[1ctoolfool]

The compressor I have Chicago Pneumatic QRS7.5 Rotary looks like the identical compressor unit for 3-5-7.5 units with just a different motor and pulley set up.

My latest plan is to order a 5 hp motor, pulley, and belts from CP and swap out my unit down to 5HP.

The other option is to sell the 7.5 and buy a new 5 HP Unit.

Anyone know details on these units, Is this a valid assumption?

Thanks
Joe V

[Geof]

The compressor I have Chicago Pneumatic QRS7.5 Rotary looks like the identical compressor unit for 3-5-7.5 units with just a different motor and pulley set up.

My latest plan is to order a 5 hp motor, pulley, and belts from CP and swap out my unit down to 5HP.

The other option is to sell the 7.5 and buy a new 5 HP Unit.

Anyone know details on these units, Is this a valid assumption?

Thanks
Joe V

Hang loose until the end of the month. I have a 5hp unit on order with delivery promised on June 25. I can take pics for you to compare.

I think your assumption is correct, I came to the same conclusion looking at the overall dimensions.

Also when I bought my big rotary the salesman said something about the same head being used with different motors for different output. I think rotaries can operate over a wide range of rpm.

It just came to me...maybe you don't need to get a 5 hp motor. You are going to get a lower output at 5hp because the motor pulley is smaller. Just put a smaller pulley on your 7hp motor. That will allow it to come up to speed faster and with less load so your voltage drop will be less and for a shorter time.

But I still think the best solution is the centrifugal clutch pulley .

[HuFlungDung]

Anyone use a VFD on a rotary screw compressor? The VFD gives a nice soft start to the motor, plus, maybe you could even throttle back the rpms a bit when the demand is low.

I've been mulling over the idea of replacing my old 5hp piston compressor for something quieter, and with more capacity, in case I get bitten by the Haas bug a second time

[Geof]

Anyone use a VFD on a rotary screw compressor? The VFD gives a nice soft start to the motor, plus, maybe you could even throttle back the rpms a bit when the demand is low.

I've been mulling over the idea of replacing my old 5hp piston compressor for something quieter, and with more capacity, in case I get bitten by the Haas bug a second time

I think for the combined cost of a Chicago Pneumatic rotary and the VFD you could get a Kaeser or Atlas Copco. Both of these start off-load, which is more or less equivalent to soft-start, and then just cycle the compressor while the motor keeps running. If there is no air drawn for several minutes the motor shuts off and then kicks back on when needed. If your air system is completely leak free you can leave these things powered up 24 hrs.

The noise difference compared to a piston compressor is dramatic. It is possible to stand right beside either of these units and have a normal conversation.

[1ctoolfool]

i've found some inexpensive VFD's with built in phase converters, but they only work on 3 phase, mine's a single phase 7.5HP unit, I haven't found any motor controls for single phase AC.
waiting to hear from CP customer support.
jv