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How much difference does a valve make?

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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How much difference does a valve make?

Unread postAuthor: HunterT » Wed Jul 14, 2010 1:05 am

I was wondering, if I used a sprinkler valve instead of a ball valve how much will that increase my air cannons performance in terms of velocity? Does using a faster valve increase performance even more?
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Re: How much difference does a valve make?

Unread postAuthor: jackssmirkingrevenge » Wed Jul 14, 2010 1:11 am

HunterT wrote:I was wondering, if I used a sprinkler valve instead of a ball valve how much will that increase my air cannons performance in terms of velocity?


It depends whether you are opening the ball valve manually, or mechanically with a spring, it's difficult to quantify without knowing all the parameters.

Does using a faster valve increase performance even more


A faster valve means a faster increase in pressure in the barrel and naturally, more performance. With a long barrel and heavy projectile, valve speed is less important than valve flow (ie the size of the opening through which air can flow) but it will only improve performance.
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Unread postAuthor: Technician1002 » Wed Jul 14, 2010 1:15 am

If you can open a ball valve fast enough, it will outperform the same size sprinkler valve due to the better flow when open. Unmodified sprinkler valves are prone to closing during the shot several times as the chamber pressure may drop much faster than the pilot pressure drops. This is the common air horn honk they are known for.

The honk is worse when launching light projectiles from relatively short barrels. Heavy projectiles in long barrels limit the rate air is taken from the chamber and do better.

A fast valve increases performance. This is most significant with lighter projectiles that can accelerate faster. If you get into a marshmallow launching competition, a fast valve is a must to win.

I have damage pictures posted in several places of damage to objects hit with high speed marshmallows. They include a dented car door, split open pop cans, holes in poly buckets, and other damage you would not expect a marshmallow to do.

A combination of few flow restrictions for high flow and high speed provides the best possible performance. My design in the sig below won an engineering competition. Side by side testing with a sprinker valve showed the huge performance difference.

Testing a sprinkler valve next to a higher flow valve in Arlington. Both cannons have a 3 inch barrel. The unfair test is a 1.5 inch sprinkler valve vs a 2 inch QDV. Chamber volumes are about the same. One long and slender the other short and fat.
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Unread postAuthor: Zeus » Wed Jul 14, 2010 6:03 pm

Some people say that a fast valve is important no matter what, others
say that it's dependant on the projectile. I think that a fast valve can't
hurt performance, you might not pick the difference, but it won't
hurt.

For the same reason as Technician1002, I won't recommend sprinkler
valves, because for about the same price (or less) you can get a
Quick-exhaust valve

Price depends on size of course, but I'd rather have a valve
that was designed for pneumatic systems, than a valve
that was designed to open slowly.

Of course, some people like sprinkler valves, so this is a
very subjective answer.
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