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Push type QDV explained.

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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Push type QDV explained.

Unread postAuthor: Brian the brain » Mon Aug 13, 2012 3:13 pm

At the request of airatomic I decided to scetch up a drawing of how my counterbalanced hammervalve works.

Basically it is a push type QDV.
It could be scaled up quite a bit and could be made to perform just as well as the pull type.

The biggest difference I see is the flat seal.
This will prevent wear and O-rings popping out but it could also be a headache to closely match seal diameters.
That of the flat front and the O.D. of the O-rings.

The flat seal ( and seat) could be made slightly larger ( just a fraction!) to ensure a firm seal but especially in large scale this will need a bigger push to open.
You might have to use a sledgehammer if you mess it up big time...

Anyway..

Not so different from poking a stick down the barrel of the pull type QDV is it?
Just redirect the air to the barrel with a Tee, or connect the barrel itself to the rod if you like..

The low pressure zone could also just run straight to atmosphere( keep that piston from popping out!!)
I'd prefer a spring to reset the thing..
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Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: wyz2285 » Mon Aug 13, 2012 4:39 pm

I knew how it works, but the construction of the stem it´s just out off the reach for people without a lathe. Also the flow it´s worse than a normal hammer valve of the same seal area (at least in my designs) even through a lot easier to open, witch it´s practically the only reason I decided to use this valve, too many turbulence and I belive that will have a influence on the pellet. But all my opinion are based on my version of this type of valve.
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: JDP12 » Mon Aug 13, 2012 4:59 pm

why is that out of reach? just machine a UHMHW piston and use a threaded rod as the stem. Slap a tee on there and you have a barrel output.

I don't see why you think its out of reach. a simple UHMHW piston can easily be turned on a drill press.

Unless I'm missing something?
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Unread postAuthor: wyz2285 » Mon Aug 13, 2012 5:13 pm

JDP12 wrote:why is that out of reach? just machine a UHMHW piston and use a threaded rod as the stem. Slap a tee on there and you have a barrel output.

I don't see why you think its out of reach. a simple UHMHW piston can easily be turned on a drill press.

Unless I'm missing something?

You are not miss anything, if you are thinking about making a 1/2 inch one, it doesn´t sounds difficult, but when you are trying to make it 1/8 inch it´s a differente story, when the piston it´s just few milimeter wider than the bolt and still need to have the o-ring grooves cut, it´s starts to be headache. The smaller it gets, harder it gets. Nothing are impossible I know, but for me it just doesn´t worth the time+effort, so I had the parts made in a factory.
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Unread postAuthor: JDP12 » Mon Aug 13, 2012 5:26 pm

Oh ok. I've been gone for awhile so i haven't been keeping up on peoples projects. I can see how making one that small would be extremely difficult.
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Unread postAuthor: MrCrowley » Mon Aug 13, 2012 5:36 pm

Not so different from poking a stick down the barrel of the pull type QDV is it?
Just redirect the air to the barrel with a Tee, or connect the barrel itself to the rod if you like.

You could use the barrel as the rod you mean? I think I understand the design correctly, so theoretically you could make the barrel as the rod (say the yellow housing is 15mm I.D. the barrel/rod could be 8mm) and even have some loading mechanism that opens when the barrel is forward and closes when the barrel/rod is pushed back to open the valve. At the breach of the barrel/rod, you would cut a long slit which would allow the compressed gas to flow from the chamber inside the barrel/rod.

Or am I missing something? Been a long time since I played around with non-piston valve valves :D
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Unread postAuthor: JDP12 » Mon Aug 13, 2012 5:57 pm

quick question here.. actually like 2.

so the low pressure zone- the reservoir i'm building will probably be very long and narrow, and I'm tryin to figure out how to to the low pressure zone..

I don't want it to run the whole length of the reservoir and lose that chamber volume. how could I do this? could it just be sealed off at atmospheric pressure?
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Unread postAuthor: POLAND_SPUD » Mon Aug 13, 2012 6:08 pm

what about this ?? pretty much same concept but it's based on unbalanced piston/spool

and at least in theory one could turn it into a multishot hammer valve - but in this case it would be the other way round - the hammer would pull the bolt backwards
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Unread postAuthor: Brian the brain » Tue Aug 14, 2012 12:48 pm

Well...Poland...

The idea was to explain the push type QDV as airatomic is already familair with the pull type.
The design you've dug up has been pioneered by JSR and it prooved to be very powerful.

when you are trying to make it 1/8 inch it´s a differente story, when the piston it´s just few milimeter wider than the bolt and still need to have the o-ring grooves cut, it´s starts to be headache.


