25 replies to this topic

[imaseoulman]

So, I've mentioned this in a few other places and I was very excited about this, as early tests were very promising. The seal between the poppet and the valve opening worked well when everything was just pushed together (not sealed with primer/cement), but for as is often the case with homemades, it didn't want to work when I put the finishing touches on. It will seal now about maybe one in six times (definitely efficient enough for an actual blaster), but I have a solution that I'm pretty convinced will work, if I can find the parts.

Here's roughtly I did:

Materials:
2" PVC coupler (slip)
2 2"-3/4" flush reducing bushings
1' 1/2" PVC
3/4"-1/2" flush bushing
3" 1/2" PETG
Rubber washer seal thing from home depot



Start with a 2" PVC coupler and two flush bushings reducing to 3/4". Make a sort of tank out of this.
Next, sand the rim off of the base of the 3/4"-1/2" bushing so that it can fit into the 3/4" opening the way it's not supposed to (this will allow you to use the stock, clean, unsanded end for barrel attachment).
Run the 1/2" PVC through the 'tank' and into the 3/4"-1/2" bushing so that it is held straight in place. Use some epoxy putty to seal the end without the 3/4"-1/2" bushing.
After it has set (about five minutes) remove the coupler and seal off the inside of the connection with plumbers goop for good measure and let it dry.

Cut down the 1/2" PVC running through the tank so that it comes up about 1/2" further than the wall of the bushing. (You'll just have to play with this to make sure it's the right length by assembling everything and cutting off a littlle bit at a time until it's the right length).

To make the poppet, simply superglue the washer to the PETG. Make sure you only glue around the rim where it's attached. It doesn't have to be super secure because of the nature of the poppet. There's never much stress on the connection because when the poppet is "sucked back" the suction is acting on the rubber washer itself. This action, instead of pulling the PETG away from the washer (which would happen if the whole thing were covered in glue) causes the rubber washer to push the PETG as it gets sucked back, so there's never really a chance for it to come undone.



Stick the poppet into the PVC and do a "blow test." The poppet should easily move forward when you blow into the PVC and slide back in when you suck. I lubricated mine with mineral oil.

Now you need to put a small segment (about 1") of 1/2" PVC into the 3/4"-1/2" bushing so that when the 3/4"-1/2" bushing is inserted into the 2"-3/4" bushing about 1/3" of the 1/2" PVC protrudes down into the tank. This piece of PVC is going to be what the washer seals against.

All you have left to do is put everything together and seal it up. Attach a pump and a valve and maybe you'll have better luck than I did.



To improve the seal I added a 9/16" o-ring to the base of the PVC that seals against the washer, but it didn't seem to make much difference.

What I'm convinced would absolutely work is a "hemi-seal." Instead of using a flat washer, what is needed is soft (low durometer) rounded washer and a rounded opening to seal against. Something like this:



I'm convinced that if the washer (the red part) were made of a soft enough material, it would not be at all difficult to get this to seal perfectly. Does anybody know of any washers/seals that fit this description?

Any questions? Comments? Suggestions?

[silentsnipe]

Nice, do you have ranges? Or does it not work yet?

[BustaNinja]

Nice, do you have ranges? Or does it not work yet?

Its an air tank... are you retarded?

Would using some Foam Rubber work? if you can get it depressed enough would it work? I didn't see a spring in your diagram. I would put one in under neath the seal piece. It would have less miss seals.

[imaseoulman]

Nice, do you have ranges? Or does it not work yet?

I never tested ranges. The few times that it worked, the air came out very quickly with great force. The narrowest space is the ID of 1/2" PVC, so flow rate is very high and the volume is about equal to a Blast Bazooka.

Would using some Foam Rubber work? if you can get it depressed enough would it work? I didn't see a spring in your diagram. I would put one in under neath the seal piece. It would have less miss seals.

I've thought about foam rubber, but I'm not sure how well that would seal. I think the air may just go right through it before I could get it depressed enough to seal.

I didn't use a spring because that would make it difficult for the valve to open (it's opening solely on the basis of back pressure) and then it may reclose before the air were able to fully exhaust.

