SpudFiles

Well, I have always known how useful bike hand pumps are, they are essentially ready made pistons with a removable one way valve at the end.
I use them to fire kebab skewers, powerful shots of water and most recently as shock absorbers. I noticed that by covering the air exit port with my thumb (after removing the one way valve) I could compress the air inside without any leaks. I used this idea to make adjustable air shocks, but my next use for them is going to be the following design for a simple piston valve.
Pump air into hand pump through schrader (valvless), close ball valve, plastic washer seals barrel, pump chamber, air trapped, open ball valve, seal releases (another part of the piston is not shown, the part that seals inside the tee or a spring can be used), air escapes through barrel
I am not going to go into too much detail, I think the pictures explain a lot, but do not hesitate to ask about anything in particular.

Also any suggestions will be useful when I decide to finally build it so speak up!

Did you use 1 of them scetch toys with the 2 white nobs at the bottem to do your drawlings? If so-dam good job! It seems to have a lot of parts to it, wouldn't building a simple piston valve with a tee/end cap/1/4" bolt and rubber washer for a seal be easier?

Heh, no, I used MS-paint ( I know its laughable seeing as I study engineering drawing..). I was planning to take advantage of the fact that those handpumps are quite effective air pistons.
Plus I believe that this saves time, since the piston is ready made.
If needed the piston the sealing end of the handpump can push a larger sealing face for larger bore cannons. This design has many problems but it shows the basic idea.

Oh, and by the way for some reason when I click on the images myself, they are poor quality, but when I zoom in once they are perfect, I don't know why though (I am using Firefox).

They looked clear to me. How much presure do you think a bike pump can hold back? 70psi? 100psi?? 125psi???

It depend how much you pump up the handpump. When I had made my shocks. I put a fair bit of my bodyweight onto them and still about 2 inches of handle stuck out, the gauge showed that it was at about 80PSI , now I don't really know if this is safe since the walls of these things are not made out of pressure rated PVC.

I've seen high-end pumps with gauges that go up to 120 PSI, but they were 40 to 50 USD.

mine says it goes up to 140 psi easily not the guage it said that but it leaked pretty bad above 80 pounds but that was not around the slid it was around a different spot

Remember that the pump has to be the correct kind, are you by any chance talking about a stirup pump when you say 120 PSI?

i have a shock pump made out of thin aluminiom that goes to 300 psi.

idn its a regular old 10 dollar bike bumo from fred myers

Iam trying to make a piston valve out of a 4" tee, and i was wondering if a 3" coupling wolud fit in it like in a cannon? I think it will with some orings, what do ya think?

Josh

yes it will if you make it like this



Parts List: (The numbers in the diagram correspond to the list; all parts are SCH 40 PVC)

01] 2" 90 degree elbow modified [the piston face of the elbow was cut off 0-1/2" to fit through 4" "Tee" opening during assembly]

02] 2" pipe cut to 4-7/8" in length

03] 4" x 2" bushing modified: [interior flange was removed to allow 2" pipe to slide through bushing]

04] 4" "Tee"

05] 4" Pipe cut to 4-1/2" in length

06] Piston