Air compressor not building up full pressure

[BTDT]

Compressor is chinese 2 stage from traveling tool show/sale. Unit is about 5 years old. Only builds about 50#'s pressure. I have pulled heads, gaskets good, pistons appear good, valves (spring steel strips) appear good. I can hold finger over each intake to filter and 1 sucks harder than the other. I think it has a check valve where it discharges into tank, and that's something I haven't checked. Any ideas on what I need to check next (other than sales brochures for new unit )?

 

[SPYDERLK]

Are the 2 pistons the same size? Is it oiless or oil in crankcase?
larry

 

[Bird]

Is that really a two stage compressor, or just a two cylinder one? Do you hear air escaping anywhere? You say the valves are spring steel strips? Isn't that reed valves?

 

[BTDT]

I looked again, the pistons appear to be the same size, so I guess it is a 2 cylinder, not a 2 stage. It has oil in the crankcase, and is about midway up the sightglass. No air can be heard leaking anywhere. It has one air valve near top of tank with 1/4 turn handle for on/off, and then a small "header" with 2 slide air valves for on/off. Not blowing oil out air hose, so I'm guessing the rings are ok. Even though the "reed valves" appear to be ok, I may need to check into getting some replacements to see if that will fix problem. I'll try to take pics of unit this evening, and later in the week, if I tear it down I'll post pics of that also.

 

[SPYDERLK]

BTDT. Yes, you have a single stage 2cyl compressor - and from my standpoint a real mystery. If it was oiless, piston seals would be likely. Not so with oil. A leaking exhaust valve on either cyl would cause your type of problem. Check the reeds and the faces of the ports they seal against. It should be an obvious defect with the serious symptom you have. The reeds self seat during operation so you are just interested in smooth seating surface - not a tight static seal. Also, do you have an unloader valve that automatically releases head pressure when the compressor stops. This may be leaking during operation. With all the other noise you may not hear it. The line for this valve usually leads back to the pressure switch, and the valve is incorporated in the switch somehow. Youll have to take the cover off.
luck,
larry

 

[BTDT]

BTDT. Yes, you have a single stage 2cyl compressor - and from my standpoint a real mystery. If it was oiless, piston seals would be likely. Not so with oil. A leaking exhaust valve on either cyl would cause your type of problem. Check the reeds and the faces of the ports they seal against. It should be an obvious defect with the serious symptom you have. The reeds self seat during operation so you are just interested in smooth seating surface - not a tight static seal. Also, do you have an unloader valve that automatically releases head pressure when the compressor stops. This may be leaking during operation. With all the other noise you may not hear it. The line for this valve usually leads back to the pressure switch, and the valve is incorporated in the switch somehow. Youll have to take the cover off.
luck,
larry

Yes, it does have the unloader valve, I may have to check this. I still kind of think it is with the reed valves, due to one cyl. having more (it seems) suction when you cover intake with finger. Thanks for the reply's, keep them coming.

 

[Bird]

I still kind of think it is with the reed valves

We might be wrong, but that would sure be my best guess.

 

[George2615]

Does it continue running and just not build over 50 PSI or does it shut off at 50 PSI? If it shuts off at 50 maybe your pressure switch is bad. If it continues to run and not build its probably an exhaust valve problem like Larry said.

 

[BTDT]

Does it continue running and just not build over 50 PSI or does it shut off at 50 PSI? If it shuts off at 50 maybe your pressure switch is bad. If it continues to run and not build its probably an exhaust valve problem like Larry said.

It continues to run, but that's all the pressure it builds to. And it seems it did this all at once, not gradually over a period of time, so it's like one of the valves stuck, got weak, or something.

 

[Bird]

I once had one of the oilless single cylinder compressors that would continue to run, but never could get over 35 psi, but the broken reed valve was obvious on that one when I opened it up.