# gpm question

Discussion in 'Irrigation' started by lugnut#6, Jun 30, 2006.

1. ### lugnut#6LawnSite Senior Memberfrom Ocean Springs,Mississippi.Messages: 404

At 60 PSI what is the maximum gpm that 1" CL200 will carry?

thanks

2. ### firefightergwLawnSite Gold Memberfrom TexasMessages: 3,340

How many feet of 1" pipe?

3. ### jerryrwmLawnSite Bronze Memberfrom Central WisconsinMessages: 1,274

To keep the velocity at 5 fps or under 16.0 gpm is the maximum.

5. ### lugnut#6LawnSite Senior Memberfrom Ocean Springs,Mississippi.Messages: 404

im hoping to put 13 1800 pop ups on 1 zone with 10van nozzles on 1" CL200 to water the neutral area between the side walk and the street.
i come up with a 18.85 gpm need.
the main line that the laterals are connecting to is 1 1/2" and 60 psi.
im running 90' one direction and 50' the other.(corner lot).
am i going to have too much pressure?should i drop down to 3/4 or 1/2 to keep from blowing the pop ups?

thanks for the input

6. ### HooKooDooKuLawnSite Memberfrom Birmingham, ALMessages: 70

It's not a question of pressure but a question of water speed.

It's like a car. Regardless of your car's make and model, the engine's horse-power, RPM, or gear selection; you are required to keep the speed of your vehical at or below the speed limit.

As jerryrwm tried to point out, it is considered a plumbing standard that the speed limit for water is 5 feet per second. The speed of water flowing through a pipe is going to be a function of gpm and cross-sectional area of the pipe, and the value doesn't chage regardless of pressure.

The larger the pipe, the slower the flow, the smaller the pipe, the higher the flow.

Now to prevent you from having to do the math, there are a lot of charts out there that will provide you with the correct information.

In the case of 1" CL200 pipe, by virtue of the cross-sectional area of the inside of the pipe, we get the following numbers:
5GPM = 1.44 ft/s
10GPM = 2.88 ft/s (double the flow, double the speed)
16GPM = 4.61 ft/s
18GPM = 5.19 (you are now in violation of the speed limit).

If you've got to have more than 16GPM and you're going to use CL200 pipe, then you should use 1.25" pipe (that can safely handle upto about 25GPM).

BTW, if you converted to Sch40, due to extra pipe-wall thickness, your maximum GPM for a 1" pipe drops to 12GPM. with 22GPM being the max for 1.25" pipe.

There's a lot of energy in moving water. When a valve suddenly closes, that energy has to go somewhre

7. ### lugnut#6LawnSite Senior Memberfrom Ocean Springs,Mississippi.Messages: 404

ok,at the head i need 30 psi.correct?
a velocity of 5 fps and 17 gpm in 1" is optimal.correct?
if i go down in lateral size it will increase the psi and fps but reduce the gpm.correct?

i have 13 heads and a 18-19 gpm need.should i go up in diameter?
if i go to 1 1/4 cl200 and get 27gpm at 5fps what psi will i need?
at what pressure will i get a velocity of 5 fps and 17gpm thru 1"CL200? 30?

now im getting the 55-60PSI info from a city engineer who was working down the street on the city lines.he said the homes in this area have a psi of between 55-60 at the meter

i can increase the length of the 1" lateral by connecting closer to the home.
as it is now im connecting to an existing section of the previous system that is 30yrs old and has iron or galv 1 1/2 pipe.
before it was tore up the system ran 23 pop ups per zone on 1/2 laterals.....

on 1 zone i plugged the existing pop ups and put a 5000 rotor on 4 corners and 2 on the other side of a walkway leading to the home with 3.0 nozzles.that makes 6 rotors and 5 pop ups on 1 zone.and amazingly it works.and its strong.
on paper though...it shouldn't work.correct?

(yes i know not to have rotors and pop ups on the same zone....the explanation is long....childhood friend of the wife....home destroyed....overpaid for this home....which was also flooded and had to be gutted....not enough insurance....no money left...yadda,yadda,yadda)

well after 2 weeks of re-tapping,plugging and removing corroded nipples,pipe,fittings,etc....ive givin up on repairing it.ive got a fairly good section of the old mainline dug up and im gonna cut and connect to it and leave the old system buried and disconnected.there are 5 zones and they stub up thru the foundation in her garage.no timer or valves as of yet.just manual faucet knobs.1 zone was un damaged.1 zone i jerry-rigged.2 zones im replacing.and im replacing a couple pop ups on the other.all this as a favor to my wife.......shoot me....please.

8. ### lugnut#6LawnSite Senior Memberfrom Ocean Springs,Mississippi.Messages: 404

so the psi dose'nt effect the fps of the water flowing through the pipe?

i love math and im fairly good at it...im a Crap dealer..or was for 10yrs.

i just need someone to teach me.thank you for helping