K14 Elevated CO2

[Wallowa]

The Pressure Maintaining Valve is basically a strong spring that pushes against a seat, closing airflow.
Once the pressure on the other side of that seat reaches ~130bar, the force is strong enough the push the spring back, and the air starts flowing through.

The reason:
Air at ambient pressure can hold a lot of moisture. Increasing the pressure causes the moisture-holding-capacity to drop. By keeping the pressure high, 99% of all the moisture in the (compressed) air will condensate on the internal filter walls and drips down.

That last 1% of humidity is finally removed by the molecular sieve material inside the filter (the white grains). To make your filter last a long time, the pressure inside the filter needs to be maintained.
That is achieved by a one-way-valve (a.k.a. non-return-valve) after the last stage and before the final separator-and-filter,
and by the PMV that is places after the filter and before the fill-whip or bank connection.

The separators between the compressor stages are depressurised/opened when the compressor stops, and that's when all the water drips out. The final filter always stays pressurised, and is only manually depressurised when changing filters.

If the filter (or molecular sieve) is in contact with air at ambient pressure, it will continuously collect moisture from the air and reach saturation within days. From that moment on, the filter is useless. Depressurising the filter housing has the same effect.

There is another component in the filter housing: active carbon. It's job is to take out anything toxic (bad smells). But it can only do the job if it stays dry. Any humidity will render the carbon inactive.

What the active carbon does not do: take out carbon-monoxide. If you're running the compressor and your neighbors are having a bbq within 100m, the CO level in the compressed air already rises above 1ppm. To take out the CO, another filter housing with hopcalite can be used. Hopcalite is rendered inactive by the slightest humidity, so if you have a hopcalite filter, keep that one continuously pressurised as well. Hopcalite is a catalyst (meaning that the hopcalite itself doesn't chemically change) that turns CO into CO2 and when it does, the reaction process produces heat. A rise in filterhousing temperature is an indication that the compressor is taking in elevated levels of CO.

Excellent information and appreciated.....

 

[Wallowa]

View attachment 895191

Compressor Filter System Theory - Scuba Engineer

High Pressure Breathing Air Compressor Filtration System Design author:- Stephen E Burton BSc(hons) C.Eng, MIET - Email to:- scubaengineer@gmail.com

scubaengineer.com

Good article ...thanks.

 

[Agro]

Good grief....will you stop with the bashing of Coltri.....I get it you don't like the Italian compressors....not German or Swiss....get off your high horse and present something positive.....you are a broken record.

No I don't stop telling Coltri produces very bad compressors, especially MCH6. I was owning 2 of them and had very, very bad experiences. Also I saw 2 broken Coltris on a dive boat after about 20 hours. I know what I am talking about.

Right, I don't like this compressor, I even hate it. Has nothing to do with country of production. Nardi compressors from Italy seem to be very good.

High horse? Not at all. I just tell it the way it is.

Something positive: any other compressor brand. ANY.

Broken record: Coltri MCH6 are very bad. They have been bad and they still are bad. Sorry if this is a broken record.

 

[Agro]

Flush, but not depressurize the filter. Which is only possible with a PMV.

With a WORKING PMV. Coltri MCH6's PMV does not maintain pressure for several hours, it is always leaking a little bit. While running this does not matter, it maintains pressure at a certain level. But it does not when engine is of.

 

[Wallowa]

With a WORKING PMV. Coltri MCH6's PMV does not maintain pressure for several hours, it is always leaking a little bit. While running this does not matter, it maintains pressure at a certain level. But it does not when engine is of.

What?

Why would you want a PMV to retain pressure that it is set at for several hours? I thought that pressure was to assure for optimal filtration which is when the compressor is running and not when 'off'. Never have seen a compressor run for several hours; guess it is possible. After charging a bottle I bleed the traps and compressor which negates the function of the PMV.

My MCH-6 PMV does not "leak a little bit".....holds solid when pumping and then bleeds out when compressor off.

 

[Wookie]

What?

Why would you want a PMV to retain pressure that it is set at for several hours? I thought that pressure was to assure for optimal filtration which is when the compressor is running and not when 'off'. Never have seen a compressor run for several hours; guess it is possible. After charging a bottle I bleed the traps and compressor which negates the function of the PMV.

My MCH-6 PMV does not "leak a little bit".....holds solid when pumping and then bleeds out when compressor off.

