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Ianbuckwell wrote:let say for example i want a single shot firer, am i correct in thinking that if a slide valve was used as a trigger, in one position it allows pressurized air to pass into the gun, then once the pressure equalised it was ready for firing. Sliding the valve to the second position blocks the pressurized air in the gun allowing no more to pass. the qev activates and empties the gun using only what ever is in the gun, the gun would only refill once the slide valve is put back. I am sure I have seen a few guns with no tank just the tubular frame for air storage? Is that correct or am i completely off track? If no reserve tank is used I assume it is critical to measure or calculate the fun volume?

Pretty much, if you're only doing single shots you don't need a slide valve.

Download GGDT to simulate the performance of your launcher: http://www.thehalls-in-bfe.com/GGDT/

One other thing for an 'average' gun and qev is a 1/8" valve sufficient, just looking at prices and soon as size of parts goes up so does the price often disproportionately (sp.) I need to keep this cheap and simple for my first effort, don't want to run before i can crawl

You should match the valve size to your barrel diameter.

on abay i have seen little compressor/tyre pumps it is about £7/10USD saying it will do 300psi do you thinking it really does this? Maybe it can for short periods of time which is all i am going to need.

Nope, those pumps are rubbish.

You're better off buying one of these:

Here's a rough simulation with a 2 foot 3/4" chamber and 3 foot 1/2" barrel, firing a half inch steel ball bearing at 240 psi.
You're at over 60 ft-lbs, more than 5 times the 12 ft-lbs legal limit for an unlicensed air rifle in the UK...

Thanks for all the help, when Io can get use of a PC I will have a look at it. My QEC arrived today which was a surprise, I thought it was coming from China. I xchecked the threaded ports and easily found fitimngs for the ones they go into the body, but the port with gold color fittting (which barrel connects to?) Seems to be a slightly different size, iirc its internal diameter was 15mm so may be its metric? I will need to investigate.

When you say if I am making a sclotingle shot gun I don't need a slide valve, is this because the qev blocks any further input of air when actuated? Or am I completly off course? What is used as a trigger for the qev then? Thanks.


One last thing, if I reduce the barrel size the velocity should increase If approx same volume of air is released is that correct or not?

Thanks again

Ianbuckwell wrote:Seems to be a slightly different size, iirc its internal diameter was 15mm so may be its metric? I will need to investigate.

Probably 3/8" BSP

When you say if I am making a sclotingle shot gun I don't need a slide valve, is this because the qev blocks any further input of air when actuated? Or am I completly off course? What is used as a trigger for the qev then? Thanks.

air chamber ----> QEV <---- pilot valve (eg blowgun or ball valve)

When you open the pilot valve, the QEV only allows the air in the QEV pilot area to go through the valve, the rest of the chamber is dumped through the barrel.

One last thing, if I reduce the barrel size the velocity should increase If approx same volume of air is released is that correct or not?

A smaller diameter barrel typically gives you higher velocities, but lower energies.

I have QE04, one of the black Chinese ones, I still need to red up on what the P and A and R are each for, unless someone can tell me?

P -> pilot
A -> chamber
R -> barrel

Thanks which one is used to fill the valve, I assume the chamber is used for the chamber to store air in valve and any extra air to storqge? the trigger is what my release gun valve goes on and barrel, even I can understand that! The more reading I do the more confused I am, for example this diagram uses different letters!

Is the gun filled via the same port as what the trigger valve goes on or do you fill it via the tank, just read somewhere that filling through the fill port helps for the seal to reseat quicker?

If using a blowgun as a trigger how does it work concerning how much air is released, is it just a matter of holding it in/down for correct length of time?

Is it a good idea to use a slide valve for a trigger or will that just complicate things?

I realize pressure plays a major part, but say I am running my gun at 145psi is there a rule of thumb that says the barrel should be 1/8" or 1/4" to get decent velocity and range?

Thanks again for the help, sure once I have built one I will be wondering why I was filling the forum with dumbass questions.

Ianbuckwell wrote:dumbass questions

Have a good read through this thread, I think it will clear up a lot of questions: http://www.spudfiles.com/how-to-databas ... 23626.html

I realize pressure plays a major part, but say I am running my gun at 145psi is there a rule of thumb that says the barrel should be 1/8" or 1/4" to get decent velocity and range?

