the effeect of Hp on performance

Questions & AnswersCategory: Generalthe effeect of Hp on performance
Bryon Conn asked 1 year ago


I have bought an air-end screw that its relations between rotor speed, required power of electromotor and produced pressure are described in its specifications chart. 

An interesting point that is described in the specifications chart is that for a constant rpm of the electromotor, say 2500 rpm, higher pressure could be produced by increasing the torque (or the electro motor’s power). How is this phenomenon explained while the rotating speed of the rotors is not changed?

Best regards

Bryon Conn.

specifications chart.


1 Answers
Cas Staff answered 1 year ago


Thanks for your question.

You need to think about this the other way around. Instead of

“higher pressure could be produced by increasing the torque”

read it like this:

“higher pressure requires a higher torque.

Screw air compressors are fixed displacement machines – for every turn of the screw, a fixed amount of air is pushed out.

Which means, that for a given RPM, a fixed amount of compressed air is produced.

(in reality, at higher pressures, the output is less because the losses increase at higher pressures. Also not I am talking about FAD (free air delivery), or normalized compressor output here).

Back to you question: at a higher pressure, a higher torque is required from the motor.

So if you want to use this element for a 100 psi compressor, you will need a smaller motor, compared to if you want to use this element for a 190 psi compressor.

Hope this makes sense 🙂