I really just need to find some soft, rounded rubber, and a rounded end cap or something that I can use to seal it against.

[rork]

Hmmm... You seem to be facing the same sorts of sealing issues with your valva as I am with mine. You have given me ideas. Now to find half a rubber ball of some sort... I checked at McMaster, and they have rubber balls from 3/16" on up. Here's a 1/2" one: 1854T54. They all seem to be pretty hard, though. I'm thinking that cut in half and pressed into an O-ring, this might solve a lot of problems.

Edited by rork, 20 December 2008 - 01:33 PM.

[imaseoulman]

Yeah, I've been looking at those. I didn't pick them because they have a huge hole in the middle, but I may pick one up today and plug it with plumbers goop. Any ideas for a rounded end cap type thing?

[Draconis]

Yes. I've actually been holding on to a couple of these because I knew they would come in handy at some point: The little rubber button from the valve on laundry detergent bottles. They are about 5/8" in diameter, and pretty flexible. I'll post a pic when I get a chance.

[CaptainSlug]

To make one of these work at low pressure you'll probably have to make the sealing face of the poppet with a much softer rubber so that it won't resist deformation as much.
Silicone will probably work best since it's available in Durometer 30A.

I managed to find some 1" diameter rubber bumpers made of soft Silicone.

search for part# 8926T21

Edited by CaptainSlug, 20 December 2008 - 04:30 PM.

[Doom]

Adapting an existing working piston valve design would be the best way to approach this. I took a quick look at some and something like this is worth looking in to. A simple rubber washer sealed on a pipe worked. I think the pipe makes the difference, though I don't know for certain.

A diaphragm valve might also be worth looking in to. The approach would be simpler.

[imaseoulman]

To make one of these work at low pressure you'll probably have to make the sealing face of the poppet with a much softer rubber so that it won't resist deformation as much.

Definitely. To help with the low pressure problem, though, I pre-pressurize the length of PVC running to the ball valve.

If you look at the final picture, you'll notice that that's a fair amount of volume, but not an extreme amount. I pressurize that to around 40 PSI (a complete guess) and then open the ball valve.

I'll look into the silicon bumpers, though; thanks for the tip. I'm also considering using stock dart tips. It's just a random though, but since the poppet is cheap and easy to make, I don't mind trying several different types.

[MoonMaster]

I know this is sort of off topic, as your valve works in an entirely different way, but has anyone else looked into coaxial valves for NERF? Spudfiles has plenty of good ideas that could easily be scaled down to fire a small dart. These particular valves work like big salvo blast chambers in a way. I think they could really be useful.

http://www.spudfiles...ally-t8157.html

[Doom]

I posted a link directly to a coaxial piston valve a few posts up. They definitely can be adapted for Nerf but no one has done so yet.

Still, with something as small as a Nerf dart a QEV makes the most sense, especially given the potential difficulty in building a piston or diaphragm valve.

With that being said, I plan on eventually making a gun with a tiny piston valve based on the basic cycle of my FANG Nerf gun, but that won't happen for a while at least because I intend to use my university's machine shop to make everything.

And the costs add up too. QEVs are somewhat expensive. A well made piston valve will be cheap. So it's really a trade-off, which is why I'm closely watching this to see what others figure out.

Edited by Doom, 21 December 2008 - 12:19 PM.

[imaseoulman]

I'm really not sure what the differences in all these valves are, but mine functions identically to a Big Salvo blast chamber. I pretty much took apart a big salvo blast chamber and then created a larger home-made version. You can call that whatever you want, but that's what it is.

[Doom]

On the most basic level, a QEV, piston valve, diaphragm valve, coaxial piston valve, barrel sealing piston valve, Big Salvo blast chamber, etc, are all the same. They basically describe different configurations of the same type of valve. They are functionally identical.

It'd probably be most accurate to call this class of valves "piston valves" because most of them use a piston.

Edited by Doom, 21 December 2008 - 02:23 PM.

