Need suggestions for an air-powered switch.

[Steve W.]

My air system is reasonably tight. Ingersoll Rand compressor on a 60 gallon vertical tank, ran through 1/2" copper around the room. Ball valve at the tank, then a Harbor Freight regulator/water trap (I know the location makes the water trap virtually useless), then the feed to the copper lines. Four drops, each with ball valves above a T for the 'load' and below the T for the drip leg. If all the valves are closed, the compressor will kick on about every three hours. With the ball valve at the regulator closed, it will hold pressure for days without the compressor kicking on.

One side of the regulator has the pressure gauge, the other side has a plug, in case you need the gauge on the other side. I had the idea to install a pressure switch in place of the plug, then connect a power source and a light. The light is mounted next to the exit door so it will remind me to turn the air off before leaving for the night. The light is just a trailer marker light, the power source is just a 12-volt wall wart, so nothing exotic.

My problem is the switch. I have had two switches, both have failed, so I am looking for something that will last. I don't really care what the turn-on pressure is, as long as it's between 0 and the compressor kick-on of about 90 psi. Google searches typically show the switch for controlling the compressor that have a turn-on of about 100 and a turn-off anywhere from 120 to 175 psi. That switch won't work, as I want it OFF below 90.

The two switches I have used were motorcycle brake switches. They have turned on at about 75 psi, which is perfect, but they only last a couple of months. Hopefully there is something that will last longer. Not afraid to spend a fair amount, but this shouldn't be all that expensive.

Mounting threads are 1/8" NPT, my air system runs 90-120 psi, so need switch activation below 90.
Pressure below 90, switch OFF. Pressure above 90, switch ON.

Thanks for any suggestions.

.

 

[Bert_]

Most pressure switches have two screws that will adjust cut in and cut off pressure

 

[Steve W.]

True, but compressor switches seem (to me) to work opposite of what I need.

.

 

[Bert_]

Got it. You want on at high pressure and off at low pressure.

 

[Gear Box]

This should work for you.

https://www.grainger.com/product/WOLO-Air-Pressure-Switch-3FHX3

 

[Steve W.]

Looks just like the brake switches I have tried.

Costs twice as much, maybe it will last twice as long?

.

 

[59 wagon man]

do you have a on off switch now? move it by the door and make it a lighted switch. power on switch is lit if its right by the door it seems pretty simple and cheap

 

[Steve W.]

No switch for the compressor. It's powered all the time, in the closet under the stairs.

I only shut off the air, leaving pressure in the tank, so I only need a reminder that there is still pressure in the lines.

.

 

[Mr. T]

How are the switches going bad? Have you thought about running them on AC? DC can be hard on switch contacts.

 

[The Cobbler]

this looks like it would work, seems to be n/o and n/c contacts
https://www.ebay.com/itm/Pressure-S...769427?hash=item5b5ce89193:g:Xn0AAOSwZ2BdZKb7

 

[samss]

Check with an HVACR supply house. Maybe a pump down switch like this:
https://www.supplyhouse.com/MARS-43350-Low-Pressure-Control-40-PSI-Cut-Out-80-PSI-Cut-In
There are adjustable switches also.
https://www.supplyhouse.com/Johnson-Controls-Pressure-Controls-10963000

 

[Steve W.]

How are the switches going bad? Have you thought about running them on AC? DC can be hard on switch contacts.

They are going bad by not making contact when pressurized. Not sure why AC would work any better on a motorcycle brake switch, and there's not a whole lot of current there, anyway. As mentioned earlier, this is a trailer marker light with a #194 bulb, drawing only a few milliamps.

this looks like it would work, seems to be n/o and n/c contacts
https://www.ebay.com/itm/Pressure-S...769427?hash=item5b5ce89193:g:Xn0AAOSwZ2BdZKb7

I did not see where it specified type of contacts, but have recently found something that should work.

Check with an HVACR supply house. Maybe a pump down switch like this:
https://www.supplyhouse.com/MARS-43350-Low-Pressure-Control-40-PSI-Cut-Out-80-PSI-Cut-In
There are adjustable switches also.
https://www.supplyhouse.com/Johnson-Controls-Pressure-Controls-10963000

It's a bit hard for me to decipher the terminology used in that first link. Not really sure what "cut in" and "cut out" mean for those switches, but it sounds like a compressor controller, not what I am looking for.

In the second link, it's also a bit confusing, but that's OK, they are all WAY too expen$ive.


