Watch those air compressors!

[e9999]

well, I was looking at an air compressor this weekend. This was a new unit recently (purchased by somebody better left unidentified in a place better left unidentified ). On the inexpensive side. Well, I was curious to test it to see how fast it would fill the tank. Specs on the thing were 90 - 115 psi working pressure (should stop around 115 and restart around 90), and relief valve stamped 125.

First it won't start up. Motor buzzing but no compressor action. I take it apart and find the rod frozen on the crankshaft. I take care of that. Fine. Now it's cranking great. (It's oil lubed and cast iron cylinder.) Pressure goes up reasonably fast, 90, 100, 110....





120.....













130.....














oh, oh, I stopped it.





release air, and move it far outside in a safe location. Plug it back in












120.......










130.......












140.........







still no relief release.





I stop it by remote control (unplug the extension). I wait a bit and release air.
Now what?
there are 2 gauges, both are in agreement. I take one of mine, put it on. Matches too. So it was really way up there.


So, the pressure switch did not stop the compressor when the pressure reached the 115. And the relief valve did not actuate. Unbeliveable...

WTH?




So I took the pressure switch apart. I could not believe the design of this thing. All mechanical, with an arm flipping one side or another with springs and relying on the shape of fulcrums. Seems highly dubious to me. (Note: seems like many are like that?)

Suggested note to one self: do not take switch fully apart, the thing is spring loaded and is impossible to put back together.... Also do not try to use the plastic adjustment screws, they break and have to be drilled out...


More important suggestion perhaps, for those who do have compressors: keep an eye on your pressures and switch actuation, even on the good stuff. May be good to test the pressure relief valve too. And better to put it in a location where an explosion won't kill ya and yours... Evidently it is possible to have both the switch and relief valve fail. Imagine the thing keeping on compressing more and more.... Ouch....


Sheesh....!

 

[splitshot]

Get some info on the switch adjustment from the manufacturer. sounds like someone's been monkeying with it.

Also there sould be a seperate emergency relief valve, no?

 

[Koffer]

The unit you have sounds like one I bought many moons ago from a big box store . The press release valve sounds stuck . If you pull the ring when it has some PSI behind it , it should let go . You are suppost to "test" the valve every so often by pulling the ring . keeps it from sticking .
As for the switch sounds like it bit the big one (poss rust or crap in it ) Replace it as its not worth it blowing up the whole place . Same thing with the valve if some WD40 dosnt take care of it sticking .
When you get a new switch let me know where as I need a new one too (spare unit so it just sitting at the moment )

 

[e rock]

When you get a new switch let me know where as I need a new one too (spare unit so it just sitting at the moment )

I think i've got one or two 120V switches sitting around from old compressors that I've junked. If you need one I'll try to find them and see if one will work for you.

 

[e9999]

I think i've got one or two 120V switches sitting around from old compressors that I've junked. If you need one I'll try to find them and see if one will work for you.

I could use one too for the unit I butchered if you have a spare . This one has a bottom connection to the tank over a membrane and a side actuator, but I guess something could be rigged. TIA.


And yes, the pressure relief valve was not stuck, just didn't open at 125... I wonder if the switch had maybe been fiddled with. Looked new, very clean inside. Would have been better to find out if it could be readjusted before I took it apart and the screw broke... Still don't trust it too much, though.




added: but anyway, my point was that these are hardly foolproof mechanisms and the situation could be potentially very dangerous, so keep an eye on your system...

 

[woytovich]

I recently built the plumbing for a new-to-me old compressor. I put 3 relief valves in the system... I think 1 is at 115 and the other 2 are at 130... They are cheap enough so why not. I also built a little shed outside my shop (really just a 9x12 shed itself) for the compressor and tank, to save space in my work shed but also to save ME if something were to go boom.

 

[brian]

i don't have the specs on me now, but i'm pretty sure air compressor tanks fall under pressure vessels, and should be "proofed" to something like 1 1/2 times the working pressure.
you would also be surprised at how much it takes to "pop" a vessel in good shape. you would also be disappointed at what happens when they fail.

 

[e9999]

i don't have the specs on me now, but i'm pretty sure air compressor tanks fall under pressure vessels, and should be "proofed" to something like 1 1/2 times the working pressure.
you would also be surprised at how much it takes to "pop" a vessel in good shape. you would also be disappointed at what happens when they fail.

disappointed or amazed...?

I still can't believe these guys would sell a bomb like that...

 

[-Spike-]

Tanks I've seen are rated to 600 PSI. I haven't seen a lot of tanks, or paid a whole lot of attention to the ones I have seen, so this is very limited experience. I don't think the compressor will keep running at even half that pressure though- the motor wouldn't be able to turn it.

Most of the pressure switches I've seen on smaller compressors (set to shut off at less than 150PSI) are not adjustable. Messing with the spring tension adjustments just messes 'em up. Usually the pressure relief valve will fail open, not closed, meaning it will open earlier than it should, so that sounds weird. I'd throw a new switch and safety valve on it.

-Spike

 

[woytovich]

But if it's an old tank there could be rust issues, as well as the pipe plumbing that could potentially be a problem with > expected pressure. Not to mention rubber hoses that could cause some smaller hurt if they burst. (I know we are talking about a new tank here but in the real world new tanks aren't new for long.) Better safe than sorry...

 

[FJ40_owner]

The electric pressure safety on my on board York failed one time when my wife left the compressor on and there was enough pressure when my air line blew to make a dent in the cruiuser. And it sounded like a tire blow out. This happened while we were driving.

I guess these things should be tested every now and then.

 

[e9999]

fixed the auto switch. Now it's going off at 120 and back on at 90. Better.

Will put in a second pressure relief valve in too, for extra safety.