Coltri MCH 6 humidity issue

[pisoiu]

I have a coltri mch6 compressor, serviced (by me) less than 6 months ago. Since then it had worked approx. 10 hours.
Some inside components were worn and replaced during service (crankshaft, stage 1 segments, stage valves, overpressure valve), it was completely disassembled and washed of old oil and contaminants. Of course, new oil and filters were installed (from manufacturer).
Few days ago I decided out of curiosity to measure the humidity of the air produced with this compressor. For this purpose I used a 4 liter steel tank, filled from this compressor, connected to a 1st stage and a hose without 2nd stage inserted in a plastic bag. Inside the bag is a humidity meter, this one: ST-321 - UNBRANDED - HYGROMETER, THERMO, DIGITAL | Farnell element14
The procedure was simple, blowing air inside the bag for approx 1 minute, at moderate pressure, then extracting hose (while still blowing) allowing as less as possible air from outside, then zip close the bag. The readings were taken after another 1-2 minutes.
First test was surprising, 20% humidity. From what I have read here about humidity in compressor air, I expected a lot less. My first thought was that the filter had saturated somehow after 10 working hours (out of ~50, as indicated by manufacturer) at approx. 15-20 celsius degree temperature, even if I do not live in a particulary humid area. The filter looks correctly installed, the sealing oring on the filter looks ok. I do not think that airflow is bypassing the filter.
After that, I made another test. I have another filter, brand new, sealed in its original plastic bag. I opened it and installed it, then another 4L tank was purged then filled to approx. 170 bar. Repeating the same test, I got around 15% humidity.
Now I am puzzled and I do not understand why the humidity is so high. Unfortunately I do not have another humidity meter to double check the readings.
I also weighted the filters, the old one has 120,28 grams, the new one (after the first fill) has 108,77 grams.
Any idea? Thanks in advance.

 

[rcontrera]

The compressor usually ships with the fill hose directly connected to the filter tower. That means there is no back pressure in there to help the system work properly. If you have not installed a pressure maintaining valve, do so. It will GREATLY increase the efficiency of the filtration system.

 

[ti325v]

Your methodology may certainly be flawed.
Your procedure is simple, but it is simply not the way humidity is measured correctly at high pressure.

But first, as Ray said a P.M.V. (Get a good one) is an absolute necessity and it is a travesty that any compressor would ship without one.

Ambient humidity does NOT effect humidity at the output of the compressor. Separator efficiency ( Strongly Effected by a PMV) and temperature into the separator are the ONLY things that will determine how moist the the air is entering the filter. Then you have the issue of humidity in the filter housing ( A function of size and how well used it is) ..and onto your tanks.... I change my filters at about 15% humidity at 190 BAR. (About 60 ppm)
This is vanishingly low at ambient pressure.

1) No PMV and your filter is shot after 30 running minutes.
2) Get one of the eyeball moisture indicators. Ray can fix you up with all of it, just be warned....that the filter on the /6 is SO small..it may not last long enough to change the color indicator back to blue, one of mine takes about 6 running hours at 10 CFM, the other about 4 hours at 12.5 cfm.. Likely your filter is beginning to get overwhelmed at that point you have pumped enough gas through the indicator to change the color back to blue.

Read this....Understanding SCUBA Compressors and Filtration
Good luck....

