Whats best valving for pneumatics

[golf45]

I have built a nice little 1kg chamber golf ball launcher with QEV valve and slide release, the barrel about 13inches long with bore diameter .5mm windage play with ball. Using a skirted ball from pvc tubing the ball shoots fine at 100psi, twice as far with 200.
A bit new to the game and asked many times by members although i did look, i was wondering what the best type of valve system is better and faster for quick air release, qev or sprinkler or something else. What would be the best barrel length for bore size, although i did look it up, it seemed a short barrel was just as good, mentioning 20 inches as good as 60inches.
assume going large in volume with fittings from 1/4 inch to 3/4 or 1 inch would give better release air flow than the smaller. Any advice welcomed.

[hectmarr]

A piston valve works well, and you can build it yourself. Actually, it is quite simple.
viewtopic.php?f=26&t=8157
spud_wiki/index.php?title=Piston_valve
This type of valve releases the air very quickly.

[jackssmirkingrevenge]

Are you going for maximum performance?

If so, a burst disk is one of your best bets. The disadvantage is practicality, needing to install a new disk every time limits your rate of fire somewhat. That being said, going by your other thread you're pumping by hand so it doesn't really add much.

[golf45]

I am going to have a go at finding a longer barrel about a meter or yard long and use a 2kg co2 fire ex bottle but pump to 100 psi which hopefully be equivalent to using a 1 kg bottle at 200 psi. 100 psi on most track pumps is not that much effort to get to pressure. I am also going to up the QEV valve and pipe work and fittings to 3/4 bsp which is i think far better than 1/4 i am using now, what do you think.
I want to be able to launch some parachute rounds as high as i can which i am fiddling about with on the release mech, hoping they will fly straight up without tumbling and rely on gravity as they start to fall to release the top to open the sides exposing the parachute. I got a large supply of fired spent signal rocket illum parachutes which i find left over the local common by the army when i go out for a bike ride, nice size well made, shame not to make use of them.
I did make a air cannon from a old fired confetti gun when i first started a mech that released a rubber bung that sealed the air chamber held down with a metal hinge, released by twisting for release. Worked ok but not as high as i would like. Needed a bigger air chamber which was working at 100 psi. the barrel was about 25 inches, the parachutes i made for them worked well but opened too soon. I want height.

Would the quickness of releasing the slide valve make any difference on a QEV to the speed of the projectile being launched. I have seen ball valves open by hand which i would assume be slower. I have seen ball valves fitted with a strong close spring, if altered fitting the other way round and held by a trigger would be quite instant or is it really down to barrel length just like you get more power from an air rifle. If you dont make much use of the extra air no matter what size of bottle, its just wasted, what do you experts think.

[Luke31]

I have done test with sprinkler valves, duel sprinkler vales, triple sprinkler vales, piston vales, and ball valves.

I have surprisingly found that a basic ball valve performs the same if not better than the triple sprinkler valve system.

I built a 2'' piston valve but never really recorded anything because my payload kept exploding in the barrel. I am shooting 3'' water balloons and the piston valve was just destroying them, probably because it was releasing too fast. Like a combustion gun.

If your shooting hard objects like golf balls, piston valves will probably outperform everything. But a ball valve might be all you need.

[jackssmirkingrevenge]

Would the quickness of releasing the slide valve make any difference on a QEV to the speed of the projectile being launched.

Faster piloting means faster valve opening which means better performance, to a point.

Here is a virtual launcher modeled in GGDT:



As it is, we have 138 ft lbs of muzzle energy with a 100 gram projectile.

I will alter some parameters so you can see the effect on muzzle energy which we will use as a yardstick for performance.

At each stage I will change one parameter at a time, keeping everything else equal.

Valve opening time:

Reducing the valve opening time to 1ms from 3ms gives the same energy.
Increasing the time to 9ms gives 127 ft lbs

Valve diameter:

Using a 0.5" valve instead of a 0.75" valve gives 73 ft lbs
Increasing valve diameter to 1" gives 191 ft lbs

Pressure:

Increasing pressure to 150 psi from 100 psi gives 185 ft lbs, 200 psi gives 227 ft lbs
Keeping pressure at 200 psi and halving the chamber volume gives 215 ft lbs
Reducing chamber volume to 25% and increasing pressure to 250 psi gives 230 ft lbs

Chamber volume:

Doubling chamber volume gives 143 ft lbs
Halving chamber volume gives 128 ft lbs

Barrel length:

Doubling barrel length gives 176 ft lbs
Halving barrel length gives 86 ft lbs

I hope this gives you some idea of the factors at play, and strongly suggest downloading GGDT to do your own modeling.

Note that a small high pressure chamber gives more power than a large low pressure chamber, and that having a valve diameter that matches your barrel is ideal.

So having a QEV that opens fast is of less benefit if the barrel diameter is large compared to the valve, and by having a bigger chamber at lower pressure, you are going to lose performance.

I have seen ball valves open by hand which i would assume be slower. I have seen ball valves fitted with a strong close spring, if altered fitting the other way round and held by a trigger would be quite instant or is it really down to barrel length just like you get more power from an air rifle. If you dont make much use of the extra air no matter what size of bottle, its just wasted, what do you experts think.

Have a look here for some discussion on timed vs dump valves: viewtopic.php?f=26&t=26916