Air Compressor Doesn't Keep Up

6 hp 33 gallon Craftsman Oil Free Air Compressor 240V. I got this unit
used, was previously used for spray paint duty by a homeowner, so it
did not get much service. Looks new, actually.
It takes quite a while to pump up to a max of about 90 psi (should be
able to go to 125 psi). When I try to run tools on it, even ones well
within the demand of the unit (sorry, don't have that info handy, but
something like 11 cfm at 90), it quickly peters out, the compressor
runs, but just can't keep up. The filter material is clear, actually
run it without one to see if that was causing restriction. If I set
the gage low, say 60 psi, it pumps up to it and stops, and will
actually hold pressure, I did this and it held for 2 hours, so there
isn't an obvious leak.
So the compressor has gone weak. Are these types of compressor's
rebuild-able? It is craftsman, so parts should be available, just
wondering what might be the cause of the compressor not having the
power to do its job, worn cylinders maybe?
Reply to
Rob
For reference my 5HP/110V/30 Gallon Coleman compressor takes about 10-15 min to pump up to indicated 125psi from empty. Just estimating. never actually timed it. Gauges aren't very accurate so your probably not even getting 90PSI. If you can adjust the shut off pressure it could either be in the switch or that the compressor isn't able to supply enough pressure. Does it shut off at the "90PSI" or just doesn't go higher, without any air being used.? My compressor's switch only has the one pressure it shuts off at. I just partially disassembled it to see how it works. When the switch kicks out it releases a valve that removes pressure on the compressor side of the check valve that keeps tank pressure from going back through the compressor. On most units it's connected by the little black hose. Must relieve the pressure quickly so the check valve seats forcefully. Apparently this leaks a little by design while the compressor is running. This does and other things could be leaking while in use but wouldn't after the check valve closes. Doesn't seem to be much traffic in this group.
Reply to
T Shadow
It could be the reed valves are not seating like they should, or one of them is broken not allowing the compressor to work as it should. If you have a model number, you can go to Sears parts and see if they have anything for your compressor. These compressors aren't that hard to rebuild, but if the cylinder is worn to where the new rings won't help, you might consider another compressor block.
Reply to
Mike
The model number is 919.152930 and Sears seems to have all the parts for it and the engine. So I should disassemble, inspect the reed valves? Are there any manuals out there that might help with disassembly that you know of? I'm up to the job, I have done head work on motorcycle engines, this would be alot cleaner at least.
I have also put a clamp meter on both legs and they are both drawing adequate current, so a simple electrical problem it is not.
Reply to
Rob
It also looks like they have replacement sleeves and rings. One good reason for buying Craftsman, they seem to do a good job keeping parts available. I can still find parts for a 30 year old chipper I have.
Reply to
Rob
If you can repair cycle heads, you'll have no problem with this compressor. I don't think there are repair manuals from Sears, but if you look at the parts page on the Sears site you can get an idea of what goes where. I'd order the valve plates and the o rings that seal them and while I was at it order the rings that go on the pistons along with the o rings that seal the valve plate to the cylinder. Part numbers I'd order would be 61, 64, 65, 66 (two of each) Hope this fixes your problem.
Reply to
Mike
Thanks for the tips. I plan on disassembling before purchasing any parts in case there is an obvious fix found in the process.
Reply to
Rob

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