Converting GPM flow and presure loss to CV

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Postby utcpyro » Tue Mar 15, 2005 3:18 pm

I've searched, didn’t really find any thing, but because I know I've seen this SOMEWHERE in the past (Maybe on theHalls page?) I'm going to put it here.

On sprinkler valves, as many of you know, they don’t list the CV of valves. Instead they list the pressure loss at different flows. Now, I know that the CV is how many gallons of water that can go thought the valve at 1psi loss, but there is a problem in converting. When you graph the info you get (or find) with your valves, it's curved instead of a nice leaner line.

Now we get to my question: How do you convert the info from the sprinkler valve documentation to a CV you can use in GGDT?
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Postby Freefall » Tue Mar 15, 2005 3:54 pm

Can you extrapolate the plot to find a flow that would yield 1 psi loss?
I've lost my documentation. Could you post the data from yours here?
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Postby utcpyro » Tue Mar 15, 2005 4:18 pm

The problem with doing that (if I remember from this thing that I saw) is that the valve does not open all the way at low flows or something like that. Also, some of them NEVER get to 1PSI loss. This I supose is because of the required pressure diffrence to actually open the valve.

On my new valves:
http://www.nelsonturf.com/products/doc.cfm?DOC=173

On my older vainbirds (not exactally the same ones at the CV searies, but verry close):
http://www.rainbird.com/landscape/produ ... dv-dvf.htm

The 3/4" Toro's I like for pilot valves or really small guns:
http://www.toro.com/sprinklers/valves/i ... -valve.pdf

The Orbit valves that a lot of you like to use, but I think offer lower proformance:
http://www.orbitonline.com/files/manuals/94080.pdf
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Postby Freefall » Tue Mar 15, 2005 4:55 pm

I see your problem. I've plotted them in excel, and the "add trendline: polynomial" function says at 1 psi, you'll be flowing -90 GPM. Obviously, that's not right.

All I can suggest is what we've been doing in the past: Test the gun, and compare the numbers to GGDT.

Somewhere on D_Hall's page there is (was?) a general formula for estimating Cv based on area, but it's been a while since I've looked at it.
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Postby utcpyro » Wed Mar 16, 2005 1:17 am

Well, the CV is going to vary a bit on how efficient the valve is.. That why I was asking this, I want to know how much better performance I'll be getting my using my valve in a angled set up instead of the normal straight through setup.
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