My Google-fu pretty much *****. While others will do a quick search and find stuff, I just don't seem to use the right words, and have trouble. All my previous searches only found compressor switches. Seeing some of the suggestions here, I added the word "air" to the search criteria and several items popped up. One that I thought was perfect was only for hydraulic and hydrocarbon-based fluids, not air or water. (It might be the water vapor right at the tank outlet that might be compromising the switches.) I found THIS ONE at Amazon that should work. I'll find out in a few days.

.

 

[Mr. T]

They are going bad by not making contact when pressurized. Not sure why AC would work any better on a motorcycle brake switch, and there's not a whole lot of current there, anyway. As mentioned earlier, this is a trailer marker light with a #194 bulb, drawing only a few milliamps.

DC sustains an arc when a contact makes and breaks. AC (since the voltage is crossing zero many times a second) does this to a much smaller extent. The arcing in the extreme can weld the contacts together. But what happens much more often is that it erodes and oxidizes the contact surface to the point that continuity is lost.

For your #194 bulb (3.8-5w from what I can find) on a 12V supply you would be putting 317-417mA of current through your switch contacts. This might not seem like a lot but the switch you linked is only rated for 500mA. This is also not taking Voltage drop into account (which almost certainly exists here and would up your current across the contacts).

If you still have one of the old pressure switches (or both) still laying around it might be worth it to pull them apart and see what the contacts look like.

One bad switch might be a fluke but two would make me look for another issue in your setup.

Just trying to help.

 

[capww8]

That is a really excellent explanation.

 

[Innovate1]

DC sustains an arc when a contact makes and breaks. AC (since the voltage is crossing zero many times a second) does this to a much smaller extent. The arcing in the extreme can weld the contacts together. But what happens much more often is that it erodes and oxidizes the contact surface to the point that continuity is lost.

For your #194 bulb (3.8-5w from what I can find) on a 12V supply you would be putting 317-417mA of current through your switch contacts. This might not seem like a lot but the switch you linked is only rated for 500mA. This is also not taking Voltage drop into account (which almost certainly exists here and would up your current across the contacts).

If you still have one of the old pressure switches (or both) still laying around it might be worth it to pull them apart and see what the contacts look like.

One bad switch might be a fluke but two would make me look for another issue in your setup.

Just trying to help.

Good explanation over all but voltage drop would reduce the current not raise it. Probably not enough change to be significant though. And the current is below the switch rating.

How often does the switch operate? Maybe the number of cycles the switch is rated for is exceeded? I doubt it but I don't see any other issues. Current is below the rating and the switch normally is used at 12V DC, same as this application.

You could try a standard compressor switch that is closed when pressure is low and a relay to change to on when high.

 

[rlitman]

I have a 12V motorized ball valve on my tank outlet. A 3-wire valve that is powered in both direction (not spring return). I power that off a small 12V supply and a DPDT relay. In my case, I have the relay controlled by a WiFi cloud controlled switch, so I can open or close my valve from anywhere in the world, set schedules, etc. But it would be easy enough to use a 120V coil relay and have it controlled by your lighting, or whatever you wish. Why bother walking all the way to the valve to operate it?

 

[larry_g]

Forget all the electrical work for an indicator. Just use a pneumatic indicator, https://www.mscdirect.com/browse/tn...ol-Devices/Pressure-Indicators?navid=12104419

lg
no neat sig line

 

[Mr. T]

Good explanation over all but voltage drop would reduce the current not raise it.

Yup. Brain fart on my part. Thanks for correcting me.

 

[59 wagon man]

ti'm not an electrician but I would think there would be an electric power shutoff within a few feet. if not maybe now is the time for that and then the indicator light is easy

 

[exranger06]

Get a regular compressor pressure switch and have it control a relay. Wire the light to the "normally closed" contacts of the relay. That way, the pressure switch will turn the relay "on" when the pressure drops, BUT the light will only turn on when the relay is OFF (the light will be on only when the pressure is high)

 

[Steve W.]

How often does the switch operate? Maybe the number of cycles the switch is rated for is exceeded?

In normal operation, the switch comes ON when I turn the ball valve to pressurize the air lines. Switch goes OFF when I turn off the ball valve and de-pressurize the lines. Does not happen every day, maybe three or four times a week, sometimes less than that. The switch is rated for quite a few more cycles than that.

DC sustains an arc when a contact makes and breaks. AC (since the voltage is crossing zero many times a second) does this to a much smaller extent. The arcing in the extreme can weld the contacts together. But what happens much more often is that it erodes and oxidizes the contact surface to the point that continuity is lost.

I had not thought of the difference between AC and DC, but the switch is MADE for a DC application (motorycle). Not only that, but since it's a brake light switch, it should be able to control at least a single brake light bulb. A #1157 bulb draws about 2.5 amps, I'm using a LOT less than that.

