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Valve flow coefficient question.

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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Valve flow coefficient question.

Unread postAuthor: Alanstone » Tue Nov 15, 2016 3:30 am

I have a barrel sealing piston of 12mm diameter. When unseated, the CO2 flows into 4 separate 6 mm diameter holes into the barrel. Is it possible for someone who has a feel for these things to give me your gut feel on what the valve flow coefficient will be?

I have attached a few pictures so that you can see the flow layout.
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Alanstone
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Re: Valve flow coefficient question.

Unread postAuthor: matti » Tue Nov 15, 2016 12:49 pm

Are you asking this for GGDT inputs? GGDT User guide says it like this:
"Valve -> Flow Coefficient
Typically, valve performance is specified by a valve manufacturer in one of two ways: (1) by Cv or (2) by Kv. GGDT allows for either of these methods and a third; efficiency. Which method is used is defined in the configuration dialog box. For those who may not be familiar with these nomenclatures, a few words are in order. A valve that has a Cv of 1.0 will allow one gallon of water to flow through it per minute with a one psi pressure drop. If I remember correctly, a valve that has a KV of one will allow one liter of water flow through it per minute with a one bar pressure drop. In general, these two parameters will be listed in the manufacturer's literature. If it is not, I suggest using efficiency (30-50% would be typical values)"

Hope this helps..
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Re: Valve flow coefficient question.

Unread postAuthor: Alanstone » Wed Nov 16, 2016 10:39 am

Thanks for taking the time to reply Matti. I am aware of the GGDT user guide info and that it suggests 30-50% efficiency.

Here is my problem though. I was looking at 1/2" QEV'S on the net to try get a feel for what kind of Cv they have and came across numbers I did not expect.

This 1/2" QEV is rated with a Cv of 8.8 ( http://www.versa-valves.com/quick-exhau ... less-steel). In GGDT that translates to 132% efficient. This 1/2" QEV ( http://www.humphrey-products.com/dynami ... s?part=QE4) is rated Cv 6.2 which is 93% efficient. So there is clearly something wrong here. I expect it has to do with unit values in various countries but it hasn't helped me much with trying to determine what the flow of my valve would be. So I was hoping maybe one of you gurus would have played around with valves enough to be able to guestimate a viable Cv for my valve :lol: . Anyhow, I am going to see if I can do it with solidworks.

Thanks again.
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Re: Valve flow coefficient question.

Unread postAuthor: matti » Wed Nov 16, 2016 4:10 pm

I think CV/efficiency is about the outlet orifice size of the valve so you should know the exact inside diameter of QEV port to calculate the efficiency of the valve from the CV value ? Not sure what you mean by "GGDT that translates to 132% efficient" but clearly some input is wrong..

But still.. I don't know how to actually calculate the Cv or efficiency for your valve, have you searched google?
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