I am planning to get a hand pump with a molecular sieve filter at the output for removing moisture. Obviously the filter need be as small as possible or I will be having a hard time to get the pressure to 200 bars . However, having a small filter also means that the effectiveness of removing moisture will be reduced. Are there any ways to check the moisture level at the output ? may be some kind of test paper ? will appreciate some advice.
how to check the humidity at the output of hand pump ?
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It is not worth trying to measure it, because in terms of relative humidity it will be very high - 100% without a molecular sieve filter (by definition, more in a moment), and probably well over 80% at best with a small size one, and probably to about 70% or so with a bigger one. While that sounds like the filter is not doing a lot, the key is that it is drying the air enough to get it below the condensation point with either one.
I've written a lot about this and will link to more detailed info if you want it, but the key is that when air is compressed, the ability to hold moisture as vapor is reduced - so water comes out as liquid, and what remains is as a vapor. The condensation occurs because the air charge's temperature becomes the dewpoint for those pressurized conditions, so what is left is the vapor that "does not need" to condense out, leaving you with 100% humidity air, but no further condensation. The desiccants don't remove that much more in practice, but the amount they remove becomes critical if the air charge is hot as it leaves the pump and will cool down later - which is the case with powered compressors.
With a hand pump, if you do like @beerthief says and pump slowly then you won't have an issue - because if you pump at a rate of about one stoke every three seconds or slower, the compressed air charge will cool down in the base of the pump (as they are designed to achieve) and the condensation will occur there and not in your gun. Of course along with slow pumping, you have to keep your sessions short in terms of the number of strokes too, as each one adds heat to the base. So go slow, and keep the count under around 50 strokes or so - when you hit about 50 strokes, stop and vent the line and then let the pump cool for 10-15 minutes before resuming. This will keep moisture out of your gun regardless of how humid the air is where you are pumping.
This is why I made a point of using my guns such that I did not need to refill with more than about 50 stokes (after a few to charge the line some) back when I used to use a handpump - my shot count was defined by that parameter, unless I wanted to have my shooting impacted by waiting for the pump to cool.
Here is more on the physics of moisture in air. if you are interested. https://www.airgunnation.com/threads/moisture-in-pcp-airguns.1321274/page-2#post-1839770
I've written a lot about this and will link to more detailed info if you want it, but the key is that when air is compressed, the ability to hold moisture as vapor is reduced - so water comes out as liquid, and what remains is as a vapor. The condensation occurs because the air charge's temperature becomes the dewpoint for those pressurized conditions, so what is left is the vapor that "does not need" to condense out, leaving you with 100% humidity air, but no further condensation. The desiccants don't remove that much more in practice, but the amount they remove becomes critical if the air charge is hot as it leaves the pump and will cool down later - which is the case with powered compressors.
With a hand pump, if you do like @beerthief says and pump slowly then you won't have an issue - because if you pump at a rate of about one stoke every three seconds or slower, the compressed air charge will cool down in the base of the pump (as they are designed to achieve) and the condensation will occur there and not in your gun. Of course along with slow pumping, you have to keep your sessions short in terms of the number of strokes too, as each one adds heat to the base. So go slow, and keep the count under around 50 strokes or so - when you hit about 50 strokes, stop and vent the line and then let the pump cool for 10-15 minutes before resuming. This will keep moisture out of your gun regardless of how humid the air is where you are pumping.
This is why I made a point of using my guns such that I did not need to refill with more than about 50 stokes (after a few to charge the line some) back when I used to use a handpump - my shot count was defined by that parameter, unless I wanted to have my shooting impacted by waiting for the pump to cool.
Here is more on the physics of moisture in air. if you are interested. https://www.airgunnation.com/threads/moisture-in-pcp-airguns.1321274/page-2#post-1839770
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Here's what I do:
1) Measure the ambient humidity using my lab hygrometer and or humidity gauge.
2) fill a bottle, tank, reservoir from the pump/compressor.
3) vent the bottle, tank, reservoir slowly, into a void such as a plastic bag
4) after a short interval, sufficient to purge ambient air from the bag, I use the same instrument to measure the humidity in the bag
Ambient humidity is typically 50%+ in this area, confirmed by weather data and several instruments. I measure less than 10% humidity from my compressed air, which I cannot imagine is a problem. Industry standards describe 10% as in the "very dry" range for metal storage.
In addition, I have found no evidence of liquid water, or corrosion in any part of my tanks, bottles, regulators, guns, etc.
