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11

Tuesday, October 12th 2010, 6:08pm

Am I crazy? First of all, thank you for all your replies. I really appreciate your knowledge and experience. I just came up with an idea and want to run it by you for your opinion. I'm probably not the first one to do this but I was thinking of making up a small manifold that I would attach to the PVB about a foot or two away. The manifold would allow for 4 attachments. 3 spots would be occupied by pgp rotors with nozzles that would give me my goal of 15 gpm output and the 4th spot would be the pressure gauge. This would allow me to read working pressure while putting out the 15 gpm. All that would be missing would be to account for pressure loss for the valve (planning on Hunter PGV about 1-2 psi loss), and the eventual length of the piping to the zone and the head (1-1/4 sched. 40 or 1-1/4 poly). I could then swap nozzles with lower or higher output to see what the optimum gpm would be to get that 35 - 40 psi working pressure all the while accounting for the additional loss from the valve and piping that are missing. Am I crazy? Your thoughts?

Central Irrigation

Supreme Member

Posts: 359

Location: Central Minnesota

12

Tuesday, October 12th 2010, 9:57pm

Not crazy at all. I've actually experimented in much the same way.



While running your test, you can close the valve slightly to simulate lower pressures.

HooKooDooKu

Supreme Member

13

Wednesday, October 13th 2010, 9:00am

Depending upon exactly what you are trying to do, you might be putting the cart before the horse, or you might be doing a good piece of testing.

First of all, I assume this "manifold" (which most irrigation people associate with a manifold of valves for your various zones) isn't really a "manifold" of valves. (If it was, then you might be getting the cart before the horse because you're trying to set the number of zones before you've finished all the design work).

So when you say "manifold", I assume you really just mean a bunch of test pipes/fittings to allow you to run three PGPs at once and test the working pressure as they opperate (minus the pipe length pressure losses you can calculate afterwards with lookup tables).

If my assumptions are correct, then it sounds like a pretty good way to make some direct measurements. You will even be able to use your water meter and a watch (if no one is using any water in the house) to directly measure your flow rate as well as the pressure (basically, the bucket test without the bucket... use the meter to measure the number of gallons used).

As "Central Irrigation" alluded to (but you didn't specifically mention in your idea), you should include a zone valve of the type you intend to install between the PVB and the PGPs. That way, you will be including pressure losses through the valve in your measurements. Valves with flow control are recommended, because they will give you an additional measure of control at little extra expense. The flow control is basically just an extra valve that allows you to restrict the flow rate to the valve. When you start closing this flow control valve, you basically start make the valve input hole smaller partially cutting off the water flowing to the valve. By partially cutting off the water, you can simiulate lower static pressures (by basically increasing the pressure losses through the valve).

Hope that made some sense (I know it rambles on a bit), so let me know if it needs some clarification.

ReddHead

Advanced Member

Posts: 67

Location: South Jersey

14

Wednesday, October 13th 2010, 10:53am

Am I crazy? First of all, thank you for all your replies. I really appreciate your knowledge and experience. I just came up with an idea and want to run it by you for your opinion. I'm probably not the first one to do this but I was thinking of making up a small manifold that I would attach to the PVB about a foot or two away. The manifold would allow for 4 attachments. 3 spots would be occupied by pgp rotors with nozzles that would give me my goal of 15 gpm output and the 4th spot would be the pressure gauge. This would allow me to read working pressure while putting out the 15 gpm. All that would be missing would be to account for pressure loss for the valve (planning on Hunter PGV about 1-2 psi loss), and the eventual length of the piping to the zone and the head (1-1/4 sched. 40 or 1-1/4 poly). I could then swap nozzles with lower or higher output to see what the optimum gpm would be to get that 35 - 40 psi working pressure all the while accounting for the additional loss from the valve and piping that are missing. Am I crazy? Your thoughts?


I like the test manifold idea. Just make sure your gauge will drop as the pressure drops. Like I said earlier, the cheaper gauges will stay pegged at the high pressure even though it may have dropped by 20psi and give you a false impression. If you run 15GPM and the gauge doesn't drop something isn't right.

Also, see if 1" poly will meet your requirements for the length of your lateral lines. The pipe is easier to find and the fittings more common (in my neck of the woods anyway). I don't think 1 1/4" will buy you enough PSI to be worthwhile. I kind of complicated my design and had my 1" poly lateral line for each zone tee off into 3/4" poly runs which then feed the sprinkler heads. There is a company that makes a neat 1" and 3/4" poly tee that connects directly to funny pipe. I probably could have use all 1" poly but it would have been overkill since my heads are using such a low GPM. 1 1/4" poly fittings are also more expensive than 1".

15

Wednesday, October 13th 2010, 4:09pm

Hey Readdhead thanks for your input. Yeah, i remember what you said about those cheap gauges staying pegged to the initial pressure reading. I ran a test the first time I read your input. I turned the water on slowly and the gauge read about 52 psi. I then went in the house and turned on a few faucets and the the water in the bath tub and while they were running took another reading and the pressure was like 47. So I guess the gauge I got is a decent one. Nevertheless, when I do this manifold test, I plan to turn the water source on very slowly so there is no surge or pegging action.

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