[rork]

A question for those who know a lot more about piston valves than myself: How much flow does one need to actuate the main valve? From what I've gathered, blowguns are often used, and in my experience, those things have very low flow rates. I love the valve, but hate the idea of a ball valve as a trigger (although I realize that this is just a prototype).

[Doom]

For Nerf you can use essentially any valve as a pilot valve. A pilot valve is the technical term for the actuating valve you're referring to. The DCV I used in FANG has about half as much flow as a normal blowgun from what I know and power is no problem. In fact, I intend to decrease the power.

In spud guns people will often use a series of valves to pilot the main chamber as fast as possible. It's not uncommon to see a huge piston valve actuated by a large QEV which is actuated by a blowgun or ball valve. The series of valves is only necessary in large valves because the pilot volume is comparatively large (The pilot volume is the volume that must be released by the pilot valve).

I might need to upgrade my pilot valve in FANG if I use a tube leading from the QEV to the DCV to put the DCV in the trigger area because the pilot volume would increase. But, I doubt that would be necessary because the pilot volume would still be very small.

The main limitation in valves I suppose is what you find convenient. Ball valves have high flow rates for their size and price but are not the most ergonomic choice and can be inconsistent. Blowguns have lower flow rates with improved ergonomics and better consistency. DCVs sometimes have lower flow rates than blowguns but allow for semi-auto operation.

[rork]

Thanks. This valve design has really struck my fancy. I looked at DCVs on McMaster, and they look great--a little more expensive than blowguns, but more easily integrated into a blaster. How does part #62475K11 look? As far as ball valves go, I'm not really interested in building much of anything that I can't shoot people with, and a ball valve would be death to accuracy and ergonomics.

[Doom]

From a flow perspective, that valve is pretty good (it has about 2.5 times the flow of what I'm using). From my reading of how those valves worked you'd have to unpress the button to shoot, but I'm not sure about that. I think CaptainSlug's using the exact same valve in ARR so it should be fine. If you find it's unacceptable, mail it back to McMaster-Carr for a refund. They've generally been good about refunds with me so I'm willing to try things and return them if they don't work.

Edit: I'd be interested in knowing how well that particular valve works because I was eying the same one for FANG 2.

Edited by Doom, 21 December 2008 - 07:37 PM.

[CaptainSlug]

A question for those who know a lot more about piston valves than myself: How much flow does one need to actuate the main valve?

Hardly any.
Anything rated higher than 4CFM @ 100psi should work fine. Especially so on a low pressure QEV with a lightweight poppet.

[MoonMaster]

If someone actually uses the coaxial setup, they could use a Big SNAP gasket system on the piston for the sealing face, maybe some of the gasket cut so it doesn't seal with the walls of the chamber. And a hose handle pilot valve... Hmm. I know what I'm building sometime soon.

[Draconis]

A question for those who know a lot more about piston valves than myself: How much flow does one need to actuate the main valve?

Hardly any.
Anything rated higher than 4CFM @ 100psi should work fine. Especially so on a low pressure QEV with a lightweight poppet.

I built a 'blast' valve from a tire inflation chuck, on which I replaced the floating center post with a small machine screw with a cap nut on top. It works pretty well for actuating a number of BS and hornet chambers all at once.

[rork]

And, one google search later, I have a pretty good idea as to what I'll be piloting my valve with. Thanks.

EDIT: Sorry, I was commenting on Draconis' tire chuck idea, not trying to be mysterious. This looks like it would be pretty easy to add a push button to, and it's less than half the price of a push button valve from McMaster.

http://www.homedepot...catalogId=10051

There's also McMaster part #6146A23. $2.18

Edited by rork, 22 December 2008 - 11:48 AM.

[imaseoulman]

Care to fill us in?

[rork]

Last post edited to reflect what I was actually talking about. Any ideas as to how one would go about adding a trigger to the valve (preferably for cheap)?

[Draconis]

Harbor freight has the for $0.99. Then just pick up one of the 1.4"MIP to 1/4" OD tubing connectors. I like the plastic ones that HD has.

Edited by Draconis, 22 December 2008 - 03:40 PM.