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mark2457

New Member

Posts: 2

Location: Skokie, IL

1

Monday, May 2nd 2016, 5:18am

Pipe size reduction on laterals

Hi All

Was reading hunter's design guide and has a question about this diagram:

Is it necessary to reduce the pipe size as it passes heads? For example on the left branch, could I just stick with 2/4 inch all the way?


TIA

Mark

hi.todd

Supreme Member

Posts: 480

Location: Houston, Texas

2

Sunday, May 8th 2016, 1:21pm

First, I have to say this.
You mean 1/2"?

No

Yes, it is necessary to reduce pipe size as your GPM falls.

On the left side you could start with 3/4" until you get to 5 GPM. 1/2" pipe is usually used for 5 GPM and lower flow.

This is in an effort to control the velocity of water velocity through the pipe and friction loss issues.

Good Luck
:thumbup: :thumbsup:
LI0006121, BPAT0011021, CI0009500

Wet_Boots

Supreme Member

Posts: 5,136

Location: Metro NYC

3

Sunday, May 8th 2016, 5:09pm

Another reason for the gradual reduction in pipe sizes is to act as a brake on water rushing at high speed through a long run of air-filled pipe, to collide with destructive force at the final head in the line.

4

Sunday, May 8th 2016, 6:13pm

I think the design guide is trying to save you some money. It is best (low cost) to use the smallest pipe you can but the smallest size is determined by how much water flows through the pipe (measured in GPM), the pressure at the supply end and the required pressure at the end. Note that the first segment is carrying much more water, enough for four heads than the last segment which is carrying enough only for the last head. For most of us installing smaller systems the cost of the pipe is unimportant so we over size it and use 3/4 where 1/2 would do. We figure the effort to determine when we can downsize is not worth the $2 saved. But on larger systems the saving is worth it.

hi.todd

Supreme Member

Posts: 480

Location: Houston, Texas

5

Tuesday, May 10th 2016, 8:57pm

This is in an effort to control the velocity of water velocity through the pipe and friction loss issues.
:thumbup: :thumbsup:
LI0006121, BPAT0011021, CI0009500

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