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Keep blowing 120V compressor head gaskets

(05-24-2023, 02:02 PM)Richard Wrote:  I may see a potential problem. May is the operative word.

Your unloader valve is wired into the HWH over ride box.

In my opinion it should be wired into the well pump switch box.

How to wire, you may ask. Can’t answer that until we know if the unloader valve you are using is NC normally closed or NO normally open. Meaning if the valve is NO to atmosphere, then the 120V leads will attach to the pump leads, not the power in leads,  at the well pump switch. That way, when the pump turns on, the unloader closes the path to the atmosphere and opens the path to the system.

You may already know the answer to this, but a very quick and simple sanity check is to dump enough air to start the pump. When it finishes it’s cycle and the well pump switch turns it off, you should hear a whoosh of exhaling air from the unloader valve.

I was wrong about not being able to find out if I had a normally closed or open valve, the 3922 is a normally closed valve.  Would love some insight on how this should be powered by the Square D.

Brad Aden
2003 Newell #653 Quad Slide Cat C-12 engine
St. Louis, MO

I do not know the particulars of your valve. So this is a conceptual explanation of what needs to happen.

The valve normally will have three ports. In the non powered, normally closed position, the two ports that will allow air to pass through to the atmosphere. In the powered position, the through passage should connect the pump to the check valve.

The valve changes the air path when power is applied. In the non powered state, the valve should allow the air in the line between the compressor and the check valve to escape. When the valve is powered, the path should close the path to the atmosphere and open the path from the compressor up to the check valve.

If you go to the Square D box, you will see two leads which power the compressor. The leads for the solenoid valve will connect right there. Do not connect the solenoid leads to the power in. When the Square D box tells the compressor to come on, then the solenoid valve will be powered at the same time. That should close up the path in the system and allow the compressor to build pressure.

Can you give me more detail on the solenoid valve, so I can look it up and confirm what I told you? I can’t read the label in the photo, since part of it is obscured.

Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )

(05-26-2023, 06:41 AM)Richard Wrote:  Can you give me more detail on the solenoid valve, so I can look it up and confirm what I told you? I can’t read the label in the photo, since part of it is obscured.

Attached Files Thumbnail(s)

Brad Aden
2003 Newell #653 Quad Slide Cat C-12 engine
St. Louis, MO

Spartan 3922-1E03-BBA7A1

The Spartan Scientific Series 3922 is a 2-Way & 3-Way, 2-Position Normally Closed solenoid valve for control of air, caustics, inert gases, oil, and water. Constructed from highest grade materials, the Series 3922 features a completely glass filled nylon encapsulated coil, stainless steel plunger and stop, and spring compensated plunger seals for long trouble free service. Key to the 3922 is a stackable body giving the customer the ability to build manifolds as needed using one inlet and many outlets. The 3922 is available in orifice sizes from 0.6 (0.02 Cv) to 2.4mm (0.24 Cv). Seat materials are EPDM, FKM and NBR standard. Coils are class F 100% duty and incorporate the DIN 43650 industrial quick connect, DIN 43650 Female or flying leads. The valve body is made from robust zinc-aluminum die casting and comes standard with 1/8” NPT connections. The body is designed to incorporate our interchangeable “basket” style orifice simplifying valve assembly and re-fit. The Series 3922 is a long life, low cost solution to many automation applications.


Electrical hookup

Attached Files
.pdf 28-03-2017-13-38-39-4.pdf Size: 2.01 MB  Downloads: 8

Bill Johnson
Birmingham, Alabama

I replaced the Spartan Scientific Valve with an ARO CAT33P-012-D-G,
I was 10 miles from Spartan and they would not sell to me.  I actually got the valve from Grainger a few miles from Spartan.

2014 Newell Coach 1482 Mid Entry 45'8" Valid Slides and Valid Levelling

Thanks Mr Bill !!

Richard and Rhonda Entrekin
99 Newell, 512
Subaru Outback Toad
Inverness, FL (when we're home Cool )


Thanks for the pictures, Brad.  Here are some thoughts about how I perceive the system to work.   If anyone has other ideas, chime in please!

Here is what I see…though I am not sure I really understand it.

The compressor is connected to the inlet of the solenoid.
The outlet goes to a check valve which goes to the rest of the plumbing.

- Be sure you are careful around 120VAC.  If you dont feel comfortable with these tests, get a technician to perform.
- Be careful around the air fittings.   I once tried to slightly undo an air fitting to release the air….when I got the fitting kinda loose, it shot out like a bullet and released all the air from the system at once.  I was inches away and it was LOUD.    Don’t be like me.

Assumptions which should be verified:
-  The leads on the solenoid have 120VAC when the compressor is running.
-  The leads on the solenoid DO NOT have 120VAC when the compressor if off.
-  The well switch turns the compressor off and on at appropriate air pressures.

How it the unloader system solenoid works…

1.  With the compressor OFF, The outlet port is connected to exhaust.  Which means there is no pressure in the air line between the outlet and the check valve.   Pressure remains between the inlet and the air compressor.

2.  With the compressor ON, the inlet port is connected to the outlet port.  The pressure will activate the check valve and air will flow to the rest of the plumbing.

3.  When the compressor turns OFF, the solenoid will return to the normally closed position.  In the normally closed position, the outlet is connected to the exhaust.  This releases the pressure from the outlet to the check valve which causes the check valve to close.  

4.  When the compressor turns ON, the solenoid will connect the inlet to the outlet, releasing any pressure in the line between the output of compressor and inlet to solenoid.   This will “unload” the compressor and allow it to start more easily.  As pressure builds, the check valve will open.


1) with compressor off, verify that there is no pressure in the line between the output of solenoid and the check valve.   You should be able to blow into the outlet line and hear the air come out the exhaust.

2) with the compressor off, verify that you cannot blow into the inlet side of solenoid.  In the normally closed position, input of solenoid is capped, and outlet is connected to exhaust.

3) apply 120VAC to solenoid.  You should be able to hear a “click” and the inlet should be connected to the outlet.   You could use the on off switch on the well pump switch to do this.  1. Turn compressor off. 2.  release air in the system using quarter turn valve.  3. Disconnect the air line from compressor and the check valve.   4. Turn on well pump switch turning on compressor.  Blow into line going to inlet and see if air makes to out of solenoid on line going to check valve.
-  If check valve gets stuck closed, the compressor can run but not provide air to system.

-  If the solenoid fails to operate it will block air pressure from the compressor to the rest of the system.

-  If the solenoid gets stuck in the “on” position, the compressor will have a hard time starting because there is no unloader circuit.

- Also, You might want to think about extending the line between the solenoid and the check valve.  Maybe put another foot of tubing in a loop.   This will create more air volume to unload the compressor making it easier to start and run.  


Bill Johnson
Birmingham, Alabama

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