New piston rings needed?

[wdeutsch]

I'm continuing in my quest to bring an old Hypress compressor (NA9 block) back to life and have completed most of the routine items. However, I'm still not getting the expected output or final stage pressure. It's spec'd at 9CFM and 5000 max PSI. I'm getting around ~5 CFM (measured by filling AL80) and topping out at about 3000 PSI. First and second stage pressures are exactly what the manufacturer says they should be (~100 and 1000 PSI respectively), but final stage pressure tops out at 3K instead of 5K as it should.

I'm thinking this may be because the 3rd stage rings are worn and need replacement? Thoughts on that?

Other symptoms that may support the diagnosis :

• The 3rd stage (I *think*) becomes pretty noisy at higher pressures, making a clicking/clacking noise.
• When I shut down the compressor at higher pressures, I get bubbling/boiling noises from the oil sump and an oily mist often comes out from the air intake port. I don't think either of those should happen?

Thinigs I've done to eliminate other possible low output/final pressure diagnoses:

• Check/clean/replace 2nd and final stage inlet and outlet valves. First and second stage are now hitting appropriate pressures.
• Replace all 'plumbing' fixtures in filter stack and eliminated all air leaks there.
• Found/fixed all air leaks in inter-stage plumbing and pressure gauge lines
• Disassembled/cleaned/reassembled (or replaced) inter-stage pop-off valves.
• Verified correct function of auto-drain and the fact that it's not leaking continuously.

To do this week:

• New oil/filter
• New intake air filter

Thoughts on the piston ring diagnosis? What else would give the low output, low final pressure and oil bubbling/mist?

 

[Wookie]

How many hours? On Compair/Mako blocks we replace the final stage rings every 1500-3000 hours depending on use (air or nitrox) and duty cycle.

 

[wdeutsch]

How many hours? On Compair/Mako blocks we replace the final stage rings every 1500-3000 hours depending on use (air or nitrox) and duty cycle.

1400 hours. Air only, no nitrox. No clue on duty cycle, as it was used by a rural fire department. The manual says rings should go 2-5000 hours. That said, there are plenty of indicators that this compressor may not have been driven gently by the previous owners.

 

[Wookie]

1400 hours. Air only, no nitrox. No clue on duty cycle, as it was used by a rural fire department. The manual says rings should go 2-5000 hours. That said, there are plenty of indicators that this compressor may not have been driven gently by the previous owners.

I used to service Mako compressors for the fire departments. By far, the best fire departments were the ones that had a quarterly service contract where we came in, sampled the air, sampled the oil, charged the banks, changed the filters.

The fire houses that had a fireman that thought he was a compressor mechanic had a far higher annual bill, about 2X what the fire department with the quarterly service contract had. Part of that 2X bill was for service calls in the middle of the night where they had pulled apart the auto drain and didn’t have parts to put it back together, or installed their own filter, typically a Lawrence Factor, (nothing wrong with LF, but folks buy them to “save money”) and done it wrong, so they had oil throughout their system.

As an aside, we offered the same quarterly service contract to dive shops. It was always too expensive and we never signed up a single dive shop, but we did lots of very expensive repairs…..

 

[Agro]

Yes 3rd stage o-rings is my guess as well.

Measure cylinder and piston, perhaps they must be exchanged as well.

 

[wdeutsch]

I used to service Mako compressors for the fire departments. By far, the best fire departments were the ones that had a quarterly service contract where we came in, sampled the air, sampled the oil, charged the banks, changed the filters.

The fire houses that had a fireman that thought he was a compressor mechanic had a far higher annual bill, about 2X what the fire department with the quarterly service contract had.

I come from the world of scientific instrumentation, and it's the same there. You're gonna pay one way or the other. Up front for a pro is almost always cheaper - at least until you build a relationship with your tech and get some mentoring from them about what you should and should not do yourself. (Yes, I realize the irony that I'm doing the opposite right now....)

I believe you've met the folks I bought this compressor from. Flare fittings with O-rings jammed on instead of correct ORB ones for filter housings. Filters WAY past service life (and with cracked cases). No final breathing air cartridge (just 13x and carbon, but no hopcalite). Rust and oil on every connector in the filter stack. No backpressure regulator at all on the filter stack. Etc.

It's been a good compressor to learn a LOT about what not to do... Lol. It's getting there, though. Fingers crossed that the last 'gotcha' is the rings.

 

[Agro]

Yes 3rd stage o-rings is my guess as well.

Sorry, piston ring, not o-ring