Humidity and hand pumping

[Madd Hatter]

What's the highest humidity you would pump up your PCP with a handpump? Right now the humidity is at around 24% which actually is high for the high desert. Normal humidity is single dig or maybe the high teens.

 

Forgot to put the qualifier, NO water separator and a chicom floor pump.

[redlined_b16a]

I pump in about 90% all the time.
Some people mount dessicant filters on the intake side of thier pumps.

[Madd Hatter]

I think my pump intakes right under the pump handle but not 100% sure, so I don't think I could put any desiccant on the intake and just don't have the money for one of those gold cicom water removers right now for the HP side.

[Mole2017]

Hopefully someone will post a picture of their setup, but some are just using jugs of silica gel on the inlet side. I made an adapter out of metal that would fit under the handle so I could hook up to a tank of dry air, but there are other ways to do it if you are handy.

[robertr]

 At 24% humidity I would not worry.

[Madd Hatter]

Hopefully someone will post a picture of their setup, but some are just using jugs of silica gel on the inlet side. I made an adapter out of metal that would fit under the handle so I could hook up to a tank of dry air, but there are other ways to do it if you are handy.

I love it! Oh that I still had access to a mill. 

[Doug Wall]

Personally, I wouldn't pump at any humidity without desiccant. I made a desiccant for the inlet of my pump out of a plastic peanut jar, a couple of plastic fittings, and some hot glue. Plug one end of the handle, seal around the stem of the pump handle, and run the hose from the desiccant into the other end of the pump handle.

[Madd Hatter]

Hopefully someone will post a picture of their setup, but some are just using jugs of silica gel on the inlet side. I made an adapter out of metal that would fit under the handle so I could hook up to a tank of dry air, but there are other ways to do it if you are handy.

Would you be up for making another one and if you would how much would you want???

[Madd Hatter]

I sucked a lot of silicone oil into my hand pump using the up stroke to not so good in the oil. I then pumped up the pressure as high as I could go and then using the bleed screw blead the air and with it a lot of the dirty oil that is in the pump. Repeated it a few times and soon the oil was blowing out with only a little gray tint to it. Sure was messy though. lol I'm hoping when it gets cooler or even cold I'll be able to disassemble the pump to really clean it out and lube it up with some silicone grease. The cap that seals the second stage I believe is made out of brass and the wrench that came with the pump that fits that brass peice is very thin and it is chewing up the notch that it engages. I don't know the cte of brass but it has to be less that SS and so should shrink.

[Alan B]

It almost doesn't matter what the inlet humidity is with HPA. Compression multiplies relative humidity by the volume ratio. So pumping to 3000 psi it is increasing the humidity by about 200 times. So the output air is going to be 100% humid unless your input humidity is less than 0.5 percent. If you wanted the output air to be under 10% the inlet air would need to be under 0.05% humidity.

So always assume air from the pump is at 100% humidity for whatever temperature it is unless you have an extremely effective inlet dehumidifier.

If that moist air goes into a tank or a gun at a lower temperature it will condense some water inside, and the air will still be at 100% humidity. The only way to prevent condensation is to heat the tank/gun above the temperature of the air that was pumped in.

[AlanMcD]

Building on what Alan said (from another Alan), that is exactly why the advice with a handpump is to fill using short pumping sessions of no more than around 50 strokes, then vent the pump, let it the pump cool down for a while, and then repeat as needed.

The metal in the pump tubes and the base in particular absorb the heat of compression causing more of the water vapor to condense out into liquid water, and venting will blow that water out of the base of the pump.  The air exiting the base of the pump will still be at 100% relative humidity for those temperature and pressure conditions (thus the "relative" in the description), meaning it is carrying as much water vapor as possible for the temperature.  That is why you want the air charge to cool down to as close to ambient as you can before it goes into your tank - cooler air holds less water vapor at any pressure.

If you keep pumping away, the air charge will get progressively hotter and thus be able to hold more water vapor - and that will get carried into your gun and condense out there. 

So slow and steady is the key, with multiple short sessions.  A desiccant dryer can help, but even with one the advice holds - it is very difficult to remove enough water vapor from ambient air such that we have air at less than 100% relative humidity at 3000 psi at room temperature after compression . . . . it takes a lot of desiccant and long dwell time at atmospheric pressure to get it done.

If you want to know more about what is happening with respect to water vapor, you could read this post: https://www.gatewaytoairguns.org/GTA/index.php?topic=139845.0

[Mole2017]

Hopefully someone will post a picture of their setup, but some are just using jugs of silica gel on the inlet side. I made an adapter out of metal that would fit under the handle so I could hook up to a tank of dry air, but there are other ways to do it if you are handy.

Would you be up for making another one and if you would how much would you want???

I just realized there was a question for me. To tell the truth, I was scrounging to get the parts around for this one. I just happened to have a copper heat sink that was stepped like that and hatched a plan from there. By doubling up, I created a top and bottom between which I layered another piece of copper that had a slot cut in it. The slot let me "connect" the inlet and outlet holes. The hose fitting was turned on a lathe, but the rest of it was drill press, hand file, and sanding disk. (I remember now that a friend helped with a quick pass on the mill to save me a bunch of filing after I had soldered it together...)

That part at the left side has an extra hole from its former role and all of the them have a pair of alignment holes through each of which I had fit a nail and crimped it over to hold the parts for soldering.

I'm not really in a good spot to make another, between materials and time, but there are a number of ways to do this. It doesn't have to be metal. For example, DIY cast polyethylene is an option.

[Wayne52]

I was pumping up my Freedom this morning after I got it sighted in good at the state land, I was going to go hunting too but I had forgotten to put the end cap in the shroud and I just don't like how loud it is without it, it's deafening to shoot very much, luckily it only took five shots to get it sighted in.  Its super muggy out there right now but tomorrow the humidity is supposed to drop way down plus its going to be about 10 degrees cooler in the morning than it was today.