SpudFiles

Following on from here, I'm making a prototype using a new design. The concept is similar, air pressure causes the piston to accelerate, eventually opening a port that lowers the air pressure allowing the piston to be returned by a spring, after which the cycle continues. In this however there's a one piece piston, meaning it's simpler than my previous idea and there's less to go wrong.

Perfect example of how simpler is better. Would be great to see this in action.

Hmm... looks not unlike a regulator to me.

Looks good to me. I wonder if instead of a sporadic spring you could use a small resovoir of air to push against the chamber. Then you could adjust the pressure in the chamber for each shot.

you would need a small lip to keep the piston from shooting into the chamber after every shot. Otherwise it looks like it should work, but sometimes things that look good on paper still don't work. Have fun trying to find a spring strong enough that will let enough pressure build up in the chamber for a decent sized shot. Maybe the type of spring that you pull running the length of the chamber would be easier to obtain

instead of a sporadic spring you could use a small resovoir of air to push against the chamber.

I tried this with the previous version by removing the spring and sealing off the vent behind the piston, I prefer to use springs though.

you would need a small lip to keep the piston from shooting into the chamber after every shot.

Naturally, I had this in mind but omitted it in the diagram.

Have fun trying to find a spring strong enough that will let enough pressure build up in the chamber for a decent sized shot.

The idea here is that the piston has to travel a certain distance to open the firing port, it's that delay which I'm hoping will give time for the pressure to build up. Of course it's important the the feed into the chamber is significantly less than the firing port, otherwise there won't be a pressure drop sufficient to allow the piston to reset.

it's important the the feed into the chamber is significantly less than the firing port

maybe you could use a bicycle pump needle like this because it has a very small amount of flow

EDIT:yay 4 stars

JSR don't get me wrong but i don't really understand how is it supposed to work?
for me it seems that it would work more less the same as your original bolt mechanism - it's going to cycle to fast....
Why do you really need pulsed suorce of air to build that ?

Did you by any chance try a solid piston rather than the floating one in your last version?

POLAND_SPUD wrote:it's going to cycle to fast....
Why do you really need pulsed suorce of air to build that ?

I thought about that, but there are differences here, I think it has potential - even if it's a complete flop, at least I can say I tried going down that avenue and failed.

clide wrote:Did you by any chance try a solid piston rather than the floating one in your last version?

Yes, with predictable results, that can be summarised as "fssssssssss..." - basically, the piston moves down a little, enough to bleed the air, and stays open. The idea with the floating piston, and the above design, is that the piston is required to travel a certain distance before venting the chamber, thus allowing a time delay for the chamber to reach full pressure, as well as letting the piston gather enough momentum to sufficiently compress the spring to enable it to cycle.

I still think your gonna have trouble lowering the ROF with this design........... but whatever.

its basically the blow-foward bolt, exept youve removed the bolt and just made it a valve.

My instincts tell me that you would still have the problem of the thing moving just enough to bleed off pressure, then sitting around that point spitting air intermittently. I would think you'd need something to hold it in place till the pressure reached a certain point.

VH_man wrote:its basically the blow-foward bolt, exept youve removed the bolt and just made it a valve.

Yes, but it will now be 100% airtight thanks to a syringe seal on the piston, plus since there's a buffer chamber I can afford to restrict the flow. I'll have it ready for testing before Sunday hopefully.

I really designed this as a one shot air source for a BB gun, a blow forward bolt would be on the outlet or something like that and a hand valve on the inlet. The ports in the brass piston have to choke the air flow to continue travelling forward. The only thing that might keep it from stuttering at the half way point is atmospheric pressure on the left side and with the wasps waist in the piston it would give it a little more surface air to push on at low PSI. This is more like a pop off valve I think. I'm just wondering if you could adapt it with that clever brain of yours. I haven't built it but I intend to when I grind an O-ring tool for my lathe.

Interesting variation there, animated it for clarity.

My third prototype is ready and curing, expect the usual results in around 24 hours. I'm not expecting it to work to be honest, it's just a design I wanted to get out of the way, so I can safely say I've explored this possibility to death and can move on to something different.