Problem with Coltri MCH6

[Noomi SY]

Hey guys. Thanks for your help. I took the whole thing apart and it's not good. The problem on the 4th stage looms like just the valve spring, but since the head is seized I can't get to it, so it looks like I will have to get a whole new 4th stage.

Than I opened the 3rd stage and one of the arms on the piston is broken. Apparently Nuvair won't sell just a new piston so a whole new 3rd stage is also on the cart.
About $600 in parts so far...

Thanks for all the help.

Dan

 

[zider]

Man that really stinks. At least you identified the problem so it can be repaired. Make sure you buy a replacement O-ring for the crank case flange. When I first pulled my unit apart that O-ring basically fell into pieces and it’s needed to seal the crank case correctly.

 

[Wallowa]

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

Dan...any idea how many hours on your compressor?

 

[Alex Ouroboros]

I just found this post as I am also having problems with my Coltri MCH6. mine has a similar issue in that it won’t pump over 200 bar (ish) so I did a bit of home work and asked about, my best advice was (from an authorised maintenance fella) it would be a problem with the forth stage he sent me a link and I purchased the part along with a service kit and sorted it over the Christmas break, this weekend after running it for a little while with no load I tried to top off a cylinder and again the opv fired although this time it was very easy to determine it was definitely coming from the 3rd stage, when I installed the new 4th stage I checked the compressor in its cycles by hand and everything appeared fine (much better than before I removed the old 4th stage)​

would anybody be good enough to diagnose the problem? Thanks.​

 

[Wallowa]

I just found this post as I am also having problems with my Coltri MCH6. mine has a similar issue in that it won’t pump over 200 bar (ish) so I did a bit of home work and asked about, my best advice was (from an authorised maintenance fella) it would be a problem with the forth stage he sent me a link and I purchased the part along with a service kit and sorted it over the Christmas break, this weekend after running it for a little while with no load I tried to top off a cylinder and again the opv fired although this time it was very easy to determine it was definitely coming from the 3rd stage, when I installed the new 4th stage I checked the compressor in its cycles by hand and everything appeared fine (much better than before I removed the old 4th stage)​

would anybody be good enough to diagnose the problem? Thanks.​

Alex,

Couple of questions....how many hours on this compressor and to how many bars....you mentioned 3rd stage PPV popping off but then referred to 4th stage replacement...can you describe exactly what you believe the issue is and how a new 4th stage will fix it?

Thanks...Phil

 

[Alex Ouroboros]

Alex,

Couple of questions....how many hours on this compressor and to how many bars....you mentioned 3rd stage PPV popping off but then referred to 4th stage replacement...can you describe exactly what you believe the issue is and how a new 4th stage will fix it?

Thanks...Phil

Compressor has something like 50hrs on it, it’s had filter and oil change before this recent strip out and rebuild also, for the last 7-8hrs or so she hasn’t pumped past 200bar, with an OPV firing sometimes as low as 180 bar, quite bizarrely it was hard for me to tell which OPV was going off, after talking with a Coltri technician he said it was probably a problem with the 4th stage and that they can be prone to crap buildup and it may need a good clean or replacement, so I studied the YouTube Coltri guides bought a new 4th stage and went to work, after the rebuild of the compressor pistons on the block I turned it by hand and it did feel much better so was satisfied I’d solved the issue, so completed the rebuild to finish and now the OPV that points downwards from the third stage is definitely the one cracking at 200bar, I do find it strange as it didn’t seem as obviously the culprit as before, but maybe now I’ve had the compressor in bits I just understand it better so it’s easier to fault find, do you have any theories? Many thanks for trying to help

Ps the final stage is fitted with a 300bar OPV.

 

[Wallowa]

Compressor has something like 50hrs on it, it’s had filter and oil change before this recent strip out and rebuild also, for the last 7-8hrs or so she hasn’t pumped past 200bar, with an OPV firing sometimes as low as 180 bar, quite bizarrely it was hard for me to tell which OPV was going off, after talking with a Coltri technician he said it was probably a problem with the 4th stage and that they can be prone to crap buildup and it may need a good clean or replacement, so I studied the YouTube Coltri guides bought a new 4th stage and went to work, after the rebuild of the compressor pistons on the block I turned it by hand and it did feel much better so was satisfied I’d solved the issue, so completed the rebuild to finish and now the OPV that points downwards from the third stage is definitely the one cracking at 200bar, I do find it strange as it didn’t seem as obviously the culprit as before, but maybe now I’ve had the compressor in bits I just understand it better so it’s easier to fault find, do you have any theories? Many thanks for trying to help

Ps the final stage is fitted with a 300bar OPV.

No magic bullet here...but you when you turned it by hand that "it did feel much better"; denoting that prior to your work the compressor was tough to turn by hand or had a rough feel? I assume that 50 hours minus 8 hours means you started with a new compressor so you know the maintenance/lube history for those 42 hours...offhand I do not know the OPV setting for the valve [3rd stage] you say is cracking/opening at 200bars; is it possible that the OPV has failed and not the cylinders? Also I am fuzzy about which OPV you mentioned was opening "sometimes as low as 180bars" and was the replaced 4th stage faulty?

Phil

 

[Gone for diving]

A bit confused....
But my experience with compressors,
If the pressure relief that's blowing off is good and set right. Then the stage after it is not working...
More than likely bad check valves,
Not sealing properly or something like that.

Sounds like you need to take a closer look at that stage.

If the inlet air is the same temp as outlet air, then that stage is doing nothing.

 

[Alex Ouroboros]

No magic bullet here...but you when you turned it by hand that "it did feel much better"; denoting that prior to your work the compressor was tough to turn by hand or had a rough feel? I assume that 50 hours minus 8 hours means you started with a new compressor so you know the maintenance/lube history for those 42 hours...offhand I do not know the OPV setting for the valve [3rd stage] you say is cracking/opening at 200bars; is it possible that the OPV has failed and not the cylinders? Also I am fuzzy about which OPV you mentioned was opening "sometimes as low as 180bars" and was the replaced 4th stage faulty?

Phil

Tbh the 180bar episode only happened once so I discount it really, and yes I bought it new.
When the compressor was at a state I could turn with no pipework on, it did become a little stiffer at a certain part of the cycle than it was after the rebuild, (I thought this could be expected due to all the different stages) it wasn’t requiring much more effort than the rest of the cycle but was noticeable, after rebuild it had a little drag at the same part but not as much, this was all done with one hand and not much resistance, I could also hear the little pops of air coming through the stages,
The 4th stage didn’t seem bad but as I had a brand new part next to me (and bearing in mind I’ve not had a compressor in bits before so this is a learning experience also) I replaced it,

Next time I’m home I will run it up and see if the 4th stage gets any running heat in it, if this doesn’t offer an answer I am thinking of taking it all apart again and having a good look as now I understand what’s going on better,

Does this sound a sensible course? Thanks.

 

[Alex Ouroboros]

A bit confused....
But my experience with compressors,
If the pressure relief that's blowing off is good and set right. Then the stage after it is not working...
More than likely bad check valves,
Not sealing properly or something like that.

Sounds like you need to take a closer look at that stage.

If the inlet air is the same temp as outlet air, then that stage is doing nothing.

Going to take your advice and check the in - out heat next I’m home, thanks.