SpudFiles

I am in to pneumatic spudding (I have produced three cannons) and recently had an idea for a new kind of piston.

As opposed to sealing against the end of the barrel the end of the barrel is capped off and a piston (The piston is shown in grey) slides around the outside.

When the piston is forward it covers a few large holes ( A bit like a breech) put when it is piloted it slides back opening them

Two (or three or four etc.) home-grown one way valves ( The valves are similar to the one in Ant's simple airgun) are installed in the Piston itself.

They are simply mildly strong springs pushing a ball bearing against a bit of rubber to seal them.These might be unnecessary ( You could get away with just small holes) but will improve effiancy

The second diagram shows a gun using the piston, and is relatively simple once the above is understood. The only things that need to be noted are
- The barrel passes through the tee which only supports it.
- The the tee and the pipe leading to the valve has holes in it so when the valve is opened air is released

I am posting to share the idea and to ask if the extra expense (This requires O-rings and a lathe) counters any improvement in power.

P.S. If anyone spots any problems with the design let me know.

P.P.S. I apologize for my appalling art-work (The computer was giving me trouble) and voracious use of brackets.

-Sorry, Just noticed, there should be a tee were the piece with the valve meets the barrel but the atachment keeps deleting it

maybe if you could make a animation it might just clear up a few things, looks pretty resonable from what i can work out, good work keep it up. Welcome to spudfiles.

Wow i think you might have just created an entirely different type of valve.

It's a slide valve inside a coax.
Hard to get it right and make it seal but it will work.
Not more efficient than a regular piston valve, but it opens up possibillities.

that will work but has some extreme amounts of pilot volume

With holes in the barrel large enough to not restrict flow the sealing end of the barrel would be to weak to with stand a decent amount of pressure. Thats if the slide didn't pull the end of the barrel off inside the tee.

he just need 4 1/4" holes for a 1" barrel and 4 1" holes for a 4" barrel

Well it may work, but a normal piston will probably more effective.
Your pilot volume is HUGE. And as far as I can see there are no flow improvents. It has no benefits above a normal piston valve.

It wont do any good, but atleast you tried coming something innovative.
And thats always good.


Btw, one check valve in the piston will be enough.

spudfarm wrote:he just need 4 1/4" holes for a 1" barrel and 4 1" holes for a 4" barrel

You just cut the end of the barrel off.

what do you mean jrrdw?

4 quarters equals 1 whole. 4 one's equal 4. The 4D rule applies to the end of a pipe diameter, not the circumference of the pipe. Also it's not 4:1, it's the piston only needs to move 1/4 of the barrel diameter to get optimun flow (for lack of better description of the 4D rule).

The only problem I see is this piston will probably need o-rings. Either on the barrel(easier, but weakens barrel) or on the interior of the piston(harder). Pilot volume is easy enough to limit by blocking off the end of the chamber. The strength of the barrel, if everything is made out of PVC than the mostly accepted maximum PSI is 150psi, as long as the ports are small and alternated it should hold up to 150psi.

I can see this as a good start to a breech loaded RPG or Vogt pattern.

spudfarm wrote:he just need 4 1/4" holes for a 1" barrel and 4 1" holes for a 4" barrel

No...

If you want the flow into the barrel to equal the flow out of the barrel, then (pi)(R^2) = (x)(pi)(r^2), where R is the barrel diameter, r is the diameter of the drilled holes, and x is the number of drilled holes. So say you had a 1" barrel, and you wanted to drill 1/4" holes in it. Using the equation:

(pi)(1/2)^2 = x(pi)(1/16)^2
x = 64 holes

jrrdw wrote:

spudfarm wrote:he just need 4 1/4" holes for a 1" barrel and 4 1" holes for a 4" barrel

You just cut the end of the barrel off.

Holes can be staggered.

D_Hall wrote:

jrrdw wrote:

spudfarm wrote:he just need 4 1/4" holes for a 1" barrel and 4 1" holes for a 4" barrel

You just cut the end of the barrel off.

Holes can be staggered.

And anyways, the circumference of the outside of the barrel is not equal to the diameter; it is equal to the diameter times pi. Therefore, it would really take more like 12-13 1/4" holes to cut off the barrel.