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Repeating Hammer Valve Design

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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Repeating Hammer Valve Design

Unread postAuthor: SubsonicSpud » Sat Apr 04, 2009 3:14 am

G'day everybody.

I've been toying around with repeating valve pilots for an auto shot gun i am designing. I was going to use a pop off style pilot like "psycix" QEV gun, but i want to make something a little MOAR efficient and stable.

I don't know if this has been tried before but here is what I am planning to make as a pilot valve
Image

Basically it's a simple hammer valve.
The hammer, after being released by the sear, will slide into a loosely fitting cylinder prior to striking the Schrader valve. The air released from the schrader will then fire the hammer backwards prior to being released. The hammer can then be recaptured by the sear, or continue on another cycle.

Has anybody tried this style of valve before? or do you have any reasons why this may not work?

Cheers

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Unread postAuthor: inonickname » Sat Apr 04, 2009 4:07 am

It will work fine.

What barrel size are you planning on using? Dimensions would let me give a better answer.

As far as the schrader goes I can recommended two things.

1. Use a hacksaw to cut off just before where the threads for the core start, then file it smooth.

2. Get some long valve cores, they look the same as short ones except they have a shaft that extends from the bottom and a spring on it, rather than having an internal spring. I removed it completely for my micro repeater (you'll see it soon).

Oops you want it as an exhaust valve. Yep, you've got little worries there. Still, what I said still goes.
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Re: Repeating Hammer Valve Design

Unread postAuthor: jackssmirkingrevenge » Sat Apr 04, 2009 4:08 am

SubsonicSpud wrote:do you have any reasons why this may not work?


The QEV pilot alone might have too low a volume to provide a big enough burst of air to cycle the hammer.
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Unread postAuthor: ALIHISGREAT » Sat Apr 04, 2009 4:17 am

I think it could be tricky to balance out hammer weights, spring strengths and it might need quite high pressure to work too... but its worth a go.
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Unread postAuthor: SubsonicSpud » Sat Apr 04, 2009 4:29 am

Thanks for the quick replies guys

Yep i know it will rely a lot on the weight and pressures, I will be making the hammer weight adjustable along with the spring pressure. It will be running at about 400psi, so i should be able to get some pretty good hammer return from a small pilot volume. I will try it without a QEV to start with and see if it gives enough pressure drop to pilot the piston valve.

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Unread postAuthor: ALIHISGREAT » Sat Apr 04, 2009 4:39 am

You'll also have to perform a BtB style QEV mod:

I think you take the piston out, drill an equalization hole and put a spring behind it... but i'm not sure.
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Unread postAuthor: SubsonicSpud » Sat Apr 04, 2009 9:17 pm

ALIHISGREAT wrote:You'll also have to perform a BtB style QEV mod:

I think you take the piston out, drill an equalization hole and put a spring behind it... but i'm not sure.


I was planning not to mod the QEV and have a bypass pipe with a check valve going to the main chamber, the check valve should provide enough back pressure to the QEV to seat the main valve (if that makes any sense :roll: ). I would not be able to get a decent ROF if the main chamber was being filled through the QEV. Aiming for about 2 rounds per second with this thing.

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Unread postAuthor: VH_man » Sat Apr 04, 2009 10:40 pm

your going to find the Presta/Schrader will not yield enough flow to do much of anything.

Go with something Bigger. alot Bigger. Like a nail against an O-ring or something.
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Unread postAuthor: SubsonicSpud » Sun Apr 05, 2009 4:32 am

VH_man wrote:your going to find the Presta/Schrader will not yield enough flow to do much of anything.

Go with something Bigger. alot Bigger. Like a nail against an O-ring or something.


I think the Schrader or Presta should have no problem piloting the QEV. But i am thinking there may not be enough flow to overcome leaking past the piston section of the hammer. I cannot make the piston a perfect seal, as the air in that area would have nowhere to vent and would prevent the hammer from striking the schrader valve. I will have to make a kind of lightly sprung check valve next to the schrader to vent the air as the hammer slides down the cylinder, but will then close off once the air from the schrader is released.
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Unread postAuthor: Brian the brain » Sun Apr 05, 2009 12:21 pm

You don;t need to mod anything.
The equalisation hole was unnessesary.
I tried it again with the hole plugged and it repeated just fine.The spring is all you need. :oops:
The unmodded version will even save air compared to the modded one.

