Air Compressors

[AZRedhawk44]

My Husky 19 gallon air compressor just failed on me.  Need a new one.  The pressure sensor's diaphram failed so that it has a high pitched whistle.  Replacement air pressure sensor switch is $140, the whole unit is only a $200 compressor and is 12-14 years old.

I've probably done a disservice to that poor Husky.  I think it was rated for 4-ish CFM @ 90psi, and there were quite a few times it was running pneumatic metal shears and die grinders in the 5+cfm range, and definitely not keeping up.  It's time for something that can put out 6+ CFM.

A Quincy has caught my eye.  26 gallon tank, 7.4 CFM @ 100psi, 120v or can be rewired for 220v.  Rolling unit, not a stationary, but it's about 165 pounds.  Iron cylinder, oiled, so it should last longer than my oilless Husky.  And it is of a far more serviceable design and manufacturer.  Looks like it's a clone of a common design also sold by Bel Aire and Chicago Pneumatic.  They all 3 tend to retail online for $675 to $725.

Anyone got any recommendations or advice?

Also, I think I'm going to take the compressor off the old Husky and convert its tank into an auxiliary air tank.  That would give me 55 gallons at 7.4CFM 100psi, close to a proper stationary shop compressor.

[zahc]

I'm going to buy an Ingersoll Rand garagemate because they have TEFC motors.

[zxcvbob]

Does it really need a "pressure sensor"?  You can get a generic pressure switch for less than $20; some of them even have an unloader valve --which I think is used when the compressor is powered by a gasoline engine instead of an electric motor.

I had an old Quincy compressor.  With just a 2 HP motor, it would run circles around my new Coleman (?) 5 HP compressor.  (both belt driven and wired for 220V)  After many years, it threw a rod and self destructed when I started it up one winter morning.   

I didn't know Quincy was still in business.

[Doggy Daddy]

I didn't know Quincy was still in business.

There will always be a place for an old-timey doctor with a talent for sleuthing.

[AZRedhawk44]

I'm going to buy an Ingersoll Rand garagemate because they have TEFC motors.

I was looking at those, but they seem to cap out at just shy of 6 CFM.  And I really want vertical orientation.  Definitely stronger than my Husky, though.

You find a good deal on one that's particularly compelling?

[Brad Johnson]

Does it really need a "pressure sensor"?  You can get a generic pressure switch for less than $20; some of them even have an unloader valve --which I think is used when the compressor is powered by a gasoline engine instead of an electric motor.

I didn't know Quincy was still in business.

Ditto.

Do you have a pic of the part that failed, or a part number we can research?

I didn't know Quincy was still in business.

They are ... kinda. It's no longer a standalone U.S. company. It's now a subsidiary of Atlas Copco, a Swedish conglomerate that owns, among its many brands, Milwaukee Tools and Chicago Pneumatic.

Brad

[AZRedhawk44]

Does it really need a "pressure sensor"?  You can get a generic pressure switch for less than $20; some of them even have an unloader valve --which I think is used when the compressor is powered by a gasoline engine instead of an electric motor.

It has a proprietary plastic housing that the switch fits into.  I guess I could run the wires out of the housing and tape/screw a generic switch to the outside... but there's also the problem of connecting/disconnecting the hose for the pressure switch.  It's a goofy little 1/4" plastic tube with no external clamp or retaining ring, just a push-fit onto a nipple.  I worry that it won't retain if I pry it off the current pressure switch, or that I won't be able to secure it to a new one.

Unloader valve is necessary for the compressor piston to re-start after stopping.  It relieves pressure in the piston without draining the whole tank.

[AZRedhawk44]

Do you have a pic of the part that failed, or a part number we can research?

Compressor that failed is a Husky 136424.

This site:

https://mastertoolrepair.com/portable-oilfree-air-compressor-parts-hpa158190901-136424-p-759524.html?osCsid=1bcim7gicv6hej2ic3arlh1oqb

shows two different replacement pressure switches.  One for $50 and one for $135, slightly different configs supposedly, but as far as I can tell both have the same product picture and I can't tell the difference, or which one I have in my compressor.

I don't have a pic right now of the failed part.  But it's the diaphragm between the plastic housing and metal plate where the black tube attaches, that has failed.

[AZRedhawk44]

It's also possible that it's the check valve that has failed rather than the pressure switch, but that the problem is manifesting at the pressure switch.

[zxcvbob]

The major complication looks like it's a variable-speed motor.  But not sure if it has to be... 

Also I notice they charge $40 for the power cord. 

I would try to see if I could take parts off to make the compressor run all the time.  (not as dangerous as it sounds because of the overpressure relief valve)  If that works, put a generic pressure switch on the manifold, teed off of either the popoff valve or the tank pressure gauge, and use that to turn the power on/off.  Cap any little plastic hoses.