???
Why would you make one that small?
The reason for the low pressure zone is that you can scale UP s conventional hammervalve without it being harder to knock open.

1/8" is perfectly doable as a traditional hammervalve..
And if the bolt is almost as thick as the piston...how could you expect any performancegain??
you're chocking up the valve with the valvestem...


The low pressure zone doesn't need to be connected to the outside, although that would be best.
A possible leaking O-ring would not cause the piston to be forced shut, as any pressure leaking through bleeds off.
In case of a blown O-ring you's know what the issue is immediately.
I had to go through a checklist of possibilities before I figured out what was causing the weak shots..

So..how would you create a low pressure zone inside of the chamber without a lathe?

I'd take a reducer, as this provides a ridge for the piston to seal on..and I'd connect a pipe and endcap on the wide side and cut holes in the wall of that pipe.
Just make sure everything is servicable.

In a long and narrow reservoir...you could just do it toolie style and place the "counter" piston on the end of the chamber and connect the two with a long threaded rod..

or..

reverse my CBHV so the counterpiston is on the opposite side..."fed" by an airchannel.

The valve is lathed( or drillpress-cut) from solid stock roundbar.
Drill a hole all the way through the center axis, the diameter of your chosen rod.
Then drill out both sides, not all the way through.

Cut out three O-ring-grooves ( two in the back as you'll be drilling in from the side) and one in the front.

Then drill out the airpassages and construct the piston and rod assembly.
Use a capnut on the front as this will make an airtight head.

Put it all together, slip on the O-rings and slide it into the reservoir- pipe ( wich needs an exit hole drilled lining up exactly with the valves outport, or, if you like, you can use a Tee for that purpose.)
put a rubber washer in to seal around the rod.
Screw on the endcaps and voila!


The valve is held in place by the endcap and the airpressure.
The endcap takes most of the stress.

I'd drill and tap the pipe from the side however and use a screw to keep it locked in place and prevent rotation and other movements cuased by pressure and hammering and so forth.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: POLAND_SPUD » Tue Aug 14, 2012 1:00 pm

The idea was to explain the push type QDV as airatomic is already familair with the pull type.
The design you've dug up has been pioneered by JSR and it prooved to be very powerful.
I do remember his gun - what I was trying to show is that one could easily use the piston as the valve and bolt action mechanism at the same time
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Unread postAuthor: Brian the brain » Tue Aug 14, 2012 2:38 pm

Yep.
going into "PAC without loss" type designs.

Put two smooth couplers on a coaxed barrel.
O-rings on the front one, flat seal on the back.
Use them to make a sealed forward sliding barrel inside of the reservoir.

Cut slits in the barrel rearwards of that flat seal and hammer or even just push the barrel forward to break the seal and fire.
Of course a boltaction type set up would feed the ammo and seal the back end of the barrel...

Real interesting stuff.
Amazed I never saw a functional prototype.

I'd build one for my son that way if he was only two years older..

[youtube]http://www.youtube.com/watch?v=8PsYiKIlmVQ&feature=plcp[/youtube]
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: wyz2285 » Tue Aug 14, 2012 3:49 pm

While you want a big bore, I was tring to make a accurate .144 and I want to use a hammer as weak as possible.
Your second design it´s going to be hell to make on a drill press :lol:
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CpTn_lAw wrote::D "yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? " :D
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Unread postAuthor: Brian the brain » Tue Aug 14, 2012 3:55 pm

Not really...
If the reservoir diameter is large enough..

The rod doesn't have to be in the exact centre.
You could just drill it above the centerline and reduce dead space.
The actual valve will be closer to the barrel.

That also leaves more room for the channel.

keeping it in the centre will just help you to centre it in the drill as you cut the O-ring grooves.

If you have enough room ( big diameter tubing) you could put the channel in the centre and the valve core above it.
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Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
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Unread postAuthor: far_cry » Wed Aug 15, 2012 6:06 am

BTB

your valve have a high chance of leaking because there is very little force pushing the rubber , if you can make groove in the head of the piston ,that can make the job done.

didn't you saw my new valve? it will share the talon ss mechanism
QDV activated with hammer strike
this test was done with about 600 psi and the chamber was 55cm of 1/2" pipe
[youtube]http://www.youtube.com/watch?v=fk2BRaL70GQ&feature=youtu.be[/youtube]


http://www.spudfiles.com/forums/my-new-old-valve-system-t24489.html

:D :D :D :D :D :D :D :D :D :D :D
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