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QEV trigger release

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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QEV trigger release

Unread postAuthor: Ianbuckwell » Tue Apr 01, 2014 1:26 pm

Hi, just signed up, so hello everyone. I have tried googling before joining but was after a definitive answer from the experts.

I have purchased a 3\4" QEV ( cheap Chinese black rectangular style) I thought I could just bush down any connection as necessary, is there any advantage to going for a 1/2" QEV? Also is there any advantages of the round silver QEVs and the black block versions? Do these valves come with proper sized bsp fittings/holes?

Last thing, please bear with me as I am trying to read up all I can as I am really excited about making my first projectile first, from what I understand the QEVs are emptied by draining off air from one of the ports, my question is how fast/slow does this have to be done to effectively actuate the valve to its full operating speed.

Thanks, all help appreciated.
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Re: QEV trigger release

Unread postAuthor: jackssmirkingrevenge » Tue Apr 01, 2014 7:38 pm

Ianbuckwell wrote:Hi, just signed up, so hello everyone.


Hello Ian.

I have tried googling before joining but was after a definitive answer from the experts.


Good.

I have purchased a 3\4" QEV ( cheap Chinese black rectangular style) I thought I could just bush down any connection as necessary, is there any advantage to going for a 1/2" QEV?


The porting is not always congruent with the thread size, a 1/2 inch valve and 3/4 inch valve might indeed have the same porting and therefore no discernible difference in performance.

Also is there any advantages of the round silver QEVs and the black block versions? Do these valves come with proper sized bsp fittings/holes?


No real benefit one way or the other, just variations of a theme. Unless otherwise stated, and in spite of the odd way they are often advertised on eBay, these things usually have BSP threads.

Last thing, please bear with me as I am trying to read up all I can as I am really excited about making my first projectile first, from what I understand the QEVs are emptied by draining off air from one of the ports, my question is how fast/slow does this have to be done to effectively actuate the valve to its full operating speed.


The short answer is "as fast as possible", what did you intend to use as a pilot valve? Most people seem to prefer to use blowguns as they often come trigger-shaped and are effective pilot valves:

Image

Thanks, all help appreciated.


I take it you are probably in the UK, it would be advisable to be aware of your country's draconian laws when it comes to projectile firing devices and keep a low profile with your experiments.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Wed Apr 02, 2014 3:14 am

Hi, thanks for the help, I had seen the airline trigger guns and was thinking of using something like this with the pass through passage blocked off, to keep it compact and the air jet nozzle removed..

http://www.prestavalve.info/tools-air-tool/

Sorry haven't learnt how to post pics yet!

Thanks for the heads up on the law, yes they are pretty strict, although I will only be using it on private land away from view.

Will a 120psi compressor provide enough pressure? If so what barrel bore could I use or is that more to do with suffient airflow rather than pressure?
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Re: QEV trigger release

Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2014 5:58 pm

Ianbuckwell wrote:http://www.prestavalve.info/tools-air-tool/


Link not working...

Will a 120psi compressor provide enough pressure? If so what barrel bore could I use or is that more to do with suffient airflow rather than pressure?


At 120 psi, you want around a 3/4" barrel for some really impressive shots, like say putting a marble through a coffee tin full of water ;)

Image
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Thu Apr 03, 2014 2:26 am

That's cool, need to try to scoure a tank, could but don't really want to spend out on a paintball one, so I was thinking of sodastream cartridge, small 600g ish fire extinguisher or one of the small argon/co2 tanks you can get for migs,

what is the best way to only release the correct ammount of gas per shot or do you have to do it manually with experience.

Sorry link didn't work, it was just an image of a small inline blow gun, so basically a button an in and out for the air and a nozzle.

ps out of interest I received an email saying from what i remember that I had posted something dangerous or otherwise which was not allowed by the rules, but cant think what I did wrong, unless it was my double post when trying to edit. I will have to read up on them as this seems a great knowlegable place.
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Re: QEV trigger release

Unread postAuthor: jrrdw » Thu Apr 03, 2014 9:02 am

Ianbuckwell wrote:That's cool, need to try to scoure a tank, could but don't really want to spend out on a paintball one, so I was thinking of sodastream cartridge, small 600g ish fire extinguisher or one of the small argon/co2 tanks you can get for migs,

what is the best way to only release the correct ammount of gas per shot or do you have to do it manually with experience.

