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Electronic activation Vs Blowgun

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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Electronic activation Vs Blowgun

Unread postAuthor: kainevg » Tue Aug 17, 2010 7:22 pm

Hello,

I was wondering if there is much of a power decrease if you activate a sprinkler valve electronically rather than using a blowgun trigger..

-Kaine
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Unread postAuthor: kjjohn » Tue Aug 17, 2010 7:40 pm

There is a performance difference. I am not sure how great it is, but in some cases it can be noticeable. The main difference between electric and pneumatic activation is that the pilot vent hole is much smaller with a standard electric sprinkler valve than it is with a blowgun, so the pilot can be exhausted more quickly with a blowgun, therefore opening the valve quicker and resulting in better performance. If you are set on using electric activation, and don't mind paying a bit more, you can still mod the sprinkler valve, but replace the blowgun with a smaller electric solenoid valve instead.
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Unread postAuthor: Technician1002 » Tue Aug 17, 2010 8:03 pm

The difficulty with a unmodified sprinkler valve is not the speed at which it opens. This is fine. The difficulty is when it does open the chamber pressure drops at a much faster rate than the pilot. This results in the pilot pressure being higher than the chamber pressure, so the valve immediately closes again, until the pilot drops lower and the process repeats.

This is the well known sprinkler valve foghorn, and yes, it does take a lot of power out of a shot when the valve closes while the projectile is still in the barrel. A big ball valve trigger goes a long way toward curing the sprinkler valve foghorn.

This is more of a problem for light projectiles than heavy ones. With heavy projectiles, the chamber pressure drops slower as the projectile limits flow and thus the rate the pressure drops.

This pilot pressure when the valve is open is one of the reasons I designed my own valve. I wanted one that had zero pressure when it opened so it would remain open for the entire shot.
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Unread postAuthor: kjjohn » Tue Aug 17, 2010 8:30 pm

@Technician - Thanks for correcting me. I didn't really consider the foghorn, as I haven't really worked with sprinkler valves much. :)

I do believe modded valves do open slightly faster than un-modded ones though in addition to fixing the higher-pressure pilot problem, and are certainly more efficient. In fact, if you are a skilled builder, I would just skip over sprinkler valves and try building a piston valve.
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Unread postAuthor: kainevg » Tue Aug 17, 2010 10:58 pm

I have actually already made a a pneumatic with a sprinkler valve and I like to keep things simplistic so i've refrained from using a piston valve
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Unread postAuthor: Technician1002 » Wed Aug 18, 2010 12:18 am

In a side by side test with a piston and sprinkler valve and a shooting chronograph, the piston outperformed the sprinkler valve delivering 4X the energy to the projectile.

In reverse, this means we used 1/4 the air per shot for the same distance as the sprinkler.
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