Compressor Pressure Switch

[GarageGuy89]

My switch is leaking, I can hear it when the pump kicks off. It's a two stage, 5hp compressor.

Can I buy any ol' switch rated up to 200 psi, or is there an amperage/hp rating I need as well? I see some have an on/off switch too. Can you use these on the 5hp motor instead of using my disconnect switch to turn the pump on and off? Obviously I would leave the disconnect, just always keep it on, and just use the new pressure switch for turning it off at night.

 

[wyliesdiesels]

My switch is leaking, I can hear it when the pump kicks off. It's a two stage, 5hp compressor.

Can I buy any ol' switch rated up to 200 psi, or is there an amperage/hp rating I need as well? I see some have an on/off switch too. Can you use these on the 5hp motor instead of using my disconnect switch to turn the pump on and off? Obviously I would leave the disconnect, just always keep it on, and just use the new pressure switch for turning it off at night.

If indeed the pressure switch is bad, then the replacement needs to be rated at the same or higher HP as the motor IF you do not have a motor starter....

Also, a disconnect is meant for servicing....

 

[mm08822]

My switch is leaking, I can hear it when the pump kicks off. It's a two stage, 5hp compressor.

Can I buy any ol' switch rated up to 200 psi, or is there an amperage/hp rating I need as well? I see some have an on/off switch too. Can you use these on the 5hp motor instead of using my disconnect switch to turn the pump on and off? Obviously I would leave the disconnect, just always keep it on, and just use the new pressure switch for turning it off at night.

You can buy a lever controlled on/off pressure switch as mentioned. The switch needs to be rated for 5hp at 240vac Not all are, so check before you buy. Also rated greater than the intended operating pressure.

Just to be sure, you aren't confusing the unloader valve bleedoff? That should be a momentary release of pressure.

If a continuous release, as the Cobbler stated, you may have a bad check valve. It could simply be dirty and just not sealing off well. You should be able to remove it and clean it. Otherwise replace it. Bleed the tank down first!

 

[GarageGuy89]

Good to know. I'll inspect the check valve.

Yes, it does have a motor starter.

 

[walta]

Some pressure switches have a unloader function that will release air for a few seconds after the motor turns off.

When the switch turns off the motor it releases any pressure above the piston so the motor will have less resistant when it tries to start.

If it continues to release air the check valve where the air enters the tank may be bad and allowing air from the tank to escape back to the head of the compressor and leak out the unloader.

Walta

 

[GarageGuy89]

Here are some pics of the current switch. I can feel the leak coming from the bottom where a screw is, almost like the gasket has blown out.

I'm not seeing any thing that looks like a check valve on the switch. The unloader for the head goes in at a different spot.

Sent from my iPhone using Tapatalk

 

[Citation]

Here are some pics of the current switch. I can feel the leak coming from the bottom where a screw is, almost like the gasket has blown out.

I'm not seeing any thing that looks like a check valve on the switch. The unloader for the head goes in at a different spot.

Sent from my iPhone using Tapatalk

Ok, that looks like an older, higher end compressor that uses a magnetic starter. All you need is a basic pressure switch. No built in unloader (likely built into your pump in this case). Based on the wiring that should be just switching your starter relay so you don't need to worry about a high current switch. Double check your working pressure range. 200 sounds high for most larger compressors. I would assume something like a 175 psi cutoff.

Probably something like this
https://m.grainger.com/mobile/produ...ch-2FG89?breadcrumbCatId=29375&fc=MWP2IDP2PCP

 

[TRWham]

You can get rebuild kits for Square D 9013 switches like that. Includes new diaphragm and contacts.

 

[The Cobbler]

it sounds like the check valve is bad, not the pressure switch, when the compressor is off, the pressure switch is at atmospheric pressure

my apologies, I gave incorrect information. surprised no one caught it. I must have had a brain fart .
pressure switches do see the tank pressure and can certainly leak.

 

[GarageGuy89]

Thanks guys. Max working pressure is 175 psi, I say 200 psi for the switch because that is the range they seem to be rated for. I set the compressor to kick off at 150 psi so the pump doesn't work as hard.

So, for this type of setup, can you can put a new switch with an on/off lever to turn the pump on and off? I currently use my switched disconnect to turn it on and off, and would like to avoid that if I am replacing this pressure switch now.

 

[Citation]

Yes, because the switch only sees the low starter current, not the motor current, you could easily replace it with a switched version. One with an unloader would also be ok even though you wouldn't use it. The big thing is make sure it has the opening for the cable clamp.

 

[Norcal]

Need to replace that green colored conductor, it should never be used for a current carrying conductor under any circumstance.

 

[Bert_]

A couple times I've replaced the diagram in those pressure switches. The bottom unscrews and the diaphragm is just a round piece of rubber.

Need to replace that green colored conductor, it should never be used for a current carrying conductor under any circumstance.

Off topic a bit. It must have been somewhat common at one time. I've been in a couple schools that have entire wings that are wired with green for all the switch legs. I think those wings were built in the late 50's or 60's.

 

[Norcal]

A couple times I've replaced the diagram in those pressure switches. The bottom unscrews and the diaphragm is just a round piece of rubber.



Off topic a bit. It must have been somewhat common at one time. I've been in a couple schools that have entire wings that are wired with green for all the switch legs. I think those wings were built in the late 50's or 60's.

I have come across it also, both in older and in more recent work where it was not code compliant.