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auto-recock no tool hammer valve?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: BigJon » Tue Nov 20, 2007 11:13 pm

Why do you have two chambers though? You really only need the first one. It seems to me that the second chamber is creating more dead space. Am i missing something?
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Unread postAuthor: Hailfire753 » Wed Nov 21, 2007 5:19 am

Sigh... :? Lets try this again...

There are "two chambers" to support semi auto fire. The first chamber, the refill, is pressurised from the schrader. The hammer is cocked, filling the primary chamber from the refill chamber. The hammer is fired, closing the refill chamber before the primary chamber is opened to the barrel and bolt.

The secondary tank is closed before the primary chamber so that only a small, pulsed bursts of air are released, instead of one big blast. There is no dead space. Without the so called "dead space" the entire charge would be released at once. I want to fire 1000 paintballs on a 5$ C02 tank fill, not 1 metal-piercing paintball.

Sorry, I'm just in a nasty mood today. :D Hope that wasn't too harsh.

...Or maybe I'm missing something? Can you be more specific, 'cause I don't see any problems.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 22, 2007 12:10 pm

On closer examination it seems to be overly complex for little practical gain - I would go for something similar to the diagram below, which is proabably closer to what mopherman originally had in mind.
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Unread postAuthor: Hawkeye » Thu Nov 22, 2007 12:24 pm

I don't like the plunger closing off the exit to the bolt. O-rings on the plunger/ striker are also going to limit the speed it moves at. It needs to slide freely and rapidly. It may be better to have a fairly weak spring that gives the plunger a longer stroke which will allow a bit more momentum. That minimal air pressure will have trouble resetting it against a strong spring.
Personally I like my own piston/hammer valve combo idea a bit better. Still have to make it to find out though.
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Unread postAuthor: Hailfire753 » Thu Nov 22, 2007 12:41 pm

Ok, thanks JSR! Do you think the piston will be stable enough without the second stabliser? And shouldn't the space between the piston and hammer be larger? That space kinda functions as the chamber, as only the air between the two is directed into the barrel.

And morpherman, don't go cry. From what I understand, the air will only exit the Tee once it pushes back the spring. :roll: This means that the air pressure has to overcome the hammer pressure. If I did not screw my math up, 200 Pounds per Sqare Inch are pressing on 2.355 square inches of piston (3/4 x 3.14). Thats... 471 pounds of pressure. So if you wanted the hammer to open at 200 psi, you need a spring that comprsses at about 450 pounds. This also regulates your shots to a certain degree, adding to accuracy. However, the time between trigger pull and fire is increased in this version, as the chamber has to charge within that time.

Also, the bolt will not need o-rings if it is made of epoxy. Uhh.. right jack?
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Unread postAuthor: Hawkeye » Thu Nov 22, 2007 1:20 pm

Something about that sounds wrong. It sounds like a spring of that strength will just shoot the gun all by itself. The weight of the hammer and momentum will knock the valve open.
When I look at that diagram I can only see the hammer knocking the valve open and realistically the max amount of air released is going to be roughly the volume of the area between the valve and the T. As soon as the hammer starts to get pushed back by the escaping air, the valve will snap shut.
Perhaps there should also be a better definition of the terms, bolt, plunger and hammer.
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Unread postAuthor: Hailfire753 » Thu Nov 22, 2007 1:34 pm

Exactly my point. The spring does nearly have the same amount of power as the air, so it becomes very inefficent. Without a strong spring, only a small burst of air at a lesser pressure is released. The first design has all of these problems, but my design does not. (I hope this does not sound conceited or whatever) There is air pushing on the front AND back of the piston (likeall barrel sealers should), so that this huge amount of pressure is not put on the spring and hammer. Also, there is the secondary sear to lessen the time between tiger and fire. What do you think?

Bolt: The thing that pushes the ammo foward as it closes the breach
Hammer: The second, o-ringed epoxy thing with a spring
Plunger: same as hammer
Piston: the epoxy w/rubber, small spring and actuating rod.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 22, 2007 2:17 pm

Hawkeye wrote:O-rings on the plunger/ striker are also going to limit the speed it moves at. It needs to slide freely and rapidly. It may be better to have a fairly weak spring that gives the plunger a longer stroke which will allow a bit more momentum.


