Teach me how to use my compressor

It's a used, not virgin compressor. Sanborn Blackmax, 25 gallon, single stage, two cylinder, "5" hp, 15 amp 220V job that I have mounted to the ceiling. It's been sitting there for a while while I worked up the nerve to add a 220 Vac circuit.

So, I did that.

The thing runs, and does fine, but the safety relief valve blows before the compressor shuts off. The rating on the tank is 125, and the relief blows at around 130, but the thing is still running. How does one adjust/test/find the pressure switch?

the pressure switch is what the power runs through. May be adjustable. May not be. You can replace it with one set to where you want it. D Squared makes them.

The threaded part of that steel pipe where it exits the tank? the pipe that the pressure switch, safety valve, gauge and moisture trap are all on?

Right at the bottom thread where it exits the bung on the tank is were it's going to break. A compressor shakes, a lot, and that's a long lever with a weight at the far end cantilevered off a threaded interface w/ cut threads which are essentially perfect stress raisers.

I'd re-plumb that stuff with a short double-threaded section above the tank to a tee with the safety valve on one leg and pressure switch on the other. Use iron pipe in a configuration like the image in the link to make a drip leg.

TP Tools has more info about air plumbing, but you'll need to dig around a bit.

The pressure switch is under that plastic cover where the on/off switch is. It could be faulty. If so, replace switch and have a nice day.

But... what I'm thinking is that your relief valve is faulty. Usually the relief valve is set to blow off at about 10-20% above the rated pressure. I have also noticed that the PSI on the tank is usually conservative. I have a 150 psi compressor, but it doesn't shut off until about 158. Likely production tolerances in the switch, or the fact that the gauge is supplied with a 1/4" pipe nipple while the switch is supplied with a capillary tube.

Another thing I'm seeing is that your pressure tube to the switch is a little questionable. Possible leak there that isn't supplying full pressure to signal the switch to shut off?

Here is what I would do first: Fire it up. When it reaches the pressure where the safety valve starts to open, push it closed. Hold it until the compressor shuts off, or 135-140 psi whichever comes first. If the compressor shuts off at 130, you know you just need a safety valve. They fail frequently. The springs rust and fatigue. Just get one rated for 135 or 140.

But, if you get to 135-140 and the compressor is still going, then something is wonky with the switch. Many are adjustable, but they're not dreadfully expensive to just replace.

The pressure switch is the black thing at the top of that arrangement, has an aluminum line? and electric cord running to it.Works like a well pump switch sorta, when pressure is great enough to overcome spring pressure, electrical contacts open cutting electricity. When pressure falls contacts close. They can get sticky if the sit for a long time.Pull the cover off and see if you can identify which screw does what or if its sticky. EDIT: because Curtis is faster

https://www.youtube.com/embed/obI6wiCvjfU

How to switch adjustment:

https://www.youtube.com/watch?v=zh_hfD3rCA0

Bet your switch is adjustable because unloader, moar better/ $$. Leak test that 1/4" tube and nut off the switch while you're at it, appears might be too sharp a bend, maybe leaky, not that it would cause your problem, it just unloads the head after switch contacts open when cut out pressure reached.

Had safety valves weep before but never blow off, just needle on seat they can get mucky. Pull that ring out very briefly, oughta clear any muck around seat. Still think it needs adjusted tho or if any mechanical links maybe need cleaned.

Moto moron makes a good point. Plumbing is sketchy, galvanized is a nono. Galvanize flakes off and plugs orifices.

Curtis nailed it. Premature safety valve. I'll grab some black pipe and a new valve tomorrow if I can figure out where to get one.

Dumb idea, but Home Depot has a fair selection of those compressor parts. They might have one. Harbor Freight, Airgas (or your local welding/gas supply), TSC, Agway, or any variation of those farm/home/feed places would be good places to look. Grainger would have it for six times what its worth.

Sch. 80 black for strength if yur gonna use that same piping configuration.

Appears you might be missing the sintered bronze or expanded poly filter out of your filter/ separator.... so no filtering. Check it.

I'd move move the quick disconnect couplers to the tank if there are provisions, less weight on that tree of things.

Curtis said Agway, still a thing?

TRoglodyte wrote: Curtis said Agway, still a thing?

We still have one in Carlisle

curtis73 wrote: ..., or the fact that the gauge is supplied with a 1/4" pipe nipple while the switch is supplied with a capillary tube....

The capillary tube you see, is really a brake line. It is attached to the blow off valve on the pressure switch to relieve head pressure after the compressor stops, to allow restart. I normally run this in copper, but steel is fine. It is very necessary. The pressure switch gets it's pressure reading from the 1/4 inch pipe on the bottom.

oh yeah... got em confused

aka unloader

fasted58 wrote: Sch. 80 black for strength if yur gonna use that same piping configuration. Appears you might be missing the sintered bronze or expanded poly filter out of your filter/ separator.... so no filtering. Check it. I'd move move the quick disconnect couplers to the tank if there are provisions, less weight on that tree of things.

Can you draw that? I am having trouble putting that all together

In reply to tuna55:

If you're replacing the galvanized nipples w/ black like I think you said go w/ schedule 80 (heavy wall) nipples for strength w/ all that stuff hanging off of it... vibration thing like MM said.

If there is a plug in the side or top of tank you can move the quick disconnects to there to remove weight off all that stuff on top.

Pic was fuzzy of the filter/ separator but check to see if there is a bronze or poly type filter in there. It'll look something like bronze fuel filter from old GM carbs.

You can also isolate vibration with a single braid hydraulic hose. Vibration,heat,pressure, condensation can be complicated but not insurmountable. Isolate vibration first?

Is that separator any good?

How much sediment is it capturing? First step.

TRoglodyte wrote: How much sediment is it capturing? First step.

It's run for approximately 2 minutes cumulatively since I've owned it.

That clear bowl should come off looks like it is passing sediment?

No idea if it's passing or not. I'll play a little more.

Also no other places on the tank to get air from, just here.

tuna55 wrote: Is that separator any good?

You're prolly OK, jus make sure there's an element in there.

Sorry, that was just my PTSD speakin' from my old plant maintenance job. That plant ran on air, there were prolly hundreds of filter/ separators. When I came in the gang they knew it was some kinda filter but not how it worked. They'd steal parts from new units till they ran out, then they'd just strip the guts out. When the drain valve blew through ya just put a 1/8" pipe plug in the bowl... problem solved. We had a ton of water in the air btw. Lubricators were another nightmare.

They ran more equipment into the ground and never blinked an eye. Swear I need a therapist after that job, drove me berkeleying nuts.