Help with old Sanborn air compressor

[rlanicek]

I inherited this compressor from my father and it has served me well.

Recently I noticed it doesn't start/stop when the tank gets full. Instead, air bleeds out from what I believe is the safety valve?

Not sure what to do - I don't know much about air compressors. Do I replace the safety valve or is it an indication of something else gone wrong?

 

[The Tool Tyrant]

If the receiver is reaching maximum (cut-out) pressure and not shutting off, it's a bad pressure switch. If it's not reaching maximum (cut-off) pressure before it starts bleeding off, then it's the safety valve...could be it just needs to be cleaned, or it's worn out and needs to be replaced.


Edit: This may help...https://mastertoolrepair.com/portab...rts-104b200-104b200-14-104b250u-p-747282.html

 

[rlanicek]

Thanks!

 

[rlanicek]

I changed the safety valve and same problem. Is this gray box the pressure switch?

Dammit, not sure why the pic isn't displaying...

 

[The Cobbler]

You need to be clearer on what it's doing/not doing .
is it not reaching pressure before it shuts off?
does it keep running until the overpressure valve blows off?
by safety valve, are you meaning the unloader valve on the pressure switch ?
the pressure switch is behind the box where the pressure regulator etc is.

 

[rlanicek]

Keeps running after the safety valve blows off.

Used to be that the compressor would run until it reached the pressure it was set to. Now it runs, the safety valve blows, and it keeps running.

 

[The Cobbler]

you have a pressure switch problem .

 

[rlanicek]

View media item 102671
Finally. Is this gray box the pressure switch? I believe it is, just checking for advice.

 

[The Cobbler]

the grey box

 

[rlanicek]

Thanks. Looks like a PITA to replace. Anything I need to know before I begin?

 

[The Cobbler]

not really.
discharge pressure in the tank , unplug power
remember how everything went.
you want one that has an upper cut off off about 120psi, some are adjustable, some are not .

 

[rlanicek]

Thanks a lot, Cobbler

 

[yardiron]

I have that same compressor, I bought it new in the 80's.
At what pressure does the blow off valve pop?
On mine it pops off around 150 psi, far above what the electrical switch is set to stop the motor at. Mine runs up to 125 psi, then shuts off, it turns back on at 79 psi as air is used. Both of those settings are adjustable under the cover on that gray box.

Run the compressor and see where its popping off at, the purpose of that valve is to prevent the tank from rupturing in the event that the pressure switch fails.

I had to replace the blow off valve on mine once, I had gotten in the habit of pulling the ring to empty the tank when I stored the thing, the valve eventually got dirt or rust in it, and the thing would leak and blow off early. I took the valve on mine apart and cleaned it out and got it seat again and stopped messing with it, its been fine ever since.

Step one though is to watch and find out what the pressure is when the blow off pops open and vents the tank. I'd say if its under 140 psi or so that blow off valve is bad. If the compressor is achieving more pressure than the valve is rated for, then your going to have to remove that gray cover and see what's going on.

They were good compressors, they were built with pretty generic components so parts shouldn't be a problem. In other words, they didn't use any proprietary parts.
The pressure switch on mine is from Square D, the motor is from Century, the pumps were mostly Tecumseh or Ingersol clones.

 

[rlanicek]

Thanks yardiron

 

[patcola]

I just replaced my sanborn compressor unit only after
40 yrs of service.