SpudFiles

I have a pretty good idea on how to build a small hand pump but I'm not positive. I swear I saw some detailed instructions on how to build one but I can't find it now. I found the high pressure pump on page 10 or something like that but I know there's another one.

Do you have to use two check valves or is there some other trick?

On the plunger there is a rubber gasket like thing over a hole so when you push down it seals and pressurizes and when you pull up air comes in.

I found it again.

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

for those who are interested...

Thats a vacuum pump ( it sucks things up not blows out).

the second half of the article is instructions on how to make a pressure pump.

Ummm, to make a pressure pump from the link all you have to do is reverse your check valves.

I'm off topic a little but anyway...

First take a quick look at this: http://nerfhaven.com/homemade/zero_semiautovalve/

K, will the air from the temporary chamber flow into the final chamber fast enough to shoot a projectile (with some speed)? It seems like the holes in the brass tubing are rather small.

I wouldn't build any of their valves. They haven't even tested them.