I have a coltri mch6 compressor, serviced (by me) less than 6 months ago. Since then it had worked approx. 10 hours.
Some inside components were worn and replaced during service (crankshaft, stage 1 segments, stage valves, overpressure valve), it was completely disassembled and washed of old oil and contaminants. Of course, new oil and filters were installed (from manufacturer).
Few days ago I decided out of curiosity to measure the humidity of the air produced with this compressor. For this purpose I used a 4 liter steel tank, filled from this compressor, connected to a 1st stage and a hose without 2nd stage inserted in a plastic bag. Inside the bag is a humidity meter, this one: ST-321 - UNBRANDED - HYGROMETER, THERMO, DIGITAL | Farnell element14
The procedure was simple, blowing air inside the bag for approx 1 minute, at moderate pressure, then extracting hose (while still blowing) allowing as less as possible air from outside, then zip close the bag. The readings were taken after another 1-2 minutes.
First test was surprising, 20% humidity. From what I have read here about humidity in compressor air, I expected a lot less. My first thought was that the filter had saturated somehow after 10 working hours (out of ~50, as indicated by manufacturer) at approx. 15-20 celsius degree temperature, even if I do not live in a particulary humid area. The filter looks correctly installed, the sealing oring on the filter looks ok. I do not think that airflow is bypassing the filter.
After that, I made another test. I have another filter, brand new, sealed in its original plastic bag. I opened it and installed it, then another 4L tank was purged then filled to approx. 170 bar. Repeating the same test, I got around 15% humidity.
Now I am puzzled and I do not understand why the humidity is so high. Unfortunately I do not have another humidity meter to double check the readings.
I also weighted the filters, the old one has 120,28 grams, the new one (after the first fill) has 108,77 grams.
Any idea? Thanks in advance.

 

[pisoiu]

Your methodology may certainly be flawed.
Your procedure is simple, but it is simply not the way humidity is measured correctly at high pressure.

Yes, it definetely may be flawed, I improvised with what I had in my toolbox. Also, there may be some things that are missing from my understanding of the physics involved.
Can you recommend me a good valve? Are there any valves ready for mch6 or do I need to get a generic valve and find a way to connect it to my mch?
Thank you.


LE: I have several tanks of various sizes I use (4 liter, 12 liter) and I think I can find a way to tranfer with a whip from one tank to another some gas in such a way that I can begin filling with the compressor not from low pressures (where I understand the filter is not efficient), but from over 100 bar up to top. Can this be a temporary solution until I find and install a back pressure valve?

 

[rcontrera]

The priority valve we install on all our MCH6 compressors is a very simple little guy. We pull the fitting out of the filter housing and replace it with another that screws into the valve. Then we put an adapter on the outlet of the valve to hook to the hose.

 

[ti325v]

Yes, it definetely may be flawed, I improvised with what I had in my toolbox. Also, there may be some things that are missing from my understanding of the physics involved.
Can you recommend me a good valve? Are there any valves ready for mch6 or do I need to get a generic valve and find a way to connect it to my mch?
Thank you.


LE: I have several tanks of various sizes I use (4 liter, 12 liter) and I think I can find a way to tranfer with a whip from one tank to another some gas in such a way that I can begin filling with the compressor not from low pressures (where I understand the filter is not efficient), but from over 100 bar up to top. Can this be a temporary solution until I find and install a back pressure valve?

I have in the past, when I had a failed pmv, no spare...(now I keep 2)......filled 2 tanks at once. (But I have online moisture monitoring) Start with one full, preferably much bigger then the little other, equalize the two tanks, then you are pumping against the remaining pressure in the tanks, which is back pressure, and does work, fill both tanks, remove one, equalize, fill, lather rinse repeat....but....if you use equal size tanks, starting at 200 BAR, you will only be pumping against 100 bar. This is too low, you should be pumping against at least 140 bar. Separator efficiency and filter life go up exponentially with increasing pressure. Though I fill direct to 200 BAR I keep my PMV at a minimum of 160. (YmmV and we all have our reasons) You can expect double the filter life or these about increasing the pressure from 100 to 150 BAR. It is all in the article I lined you to. No PMV, you are pumping water in your tanks in 20 minutes..
I have seen one guy with a failed PMV ruin $9000 in steel tanks in a very short time, like 3 weeks as far as we could determine....
As I said a travesty that it is not supplied.
When you have sorted all of that out...P.M. me and I will send you more information.
But don't pump with out the PMV, you do not know enough enough yet. Please.

