11 replies to this topic

[venom213]

As long as I have been working with air guns, I have always wanted a cheap, mass producible, and efficient homemade pump. I didn't quite achieve that this time, but it's a start. This was built entirely out of parts available locally. This pump is by no means thoroughly tested. I'm posting it now so that I can receive immediate input on how to improve it and to initiate others to build off of this.

The basis of this is the check valve. These are available at Wal-Mart for about $2 and Petco for a bit more.



I cut off the one of the connectors on the valve with a dremel. I then sanded it down flush. I also roughed up the sides of the valve so it will bond into the PVC better.





I drilled into some 1/2" SCH 40 PVC using a 5/8" countersink bit. For some reason, using a standard 5/8" Spade bit made the hole too large. You want the check valve to fit in snugly. Drill in as far as roughly the length of the check valve (it doesn't need to be super precise).



I solvent welded the check valve into the PVC. I then used a rag (avoid contact with skin!) to clean up and even off the excess.





I took a length of 1/2" CPVC, drilled through it with a 1/2" Spade Bit, and cut some small pieces off of it (about 1/4" or less). Next, I took some 3/8" ID 1/2" OD PEX (this is the pump rod) and test fitted the CPVC pieces on it. They need to slide on with a little friction, but not too much. If the CPVC doesn't slide on well, expand the ID of it more using a dremel with a sanding drum bit. Once I had the CPVC on the PEX how I liked it, I ground the CPVC rings down using a bench grinder. They need to be able to slide easily in and out of the 1/2" PVC pump tube. Test fit them as you go.



To plug up the nylon rod, I use a small section (1" long or less should be fine) of 3/8" Threaded Rod. I cut a slot in it with my dremel to make a crude set screw.



I tapped out the nylon rod with an according tapping bit. I could have probably threaded the 3/8" Rod in without tapping, but I figured why not. I didn't use any adhesives on this part, but if it ever leaks I plan on threading it in with some plumbers goop on it. I threaded the rod so that the head of it was about 1/4" in past the edge of the PEX.



I took a 5/8" OD 1/2" ID O-Ring and put it on the pump rod between the CPVC rings. I spaced the rings accordingly to make room for the O-Ring. The O-ring may or may not need modification in order to fit in the plunger tube. This is due to the inconsistency of PVC and (to a lesser extent) O-rings. I had to grind the outside of the O-ring down a bit to get it to fit well in the PVC. Keep lubricant in mind as it can majorly change the level of friction. Test fit the O-ring frequently and lube it some as well.



When I was sure that the CPVC was spaced apart right, I glued the rings in place with super glue. I took the O-ring off of the rod while doing this. Avoid contact between super glue and the oring as well as your flesh.



I drilled a hole right below where the pump head extends to when the pump is fully extended out. This was so that in case a vacuum was created, more air could get into the pump. I hope to phase out this element in future designs. I drilled and tapped two holes at the end for small 6-32 Screws to go into so that the pump shaft stays in. There are many ways to do this and this is not the best, just preliminary work.



The end result.....for now. The tape is on it for identification.



So, did it work? Sort of. Sometimes it wouldn't really build pressure at all. Other times it would take a great deal of pumping but could in fact make some decent pressure. This will take a great deal more experimenting to perfect. Basically, before I could get any serious testing done, the CPVC rings on the pump head broke off (I only gave the super glue a few minutes to dry) so I couldn't use them anymore. I tried this crude solution:



Just wrapping e-tape around the rod seemed to form somewhat of a seal. I also tried using an AT2K pump rod, which worked the best. I didn't seal the vinyl tubing to the check valve at all. Since the connector on the check valve is not barbed, it was probably leaking. My testing was very sparse and inaccurate, I'm going to hold off on posting my results thoroughly until I have everything more organized and thought through. The bottom line is: This isn't a reliable build, but it has much room for improvement.

Edited by venom213, 13 February 2011 - 01:32 AM.

[mysterio]

This should help you.

http://sci-toys.com/...ys/aero/vacuum/

[Doom]

Some spudgunners seem to have mastered the art of making homemade pumps. See the link below for a good and easy to make pump.

http://www.spudfiles...ump-t13277.html

The author states that he's satisfied with this pump up to 400 psi, so for the 50 psi or so us Nerfers might need, this should be very adequate.

[utahnerf]

But, the pump itself costs at least $20 to build. I think that we could get a basic plan from the spud gun pump, and build it out of cheaper materials.

[Doom]

You don't need to make the pump exactly as described unless you completely lack creativity. In fact, as described that pump would be terrible for Nerf. I intend to do something similar, but with a different size seal, aluminum tubing, epoxy putty, and a cheap check valve so I don't have to worry about that part. Reducing cost is a priority as always.

I haven't got around to it, but I'd be very interested if someone tried something similar.

[Draconis]

I'm also working on something similar, with a homemade check valve. I'll post when I get it right.

[Abyss Mods]

This is very nice. I can't wait until you finish testing so I can determine if I want to build one. What section of Walmart are those check valves in? The fish area?

[BrokenSVT]

If I recall correctly, those check valves are only good for ~5 PSI when dealing with air only. I hope I'm wrong, but in any case good luck. It's an ambitious project.

[CaptainSlug]

As long as I have been working with air guns, I have always wanted a cheap, mass producible, and efficient homemade pump.

What's so difficult about buying a bike pump? All you have to add to one to make it leak-proof is a better check valve. You can adapt them to other tubing types with either a stem valve, or a 5/16" tube stem coupler.

Edited by CaptainSlug, 15 February 2011 - 01:40 PM.

[pjotrkuh]

In order to prevent a vacuum in the pump you could use another check valve in the pump tube...........just an idea to throw in there.

And to CS: Maybe bike pumps are not the answer for some people, for instance some people want an internal pump in the body of their blasters, you can say "then grab a magstrike/hornet/2k/3k etc. pump" but this way you can build a pump the exact size of the internal space you have, for optimal pump volume and looks....

[Doom]

Bike pumps (especially the smaller ones) can be great depending on what someone wants. They're definitely something to consider.

I've been planning to make my own pump due to structural problems I would have if I used a bike pump. These problems would not exist if I made the pump myself. A homemade pump also gives me a lot of flexibility in the design.

As for vacuums in the pump, they're all supposed to have the equivalent of two check valves. Some pumps are designed to have the pressure equilibrate on the upstroke by breaking the seal. The homemade pump I linked to does this. This is simpler than two check valves.

[popatachi]

While, not readily available, hornets have a couple different check valves that you can gut and that will fit with PVC to create the pump body. You can also make a pump handle with dowel rod fairly easily. This is the setup I use in my AT3k which takes about 10 - 13 pumps to fill the tank.

This works well for me.

hornet check valve





version 1 of pump handle


version 2 of pump handle