Compressor Problem

[brotherbrown831]

I am in the process of building a compressor sound proofing box for my HF 5hp 21 gallon compressor. I will post a thread about that in more detail later. Right now my question is about compressor shutdown pressure release valves.

Part of my design is an external switch that controls a 20 amp circuit inside the box for the compressor and the exhaust fan. If I shut down the compressor while its still charging by using this power cutoff switch the pressure release valve does not bleed off residual pressure in the pump. If I turn the switch back on the compressor must work very hard to get going again.
However if I turn the compressor off with the small switch built into the compressor the pressure is released and it takes no effort at all to start back up.

Can anyone help me understand what's happening here? Thanks!

 

[Fixnair]

The head pressure is released ONLY when the pressure switch opens. The release valve is integral to the pressure switch and if you shut the power off before the pressure switch opens there will be no relieving the head pressure.
You could ,if you're handy, install a normally open solenoid valve in tHe line going to the bleed valve on your pressure switch and wired in to the power supply to the compressor so when you disconnect the power from the compressor the solenoid would open and bleed the discharge line down. When you turn your compressor back on the solenoid would then close allowing normal operation.
They also make a discharge check valve that allows air to flow through it while the compressor us running and when the compressor stops the Check valve automatically opens the upstream side to atmosphere ho relieve the load on the compressor. They work well for a year or so then they start leaking. Not a long term fix.