So I am moving to a shop without 3 phase and the VFD I bought works, but it must soft start for 2 full seconds, in the meantime it must not have any back pressure (any shorter and the VFD will overload). The problem is unless the tank pressure is under 60 psi, the compressor will not fully start and will just linger at a slow speed which I am sure is bad for the motor.
What I found work is remove the unloader valve completely, and this would allow the compressor to spin up, and then close the valve to allow the tank to fill up.
What I need is some kind of relay controlled air switch that will basically bleed air until the motor spins up fully, then close it to allow the tank to fill up.
What am I looking for? Do such a beast exist, and can be triggered with the VFD using some kind of a control output?
Or I guess another thing I can do is to hook the hose from the unloader valve to a smallish (1 gallon) tank that would come up to pressure slowly enough for the motor to spin to full speed, then the unloader valve will bleed the tank dry once the pressure switch shuts off.