New Coltri (Nuvair) MCH6 Compressor

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I'm all for adding a check valve to the line but IMO it is of more benefit if it is placed after the filters and as close as possible to the tank connection. The number 1 advantage of using a stop valve is the prevention of losing all the contents of the cylinder in the event of a leak or burst up stream. I have learned from experience. Placing the valve before the filter will not produce any advantage in moisture reduction. If your tank has 3000 PSI in it?nothing is going in unless the pressure is higher than 3000 PSI. The idea of a PMV is to let the pressure build to an optimum filter pressure before allowing it to flow, (for molecular sieve, that is supposed to be around1500- 2000 PSI) and if your tank has 3000 PSI in it, nothing is going in until the pressure is over that. The only possible unfiltered air would be a small % of the air in the hose. I've never seen any specs on how efficient the stuff is under that pressure but would guess that it would still work down to nearly fart pressure but it would not be as effective. Prefilling the filter from the tank instead of from the compressor side would make no difference. My point is that with or without a PMV, the amount of unfiltered air that will get into your bottle, would be so insignificant that it is not worth considering. There is nothing wrong with positioning the check valve down there but it will be of more benefit if it is closer to the bottle. I actually use two, one before the desiccant filter and the other at the tank inlet with a bleed between the first one and the filter.
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One thing placing the check valve at the filter inlet does is it causes most of the water to collect in the YH filter. The humidity must of been pretty low the last time I ran my YH setup a month go. My YH filter was somewhat soaked but the first stage on my gold filter was pretty dry. The first time I ever saw this. Most of the other times I have run it, the first stage media had water in it. Not a lot but it was damp.
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Yes, the relative humidity has a huge bearing on the moisture output. I have found that with mine the little filter does a reasonable job of catching most of it when just topping off from say 250-300 BAR in 40% or lower humidity but if I have to fill one of my 6.8 litre bottles from empty, the little YH filter gets a good soaking. Adding a check-bleed valve combination at the lowest point helps reduce that. Another reason that I added a bleed before the desiccant filter is that with the check valve at the pump outlet I can no longer bleed the line out with the compressor bleed. I can still bleed the line out with the one on the tank fitting but I don't like to do that because if there is any water in the line before the desiccant filter, it could get sucked up into it. This all may sound a little complicated but it is really very simple. All up I'm probably only into it for about US $35 for fittings from AliExpress including the DIN300 thank adaptor and bleed valve but not the filters or hoses. You shouldn't have to worry about this sort of crap now that you have a real compressor. For the amount of shooting I do, this little toy and my Altaros booster satisfy my requirements.
 
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I'm all for adding a check valve to the line but IMO it is of more benefit if it is placed after the filters and as close as possible to the tank connection. The number 1 advantage of using a stop valve is the prevention of losing all the contents of the cylinder in the event of a leak or burst up stream. I have learned from experience. Placing the valve before the filter will not produce any advantage in moisture reduction. If your tank has 3000 PSI in it?nothing is going in unless the pressure is higher than 3000 PSI. The idea of a PMV is to let the pressure build to an optimum filter pressure before allowing it to flow, (for molecular sieve, that is supposed to be around1500- 2000 PSI) and if your tank has 3000 PSI in it, nothing is going in until the pressure is over that. The only possible unfiltered air would be a small % of the air in the hose. I've never seen any specs on how efficient the stuff is under that pressure but would guess that it would still work down to nearly fart pressure but it would not be as effective. Prefilling the filter from the tank instead of from the compressor side would make no difference. My point is that with or without a PMV, the amount of unfiltered air that will get into your bottle, would be so insignificant that it is not worth considering. There is nothing wrong with positioning the check valve down there but it will be of more benefit if it is closer to the bottle. I actually use two, one before the desiccant filter and the other at the tank inlet with a bleed between the first one and the filter.
Click to expand...

I agree with your statement that there is not a significant amount of low pressure air going into the filter if the check valve is beyond it. However, there is also a greatly reduced air loss exposure in my system compared to one without the check valve. My additional air leak exposure is only the filter and the compressor's fill hose. Both locations add protection to the compressor setup and are better than no check valve at all.
 
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