SpudFiles

With some discussions often leaning towards attaining higher pressures more readily it occurred to me that it might be easy to quickly pump up a gun with a small chamber to the max of a track pump and then fill it to high pressure by using the barrel as a secondary pump cylinder.
The piston would make a good one way fill valve once it was set in position.
A half inch copper barrel would make an optimum diameter pump cylinder for getting up to 400 psi or so.
A simple ram rod with a piston head like a shock pump would work nicely. A reducer could be sleeved on the ramrod and slipped over the barrel end to align the piston while pumping. The gun would function as the handle of the pump and the barrel would be pointed towards the ground.
Thoughts?

I thought about this a while ago. My only worry was accidentaly shooting myself in the face . Couldnt you push open the piston with the stick and hurt yourself?

mopherman wrote:I thought about this a while ago. My only worry was accidentaly shooting myself in the face . Couldnt you push open the piston with the stick and hurt yourself?

first thing that jumped into my mind was the pump handle jumping into my skull

i dont know if it would be that safe but i think its a good idea that way you can have a portable pump built into your gun. and instead of a reducer fir the end invest in a threaded fitting so it can be screwed onto the end of the barrel might feel a bit safer.

It would work as long as the air you are pumping into the barrel end of the gun goes through the piston valve seal, otherwise the ramrod will leave a nice bruise/gash in our face.

I'm not saying never try it, just that if you do, try it with a full-face helmet on perhaps.

The ramrod is placed against the ground, not towards your face.
I really doubt you could upset the piston enough to fire the gun. The pilot volume would be resisting too strongly and the piston would be in a tube that controls it from wandering around. A low volume high pressure pump just squeaks air past a one way valve. You would have a great deal of trouble suddenly forcing in more air than it is resisting with.
You could greatly minimize the chamber volume needed with the increased pressure potential.
I will add that when air doesn't go past a valve, a pump just acts like a set of shocks. The return is not violent. It will just bounce back at the same rate you forced down on it.

I would like to ad a note to the above discussion. I have constructed 7 cannons so far from simple to high tech stainless. The first one was pneumatic. It was first charged with air than the spud was pushed down the barrel. It,s amazing how much pressure this puts on the barrel seal. Halfway down the barrel it slightly broke the barrel air seal and the spud and ramrod went flying through the wall. So it is dangerous.
To get around this I drilled an 1/8" hole near the chamber end and put a slip coupling over it. After charging the chamber I rotate the coupling to expose the air hole. This relieves the pressure when forcing the spud down the barrel. When the spud is all the way down turn the coupling to seal the barrel. The slight leak between the seal and barrel has little effect on the pressure from firing. Hope this helps.
I cad draw a diagram if this is to confusing.

Just make a spud stopper (a piston stopper in this case) at the breech end of the barrel.
This way you cant hammer the piston accedentically.

Oh btw, even with the ramrod placed against the ground, this will send your cannon flying

I am talking of very small volumes and diameter of barrel. That greatly changes how much air you are capable of forcing past the piston.
I am not talking of large caliber potato guns with giant pistons.
Of course the gun would be forced up rather than the ramrod if it is reversed and the piston is unseated.
This is really no different than making a pump that works reliably. As long as you can't dislocate the piston/check valve, it shouldn't fire by accident.

Answer to psycix. The stopper will in fact stop the spud at the breech. However it is the air pressure ahead of the spud as you push it down the barrel that can push the piston open. At sixty pounds of air in the chamber it can happen. Believe me I know. Mine went off at 90 lbs. Even if you crack the barrel seal sightly it will release all the air in the chamber. Anyway, that is my experience, I am just sharing it.

How were you measuring pressure in the barrel? I still don't follow how cracking the seal slightly will release all the air. If you don't crack the seal on each pump stroke, you would never be able to fill a chamber with a one way valve of any type and a pump that screws onto a fitting housing a valve.