Stirrup pumps - Moisture traps?

[derekm]

The moisture isn't generated by the pump, it's in the air around you, but without the moisture filter, it gets "concentrated" on the HP side.

[Monster]

I was given a rifle where the previous owner had routinely used a stirrup pump, without a moisture trap, to fill it. When I stripped it, to replace the seals, there were clear signs of internal corrosion on some of the parts. Fortunately, the corrosion was not so bad that they could not be cleaned up and the rifle now works fine.

The problem is that the dew point (the temperature at which you get condensation of the water out from the air) is higher for air under pressure than for air at atmospheric pressure. You can probably reduce this effect by filling the gun from a stirrup pump on a cold dry day outside. Cold air contains less moisture, for the same relative humidity, than warm air.

My view is that it is probably OK to just top up a rifle that has been mostly filled from a dive bottle, on an occasional basis, but I wouldn't routinely fill it from empty using a stirrup pump without some form of moisture trap.

[bobthedug]

I was given a rifle where the previous owner had routinely used a stirrup pump, without a moisture trap, to fill it. When I stripped it, to replace the seals, there were clear signs of internal corrosion on some of the parts. Fortunately, the corrosion was not so bad that they could not be cleaned up and the rifle now works fine.

The problem is that the dew point (the temperature at which you get condensation of the water out from the air) is higher for air under pressure than for air at atmospheric pressure. You can probably reduce this effect by filling the gun from a stirrup pump on a cold dry day outside. Cold air contains less moisture, for the same relative humidity, than warm air.

My view is that it is probably OK to just top up a rifle that has been mostly filled from a dive bottle, on an occasional basis, but I wouldn't routinely fill it from empty using a stirrup pump without some form of moisture trap.

Thanks for that. I think for the savings made when buying a cheap pump compared to the potential issues further down the line with moisture in your rifle, it would be best to spend the little extra for a pump with a moisture trap.

[derekm]

Thanks for that. I think for the savings made when buying a cheap pump compared to the potential issues further down the line with moisture in your rifle, it would be best to spend the little extra for a pump with a moisture trap.

Maybe better with a purpose built filter with whatever pump you decide on?

[Antoni]

I'll take the bate here and bight.

Air outside the house has a mostly slowly varying quantity of water vapour in it. It can take only so much water vapour before the vapour condenses into microscopic droplets of water - fog to you and me.

The amount of water vapour that air can hold as a vapour (that is to say as a gas) increases with increasing temperature of the air.

The air inside a house is very similar to the air outside a house because the ventilation deliberately built into the house lets it in, along with the gas-boiler pulling the air that it needs to operate. The amount of water vapour in the air inside the house is not far off the amount outside (unless you use a dehumidifier as I sometimes do).

In the UK it is usually warmer inside the house than outside. If you opened the doors and let fog in would it stay as fog? No, because as the air warms up it is able to cary more water as gas, and the droplets eVAPORate back into gas.

But there's still the same amount of water in the air in the house, if not more because of your breathing.

A digital humitity meter will read out in relative humidity, not the actual degree of water content in the air surrounding it. That's the difference between the amount of water vapour it could hold as against the amount it does hold.

So, for the same air, having come in through open doors and widows or just ordinary ventilation will read a lower relative humidity on the instrument in the house although it contains the same amount of water because .... the air has been warmed up by the time it arrives at the instrument.

With all the violence that the ususpecting air experiences as it is pumped into an airgun, all that ends up mattering is the amount of water in the air, not the 'relative humidity' of the air when it it was at peace and tranquility before it was abducted.

IMHO, best place to use a pump is a cold frosty high pressure day outdoors - or manage the vapour with dryers.

Here endeth this morning's lesson and I hope I haven't f....d it up.

[Monster]

I'll take the bate here and bight.

Air outside the house has a mostly slowly varying quantity of water vapour in it. It can take only so much water vapour before the vapour condenses into microscopic droplets of water - fog to you and me.

The amount of water vapour that air can hold as a vapour (that is to say as a gas) increases with increasing temperature of the air.

