Stirrup pumps - Moisture traps?

[bobthedug]

Hi all. Due to the Covid situation and the difficulty in obtaining tank refills, I am looking at going down the road of a stirrup pump to ensure that I will never be stuck for air as I am now.

I have a tank but is down to 1500 psi and needs topped up. All my shooting is done around the house so in the past, the problem of lugging a tank around was never an issue. My nearest fill is about an hours drive but I can go several months between fills.

Nearly all my airgun shooting is pest control and the occasional plinking session.

Anyhow, stirrup pumps. Ranging in price from around £40 up to almost £200 after quickly searching the internet.

My question is are the cheap ones to be avoided and from my understanding, I cannot see how the expensive ones with the moisture traps work.

The traps obviously filter out the moisture from the air drawn into the pump, but as moisture is generated by the heat of the pump being worked, that moisture is in the pressure side of the pump and ultimately into the gun itself.

I do not have an issue with the physical side. I've got a teenage boy who is keen to earn some extra pocket money. Lol

Can anyone with some real world experience of using a stirrup pump offer any advice or comment on the negatives or recommend any in particular.

Thanks, B

[Trumpetier]

I've got a Hill pump without a moisture trap. It's only used very occasionally, I normally use a bottle. Personally I don't have any concerns, especially for occasional use.

[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?

[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

[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