Sorry link didn't work, it was just an image of a small inline blow gun, so basically a button an in and out for the air and a nozzle.

ps out of interest I received an email saying from what i remember that I had posted something dangerous or otherwise which was not allowed by the rules, but cant think what I did wrong, unless it was my double post when trying to edit. I will have to read up on them as this seems a great knowlegable place.


Google links me to a coached copy / a link to the copy, last night it worked fine for me. Double post was the reason one of your post wasn't approved, as for "dangerous or otherwise which was not allowed by the rules" is the closest choice to double post we got to notify member why the post wasn't approved.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Thu Apr 03, 2014 10:06 am

Ok, thanks, didn't want to get banned soon as I joined! ;)

I have been searching all day for a video on youtube, i think it was, it basically shows a guy with a qev setup with an adjustable air supply, he has it setup to fire fully automatically being able to adjust the fire speed using the variable inlet, has anyone else seen it and possibly got a link?

thanks Ian
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Re: QEV trigger release

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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Fri Apr 04, 2014 2:39 pm

Found the answer to my own question, the question I have now is how difficult is this modifification to do to the qev? Do they need specialized machining of the delrim disk? My father has a lathe (currently out of operation as motor had it) I assume a lathe is required unless some delrin of similar size could be found and just sanded down, maybe by putting in bench drill and sanding/filing down.

Any advice on spring size/poundage required and what length?

All help great fully appreciated.
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Re: QEV trigger release

Unread postAuthor: jackssmirkingrevenge » Sat Apr 05, 2014 10:44 am

Ianbuckwell wrote:I have been searching all day for a video on youtube, i think it was, it basically shows a guy with a qev setup with an adjustable air supply, he has it setup to fire fully automatically being able to adjust the fire speed using the variable inlet, has anyone else seen it and possibly got a link?


This guy? He's a c*nt, don't listen to him :)

My father has a lathe (currently out of operation as motor had it) I assume a lathe is required unless some delrin of similar size could be found and just sanded down, maybe by putting in bench drill and sanding/filing down.


I made the piston on the lathe, what you can do is modifiy the existing QEV piston by making a pin-hole in the edge, you might need a heated pin to do this effectively. All you need is a very light spring, it might not even be necessary at all.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Sat Apr 05, 2014 9:41 pm

Thanks,for the answers, just waiting on QEV now,

Jackssmirking revenge, would you mind explainingg the principle behind the use of a delrin disk/piercing original? Just to help me understand, I like to know why it works rather than it just working.

Did you use a set pressure blowoff/relief valve?

Many thanks.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Sun Apr 06, 2014 2:22 am

Yippee! No more waiting for posts to be checked by a moderator, guess it is a good idea for new members as it keeps all bots and general internet goonies out.

has anyone ever compared qevs and seen the point where the inlets outlets wtc are the same size as the internals in other words a 3/4" would have no advantage of a 1/2" apart from maybe just being the size pipe the maker is using. Hope that makes sense.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Sun Apr 06, 2014 8:58 am

Oh well thought my posts had stopped being moderated, i will have to read the rules to check when restriction is lifted.
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Re: QEV trigger release

Unread postAuthor: jackssmirkingrevenge » Mon Apr 07, 2014 6:23 am

Ianbuckwell wrote:Jackssmirking revenge, would you mind explainingg the principle behind the use of a delrin disk/piercing original? Just to help me understand, I like to know why it works rather than it just working.


An unmodified QEV piston is essentially a one-way valve, which means that if you fill it from the chamber side, no air will ever get to the pilot area.

Did you use a set pressure blowoff/relief valve?


No, it's adjustable. Really helps.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Tue Apr 08, 2014 2:35 am

Thannks again for your help, I did a bit of reading up on pneumatics and for a beginner getting my head around the technical drawing symbols is a nightmare.

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?

sorry so many questions just trying to get my head around it all. Thanks.
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Re: QEV trigger release

Unread postAuthor: Ianbuckwell » Tue Apr 08, 2014 2:54 am

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

Slightly ot but I made a pot sand blaster, without the nozzle on the ammount of air is impressive. I can only imagine how my gyn will be.

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.
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