I'm not sure about the hammervalve exhaust being powerfull enough....but isn' t that how an autococker paintballgun works?


There must be some way to get it to work. :?

I'm working on another repeater right now, but with bolt action.
I'll have tp deal with some of the same issues however...well...I've dealt with them already :wink:
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Unread postAuthor: SubsonicSpud » Mon Apr 06, 2009 3:51 am

Well guys today I decided to make the design i had planned. Turned out to be quite sucessful.

Here it is

Video:
[youtube]http://www.youtube.com/watch?v=SVP7liQc3Ws [/youtube]

Image



I have tested it from 450psi down to its cutout pressure of about 70psi and it is very stable. A input pressure change has very little effect on the cycle rate, just causes a change in magnitude of hammer movement. The cycle rate is much higher than I expected, around 10-20 times a second at a guess, way faster than I require, or expect to get any breach and magazine to keep up with.

Here is the exploded view

Image

and some of the components in the assembled position

Image

Most of the internal components are machined out of Acetal. The hammer is hollowed out and filled with lead and epoxy to add to the weight.
The casing is 1-1/4 copper tube. the Schrader valve is soldered into a 1/4 air line fitting which in turn is epoxied into the Acetal end cap. I have not yet included a sear into the design yet as I will probably increase the length of the casing and hammer travel to try and slow it down a bit.

Phase 1 almost complete :)

Time to start Phase 2, a 19mm main valve and blow forward breach that can keep up :twisted:



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Last edited by SubsonicSpud on Fri May 01, 2009 8:30 am, edited 2 times in total.
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Unread postAuthor: ALIHISGREAT » Mon Apr 06, 2009 4:23 am

spudfiles has gone repeater mad!

although i have to say, your's looks the best!

i have to say, i'm tempted to jump on the band wagon and attempt one myself!

we should take bets on the next craze... :roll:

be sure to get a vid up, please say it makes a satisfying Braap sound? :D
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Unread postAuthor: SubsonicSpud » Mon Apr 06, 2009 5:20 am

ALIHISGREAT wrote:spudfiles has gone repeater mad!

although i have to say, your's looks the best!

i have to say, i'm tempted to jump on the band wagon and attempt one myself!

we should take bets on the next craze... :roll:

be sure to get a vid up, please say it makes a satisfying Braap sound? :D


Yep we all have. I have just uploaded the video of the valve to my last post.

Have to say it sounds great in real life, the video dose it no justice, but that is usually the case. It is a deeper popping noise than in the video, loud enough to echo of the nearby hills, and probably cause concern for the neighbours :shock: I can't wait to hear it hooked up to a QEV and Piston valve :twisted:

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Unread postAuthor: ALIHISGREAT » Mon Apr 06, 2009 5:27 am

How consistent is the hammer stroke, because from the video, it seems to be reasonably consistent with the odd inconsistency?

if it is inconsistent then it could harm performance, consistency of the main cannon.
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Unread postAuthor: SubsonicSpud » Mon Apr 06, 2009 5:51 am

ALIHISGREAT wrote:How consistent is the hammer stroke, because from the video, it seems to be reasonably consistent with the odd inconsistency?

if it is inconsistent then it could harm performance, consistency of the main cannon.


It seems to be very consistent. It was a little erratic the first couple of runs but all the parts have bedded in now and it runs smoothly. I tried running it at different angles but it did not change the rate of cycle. Looking at the waveform in Audacity shows a cycle of about 25-28 per second. At it's current cycle rate I would not be able to use it, so i need to slow it down. I can't see a 19mm cannon or valve keeping up at 1500RPM let alone having to make ammo for it. I am going double the hammer stroke to try and slow the cycle, unless someone else can think of another way to do it.

edit: in the video the hammer cocking bolt dose seem to be erratc, but I think it is just the strobe effect of the camera

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