The air inside a house is very similar to the air outside a house because the ventilation deliberately built into the house lets it in, along with the gas-boiler pulling the air that it needs to operate. The amount of water vapour in the air inside the house is not far off the amount outside (unless you use a dehumidifier as I sometimes do).

In the UK it is usually warmer inside the house than outside. If you opened the doors and let fog in would it stay as fog? No, because as the air warms up it is able to cary more water as gas, and the droplets eVAPORate back into gas.

But there's still the same amount of water in the air in the house, if not more because of your breathing.

A digital humitity meter will read out in relative humidity, not the actual degree of water content in the air surrounding it. That's the difference between the amount of water vapour it could hold as against the amount it does hold.

So, for the same air, having come in through open doors and widows or just ordinary ventilation will read a lower relative humidity on the instrument in the house although it contains the same amount of water because .... the air has been warmed up by the time it arrives at the instrument.

With all the violence that the ususpecting air experiences as it is pumped into an airgun, all that ends up mattering is the amount of water in the air, not the 'relative humidity' of the air when it it was at peace and tranquility before it was abducted.

IMHO, best place to use a pump is a cold frosty high pressure day outdoors - or manage the vapour with dryers.

Here endeth this morning's lesson and I hope I haven't f....d it up.

I completely agree with your analysis.

In our houses we tend to add moisture to the air in many ways over and above what comes in from outside. We do this by cooking, cleaning, washing and drying clothes . In older houses, without damp proof courses, moisture is also drawn up into the walls where it evaporates to further add moisture to the indoor air.

IMHO, best place to use a pump is a cold frosty high pressure day outdoors - or manage the vapour with dryers.

Yes, I totally agree with this.

[Monster]

In which case I don't understand your exception.

You are saying the same as I did:

"same amount of water in the air in the house, if not more because of your breathing"

I gave only one example there for brevity.

Yes I agree. I must have missed that bit. Apologies.

I will edit my post.

[Portzy]

Needs must in these times I guess. I bought a Hills Mk4 with the trap back in May and would highly recommend it, I think the advice at the time was and still is slow and steady and that's how I use it.

Just a couple of weeks ago I had my bottle filled but I am currently using the pump for up to 170 bar or so then finish off with the bottle to 220.

[rapidresponse1]

i used to use a pump to top up my guns

[tapps]

have a look at www.airriflepump.com i recently purchased there latest model a MK 5 hills pump.with DRY PACK,it's advertised as 20% less effort in pumping, time will tell as i've not used it as of yet, it's a quality bit of kit.should last for age's.

[PCPShooter]

I use an fx pump, but generally only fill up at home in nice conditions

When had a rifle serviced no problems with moisture

Considering a pcp may need service in 5 years or so anyway, not much risk

[bobthedug]

The moisture isn't generated by the pump, it's in the air around you, but without the moisture filter, it gets "concentrated" on the HP side.

Hi, thanks for the reply.

My very basic understanding of the science behind it is that the action of operating the pump generates heat which in turn causes moisture to form in the pump?

Hence my question about the moisture ending up on the high pressure side of the pump despite the filter being in place.

Maybe I need to stop overthinking things

[Antoni]

Hi, thanks for the reply. ...... the action of operating the pump generates heat which in turn causes moisture to form in the pump? ....

No, that's not true. The action of the pump does not generate, create or conjure-up water.

The water vapour which is invisible (steam from a kettle is visible because it has condensed into fog) has to enter the pump before it can leave the pump and condense back into water.

Filters, or more properly called dryers will stop most of the vapour entering a pump, either professional or amateur.

[bobthedug]

No, that's not true. The action of the pump does not generate, create or conjure-up water.

The water vapour which is invisible (steam from a kettle is visible because it has condensed into fog) has to enter the pump before it can leave the pump and condense back into water.

Filters, or more properly called dryers will stop most of the vapour entering a pump, either professional or amateur.

Smashing! Got it now. Everyday is a schoolday as they say. Thanks

[Drew 3]

I've been filling my S400 from an FX pump for years. Never any problems and rifle holds air for ever. 110 Bar up to 170 Bar, 55 perfect shots at 770 fps with 8 pumps to get up to fill pressure and 60 more to my max. easy peasy japanesey! who needs a bottle!