Pressure Switch Adjustment, what is..

by Kevin
(Calgary, Alberta, Canada)

Compressor Pressure Switch

Compressor Pressure Switch

I can't find a pressure switch that is pre-set to the manufacturers high/low setting on an older compressor I have.

I use 2 compressors in series with a rather elborate filter and air-drier setup.

until the pressure switch quit working on the one compressor, I had the high/low settings adjusted (downward) slightly so that they were perfectly balanced and supplied me with an ample volume of air to run some of my air tools that really gobble it up.

The closest switch I could find is still 20 lbs too high. I unplugged the compressor, drained the tank and popped the cover only to discover 3 spring adjustments instead of the 2 that I am used to. There are the usual 2 larger ones side-by-side, and then another smaller one off to the side. I was wondering if you can tell me what this one would be for?

I can't find any model number on this switch, it's a LaPlante, if that helps.

Bill says...

Kevin, I believe you can get info on Laplante Air Compressors and controls by contacting them here: [email protected]

Next, if it were me running a dual compressor setup, I would have the pressure switch on the back up compressor set to cut in just below the cut in pressure of the primary compressor, and the high pressure cut out to be just below the cut out of the primary.

Reason being, if one compressor could keep up, the secondary wouldn't run at all, saving maintenance life.

Periodically, maybe every six months or so, I would switch them out.

If the secondary doesn't need to run to keep up, why have it run needlessly... if I understand your set up properly.



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Oct 23, 2017
FLA etc.
by: Bill

I have read that FLA refers to the amps drawn by the motor when it is operating at full load. Just wanted to make sure we both understand what I think FLA means? :-)

Yes, it does appear as though the switch is rated for 120 / 240 volts.

If you think about it, as long as the points in the switch are robust enough to handle 240 volts, then they'll handle 120 volts too. The electrical connection / breaking has nothing to do with the switches reaction to the pressure, just whether the points touch or not, depending on that pressure.

I guess that's why many standard (as opposed to mini - in tank switches) are rated 120/240 volts.

Oct 23, 2017
120 or 240?
by: Denis

Hi again, Bill

... and thanks for a great explanation. It doesn't entirely solve my problem, though:

The LaPlante PS does not say whether it's 110 or 220, at least not that I can spot. It's a model 340005. In the cap there is a small schematic that states:

2 pole, 1 phase
120v 1.5 HP, 20 FLA
240v 3 HP, 17 FLA

Does this means the device can be used for either 110v or 220v motors? (I have both available.)

Oct 23, 2017
Pressure adjustment etc.
by: Bill

Dennis, please have a look at the following page for pretty complete info on the pressure switch.

Yeah, looks like LaPlante compressors (LP are gone.

As long as the pressure switch has access to the tank pressure to sense the pressure there, the other ports are for things like the tank gauge, and the PRV.

There are a variety of port locations to allow users to attach accessories where they don't interfere with compressor structure.

As noted on that page, ports that are not being used are plugged.

I think the brass fitting on your switch may be the unloader valve line.

Oct 23, 2017
What the heck is this?
by: Denis

Hi, Bill:

I found this page because I have the same LaPlante pressure control switch pictured on this query. Mine came with an old, dismantled air compressor I recently acquired. The LaPlante has never been installed, so I could use some guidance on connecting it.

I had no trouble spotting the brass-type connector on this unit with a compression fitting, and I can see exactly where that connects to the air -- presumably to sense the pressure at all times. But there are also four female ports (roughly 3/8") on the base of the switch. They all lead to the same place, so I think the idea us for users to pick the most convenient port and maybe block the others? If so, then do I also connect AIR here?

There is a wiring schematic inside the unit to explain the electrical -- no problem there. So it's just about the four remaining ports. The LaPlante website is unreachable, by the way.

I'm grateful for any info you can share.

Aug 02, 2011
RE: Pressure Switch Adjustment
by: Kevin

thank you for the information and quick response. The reason I have the cut-in/outs sync'd is that I do body work and the air sanders eat up an incredible amount of air. With both compressor tanks topped up it gives me enough run time to do a section of whatever I am working on before the the compressors kick in which once they do, even with both 1.5 HP compressor motors running, the air will continue to drop, and in a very short time the operation of the tool will degrade to a point that I have to stop and wait for the air to catch up.
With the cut-in set lower on one compressor (as it was originally), the one compressor ran almost none stop. As far as I know, there's no back-flow prevention on either compressor, so the one with the low cut-in was working twice as hard as normal trying to keep both tanks full.


10-4. If both lead to a common air line to your tools, I would have installed a check valve in each line before the Tee.


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setting cut in & cut out on my pressure switch

by rob

I know dont do it but in this case I bought a blow out deal at an auto parts store (mybad)and had to replace missing parts,tank relief vlv,oil breather plug,air filter, regulator/gauge dont ask i am an idiot for not seeing this anyway i fixed it all and tested it,dont ask me why but I was suspicious waiting for cut off it never happened and the safety relief saved me as i turned it off.

upon opening the cover and after reading your stuff & looking at pics YUP! some fool did some adjusting differential almost all the way out and no sealant anywhere they even clean them can you give me a safe way to adjust them with out killing myself it is kinda scary

thanx - rob

Bill says...

Hi Rob.

You need to read the pages relating to the pressure switch, linked from the nav bar.

The photos show you the adjusting nuts, and talk about how to do it.



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