Then your PMV is broken and needs a rebuild.

My PMVs held for weeks and months in the off season.

 

[CG43]

Neither the Bauer Junior II nor the Coltri MCH 6 have a non-return valve after the last compressor stage !!!
These are small compressors for occasional hobby use.

The return flow of the filter air into the compressor is prevented by the outlet valve of the last stage. This valve has a metal-to-metal sealing surface which is more or less tight, after all it must open and close once with each rotation. It would be naive to expect these valves to hold the PMV pressure for some hours or days.
Whether the PMV pressure is released via the PMV or the exhaust valve, who knows and who cares.

https://www.bauer-kompressoren.de/f...e-part-list/junior/2013-10-01/JUN2-1013EN.pdf
See page 12 figure 8

After charging a bottle I bleed the traps and compressor which negates the function of the PMV.

Not necessarily !
Open the condensate release valves as usual until no more condensate comes out,
and then close them again immediately afterwards.
This doesn't require much air, and you'll still have the PMV pressure left at the end .
If not drain the filters immediately before turning off the compressor

 

[Wallowa]

Neither the Bauer Junior II nor the Coltri MCH 6 have a non-return valve after the last compressor stage !!!

The return flow of the filter air into the compressor is effected by the outlet valve of the last stage. This valve has a metal-to-metal sealing surface which is more or less tight, after all it must open and close once with each rotation. It would be naive to expect these valves to hold the PMV pressure for some hours or days.
Whether the PMV pressure is released via the PMV or the exhaust valve, who knows and who cares.

https://www.bauer-kompressoren.de/f...e-part-list/junior/2013-10-01/JUN2-1013EN.pdf
See page 12 figure 8


Not necessarily !
Open the condensate release valves as usual until no more condensate comes out,
and then close them again immediately afterwards.
This doesn't require much air, and you'll still have the PMV pressure left at the end .
If not drain the filters immediately before turning off the compressor

Guess I am missing it...once I fill a bottle, shut it then I open the drains [2] and with bottle disconnected open the whip and then run the compressor for a few minutes to cool it under no load....then shut off the compressor..close the drains used to bleed out the pressure, close/seal the whip, and seal the intake...how can the PMV retain a back pressure when the compressor was stopped with drains open to drain condensate and pressure?

Also my PMV is definitely outboard/downstream of the compressor stages....my MCH-6 Icon [Nuvair] PMV is in-line connected between the condensate tower and compressor end of the filling whip.....

 

[CG43]

When the compressor is running, the pressure in the water separator/filter should be at least PMV pressure because separators cannot work properly at lower pressures.
As a result, the filter gets too much water which quickly exceeds its capacity.

That is why I would never run the MCH 6 compressor for cooling with both drain valves open .
If you think cooling is absolutely necessary, and there may be reasons for this , then only open the valve on the separator so that at least no moist air flows through the filterbottel .
BTW : If the seperator works well you will have no or nearly no water in the filterbottel .
I will write more about the MCH 6 later , because it's to late now .

 

[Wallowa]

When the compressor is running, the pressure in the water separator/filter should be at least PMV pressure because separators cannot work properly at lower pressures.
As a result, the filter gets too much water which quickly exceeds its capacity.

That is why I would never run the MCH 6 compressor for cooling with both drain valves open .
If you think cooling is absolutely necessary, and there may be reasons for this , then only open the valve on the separator so that at least no moist air flows through the filterbottel .
BTW : If the seperator works well you will have no or nearly no water in the filterbottel .
I will write more about the MCH 6 later , because it's to late now .

OK...will make this quick....the 2 mins of cool down will not pull in a significant amount of moisture...heat and pressure pull the moisture out of incoming air and when pressure drops the moisture condenses out inside the compressor....running with no load for even a small amount of time with drains open after filling a bottle takes that condensate created after the pressure drops out the drains and removes it from compressor...

FYI.... I use a floor fan to augment the cooling and to move/push exhaust gases down wind away from the elevated 8 foot intake hose inlet. I also fill when air is coldest to lessen water vapor entering the compressor...very little moisture comes out of either drain during cool down or when running and drains are opened [8min drain intervals when running]....

Honestly, discussions about the functional aspects of breathing gas compressors is helpful...but denigrating the MCH-6 is just white noise and of no help whatsoever...no more echo chamber please.