# Unloader valve on an old Worthington 2stage?



## Cruciform (Nov 12, 2020)

I recently acquired an old Worthington compressor, it ran well, until the old 3phase motor went south. I've since replaced it with an equal spec motor, and it runs well, but it cannot start after filling due to the high pressure left in the cylinders. It appears there are pressure actuated unloaders on the top if the cylinder heads, I took them apart and cleaned them, but also they aren't hooked up to anything. If I push them manually when the compressor is filled, nothing really happens. I think it would be best to install one in-line and block these off. The lines coming off the pump are about 2" Steel pipe, and this is a dual stage compressor, pressure is set at about 175 PSI shut off, 125 psi or so turn on. What are my options here?






























ignore the piece of pipe on the top, its not part of the compressor.


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## stevon (Mar 5, 2019)

Cruciform,

I see a 1/4" copper line in the photo with a little valve T handle going into the tank fill piping. It looks like 1/4" tubing is attached to the bleed valve under the electric pressure switch. The "T" valve on the 1/4" line should not be needed or used. When the electric shutoff switch reaches the set cut off pressure and turns off the power, the bleed valve should be open and a "hiss" should be heard for a short time until the air is let out of the fill tube. If the check valve leaks, a constant hiss sound will be heard until the tank is drained of all the air pressure(not good) The check valve needs to be replaced in that case. Open the T valve and see if it constantly leaks air under the electric pressure switch.

Stephen


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## Cruciform (Nov 12, 2020)

When the old motor was on there, I definitely heard the hiss you are speaking of. It appears that the t is just a release valve- leaving it open would let all the air out, and a short opening by the relief valve on the pressure switch wouldnt do much. My question is how do install an unloader valve from scratch on a 3 phase dual stage compressor like this one? Maybe the old motor had enough oomph to start it when the cylinders were still under pressure?


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## stevon (Mar 5, 2019)

Cruciform,

the tiny valve on the electric pressure switch _*IS *_the unloader valve, there should be no valve or blockage to the fill tube and it should only unload air in the pipe from the pump to the tank. The unloader valve stays open and vents any pressure _remaining _in the fill tube only. If there is a constant flow then the check valve is not doing it's job to stop backflow from the tank. That would be venting "both ways" airflow not the function as designed of "one way" airflow as is needed. In any other compressor there is a direct connection to the fill tube. Somebody who does not understand normal compressor functions put that little valve in, it should not be there but if it is turned open you can use it to connect from the fill tube size to the 1/4 copper connection. The check valve is a maintenance part and needs to be cleaned, repaired or replaced to make it operate correctly and to only allow airflow in one direction into the air receiving tank. This has nothing to do with the motor used.

Stephen


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## stevon (Mar 5, 2019)

Cruciform,

I see this a lot on this forum "help compressor is constantly hissing" the person asking assumes that there is a fault in the unloader valve. the unloader valve is supposed to be open position at the end of a fill cycle and working properly. It will stay open until pressure drops enough to trip the electric pressure switch. So venting is a normal function, what is not normal and the misunderstood source of constant venting is that the tank full of air pressure is flowing past a leaking check valve the wrong way. These check valves fail quite often getting clogged, blocked, gooked up, spring fatigue or broken spring allowing airflow to go the wrong way. On a removed check valve air should only flow one way, I use my breath pressure to test it. If it leaks (air flows in both directions) I clean it or replace it

Stephen


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## Cruciform (Nov 12, 2020)

I'm still slightly confused. Mind you, I'm new to compressor repair, but am pretty mechanically savvy. I see where the unloader is in the electrical switch, that part makes sense. But if it just releases some of the air in the pipe to the compressor head, (there is no one way valve or the like that I know of, just the screw out valve, like you'd find on the bottom of the tank) shouldn't there be some sort of check valve or the like in the main line going from the compressor to the tank itself?


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## stevon (Mar 5, 2019)

Cruciform,

I see the one way or check valve in your picture:









I would bet this has not been maintained and leaks air from the tank (it is not supposed to let air go back in the line. The full back pressure from the tank is what damaged the previous motor I'm guessing. Just replace check valve and open that T valve on the 1/4" line.

Stephen










https://www.amazon.com/AIICIOO-Swing-Check-Valve-Stainless/dp/B07X8GRKHX/ref=sr_1_21_sspa?dchild=1&keywords=1%22%2Bcheck%2BAir%2BValve&qid=1605279443&sr=8-21-spons&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExMzdKVU9SWTU0OTVNJmVuY3J5cHRlZElkPUEwOTM2MDAyMU1TM04xVldDR0ZMUyZlbmNyeXB0ZWRBZElkPUExMDE0Njg4MU0yUjlQWlVOSlZXUyZ3aWRnZXROYW1lPXNwX2J0ZiZhY3Rpb249Y2xpY2tSZWRpcmVjdCZkb05vdExvZ0NsaWNrPXRydWU&th=1


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## stevon (Mar 5, 2019)

Cruciform,

The last check valve I posted might be the wrong type for a compressor. You need a valve that can take heat over 450 degrees and support at least 250 PSI back pressure. There are many less quality check valves (cheaper) for well water pumps for example that do not require a design for extreme applications like for an air compressor. I would take the valve you have to graingers and tell them what you are using it in. They will offer a reliable proper part to install like:








Check Valve: 1 (F)NPT, 1 (F)NPT, 500 psi Max. Pressure (PSI), 1 psi Cracking Pressure (PSI)


Valve, In-Line With Unloader, 1In Inlet




www.grainger.com





Stephen


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