Need help troubleshooting a DeWalt Compressor

hans747

Well-Known Member
Joined
Feb 20, 2007
Location
Asheville, NC
Hi Everyone,

I am helping a friend fix his Dewalt Comproessor, but I'm at a bit of a loss. This unit is supposed to run up to 200 PSI and then turn off. It fills up quickly, but the tank-side gauge maxes out at 110 PSI. I I open in the regulator all the way, the line side gauge maxes out at 90 PSI. Since the tank never gets above 110 PSI, the compressor just runs non stop.

Does it sound like the regulator is bad? or could something else be causing this?

Thanks!
 
The air has to be going somewhere. If the regulator is bad, you should feel air leaking around the reg or out the line. It sounds like it's more probable that the pump itself is failing somewhere. The piston isn't sealing or the reed valves are messed up. You may be able to pull the head and flip the reed plate if they're bent and not closing.
 
Thanks!

I ran it up to pressure and sprayed soapy water on all the fittings that I could access. No bubbles. This evening, I will take the plastic cover off and see if there is any air escaping from the cylinder head. The parts manual shows o-ring gaskets that seal the cylinder body to the cylinder head.

Besides the lack of tank pressure, what symptom(s) would a bad reed valve exhibit? I would love to cross things off the list without unbolting the cylinder head.
 
Could be the pressure switch which is the problem with my old Dewalt Emglo compressor. $30 fix.
 
You can adjust some of them, do a Google search.
 
Blow by if it's an oil-less unit.. I've got a CH compressor that failed at five years old due to the Teflon piston ring wearing out. Would only build so much pressure and run forever.
 
GotWood said:
Could be the pressure switch which is the problem with my old Dewalt Emglo compressor. $30 fix.
Click to expand...

If it was the switch, it would build pressure beyond 100 psi, but never shut off. Or it would shut off early. He says it's not building enough pressure to trigger the shutoff, but it keeps running. Air's got to be going somewhere.
 
I would check the valves
 
Well if it's the intake valve, it would blow out of the air intake when it starts getting higher in pressure. I haven't often seen Reed valves go out unless some little kid put grass in the intake.. Wonder how that happened? If it's oil less, pull the shroud, feel carefully at the bottom of the cylinder for blowby.
 
catfishblues said:
If it was the switch, it would build pressure beyond 100 psi, but never shut off. Or it would shut off early. He says it's not building enough pressure to trigger the shutoff, but it keeps running. Air's got to be going somewhere.
Click to expand...
OK, missed the part about not shutting off. Mine will only build about 110psi then shut down. It doesn't kick back on till around 60psi. I've tried adjusting but the contacts are burnt out.
 
Hi Everyone,

Thanks for offering your help. Last night, i spent a little more time with the compressor. Here's what i did/found:

1. sprayed soapy water around the cylinder head -- no bubbles.
2. removed cylinder head
3. inspected reed valves. No obvious signs of wear or bending. Very slight surface rust on the bolts that hold the reed valves in place. No signs of blow-by along the gaskests.
4. Piston seems well seated in the cylinder. no obvious scoring on cylinder walls.
5. I put everything back together.
6. Ran the compressor. It wouldn't go any higher than 110 PSI (supposed to shut off at 200 PSI)
7. While compressor was running, I put about 2-3 drops of clean oil in the intake. Three things that I noticed:
a. the oil did not spit back out of the intake (That's a sign of a good reed valve, right?)
b. some oil sprayed out of the back of the piston (this is an oil less unit so I don't know what to make of that, since this piston presumably does not have oil rings.)
c. the pressure in the tank jumped up by 15 PSI
​
Based on what I know about working with engines, this makes me feel like the piston ring is probably worn out.

Any other ideas?
 
Be sure to buy a oil compressor when you replace this one.
 
I admit I don't know anything about Dewalt air compressors. My experience lies with Craftsman or Speedaire. I was a little shocked with the 200 psi goal. Pressure over 100 psi required a two stage compressor where a large piston first pumped the air to 100 psi to a small piston to finish the compression. 200 psi with pistons and reed valve seems like a stretch but maybe Im in for an education which is why Im here.
 
Usually they are 150-175. You can some times get a cylinder sleeve and piston kit for like $75 on flea bay. The max pressure available would be determined by the compression ratio, longer stroke => higher max pressure. Reed valves allow the piston to practically hit the bottom of the head.
 
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