 

[Peter69_56]

You could throttle the pressure at the tank valve to maintain 120 Bar in the compressor, filter and whip so effectively using the tank valve as the PMV in the interim. On my Bauer, although it already has a PMV built in, I double filter so added another PMV after the final filter to ensure that under all circumstances, my filtration system had back pressure. Before the PMV turned up I simply throttled the tank inlet to maintain 140 BAR in the fill line and final filter to ensure dwell times were maintained in the final filter. The catch is to have sufficient pressure gauges to show you what the pressure is in the whip prior to the tank valve, and you MUST stay with the tank until filled fully to ensure 140 BAR is maintained, and when the tank reaches 140 BAR then you can open the tank valve fully. I got one of those exact valve shown in the post and added it to the end of my final filter (which happens to have a Coultri filter element in it), before the end of the whip.

So the setup is from the end of the Bauer fill hose (which has combo valve/vent and pressure gauge), Coultri MCH6 Filter element, non return valve, PMV, tank DIN connector with built in vent and pressure gauge

In my crap Chinese rip off of a Coultri, it had no PMV and a tiny filter that was crap. I contaminated 8 tanks on first fill before I got rid of it. In all reality it needed the filter body throwing away and a new one with built in PMV (which I think the guy who bought it was going to do).

Also your first filter element was truly dead. The filter for the coultri MCH6 weighs about 105 grams (I have 4 that all weigh the same). They are dead when they weigh 111.5 grams. This is based on the fact that Molecular Sieve will take 20% moisture by weight. Activated Charcoal will take about 7.5% oil by weight. With the content of the filters being about 25 gm MS and 20 gm AC the calculation is that the filter weight will increase by about 6.5 gm and then it is dead.

I am not exact on the weights in the Coultri MCH6 Filter element and if someone can tell me the exact fill weights for the MS and AC when new I would appreciate it, as I have used info provided to me but like to confirm it from someone else.

 

[pisoiu]

Thank you all for answers. Until I get a PMV, I will use tank valve for that purpose, I have no choice.
Ray, can you tell me please where can I get such a valve from Europe? From US is not an option, I saw some horrible shipping fees from there..

LE: Considering the differences between what the manual say about the filter change and the reality, what do you recommend about the oil change? Should I leave it like in the manual (I think is 50 hours)?

LLE: One thing I don't understand. If approx. half of filling time (assuming filling from ~30 bar to 200) is spent at a pressure at which the cartridge is not effective without PMV, then why my filter is busted after 10 hours, when the manual says approx. 50 hours at the temperature I use it? Cartridge being ineffective does't mean that is not absorbing moisture and oil vapors?

 

[ti325v]

I wrote a long reply, then the server went down for maintenance.
I need to caution you strongly, which I did in my reply to Peter (Lost) ....Funny as he and I both learned with the same crappy Chinese compressor.
I will shorten it here and say I regret telling you what I did about using two tanks, since you posted question #2, you obviously did not read or understand the article I linked too.
If that is the case, you do not know the risks you are taking.
This is diving my friend, man up and spend the money....Shipping was over $250 for me to sort out my filtration. (Add another $1600 for the parts) if you cannot find a pmv in Europe..(simply ridiculous, you are lazy) and you do not know what you are doing, do not do it. What if you hurt or kill yourself or somebody else ? You have managed to fill tanks this far, so do it the old way till the pmv arrives, jeez, I am sure you can get one from Coltri Europe, Coltris are made in Italy, Bauers are made in Germany and in fact they Coltri have a very high quality, easy to maintain PMV, the bauer a bit more complicated then really necessary. ...we are trying to help you to fix your problem by telling you that you must have a functional PMV. You could damage your tanks in a week, and kill yourself in a dive. Come on.
You said it yourself, you do not understand the physics and you are choosing not to understand a whole lot more then that. If you do not understand then listen to those of us who do, get the PMV.
25 to 50 dives and diving solo ? Your family would think it is money well spent on the PMV, body recovery is not cheap.

 

[rcontrera]

A small flat rate Priority mail package would fit the PMV and that is about $25 shipping. First Class Mail would only be about $16 but it isn't tracked or insured.