SpudFiles

Hi everyone, im new here so i have some questions...
Im halfway in the making of my mini coaxial and i have some presta valves laying around from some bike inner tubes my dad has. I have noticed that when the pump is taken off the valve, a lot of air rushes out, and i was wondering if this would pilot the piston going off when I take the pump head off. Would schrader valves work better for this setup? I have looked around and seen some like i am making and they all have schraders.

if its a small cannon, yes. you could just buy a check valve and screw the presta into that, they are only a few dollers.

schrader and presta valves have very low flow and can only be effectively used as pilot valves when the pilot volume is very small. so yes if you have a really small cannon it will work but it would have much better preformance if you use a blow gun or ball valve

lol Are these check valves at lets say at any home depot?

ive never checked, but they might be.

I am making this with 1/2 inch pvc and it will be about 6-8 inches long. How much pilot volume should i have?

I use a shock pump to charge up my minis, the pump screws on directly to the schrader valve. What I do to avoid premature piloting is put an o-ring between the pump seal and the schrader, in such a way that the schrader's valve stem isn't actually pushed down by the pump's attachment. Air will still enter due to the pressure difference, but when I remove the pump no air leaks out because the schrader would be already closed.

Yeah, i might have to try that one since you JSR are the KING of all mini pneumatics! lol

A small check valve can be found at Home Depot. Also, as far as your question about pilot volume, is the 1/2" your barrel or your chamber and what size is the other pipe? Is it going to be a piston cannon or a diaphragm cannon?

FordGtMan wrote:Yeah, i might have to try that one since you JSR are the KING of all mini pneumatics! lol

lol, I the downside of this job is that you get a mini-throne, mini-crown etc.

My barrel is going to be one of those 9/32 brass pipes from hobby shops and will be a hot glue piston that i already made.

Using another of those efficiency rules, you will want to shoot for about 7/100 of an inch of piston travel.* This would mean that your piston only needs to travel this much, which is hardly anything at all.

Assuming you are using 1/2" sch40, (ID of .602") your pilot volume should be .019 in^3.

I think.

D/4 Rule - (9/32) / 4 = 7/100

How would i measure all of this? Would it just be a rough estimate?

Just make sure your piston only moves back 1/8 of an inch or so.

I apologize. I was kind of being an @$$. The piston does not need to travle very much, and 1/8" is easier to measure.

If you decide to build a larger piston valved launcher, you may want to keep the above in mind, however.