The rule of thumb is moar preshur = moar powah!

If you're stuck at a certain pressure and want more power, increasing the caliber is a good idea.

A 3/4" cannon at 145 psi will be an impressive beast. A 1/8" cannon at 145 psi will be much less so.

Thanks for the link, In had precopiously seen it, but às you say it is full of food info I will give it a thorough read. Think I will keep my first build basic and then maybe reebiuld when my understand is there.

jackssmirkingrevenge wrote:

Ianbuckwell wrote:dumbass questions

Have a good read through this thread, I think it will clear up a lot of questions: http://www.spudfiles.com/how-to-databas ... 23626.html

it doesn't sount loud in that link...
but he should have some power at 165 psi..with a qev. I never tested an industrial qev and a slide valve..but probably they do not offer same power as a homemade one ! ?

bravootome wrote:but he should have some power at 165 psi..with a qev. I never tested an industrial qev and a slide valve..but probably they do not offer same power as a homemade one ! ?

An "industrial" QEV features a light and well made diaphragm/piston and is very efficient indeed, it will give better performance than most "home made" exhaust valves of the same dimensions.

Thanks for the help guys I will thoroughly read the thread, I had only previous skipped through it.

If for a single shot cannon, you say a slide valve isn't necessary, what do you put in its place?

Jackssmirkingrevenge - when you talk of the firing chamber in another post, what is this actually referring to?

Thanks

Ianbuckwell wrote:Jackssmirkingrevenge - when you talk of the firing chamber in another post, what is this actually referring to?

The chamber connected to the "A" port of the QEV.

Thanks for reply, preciously I had asked about a trigger mech but my link didn't work
I hope this one does

http://www.powertoolfair.com/sg-tool-ai ... 1KVI9twaZU

just thought if I connected it on the upper inlet, blanked off the lower. And then the trigger air could pass through the nozzle port? Would using this trigger type just keep emptying air from the supply as long as it is held down? Would a slide valve only release what is stored in the gun?

what a really want is a single shot gun that just releases the air that is required for that shot, to save on wasting air can I achieve this simply? I would want to have a built in air storage cylinder. Just reread Jackssrevenge post


"When you open the pilot valve, the QEV only allows the air in the QEV pilot area to go through the valve, the rest of the chamber is dumped through the barrel"

does this mean air is released from the tank reserve for as long as the trigger applied, my 2nd noob question is do you fill the gun via the guns tank? Thinking of using a tyre valve to begin with as it is easily conected to.compressor or shock pump at a later time.

Made some progress into the world of air cannon building, I have obtained a small (600ml?) Steel pressure vessel, its primary use in life had been a gas cylinder you get on the small mig welders. Managed to unscrews the brass connector/valve, so now I can change the fitting, I don't know the size, but it is small.

I haven't real got any plans set in stone for my gun, just measured tank hole diameter and it is about 8.9mm, so once I get a fitting in there the hole will be so much small, so plan is to either use the tank with a small outlet and have enough air storage with in the guns tubing like this and still have a air storage cylinder.

http://www.spudfiles.com/pneumatic-cann ... c6013.html

And then have air for.additional shots, or to enlarge the outlet so air can be used without restriction from the tank so any other pipework can be kept short as possible, what do you guys thinks. The best option? My only concern with the 2nd option is having to drill/weld the tanks exit so it needs to be spot on if I inteemd to use 300psi in future.

Any comments, remarks, help all greatly appreciated.

Another thing! What Schrader valves/assemblies do people use? Is it just the regular rubber ones pulled through an end cap with the same size hole in as a wheel would have? Or do they go for the metal bolt on ones? It maybe my bad luck but car wise I always seem to have more luck with the regular rubber assemblies as the metal ones seem prone to snapping, say for example the gun/cannon was dropped. It !may just be that I have had cheap alloy ones in the past??

Also can someone just clear something up for me, if I build a simple 'common' gun which is filled from just before the trigger I don't need to pierce a hole in the diagphram, correct or not so?

Ps I would just like to say thankyou and give a big thumbs up to Jackssmirkingrevenge for the unseen help he has given me via PM, I realize for the knowlegable people on this forum that newbie questions from memebers such as myself the answers must seem obvious, but I thank them for their patience and help.