SpudFiles

I'm thinking about building a pump to get 400 psi. I'd probably use 1/2" copper pipe for the body of the pump. Based on what Hawkeye has said, I think I'll try to use a schrader valve for the check valve at the bottom of the pump. But I'm not sure how to make a valve to draw air into the pump on the up-stroke. Would it be easier to make a valve for that purpose somehow at the bottom of the pump, or rig the piston so that it contained a valve? I really want to go for low dead space, so I'd rather not have a tee at the bottom of the pump to accomodate two valves. Also, I've not worked with metal fittings much, so that's part of why I'm having trouble figuring this out.

buy a cheep air compresser, they go up to like 600 psi and their always filling up so u can mod the to make them full atto

Let me correct you fast cannonman, cheap compressors only go up to about 125psi. Just buy a shock pump, they go up to 400 psi with some determination and will power, and they are only like $25.

Heh, those 'cheep' compressors are such crap, mine has a 300 psi pressure gauge and it can hardly make 120psi.

I'm planning on pumping up a fair large gun (say 2 or 3 feet of 1.25" or 1.5" steel pipe, for a multishot bb/pellet gun I'm planning), so I want to have stand-up pump rather than a small handheld like a shock pump. I may end up with a shock pump in the end, but I wanted to see if I couldn't make something bigger first.

I used 3/4 inch copper for the pump cylinder and 1/2 inch for the pump handle. I bored out a reducer(1/2-3/4) so the half inch pipe would slide freely inside the reducer and into the pump body. The piston is rubber tap washers and an o-ring bolted and glued to a 1/2 inch end cap and glued to the pump handle.
You don't need an intake valve at the bottom. The air leaks past the o-ring on the upstroke and seals on the downstroke.
You need a half inch flat tap washer, a smaller washer(1/4) as a spacer and then a 5/8 flat tap washer as the guide to center the piston inside the cylinder. The larger washer has a few deep notches cut out for the air to leak past. An o-ring that is a perfect fit for the inside of the cylinder is placed between the two larger washers(around the smaller one). The o-ring is a very loose fit but when you push the pump handle down it is forced against the 1/2 inch washer and totally seals. On the upstroke it moves back against the larger bottom washer but air can leak past it because the notches in the larger washer prevent it from sealing.
On the bottom of the pump I glued another reducer the same size as the top one with a threaded bushing inside the half inch end.
The bushing was brass with an 1/8 female thread.
Then the pump can be threaded onto a homemade one way valve which is part of the gun.
There is zero dead space as the piston totally bottoms out against the bushing at the bottom and the end of the bolt holding the piston together probably just taps the one way valve open at the bottom. The pressure increase has probably already started to open it.
This pump easily reaches 350psi which is as far as I feel it needs to go.
You'll have less trouble with overheating if you minimize the number of strokes needed to reach the desired pressure.
The pump is about 24 inches long with a copper half inch t as the handle. I actually use it upside down. The t- handle goes on the ground and I hold the gun securely and use it as the conventional handle.
Hope this helps.

Thanks greatly, Hawkeye! That's just what I was looking for. I'd seen a pump with a similar principle of using the o-ring that seals one way and not another, but I wasn't sure if a single o-ring would be enough for that kind of pressure. Also, yeah, if 3/4" pipe can can get 350psi, that ought to be better than using 1/2"; more volume per stroke and probably a stronger pump. I was worried about bending the 1/2" pipe. Plus I didn't know what I'd use for a rod.

How did you learn so much about working with metal fittings and pipe? Engineering student, or own a plumbing supply store?

Otherwise you can use a normal pump up to a certain point, then use the shock pump to obtain high pressures. This cuts down on labour and time. Or make a pump

You're Welcome.
I just tried to look for parts in as many plumbing supply stores as possible and experimented to see what would work best for the job.
The o-ring assembly is a direct copy of the piston in a shock pump and likely most bike pumps are constructed the same way.
The o-ring in a pump needs replacing periodically but they last well if greased.
You will be much happier with a medium volume pump rather than a shock pump.

Yeah, that's how I learned about PVC fittings and such, but with the price of copper/brass being so dang high these days, I really want to find something that works the first time.
I'm sure I want a bigger pump that a shock. Ever since I read about Jack's little micro-pneumatics and how long it took him to pump those up with a shock, I realized I'd need something bigger.
Hawkeye, that homemade valve you mention is the same one you suggested for Jack's cartridge pneumatic, isn't it? Let me guess, the metal spindle in it is a machine screw with some washers, right?

Have you posted the gun that you use your pump with?

The one way valve is a tiny thing. It is piece of metal that has a small ridge in the middle and is only about a 1/4 inch long. I'm not even sure what it is.
I put a tiny o-ring against the ridge and a spring from a pen holds it against the lip inside the 1/8-1/4 reducer attached to the gun.
The pressure from the pump pops it open on each stroke and the spring from the pen just gives it enough return to seal. Otherwise the pump would just shoot it up into the gun.

You could just use a small nail or a screw with an o-ring for the same purpose.
Again it is just a copy of a typical schrader on a larger scale. Really designed just so that the pump end bushing can thread onto it.
I need to borrow a digital camera to take a picture. I know I have been promising this for months but I will get it done.

Hmm... you of all people ought to know that it is!

I understand the principle of the schrader, I just wasn't sure what to make that spindle out of. Come to think of it though, a 1/4" -1/8" reducer is going to be really small, so I can see that a nail might do the trick.

Yeah, I'm hoping I can convince my parents to get a digital camera; that's why I really hadn't posted any guns until recently when my friend took some pics for me.

i only read the first post, so is this has been said ignore me.


the way it sucks air in is there is a check valve on the piston.

there is a company that made a pump that pumped on the up stroke and the down stroke, so you got twice the air. i took it apart to see how it worked and what they did is they have a hollow piston with i think 4 different check valves on it.


the handle was hollow, wich went to the hollow piston.