If you still have one of the old pressure switches (or both) still laying around it might be worth it to pull them apart and see what the contacts look like.

I will have to see what it will take to crack one open in the least-destructive manner possible.

One bad switch might be a fluke but two would make me look for another issue in your setup.

My thoughts, exactly. Hence the appeal to the collective wisdom on this forum.

Forget all the electrical work for an indicator. Just use a pneumatic indicator, https://www.mscdirect.com/browse/tn...ol-Devices/Pressure-Indicators?navid=12104419

lg
no neat sig line

Thanks Larry. Instead of electrical work, I would have to run another air line over to the door, so I could attach a $75 pneumatic indicator. Not saying it coudn't be done, but it's a LOT easier to run a few wires than run another air line. (Especially when all the wires are already run, just need a new switch.)

Get a regular compressor pressure switch and have it control a relay. Wire the light to the "normally closed" contacts of the relay. That way, the pressure switch will turn the relay "on" when the pressure drops, BUT the light will only turn on when the relay is OFF (the light will be on only when the pressure is high)

It would probably work, but sounds like a Rube Goldberg solution to what I perceive as a simple problem.

Thanks for the suggestions. New switch isn't here yet, so I don't have any updates to report.

.

 

[Citation]

What about using an oil pressure switch?

Also, I don't know how much current you are running thought the switch but try switching to an LED light. It should draw a lot less current which is good for switch reliability. Heck you might try the existing switch again but user sometime like an LED market light to cut the power draw down.

 

[Steve W.]

An oil pressure switch might be my next step, if the switch I ordered (mentioned in post #12) does't work.

Not a lot of current going through the switch. A marker light with a single #194 bulb (about 0.3 amps at 12 volts). Yeah, an LED replacement would draw less, but I would have to spend money to get one.

Thanks for the oil pressure switch suggestion. That would operate at a lower pressure, which is not a problem, as long as it's under about 90 psi.

One question, though. Does pressure applied to that switch turn the light ON or OFF? On my motorcycles, the oil light is ON until there is enough pressure to open the switch and turn it OFF.

.

 

[Citation]

I think oil pressure senders come in a wide range. Some are closed with no pressure (oil light on when engine is off) but others are reversed.

If you happen to have a compressor pressure switch you could scab on a simple lever switch. The compressor pressure switch normally closes contacts when pressure goes low. However, the mechanical plates in the mechanism move enough that you could put a simple lever switch in the thing. So you wouldn't actually use the contacts in the pressure switch, you would just use it as a triggering mechanism. You would use a lever switch like this to do the electrical work. It's clugy but the lever switch can be very reliable. They also come in normally open, closed, switched etc. Depending on how you mount it would decide if you need NO or NC.

Example only. I did not verify this specific model was right for the job.
https://www.amazon.com/dp/B07XB41V6N/?tag=atomicindus08-20

 

[Citation]

Ok, this might be what you want.
A pressure safety switch. Summit and Amazon have lots.
https://www.amazon.com/dp/B00NXIXHXS/?tag=atomicindus08-20

 

[Steve W.]

That 'safety switch' shows promise. Very affordable, correct threads and correct pressure range (1 Mpa = 145 psi).

I just checked the tracking on the one I have already ordered. It's on the way, so I'll hold off on ordering another until this one fails.

.

 

[bjcouche]

Why not use an industrial duty pressure switch? They are a little pricey but designed to do exactly what you want and work forever with water, air, oil, etc. These are set point adjustable by manually rotating a dial. I've used many of these and never had any trouble with them.

https://www.automationdirect.com/ad...sure_sensors/pressure_switches/mps25-1c-p200d

Brian

 

[checkthisout]

Why don't you just run an electrical valve off the tank output with a switch by the door?

HFS 110v Ac or 12v Dc Electric Solenoid Valve Water Air 1/4", 1/2", 3/4", 1" NPT Available (12V DC 1/2" NPT) https://www.amazon.com/dp/B018WRJYUE/?tag=atomicindus08-20

 

[aczr2k]

Why don't you just run an electrical valve off the tank output with a switch by the door?

HFS 110v Ac or 12v Dc Electric Solenoid Valve Water Air 1/4", 1/2", 3/4", 1" NPT Available (12V DC 1/2" NPT) https://www.amazon.com/dp/B018WRJYUE/?tag=atomicindus08-20

This is what I did, its in the main line of the compressor wired to the 110 side of the pressure switch for power. Our compressor is shut off at the breaker every night, turn off the breaker the valve closes, turn on the breaker the valve opens, no lost air, no unnecessary compressor running when no ones around.