# finding GPM for flow test

Discussion in 'Irrigation / Sprinkler Forum' started by v1rtu0s1ty, Apr 25, 2007.

1. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
I'm back guys. I have downloaded the document from Rain Bird where we draw our property. I've finished drawing it. However, there is another form that I need to fill out. There was one item there that I don't know what to write. It is the flow test. The unit is in GPM, gallons per minute. How do I conduct the test to get an accurate GPM reading?

Thanks!

2. ### hjModerator & Master PlumberStaff Member

Joined:
Aug 31, 2004
Occupation:
Plumber
Location:
Cave Creek, Arizona
flow test

Unless you already have the connection opening in place, you will not get a true reading, but use a five gallon bucket and see how long it takes to fill it. Then extrapolate that figure into gallons per minute.

4. ### jimboPlumber

Joined:
Aug 31, 2004
Location:
San Diego, CA
5. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
Rainbird told me this but I think it's not correct.

Fill up a 5 gallon bucket and time it. Then the number of seconds I will get should be multiplied to 60. Then the product, divide it by 5.

I don't think it's correct. Even if I use 40 seconds to fill up a 5 gallon bucket, we will get 480. And they told me that 480 is the gallons per minute. LOL. I can now then provide water to our fire department. LOL.

6. ### Gary SwartIn the Trades

Joined:
Sep 1, 2004
Location:
Yakima, WA
I don't understand their formula either. Here's what I come up with. You filled the 5 gallon bucket in 40 seconds. 40 seconds is 2/3 of one minute. 5 divided by 2/3 is 7-1/2 gallons per minute.

7. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
I think that looks better. Here is the final formula

GPM = Ngallons / (seconds / 60)

example for a 2 gallon bucket, and it took 5 seconds to fill it up

GPM = 2 gallons / (5 secs/60)
GPM = 2 gallons / .08333
GPM = 24

in our earlier example, 40 secs for a 5 gallon bucket

GPM = 5 gallons / (40 secs/60)
GPM = 5 gallons / .67
GPM = 7.5

in my real test, I went outside and hooked up a hose, it took 30 secs to fill up a 5 gallon bucket

GPM = 5 gallons / (30 secs/60)
GPM = 5 gallons / .5
GPM = 10 gallons

what do you think guys about my GPM? Is it low?

and the PSI based from the tool I bought says 55 psi.

Do I have good data for me to continue my sprinkler system wish or dream?

Last edited: Apr 26, 2007
8. ### speedbumpActive Member

Joined:
Jul 15, 2005
Occupation:
Water well and pump tech.
Location:
Riverview, Fl.
Getting the flow from a hose bibb will probably not give you the figure your looking for. Most water hookups are either 5/8" or 3/4". A lot more water will flow from the larger pipe than it will through a hose bibb which is usually piped with 1/2" or smaller. Where your sprinklers are going to be tee'd in is where you need to do the bucket test.

9. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
Ah, I was actually thinking of that last night. I was telling myself that the system will not be connected to the outside faucet. But I'm thinking of hooking up new copper pipes. Unfortunately, I don't have those pipes yet. So folks, what diameter of pipe are your recommendation from the inside which is in my basement? Do I just need one new 3/4" or 5/8" copper pipe going to the device that does the zoning?

If that is the case, how do I properly measure the the GPM then?

I'm worried now with RainBird since they already failed with the formula. Or is it just because those are just sales people?

10. ### speedbumpActive Member

Joined:
Jul 15, 2005
Occupation:
Water well and pump tech.
Location:
Riverview, Fl.
Wherever your going to tee into your existing water pipe is where you should do the test. You will have to shut the water off at the meter to make the tap on the main line. Then do the bucket test from that new line which can have a valve right at the tee. You should also have a gauge in that line so you can see how any gallons per minute you get at around 40 lbs. That is what the sprinklers are going to want to work with.

bob...

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11. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
Here is a picture of the pipe that is coming from the city. It is in the basement. It's the one on the right. It's a 1" pipe. Then at the bottom, it connects to a bigger pipe that is connected to the wall(from city).

I'm wondering why the psi gauge that I bought is reading 55 to 57 when I connected it to the outside faucet. Then if you look at the other pipe which is on the left(fire sprinkler pipe 2"), it has a gauge too at the bottom but not shown. The reading is 78 psi. From what I know, psi should be the same for all right?

Is it possible to calculate the GPM if we have the PSI value?

Last edited: Apr 26, 2007
12. ### Gary SwartIn the Trades

Joined:
Sep 1, 2004
Location:
Yakima, WA
You will have to take the gpm available into consideration when designing the system so you don't overload your zones. You also need to consider friction loss through the pipes. It would be my suggestion to contact an irrigation supply house. They often will design a system for you at no cost as long as you buy all of your pipe, fittings, sprinklers, and other components from them. They know what size pipes you need, when to reduce to a smaller size, and the best sprinklers for each zone. You will need to have a good scale drawing of your property showing where everything is, have the meter size, size of the pipe coming out of the meter and how far it will run to the manifold, and static water pressure. Of course, they will be more than happy to do a complete installation for you, but that isn't a freebie.

13. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
That's why I started with asking how to get the GPM because it's one of the question in the RainBird form. I was about to send the form and drawing today to Rainbird but I learned from folks here that I should not use the GPM reading I got today via which I got when I used the faucet outside the house.

Now, I'm stucked. I don't know what to do. I don't have any faucet in the 1" pipe from the picture above.

14. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
Hi speedbump,

Can you explain to me what valve I should be getting? Is the picture below is what I should be getting? And do I connect a faucet to this valve so I can conduct testing?

What about the gauge? Is the connection suppose to be like this(from left to right)

my 1" pipe -> T -> valve -> gauge -> pipe going to whatever

15. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
Gary, your suggestion was also the suggestion last year given to me. However, I got so stucked in projects in the office. I didn't have much time. I also remember someone from this forum told me that once I receive the design, post it so that they can look at it and make changes/corrections. However, like what I said earlier, I'm stuck with some variables. Until I get those numbers, that's the only time I will be able to send this drawing.

I hope you guys can advice as to what I should do first.

Any help would be greatly appreciated!

16. ### CassPlumber

Joined:
Nov 12, 2005
Location:
Ohio
Is there a check valve on the sprinkler system?

17. ### speedbumpActive Member

Joined:
Jul 15, 2005
Occupation:
Water well and pump tech.
Location:
Riverview, Fl.
It would be 1" pipe, tee, gauge valve then add some pipe temporarilly of the same size or bigger to where ever your going to do the bucket test. You will want to run the water with the valve closed enough to see 40 psi on a (new gauge), then see how long it takes to fill the 5 gal bucket. This is the amount of water your sprinklers will have available if your city water is constant.

bob...

Joined:
Sep 18, 2006
Location:
Chicago IL
19. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
cass,

I'm sorry, I got confused when you said sprinklers. I don't have any sprinkler system for my lawn. But I have fire sprinkler system.

Please let me know what you need.

Thanks,

Ronneil

20. ### speedbumpActive Member

Joined:
Jul 15, 2005
Occupation:
Water well and pump tech.
Location:
Riverview, Fl.
I recommend a better gauge than you get at HD or the others.
bob...

Last edited by a moderator: Jun 15, 2019
21. ### v1rtu0s1tyDIY Senior Member

Joined:
Sep 18, 2006
Location:
Chicago IL
is this the exact one?

If that is the one you were referring to, how come the tube where the thread is is thin? They are just 1/4". How will I connect it to the Tee? I'm sorry, once I see how it looks like, it will be easier for me to understand.