Pulleys

[Fiji Cool]

Bula, I am a student of RAC from Suva Fiji and am finding a little bit of trouble with one question:

If you want to increase the compressor speed on an open type compressor....do you alter the compressor pulley or the motor pulley?

I assume it is the motor pulley, but how and why do you alter it?

Vinaka

[Brian_UK]

The speed of the compressor is related to the motor speed and the ratio of the pulley sizes.

You can change either pulley but you need to maintain a reasonable belt contact area on the pulley.

Also ensure that the motor can run at the increased load.

edit: Some calculations on belt drives may help you....
http://www.freestudy.co.uk/dynamics/pulleys.pdf

[Don Davis]

You can make the drive pulley (AKA Sheave) bigger or the driven sheave smaller. Generally, the drive sheave is changed because it's smaller and less expensive. However, you do have to watch that the belt contact area doesn't get too small allowing the belt(s) to slip.

Go to a belt manufacturer's web site or get a handbook- typically free- that lets you imput the actual sheave sizes and belt length to see if the combination is capable of transmitting the required HP. Be sure to use the recommended safety factors.

You may have to use sheaves that use more belts to transmit the load. Switching from standard, smooth, v-belts to the ones that have little notches cut out will increase the rating and may let you keep the same number of belts.

Make sure the motor has the required horsepower available to handle the new duty.

Make sure the compressor manufacturer is ok with the increased speed.

Make sure you're dealing with 'conventional' sheaves/belts. Some manufacturers use propriatary systems that won't interchange.

Speed change will be proportional to the change in sheave diameter.

[chemi-cool]

The motor pulley is what you change.

Compressor shaft is tapered and is not every workshop can make a pulley that will fit.

motor pulley is cheap and easy to make and change.