SpudFiles

I built this gun yesterday just off the top off my head. Ive already gone through about 3 bike pumps and dont want to mess with compressors or co2, so i built this gun with a built in homemade pump. In the pic below you can see how it works. Its got a copper tube (sleeved in 1" pvc) that seats a piston. There is one check valve to allow air into the chamber and another to allow air back into the tube as the piston retracts. Its got a psi guage, a breech loader, and a ball valve for the trigger. It works ok, there are some problems though. There is way to much dead space in the pump and the piston is not perfect and lets some air out, i still need to fix up a few things. So...I can only get it up to 30 psi. Im still very satisfied, Its still got plenty of power, enough to crush the marbles on impact. Best of all though, is that i never have to attach an air source! Its like a nerf gun, except bigger, all metal, and more lethal.

When i first read the topic, i thought it meant "pump" as in shotgun. I was quite confused when i saw the gun, but then once you mentioned your broken bike pumps....

Hehe.

You got it working then. Good for you!

You had said you couldn't get it past 5psi, what turned out to be the problem?

Nice design!

I like the built-in pump alot, neatly done.
How useful is the pump, how many strokes to fill?
You should fix the pump asap
Maybe fill up some dead volume with foam

Well, found better sized o rings, i guess i wasnt looking in metric sizes. The piston i designed is great, the o rings are the perfect size, there are two of them, and i can expand them by tightening the nuts and washers. So, i can get 30 psi, but with a perfect piston i should be getting 80-90 psi as you said.
It's about 15 pumps to get it to 30 psi, but they are very fast and easy ( only about 10 seconds.) yeah i was planning on filling the dead space with epoxy or something when i get the motivation. Its still got to have decent flow through it.

If someone else likes this idea, please go ahead and make your own. This concept has great potential. I have proven it works, its just i ran into some problems. I would love to see a better design and a solution to an airtight piston and minimum dead space. If youre really feeling ballsy id say got for the way actual bike pumps are made, and have a one-way flap inside the piston itself to eliminate alot of the dead space, including one of the check valves and the tee. Also, im sure it'd benefit from a qev or a piston.

i like the look but i think you should try a modded sprinkler valve its much faster than a ball valve

Indeed, it's a very nice idea and well executed. But the ball valve lets the potential down.

nice i would like maybe some more detail on that pump it looks interesting. Also what size is that barrel.

Guys, its mostly 1/2 so a sprinkler is pretty damn impractical, thats why i say either piston or qev. I just went with the ball valve for simplicity because the pump already had enough unknowns and uncertainty.

Woot! for months this gun has been collecting dust, mocking me with failure. Today i finally got of my bum and built a floating o-ring setup. I didnt change much i just replaced the washers with two nylon ones and gave the oring a bit more space inbetween. This also allowed me to get rid of one of the check valves and consequentaly the tee. Now i have 0 flow by the piston and a ton less dead space. Before this i was only getting about 30 psi, now i get about 90!

much thanks to gippeto and mitchza and other who have build stirrups and brought floating orings to my attention. As far as i know this is the only gun with a homemade pump attached to it. Now that this works well, id definately reccomend this setup to anyone. Its much more compact, servicable, and stands alone. I can post updated pics if you guys need.

hey I like it, it is something new...
now... if you add a QEV and upgrade the pump to get more than 200 psi and make a nice breech loading mechanism I would say it would be an ideal plinker

No worries about the pump info that you've gathered mate. That idea really is tops. I'm thinking about incorporating one into my gun... As far as upgrades go, what's next on the agender?