How to adjust compressor air pressure when machine lacks adjustment knob?

[ississauga]

I started a little woodworking business and bought a stationary air compressor. Its a Husky sold at Home Depot, I think made by CH. When I start it the pressure goes to 140 psi before it shuts off, I want to reduce this cut off to around 90. It comes with no adjustment knob but Home Depot people said it can be preset by adjusting something inside, of course HD people don't know what that something is. I actually like the fact that it has no knob, this way my employees won't fiddle around with it.

The adjustment thingie is likely inside part 9 of this diagram.

am quite handy and would like to experiment, though I need some hints on how to go about it. Any clues?

[Joe]

Do you want to adjust it at the compressor for the compressor's sake or just so your air lines don't have 140 PSI? There are cheap regulators you can get which go in-line which could solve the second desire.

[TWS]

so your tank stores as much air as possible. Get an additional pressure regulator and water filter assembly to regulate the pressure that goes to your hose. Add quick connect connector to the output of the regulator while you're at it. You can also add a lubricator if you want but then you will contaminate your hose if you want to use it for spraying (your compressor will only handle detail or lightweight sprayers like Critter). I use separate lubricator hose setups for air tools.

You use this regulator to control the pressure feeding the tool but you still have max capacity in your tank.

You can get these assemblies at any BORG outlet.

TWS

[Greg O]

Yes there may be an adjustment in the pressure switch. If you take the cover off of it there will be a nut or screw with a spring under it, backing off the screw will lower the pressure. That said, the switch adjustment is probably welded so you can not adjust it, my Porter Cable compressor is! If you need to get the discharge pressure lower buy a air regulator. Greg

[Leon]

You realize that if you do this the compressor will probably run almost always with most any use at all.

[Larry Jaques]

On 7 Feb 2005 18:51:39 -0800, the inscrutable [e-mail] spake:

switch to the motor depending upon high and low pressures. Most decent compressors also have a built-in unloader which permits the motor to start the compressor with no pressure in the compressor head.

There are usually 2 screw controls in a pressure switch, one for high cutoff, the other for low pressure re-engage.

Generally, the pressure switches are adjusted downward by rotating the screw counterclockwise. If it were mine, I'd unplug it, pop the plastic cover off, loosen the locknut, adjust the HI screw (they're usually marked) 1/4 turn counterclockwise, retighten the locknut.

Then I'd run air pressure in the tank down to about 80 psi, plug it back in, turn it on, and look at both pressures, high and low, for the results. I'd then proceed from there, knowing the correct direction to adjust.

Good luck!

P.S: Play with this at your own risk. If you're not comfy doing it, take the compressor down to most any auto or compressor mechanic and give him a few bucks to adjust it for you.

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[Larry Jaques]

On Tue, 08 Feb 2005 03:01:11 GMT, the inscrutable TWS spake:

I'll give you 10:1 that the compressor lasts a lot longer if it's limited to 90 psi.

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[Leon]

I suspect that it will run more often at 90 psi and posibly not shut off during use than at 140.

[Mike Marlow]

Doubt it Larry. Most failures besides those resultant from not watching the oil level, are tank failures resultant from moisture in the tank. Increased cycles would increase water accumulation, and likely accelerate failure. Besides that, a compressor designed for 140psi at a given duty cycle will (in my best guess) not realize a life span increase in the pump head over that same model running at 90psi, so as to be significant.

[Greg]

Clamp an amp meter on your compressor and be surprised. 90 is about where it is working hardest.

[Leon]

I'm betting that for a moment that the motor draws more amps at start up.

[Greg]

Certainly true. You will see locked rotor current when it starts. Then it settles down to about 60-70% of FLA while the air is starting to come up. That increases to FLA at about 80-100PSI and then drops back down as the pressure comes up to the 140-150 shutoff. It is the same effect that you get when you hold you hand over the end of a vacuum cleaner hose. The motor will run faster and current drops.

[Larry Jaques]

On Tue, 8 Feb 2005 12:14:36 -0500, the inscrutable "Mike Marlow" spake:

Look at any report on compressor life and you'll see stats that show: the higher the pressure, the quicker the failure.

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[TeamCasa]

Larry, I'll take that action!

A compressor set to shut of at 90psi will run more than 10 times more often. The OP needs a regulator to adjust output pressure.

I set my compressors to shut off at 180psi and re-start at 100psi. Its been operational for 15 years.

To the OP: To adjust the compressor start and stop pressures, there is a pressure controller (usually a square or rectangle box) near the tank. Its easily identified given it will have both an air line or two and electrical connection.

Inside it will have two screws, one for start pressure and one for stop pressure. Adjust one at a time, drain and gauge the result of the adjustment. All safety warnings to apply.

Dave

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[Greg O]

I would not bet on it! We have a Porter Cable pancake at work, it fills from zero to 100 PSI in very little time, that last 20 PSI to 140 takes easily three times as long. The poor thing really struggles to get to the last 20 PSI. We wanted to adjust it down to 100-120 PSI but PC welded the adjustment nut so it is locked at that setting. We use it for pressure testing gas piping so we really don't care about reserve capacity of the unit. Plug it in, run it until the test is at the right pressure and shut it off again. Greg

[Larry Jaques]

On Tue, 8 Feb 2005 15:33:56 -0800, the inscrutable "TeamCasa" spake:

That's an overstatement, but it all depends on his usage. If he's running a pair of brad nailers, probably not. If he's running a trio of roofing nailers or blow guns, prolly so.

I'm guessing that the compressor came with one and that he merely wants less overall pressure. Nearly all 1/2+ HP compressors come with regulators.

You probably spent two grand on it, too, didn't you? It's built to handle it for the long haul. Cheaper compressors aren't.

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[Mike Marlow]

Dambit, perspective is everything, ain't it? Larry thinks small, maybe cheap compressor, I think (and it sounds like TeamCasa as well) behemoth, not so cheap. We think duty cycles that are near continuous, Larry thinks more occasional. That's gonna make this discussion a draw. No winners folks, the money's going back in the pot and will be applied to the winner of the next major irrelevant discussion.

[Brian Elfert]

The Husky true 3HP compressor sold at HD doesn't have a regulator. It just has an opening on the side to screw in a 1/2" NPT pipe.

Brian Elfert

[TeamCasa]

Larry Said:

I do believe that anything worth doing is worth doing right. 90 - 100% duty cycle is a must with compressors (and welders). I did not spend 2 grand but I did spend a touch over $600 in 1989. It was a used IR 5hp on a 30gal tank.

Dave

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[Mike Marlow]

I'm generally in the bigger is better camp with these kinds of things myself. But that's because I am always picking up something new and I know I'll need more than just the minimum to do the job. I didn't spend 2 grand either but my compressor lists for near that and is normally around $1400 most places. Long story behind it, but I ended up getting it new for just over $600. It's a 7HP with a 60 gal tank.