Convert my compressor to regulator controlled?

[miketyler]

I have a 220v compressor that has served me faithfully for the last 20 years. Its a 3 cylinder Atco i believe? However, it's a constant run type that uses unloaders. The motor runs constantly but once target pressure is reached, the pump free wheels and pump valves remain closed. How can I convert this unit to motor cut-off type?

 

[z28snksknr]

You would need to add a high pressure cutoff switch that will kill motor power - these are readily available and relatively simple to install. If you do not want to mess with trying to defeat the unloaders, just set the high pressure cutoff switch a few psi lower than the unloader set pressure. That way the motor will cutoff before the pump gets unloaded, then turn back on when the pressure gets below your cutoff switch low pressure point.

Just be sure to install the cutoff switch upstream of your pressure regulator!!

 

[rlitman]

Weird. Was that compressor once made for use with a gas engine?
You can get a pumptrol, and have that switch a contactor for the motor, but if you want to do it right, you need to get a proper compressor pressure switch with an unloader valve in it, and plumb the unloader into the line between the pump and the tank check-valve, so that the motor isn't fighting pressure when it starts.

 

[Steevo]

I have an old Quincy compressor that is set up the same way as yours, with pressure driven unloaders and constant-run motor. I plan to use the pump and motor on a different tank, and use a pressure switch to start/stop the motor as z28snksknr suggested above.

 

[miketyler]

Thanks for the info. Is there an all inclusive kit I can buy that is made for converting unloader type compressors? It may have originally been intended for construction or mobile use. She's an oldie but a goodie and is actually a Fusheng 3 cylinder model. The motor is almost as big as the compressor. I have pics around here somewhere but this is the pump.

 

[MBfreak]

By all means try it.
There may be a snag in that the electric motor will struggle to start against 3 pistons with pressure on top.
However, that depends on motor type and available power supply

Good luck,

Ola

 

[Kevin C]

One thing to be aware of is motors have a rating on how many start cycles per hour they are allowed to have.

Each start generates signifigant heat in the windings.

If the duty cycle of the compressor is such that you get several starts per hour and limited running time you can overheat the motor.

Every compressor is differant.... I know about this problem from personal experiance. At one plant I worked at we burnt out two motors in a row from this. The compressor tech explained that the problem was we we were exceeding the max # of starts per hour. Once the system was converted to continuous run it was fine.

Its an obscure problem, but there is a reason that some compressors are set up that way. Your usage VS tank size may keep the starts per hour pretty low. At the very least, make sure the motor has thermal protection.

Kevin

 

[miketyler]

Is there a way I can tell if I have such a duty-cycle limited motor? The motor is nearly as big as the compressor. Pics coming, still interested in pursuing this but not at the risk of replacing a motor.