Agreed, the piston should be a tight fit but without o-rings, and a long weak spring is a better idea than a short strong one.

Do you think the piston will be stable enough without the second stabliser?


If the piston shaft is well supported in the tube its riding in, yes.

And shouldn't the space between the piston and hammer be larger?


Yeah, the drawing isn't exactly to scale

I think you want to rethink the size of your breech diameter - that's a LOT of force the hammer spring is going to need to generate to open the valve. I think it would be more realistic to attempt this as a 6mm airsoft project.
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Unread postAuthor: Hailfire753 » Thu Nov 22, 2007 2:30 pm

jackssmirkingrevenge wrote:If the piston shaft is well supported in the tube its riding in, yes.


The piston (the epoxy with rod) is not riding in the same siz, e tube. It is 1-1 1/2" while the chamber is 2". The only supporting pasts are the modded bushings surrounding the actuater rod.


jackssmirkingrevenge wrote:I think you want to rethink the size of your breech diameter - that's a LOT of force the hammer spring is going to need to generate to open the valve. I think it would be more realistic to attempt this as a 6mm airsoft project.


You probably are right about that. Would the second design work for paintball? there is no need for a uber-strong spring in that one.
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Unread postAuthor: Hawkeye » Thu Nov 22, 2007 5:26 pm

The plunger/hammer has to be more than Epoxy. It will just get chewed up being driven into the rod on the valve.
You also need far less spring force on a heavier hammer. Think of just lightly swinging a heavy hammer versus the velocity you need to swing a light one to do the same thing.
I would use something like the spring from a stapler to drive the hammer.
I'll look at your diagram again but I think it would require 0-rings on the hammer as it would have to perform a sealing function as well. Then you run into the friction and wear problem. Especially if the sear catches the o-rings in any way during the cycle.

Edit: Looking at your diagram still shows that it needs to push the valve open with one sided pressure on it. I don't follow where it is sitting with equal pressure on either side like a piston..
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Unread postAuthor: Hailfire753 » Thu Nov 22, 2007 10:54 pm

In this pic for example, the piston has pressure being put on both sides. This is easily acomplished by adding a short segment of 3/4" pvc in the bushing, so that air contacts both sides of the piston (instead of the piston being flush with the bushing, like in JSR's edited picture and my early pics).

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Unread postAuthor: jackssmirkingrevenge » Thu Nov 22, 2007 11:15 pm

In this pic for example, the piston has pressure being put on both sides. This is easily acomplished by adding a short segment of 3/4" pvc in the bushing, so that air contacts both sides of the piston (instead of the piston being flush with the bushing, like in JSR's edited picture and my early pics).


That won't really make a difference - the force holding the piston shut will be equal to the area of the vent multiplied by the pressure.
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Unread postAuthor: Hailfire753 » Fri Nov 23, 2007 8:46 am

O Rly? :lol: jk

Hmm, I always though that was the principal piston valves worked from. The pilot air pushed against the whole back side of the piston, while the chamber air pushes only on the circle of piston thet is not sealed against the barrel. If this were not true, the piston would not budge when the pilot is drained, because the front side would not have any pressure.

Maybe I don't really get what you are saying. Would it work if the 3/4" was extended to say, the center of the refill chamber?

What if the piston was enlarged to ride in the chamber (piston almost = id of chamber) and the 3/4" was lenghtened to nearly the back of the chamber? This way there would be more volume pushing less area of piston away fron the barrel.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 23, 2007 9:07 am

The pilot air pushed against the whole back side of the piston, while the chamber air pushes only on the circle of piston thet is not sealed against the barrel. If this were not true, the piston would not budge when the pilot is drained, because the front side would not have any pressure.


True, but in your case the piston is not the same diameter as the chamber so there's no separate main and pilot chambers.

In the examples I've attached, in spite of the different sized pistons, the force require to push the piston back is identical to the pressure multiplied by area of the "barrel", ie they all require the same pressure to open.
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Unread postAuthor: Hailfire753 » Fri Nov 23, 2007 9:13 am

Ahh, ok. I guess if they were separate it would work (ie o-ringed?), but then the pilot needs to be drained.

I'll take your word for it.
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