39 replies to this topic

[imaseoulman]

I thought I posted this earlier in response to this:

imaseoulman, could you explain your concept? It sounds interesting.

Back pressure valves are a form of check valve. I'll make a guess that you're going to manually push/pull the check to open the valve. That should work. I've actually thought of this before but never did anything with it so this was the first thing to come to mind. The problem with this is finding a reliable way to push the check.

But, I guess I just didn't hit the "post" buttong, so here it is now:

No, it's a back pressure valve and functions almost identically to a Big Salvo blast chamber. If I pushed or pulled the seal to open it, it would not be a back pressure valve, would it? The only thing that took the slightest amount of creativity was thinking up parts that would work, were cheap, and how to deliver enough air fast enough to create a seal. I have several designs ranging in price from $5 to $15 with my first prototype probably costing $12. The whole thing is an exercise in obtaining maximum flow rate. We'll see how it goes.

[Doom]

I'm still confused about how it would work. The Big Salvo uses something like a piston or diaphragm valve as far as I know (CaptainSlug has called these types of valves QEVs, which they essentially are). Do you mean QEV or does it work like a QEV?

[imaseoulman]

Essentially, air is pumped into the tank in a manner that forces the rubber seal against the opening that leads to the barrel. The trigger allows air to rush back out of the tank in such a way that it sucks the rubber seal back away from the barrel opening. As it is sucked back, it seals against the back opening not allowing any more air to escape out the back and all the air rushes out the barrel.

Is this making any sense? After I get a video of the first test fire, I'll post the results with a basic write-up.

[Doom]

Yes that makes sense--that's a piston valve/QEV. There's my confusion.

I've used QEVs before but they're somewhat expensive (see the FANG gun in my signature). Any cheap option with good flow would very welcome.

[Galaxy613]

Any cheap option with good flow would very welcome.

Indeed, the only problem then is coming up with a cheap, reliable trigger for those types.

Edited by Galaxy613, 08 December 2008 - 12:27 AM.

[rork]

I've got something in the works that should cast this whole problem in a very different light (based on Slug's D-CHAP 1). With any luck, I'll have a prototype up in a day or two.

[imaseoulman]

Any cheap option with good flow would very welcome.

Indeed, the only problem then is coming up with a cheap, reliable trigger for those types.

Well, my plan is to use a SMDTG trigger after I build three of these (I know, that's cheating) but a ball valve would work just fine. The usual problem of opening slowly isn't a problem with a QEV because the QEV will open very quickly. The only other problem would be the ease of actually opening the ball valve and how that would effect your aim.

Constructing a push button valve using a similar method to the QEV I made (just adding a spring) wouldn't be too hard and would cost $2-3+whatever the spring costs.

[CaptainSlug]

Yes that makes sense--that's a piston valve/QEV. There's my confusion.

I've used QEVs before but they're somewhat expensive (see the FANG gun in my signature). Any cheap option with good flow would very welcome.

The difference between an off-the-shelf QEV and the QEVs in Nerf blasters is basically just the size of the poppet, and the minimum operating pressure of the design is significantly lower.
The chamber surrounding the poppet is basically the #2 port.

Edited by CaptainSlug, 08 December 2008 - 09:06 PM.

[OnyxZenith]

It makes sense and all... but I've been reading that it will not work... now... if we can change this idea..
1) simply by applying larger rubber washers... ones that are just slighty smaller than the ID of the piping your are using (also add washers of the same diameter of the rubber ones)

2)adding a strong spring... i.e... us the chamber is only ,let's say, 3 in in length by 3 in ID... then you might want to use a maverick spring?

3)add lubricant to the inside of the chamber and on the caps to allow easy pull and seal between the rubber washer and the exit flow barrel

4) make it airtight by using PVC/CPVC concrete/cement/primer (yes use the primer/cement if you want it to be totally air tight... this will be sacrificing a spring

5) use a maverick barrel rod that you can salvage from a broken maverick revolver barrel.

hopefully this will help xP

[imaseoulman]

I don't see why larger rubber washers would make a difference. It seems to me that the larger the valve opening, the harder it would be to create a seal. Also, the larger the rubber washer, the harder it is to pull back because of how much air it needs to displace/compress. You know how opening the fridge door creates a slight vacuum making it a little difficult to open? Imagine trying to compress 30 PSI with your finger with a very large rubber washer. The smaller the washer the easier it is to pull the trigger. Make it too large and just forget about it.

[Flaming Hilt]

Somebody has thought of it before.


For the record, it held pressure, but not very much. I never figured out if the problem was the valve or something else. As of now I'd have to guess it was the one-way valve on the pump, but I can't say I know for sure.

[Galaxy613]

Neat, any other pictures? Or is that all you have? In the picture it looks like one end cap and one coupler, how did it connect?

I sadly have not been able to go thorugh with my idea because of lack of funds, tomarrow I will be getting my paycheck finally so I'll just have to get over to ACE.

[imaseoulman]

Here's my latest attempt at a homemade air tank.

Not yet fully functional, but with better parts, it definitely could be.

[Flaming Hilt]

The endcap and coupler were super glued together and held by that clamp while they dried.

Funds?
...
It's like. $5. Shovel half a sidewalk.

[rork]

What are the specs on the parts you used?