Moding a QEV

velocity3x · Wed Apr 28, 2010 4:16 pm

irisher wrote:It has a large onboard air tank that will be replenished from an outside airsource.The problem is, if the entire tank is dumped each shot then I will not have enough flow to fill it up before the next shot.

Auto cannons are nothing but several separate operations connected to run in a given order. The tank size and filling is an operation unto itself. IMO...the first issue is to resize the tank so that it holds only enough volume for one shot (1:1). That will help reduce the time required to replenish the pressure for the next shot. Making a repeating valve is another, separate operation. You might find it easier to achieve the desired result if you address each issue or operation separately.

irisher · Wed Apr 28, 2010 4:22 pm

I think you may be misinterpreting my design goals. I would like to keep the chamber as is and get multiple shots from a single charge. However I realize that for continuous operation an exterior air source is required. I need to know if possible how to get multiple shots from the chamber.

velocity3x · Wed Apr 28, 2010 4:36 pm

irisher wrote: I would like to keep the chamber as is and get multiple shots from a single charge.

I assume you are talking about a fairly large bore?

Well, that would certainly be the perfect setup but, I think developing a valve which will unleash a full charge of power all the way to the end of the barrel and yet, be fast enough to reseat and retain any useful amount of pressure in the tank is a very tall order.....unless the tank is enormous in size.

irisher · Wed Apr 28, 2010 4:39 pm

I assume you are talking about a fairly large bore?

I am constructing it with 1/2" type L copper barrel.

velocity3x · Wed Apr 28, 2010 4:48 pm

irisher wrote:
I assume you are talking about a fairly large bore?

I am constructing it with 1/2" type L copper barrel.

1/2" is capable of quickly exhausting a high volume of gas. regardless of the valve you use, it'll be hard to fire a full charge and reseat the valve before the tank is exhausted.

irisher · Wed Apr 28, 2010 4:53 pm

regardless of the valve you use, it'll be hard to fire a full charge and reseat the valve before the tank is exhausted.

Didn't shatterhands do this?

POLAND_SPUD · Wed Apr 28, 2010 6:56 pm

air is air... you don't get free air from having a single chamber...

if you want to get 10 - 20 shots from one tank it has to hold 10 - 20 times amount of air for each shot... I see where you're going here... 'that tank isn't big enough so I'll get a HPA setup that will fill it while the gun is firing'

That will work but it makes little sense in reality.... think of it a bigaxx tank plus a HPA setup...

wouldn't a small 100cubic cm chamber and a HPA setup be better?

think of it... 100ccm chamber X 18 bar = 1.8 L of air at atmospheric pressure

flow of most 1/8" 3 way valves is ~300 l/m @ 6 bar -> 5L/s at 6 bar

I moddeled this example in fluidsim and it seems that you could achieve 5 RPS with a setup like that (100ml chamber 300l/m flow and at 18 bar)

EDIT
ok here is something I wanted to show you....
have a look at this valve http://www.boschrexroth.com/pneumatics- ... eID=p31067

The valve can be used as the main valve and since it is a 3 way you won't need a separate 3 way to turn this into a semi/fullauto gun...
I am guessing that its flow is good enough for 9 - 10mm ammo

Now the best part... you can also buy this one http://www.boschrexroth.com/pneumatics- ... eID=p31131

it's a 5/2 valve so you can have two guns in one gun

(in case you don't get it... attach barrels to both exhausts and chambers to ports A and B... air source is connected to port P... when the valve is in one position chamber A is filled while B is exhausted... when the valve switches to the other position air from A is sent to the barrel at ex. A while chamebr B is filled.... clever huh ?

)

anyway I just wanted to show that you can use some DCVs as the main valves...

irisher · Wed Apr 28, 2010 8:44 pm

air is air... you don't get free air from having a single chamber...

I really appreciate all the input but rather than having a small chamber it would nice if I could just get multiple off a large one. I have 13:1 c:b with my current setup so I think the air is there and I just need to know how to keep it from escaping all at once.

POLAND_SPUD · Wed Apr 28, 2010 8:52 pm

uhmm I get your point... but you've got to measure the amount of air you need for 1 shot then multiply it by a number of shots you want to get from one fill... once you calculate it you'll see my point

EDIT
you need to cut a hole in the piston/digraph and put a sp[ing behind it... then have to build a hammer valve that will pilot the QEV for X ms... and that's it...

just PM BtB... I am sure he will be more than happy to help you

irisher · Wed Apr 28, 2010 9:00 pm

then have to build a hammer valve that will pilot the QEV

I've talked to electronically inclined person who has agreed to build me a 555 timer system. This would include a dial for adjusting the time the valve is open. Would this be sufficient to pilot or would it be too slow?

POLAND_SPUD · Wed Apr 28, 2010 9:13 pm

no idea really... I know what is needed to pilot a normal QEV... what size DCV and QEV are those ??

irisher · Wed Apr 28, 2010 9:43 pm

what size DCV and QEV are those ??

The QEV is 1/2" and the DCV is 1/4" direct acting solenoid drawing 15 watts.

POLAND_SPUD · Wed Apr 28, 2010 9:54 pm

then I guess it might work... PM BtB as he has some experience with it