Not sure this is the correct forum to use here but this applies to the whole facility, not just the CNC or Finish booth.

We're trying to find the best way to utilize the two air compressors that we have. We currently just have both of them hooked up to the same header, with their own individual air dryers and regulators that feed into the header.

One is an older rotary screw, 7.5hp and the other is a twin 10hp piston (nearly new). The rotary screw can actually supply the entire facility just fine.... until we start running the flatline sprayer and all the associated handheld air sanders. The addition of the flatline was the reason we added the twin piston.

Anyhow, I don't think we have it set up well and we're wasting energy. The rotary screw (a Sullair) has a fairly long run cycle and is obviously designed for continuous air usage. We'd like to have this all plumbed such that the Sullair carries as much of the total load as possible and the twin pistons would be there as backup.

Unfortunately the tank pressure on the the Sullair is 130 and the piston is 150, and I think what this ends up meaning is that the piston is most likely to be adding air into the system the most.

Both of them are on regulators that are set at 98psi going into the header. I've tried setting the regulator on the piston compressor to 95, and the Sullair to 100, thinking that this would help ensure the Sulliar to be providing the bulk of the CFM. This doesn't work however, because the regulator on the piston compressor will try to offgas that 5psi excess.

So I'm sorta back to square one here. How do I set these two compressors up such that the rotary screw is providing basically all the air for the shop, and the piston only feeds the header when the header pressure drops below, say, 95?

Would using check valves help with this?

Can you adjust the cut-in and cut -out psi to be higher on the screw than the piston comp or lower them on the piston pump?

Talk to a professional Compressor company. They should be able to set up a control for you. It will be a PLC control as mentioned earlier but hopefully there is an existing unit so you don't have to start from scratch. I believe you want a system that uses the rotary compressor as primary and when the pressure drops to a certain number the piston kicks in.

We have two identical rotary compressors. They are slaved to each other. Every day the primary compressor switches. The secondary comes on when the pressure drops below a certain value. Works great, we won't run out of air for a while, we can service the compressors when the factory is running and they act as a backup to one another.

I am a fan of rotary, they are 100% duty cycle. Pistons can't do that (and they are loud).

Good luck!

Bill