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Cross VS Tee Piston Valves

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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Cross VS Tee Piston Valves

Unread postAuthor: clemsonguy1125 » Sun Jun 13, 2010 5:30 pm

If a piston valve was built in a tee and cross which would have greater power. The cross would have 2 2.5 foot 2 inch tanks and the tee would have 1 5 foot 2 inch tanks. At 75 psi wouldnt the cross have greater performance because it would have better flow. Assume both had the exact same pressure, piston, chamber volume and pilot valve. Wouldnt higher pressure remain throught the shot better with 2 short chambers than one long chamber.
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Unread postAuthor: Technician1002 » Sun Jun 13, 2010 5:42 pm

Simple fluid dynamics would show that for a given flow in the barrel, the velocity in each half of a cross would be 1/2 that of a T.

Lower velocity in each half equals less losses. With the less losses in the cross, it can flow better. This is why I'm a fan of coaxial designs with large diameter chambers.
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Re: Cross VS Tee Piston Valves

Unread postAuthor: spudtyrrant » Sun Jun 13, 2010 5:43 pm

clemsonguy1125 wrote: At 75 psi wouldnt the cross have greater performance because it would have better flow. Asume both had the exact same pressure, piston, chamber volume and pilot valve.

OK air can only flow through your port so fast, so if you built both of your cannons perfectly and to exactly the same specifications they should be exactly the same power wise. but only if they both have more flow than the port size. other factors may effect them such as turbulence, but that comes down to the quality of the build.
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Unread postAuthor: clemsonguy1125 » Sun Jun 13, 2010 5:48 pm

Ok, I understand your point but with one chamber is it getting the maximum amount of flow that it could have with 2
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Unread postAuthor: Technician1002 » Sun Jun 13, 2010 5:51 pm

A piston in a T has to open farther than a piston in a cross for the same cross sectional opening between the chamber and barrel. If both pistons opened at the same speed and same distance, the piston in a cross would be open the same cross section to flow in less distance.

In other words, it open more area to flow in the same amount of time. It effectively opens faster and then opens further.
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Unread postAuthor: clemsonguy1125 » Sun Jun 13, 2010 5:54 pm

ok I think I understand, are you saying a cross piston would work better, or is the performance increase or decrease to small to notice.
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Unread postAuthor: Technician1002 » Sun Jun 13, 2010 5:59 pm

I have not built either. How much performance change is there, I don't know.

I do know my latest valves have higher flow than average cof according to GGDT.
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Unread postAuthor: clemsonguy1125 » Sun Jun 13, 2010 6:03 pm

Ok thanks, but what is cof
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Unread postAuthor: spudtyrrant » Sun Jun 13, 2010 6:06 pm

coefficient of flow, its how much flow your valve lets through
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Unread postAuthor: clemsonguy1125 » Sun Jun 13, 2010 6:09 pm

Ok, Thanks
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Unread postAuthor: Technician1002 » Sun Jun 13, 2010 6:13 pm

Coefficient of Flow. It is a measure of the ability to flow in a valve.

Low numbers is low flow.

http://en.wikipedia.org/wiki/Flow_coefficient
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Unread postAuthor: Gun Freak » Sun Jun 13, 2010 8:34 pm

Go with a cross, as said before it has some advantages. Plus it's only been done a few times before. Good luck.
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Unread postAuthor: mobile chernobyl » Sun Jun 13, 2010 9:54 pm

Cross valves just do it better...
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Unread postAuthor: Technician1002 » Mon Jun 14, 2010 1:30 am

Don't use a DWV cross. Use a sched 40 or better.
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Unread postAuthor: Gun Freak » Mon Jun 14, 2010 10:57 am

Large crossed are hard to find in sch 40, maybe try an irrigation store.
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