I am confused by the apparent focus on water while no one describes their procedure for ascertaing the content of problem.
1) Measure the ambient humidity using my lab hygrometer and or humidity gauge.
2) fill a bottle, tank, reservoir from the pump/compressor.
3) vent the bottle, tank, reservoir slowly, into a void such as a plastic bag
4) after a short interval, sufficient to purge ambient air from the bag, I use the same instrument to measure the humidity in the bag
Ambient humidity is typically 50%+ in this area, confirmed by weather data and several instruments. I measure less than 10% humidity from my compressed air, which I cannot imagine is a problem. Industry standards describe 10% as in the "very dry" range for metal storage.
In addition, I have found no evidence of liquid water, or corrosion in any part of my tanks, bottles, regulators, guns, etc.
I am confused by the apparent focus on water while no one describes their procedure for ascertaing the content of problem.
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There's a common misconception that slow pumping will cause less moisture.
Look at it this way. There's a finite amount of moisture in your air. It's the pressure that causes the water to precipitate out of the air stream. Think the old analogy of squeezing a sponge. Fast or slow makes no difference, just pressure.
Besides even if pumping slowly actually did reduce the precipitation of moisture...guess where that finite amount of moisture in the air would go? Your gun!
You want the moisture to precip out before it goes into the gun.
The only real concern with heat is what it does to the compressor.
Look at it this way. There's a finite amount of moisture in your air. It's the pressure that causes the water to precipitate out of the air stream. Think the old analogy of squeezing a sponge. Fast or slow makes no difference, just pressure.
Besides even if pumping slowly actually did reduce the precipitation of moisture...guess where that finite amount of moisture in the air would go? Your gun!
You want the moisture to precip out before it goes into the gun.
The only real concern with heat is what it does to the compressor.
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That is all true, but your missing factor is heat - the hotter the air charge, the more moisture it can carry. Slow pumping will result in a cooler air charge, so more water will condense out of the air stream before it either gets to a drier, or the reservoir.
Unfortunately the sponge analogy is not really appropriate, because there is no good way to bring that third variable into it . . . .
I am a strong advocate for active drying, but slower compression does have its benefit in this area.
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The hotter the air the more moisture it can hold ASSUMING THE SAME PRESSURE. This is the premise for water seperator filters like the GX, increase pressure-precipitate water (squeezed sponge).
The act of pressurizing air offsets it's ability to hold water.
The air entering your home air conditioner is around 50% RH, but the air coming out is around 90+% RH, but has much less moisture in it. That is an example of changing temp and not pressure to remove moisture. In this case it is true the cold air cannot hold as much water.
The act of pressurizing air offsets it's ability to hold water.
The air entering your home air conditioner is around 50% RH, but the air coming out is around 90+% RH, but has much less moisture in it. That is an example of changing temp and not pressure to remove moisture. In this case it is true the cold air cannot hold as much water.
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FWIW, as a data point,I just took apart one of those Air Venturi 1100 psi (76 bar) "regulated" bottles, the kind for using HPA on otherwise CO2 systems, and there was no liquid water inside. I took it apart because it was leaking air, and I had recently pumped it up several times from zero to 3000 psi using a Hill Mk5 pump. Dew point where I live is around 55F (13C) and I pump like AlanMcD wrote, or like that blind guy on the rails in that movie "Brother Where Art Thou?", very slow and steady like I could go on forever. I vent the pump every 100-200 strokes (every thousand psi, depending on the bottle), and a little spritz of moisture comes out the pressure release valve at the foot of the pump. The pump gets warm but noticeably less hot than if I pump faster, like one per second or two.
That said, I think the reason my tank was leaking was from a little corrosion at the fill port check valve. It looks like stainless steel, but I understand there are different grades of stainless, and the corrosion world may just be different at 3000 psi; how fares stainless nuts and bolts dropped to the bottom of the oceanic abyssal plains? Anyway, no liquid water doesn't necessarily mean no water at all or any corrosion.
PCPs and their paraphernalia seem to like maintenance and/or more paraphernalia.
That said, I think the reason my tank was leaking was from a little corrosion at the fill port check valve. It looks like stainless steel, but I understand there are different grades of stainless, and the corrosion world may just be different at 3000 psi; how fares stainless nuts and bolts dropped to the bottom of the oceanic abyssal plains? Anyway, no liquid water doesn't necessarily mean no water at all or any corrosion.
PCPs and their paraphernalia seem to like maintenance and/or more paraphernalia.
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