Need help troubleshooting low 3rd stage

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Weschap

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Scuba Instructor
Messages
25
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Location
Orange Beach, AL
# of dives
500 - 999
I have a Davey 15 CFM Compressor that I am working on. I am troubleshooting a low third stage and have I have run out of ideas. I am attaching a airflow diagram to help understand what I have done so far.
The book gives the pressures as follows @ 3500psi
1st stage: 55 + or - 5
2nd stage: 190 + or - 10
3rd stage: 900 + or - 50

I am getting
1st 60
2nd 175
3rd 600

This compressor uses a continuous drain systems that tends to be a problem. So I have capped off the drain system and made it a manual system. I have removed and capped # 43, 45, 46, 49. The drain system now cannot cause a problem.

To check for leaks to ambient, I have pressurized the system by removing the safety valve on each stage one at a time and using regulated high pressure air on each stage. The only air that I can hear leaking is the air that is seeping around the rings back into the crank case.

This system uses a complex intake/exhaust valve on the stages instead of separate valves. I have cleaned the 3rd stage valve but did not put a rebuild kit in it. I do not believe the valve to be the problem because the 2nd should be high if the 3rd is leaking back into it.

I have replaced the rings on the 3rd stage.

This compressor only has 50 hours on it, but was left sitting for 10 years or so.

Please help with any suggestion or troubleshooting ideas you may have.

View attachment airflow(1).pdf
 
I am leaning towards buying a rebuild kit for the third stage valve however I am still on the edge because I really think 2nd stage should be high if the 3rd stage valve is the issue. Any suggestions are welcome.

---------- Post added May 17th, 2013 at 05:37 PM ----------

I have taken the 3rd stage valve apart again. I am attaching pictures so you can see how the valve works. After cleaning the valve I am getting the same results. The images show the seating surfaces of the valves.






 
From what you have said about external leaks being non existant, that generally leaves blow back. You said you replaced the 3rd stage rings. Did you by chance hone the cylinder and then check the ring gap of a new ring to determine if the cylinder wear is within tolerance?
 
I did hone the cylinder. After honing there was a nice and consistent cross hatch pattern in the cylinder. I cannot find the spec in the book for the rings so I was not able to check tolerances. I did not think about simply putting the rings in the cylinder for a visual inspection. I suppose it's possible that the cylinder is bad but I would like to know for sure before sending $400 for a new one. I guess a machine shop could determine if its bad?
 
Jim,

I have a replacement 3rd stage valve that will be here tomorrow. I did want to post the pics of the ring in the cylinder and that small mark on the piston that we discussed. I do not think its anything to be concerned about but still wanted you to see the pics. Also the rings are tight in the cylinder. As well I took the cylinder to the machine shop and they took at least 10 different snap gauge measurements and all were well within spec. I will post my results tomorrow after I put the valve back in.


 
I think i am facing the same problem,did your problem solve,what should be the 4 stage reading.I don't have any documentation.Please help.
 
I need more information. What is the fourth stage pressure reading? Is the compressor building up and blowing down? If it is blowing down what pressure is it occurring at?
 
https://www.shearwater.com/products/teric/

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