 1 bar (14.5 psig). The pressure limit depends on whether you require oil-free compression or whether oil carry-over is acceptable. Our specialty is oil-free air but we manufacture all screw compressor types. For the same flow capacity, screw compressors are considerably more complex and costly than blowers: however, at pressures exceeding 0.9 bar (13 psig), an oil-free screw compressor may offer better efficiency and hence a payback of the higher initial investment through energy savings.

Both machines are of the positive displacement type and can also be used as vacuum pumps.