SpudFiles

Situation: I'd like to build a 1" bore pneumatic with full flow capability. Sure, I could make my own valve but I'm a lazy bum with other hobbies that take time too. With that said, the largest QEV I've seen that is quick/easy/cheap/etc. is the 3/4" QEVs from McMaster. Yes, there are other valves out there but the price goes up quickly from what I've seen (maybe I just haven't found the right vendor?). Anywho, flow through a 3/4" orifice is roughly half that of a 1" orifice. This leads to the though of simply ganging two 3/4" QEVs and calling it good.

Problem: If one valve opens significantly before the other, then you're just wasting your time having the second valve.

I know I've seen folks gang valves before but I never really paid attention to them. Does anybody have any experience with how well the valves sync? Did you do any "one valve vs. two valves" performance testing (TESTING, not theory!)?

General thoughts?

D_Hall wrote:General thoughts?

Use 3 valves and remove any doubt.

Connect both valves to a single pilot maybe? The air dumps and both diaphragms open. I've never messed with these, but that's the thought that comes to mind.

I was planning the same with irrigation valves. I guess the question is: how to know which one is opening first? If we knew that we could alter the tube length to the pilot valve to synchronize the openings of the main valves.

Using identical-ish valves on a long barrel launcher with heavy projectiles it probably doesn't matter, especially with high flow pilot. I'm curious though.

You could build a test rig (lay a flat plate over both valve exhaust ports and check out how much rotation it gets lol)

Moonbogg wrote:Connect both valves to a single pilot maybe?

That's certainly the plan, but all it takes is a bit more friction on one valve than the other and one will open before the other. Further, as the first piston/diaphragm slides back, it will momentarily pressurize the pilot thereby delaying the second valve from opening. The question is how long is that delay? On a scale from negligible to intolerable, where is it? Dunno. I was hoping someone else around here would though.

Anatine Duo wrote:You could build a test rig (lay a flat plate over both valve exhaust ports and check out how much rotation it gets lol)

Alternatively, just defeating one pilot (so THAT valve) never opens, measuring a few shots, and then comparing them to dual valve performance should give you a real-world result.

Ah, I understand the issue now that you explained it. Even if you managed to sync them up, I wonder if it would require occasional recalibration due to friction changes over time. At first, one valve might open faster, but after some number of shots, perhaps the other valve starts opening faster. Maybe at some point they both start opening at pretty much the same time due to being broken in.
I tend to obsess over details like this myself, so I feel for you man. It sounds like a fun problem to solve, but I think actually testing it is probably the best way.
How much pressure and what are the dimensions you are looking at for barrel and chamber? You mentioned 1" ID for the barrel. How long and what size is the chamber? Also, what ammo?

D_Hall wrote:That's certainly the plan, but all it takes is a bit more friction on one valve than the other and one will open before the other. Further, as the first piston/diaphragm slides back, it will momentarily pressurize the pilot thereby delaying the second valve from opening. The question is how long is that delay? On a scale from negligible to intolerable, where is it? Dunno. I was hoping someone else around here would though.

Would that even be a concern with a sufficiently high flow pilot valve? If you're careful to limit the amount of plumbing and therefore volume in the pilot area low, then surely a 3/4" QEV piloting 2 x 3/4" QEVs would provide an instantaneous dump that would negate any difference in friction between the two valves.

Moonbogg wrote:How much pressure and what are the dimensions you are looking at for barrel and chamber? You mentioned 1" ID for the barrel. How long and what size is the chamber? Also, what ammo?

Right now I'm still in the pondering stage. I'm thinking about stuff, but I've purchased nothing and may never actually go forward with it but... Current thought is about a 36" long barrel shooting crossbow bolts (broadhead keeps pointy end centered in the barrel while a sabot of sorts keeps the back end centered and seals for gases). Pressure on the order of 150 psi. Chamber is TBD at this point.

jackssmirkingrevenge wrote:Would that even be a concern with a sufficiently high flow pilot valve? If you're careful to limit the amount of plumbing and therefore volume in the pilot area low, then surely a 3/4" QEV piloting 2 x 3/4" QEVs would provide an instantaneous dump that would negate any difference in friction between the two valves.

Yeah, with that sort of dump I doubt it would be a problem, but I'd rather not have to use a 3/4" valve just to vent the pilot. In the same breath, I'm not sure how small I can go without running into the problem.

I hope to see you build this with shutoffs on the pilots for testing... it's very interesting. I had planned a 3 by 1" valve launcher piloted by a 1" until I realized one of the three is damaged. Piloting 2 by 1" with a 1" seems extreme, though I got the valves for free so whatever, right?

Larger pilot valve, equal fittings from both pilots to the pilot valve, inspect both for any significant defects on the casement/diaphragm and she'll be right mate.