Problem with Coltri MCH6

[Noomi SY]

Hi.

I have a Coltri MCH6 onboard and it just started acting up.
Right now I'm in Fiji and was hoping to get some help troubleshooting it so I can keep diving.
If nothing works I'll be in Australia in a couple of months and could sort it there.

The problem is that the pressure won't go over 2000.
One thing I noticed is that after I stop the compressor now there is some air and smoke coming out of the intake filter.
I've put a new belt and have recently changed the oil and looks all good on this front.
There are no air leaks as far as I can tell when I stop it either.

Any suggestions about the next steps I should take would be greatly appreciated.

Cheers

Dan

 

[zider]

Sounds like a stuck valve, maybe the 3rd or 4th stage. There is a 100hr service kit that can be purchased to replace several wear items, including the valves on the 2nd, 3rd, and 4th stages.

 

[Noomi SY]

Sounds like a stuck valve, maybe the 3rd or 4th stage. There is a 100hr service kit that can be purchased to replace several wear items, including the valves on the 2nd, 3rd, and 4th stages.

Thanks, Zider. I will look out for this kit.

Meanwhile do you think it's worth taking it apart so I can do something to get it going again and keep diving while I wait for parts?

Cheers

 

[Gone for diving]

You need to diagnose before ordering and tearing things apart

 

[Noomi SY]

You need to diagnose before ordering and tearing things apart

Thanks mate. That's what I'm trying to do.
Max pressure I can get now is 1750.
I don't see any air or oil leaks.
Got the new belt at high tension.
Oil is only 3 hours old.
New filter installed.
Misty air comes out of intake filter after it stops running.

Any suggestions of tests I should run to diagnose more?

I'm about to take the stages heads out to check the springs and valves seat.
Not sure what more I could do. Suggestions are welcome.

Cheers.

 

[Gone for diving]

Don't know that compressor at all but... you need to find which stage its leaking down from...
If there is pressure guage between each stage, if very easy to see where it stops pumping or draining back.
If not,
The start from the lowest stage while running and figure out which stage is making and not making heat,
Even hand touch on the outlet will work, one making heat is working. Next one cold and not any warmer then the last one is bad normally... probably head check valves. Sounds like its after the second stage for sure....

 

[zider]

Coltri tweaked the MCH-6 into the current "Icon" series compressor. This new version has a 1740 psi overpressure release on the 3rd stage. Since this is close to the pressure you are getting out of the system, I would start my investigations with the 4th stage. The bottom 4th stage on this unit is a common source of issues as the stage sits entirely within the oil sump. Older units were prone to having the 4th stage rust and seize due to moisture buildup if the compressor would sit idle for long periods of time. I'm guessing this is not the case for your unit since the compressor is running, but there could still be an issue with the valve sticking open which might make sense why you aren't seeing anything over 1750psi. Doing a valve job on these compressors is very easy. Coltri has great videos on their website showing how to do everything from simple belt changes to complex repairs that require disassembly of the compressor stages. Good luck!

 

[Jimchris]

Sounds like the 4th stage intake/suction valve isn't closing. 4th stage piston may also have excessive wear/blow-by.

 

[Noomi SY]

Coltri tweaked the MCH-6 into the current "Icon" series compressor. This new version has a 1740 psi overpressure release on the 3rd stage. Since this is close to the pressure you are getting out of the system, I would start my investigations with the 4th stage. The bottom 4th stage on this unit is a common source of issues as the stage sits entirely within the oil sump. Older units were prone to having the 4th stage rust and seize due to moisture buildup if the compressor would sit idle for long periods of time. I'm guessing this is not the case for your unit since the compressor is running, but there could still be an issue with the valve sticking open which might make sense why you aren't seeing anything over 1750psi. Doing a valve job on these compressors is very easy. Coltri has great videos on their website showing how to do everything from simple belt changes to complex repairs that require disassembly of the compressor stages. Good luck!

Thanks a lot.
Looks like I'm taking that head apart today.
I'm hoping a good clean might sort it, otherwise I'm probably in for one of this kits, I imagine:
Coltri MCH6 4th Stage Cylinder Head Kit
Or I might as well rebuild the whole thing with this:

MCH6 500-Hour Service Kit - Compression

500-hour service kit for MCH6 compressors. For use on compressors manufactured after March 2007. See Page 11 of the Parts Manual.

nuvair.com

My unit is actually a MaxAir 35 from about 2010. The first owner did let it sit idle for a few years, but I've been running it for the last months and got about 30 tanks filled before this issue.

The Coltri YouTube videos are definitely amazing. Looks very straightforward, if I can get all the bolts moving, it is.

Thanks for the help.

Dan

 

[Noomi SY]

Sounds like the 4th stage intake/suction valve isn't closing. 4th stage piston may also have excessive wear/blow-by.

Hope the rings are still fine and it's just a stuck spring/plate.
Will take it apart and give it a good clean before ordering any parts, but I might be in for a refit...

Thanks Jim