[Brad Johnson]

Husky 136424 crosses over to a PowerMate compressor of the same model number. Also sold under the Coleman brand name.

Pressure switch assembly 034-0192.

Not sure I'd put any money into an oilless compressor. They are throw-away. Get a new compressor (preferably one that's serviceable) and convert the Husky to use as a straight portable air tank.

https://www.lowes.com/pd/Quincy-Compressor-20-Gallon-Portable-Electric-Horizontal-Air-Compressor/50073347
(also available from Northern Tool at the same price)

Brad

[AZRedhawk44]

The major complication looks like it's a variable-speed motor.  But not sure if it has to be... 

Also I notice they charge $40 for the power cord. 

I would try to see if I could take parts off to make the compressor run all the time.  (not as dangerous as it sounds because of the overpressure relief valve)  If that works, put a generic pressure switch on the manifold, teed off of either the popoff valve or the tank pressure gauge, and use that to turn the power on/off.  Cap any little plastic hoses.

Looks like if I change out the check valve (which might be the actual culprit here), get a different one with the same 3/8 NPT threading for the tank and manifold but that uses a Tee'd offset compatible with a generic replacement switch's overpressure fitting, I could maybe get it running.  Of course, that'll be:
1. check valve... $10-$15
2. brass tee'd offset... $5
3. generic pressure switch... $20
4. piping or hose from tee'd offset to switch... $5-$10
5. unknown additional parts not currently foreseen

That's $50.  And a lot of modifications to the original design.

I worry about ordering the less expensive switch just to find I need the more expensive one for some reason.  And there's the OEM check valve design that is another $20 on top of an OEM switch.

[Brad Johnson]

What exactly is happening? Is it running fine but not kicking back on when it needs to top up pressure? Not running at all? Running away and overpressuring?

Brad

[AZRedhawk44]

What exactly is happening? Is it running fine but not kicking back on when it needs to top up pressure? Not running at all? Running away and overpressuring?

Brad

Runs, stops at peak pressure, whistles from a diaphragm in pressure switch.  Pressure drops from either work being done, or diaphragm leak, and pump turns on again.

[AZRedhawk44]

I've been digesting the failed compressor a bit more, after having a better grasp of check valves, exhaust valves, and unloader valves and trying to make a map of this particular system in my head.

I think what's failed is the exhaust valve in the pressure switch.  The machine isn't over-pressuring. 

Order of operations of this machine:
1. At empty pressure, machine is turned on by operator.  Pump begins cycling.
2. Check valve between pump and tank allows positive pressure from piston to be input into tank without backfeeding into cylinder.
3. There is no unloader valve between/on the check valve and the pressure switch.  This was 50% of my blockage in understanding it, since most serviceable compressors have an unloader valve to prolong pump life.
4. Air is stored in cylinder, and accessible via the manifold on the output hole in the tank.
5. Manifold has a dial for tank pressure, a nipple for a 1/4" nylon tube that connects back to the pressure switch and the exhaust valve, and a regulator with a quick release tool attachment.

I was interpreting the nipple on the manifold as the unloader valve.  I was about to buy a new check valve, but I stopped myself.

The pressure switch has a metal plate with a receiving nipple for that 1/4" nylon tube, a rubber diaphragm, and that screws onto the plastic frame of the pressure switch assembly.  But, there's a hole under the diaphragm and some sort of solenoid operates in that hole.  I suspect this is the exhaust valve, a safety feature to bleed pressure if too high a pressure is attained. 

What I'm hearing is the pump hitting target shut-down pressure, and the failed exhaust valve squealing and letting air out until the machine hits kick-on pressure and it starts filling again.

The handul of sites out there that carry specific parts for this compressor insist that if you hear hissing/noises from the side of the pressure switch, then the culprit is the check valve.  But the problem is, their diagrams demonstrate that the check valve has an unloader line to the exhaust on the pressure switch.  On mine, the manifold connects to the pressure switch and the check valve has no T-nipple.  There's no way for the check valve to cause the problem here.

I almost ordered a new check valve today off Amazon since I was thinking that the problem was a leak from main tank into compressor pump, and the squealing culprit was the unloader valve getting too much air from the tank.  But after looking more carefully at the pneumatic circuit of this particular device, there is no unloader valve and the air pressure that causes the squeal is coming directly from the tank via the output manifold and has nothing to do with the check valve.

I suspect, in order to fix this, I have to order a new OEM pressure switch.

Or, alternatively, I order a generic pressure switch, retrofit/kitbash a bunch of NPT fittings, use an aftermarket generic check valve with an unloader since the generic pressure switches all have unloader fittings, and block off the nipple on the manifold that is currently allowing the failed pressure switch to vent via its exhaust valve.

I'm not keen on spending $40+ on this while in doubt about the right step though.