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aerodan1

Unregistered

1

Monday, July 27th 2015, 1:05pm

flow rate

Hi,

I am working with an irrigation consultant on coming up with an irrigation design for my 1/2 acre yard and still am a little confused on the whole issue of flow rate. Stats:

- Municipal water supply
- 67 static psi
- 5/8" meter
- 3/4" galvanized/copper service line before/after meter
- According to town when I just called, there is 42' of iron cement-lined pipe running from street to slab, so I'm guessing the galvanized pipe starts around where it hits the slab based on the length of the pipe
- Will be running 1" poly pipe for mains and laterals

We both came to the same conclusion that 10 - 11 gpm would be appropriate (before I found out about the 1" from the street), although I'm still not sure whether this sounds right. We both assumed 3/4" pipe service line from the road but he said his calculation was based off 5 ft./second velocity for the 1" poly to be run for the sprinkler system. I based my calc. off max. 7 - 7.5 ft./second based on 3/4" steel/copper service line to the house (using table from rainbird and also the irrigation tutorials website).

I know professional judgment may enter the equation here as far as appropriate safe max. flow velocities and this consultant appears to be very knowledgable and competent based on a meeting we had to go over the plan. Any thoughts would be helpful, thanks.

Dan

Wet_Boots

Supreme Member

Posts: 5,287

Location: Metro NYC

2

Monday, July 27th 2015, 1:43pm

the 5/8 meter might introduce a practical limit on its own - the wisest move is to make the connection to feed the sprinkler system, and only then perform flow-and-pressure testing, creating a chart for the supply.

aerodan1

Unregistered

3

Monday, July 27th 2015, 3:18pm

If I use the 3 rule test for determining safe flow, rule one (10% max. psi loss through meter) for a 5/8" meter limits the gpm to 13, and the limit is 15 gpm for rule 2 (75% of max. safe flow, which is 20 gpm), so if the new irrigation meter is 5/8", those two rules I think would still apply, so perhaps it could raise the max gpm to 13? If we ignore the 3 rule test and look at the bucket/pressure loss test, would you be referring to the following test? Thanks

http://www.watertips.com/info/layout3.htm

aerodan1

Unregistered

4

Monday, July 27th 2015, 4:13pm

I'll add that the consultant mentioned there would probably be 10 - 11 zones needed to cover my 1/2 acre lot. I think the 10 or 11 gpm figure is conservative if anything, considering the bucket flow tests I conducted (and which I repeated several times on different days) yielded approx. 12 gpm, and that was water flowing from a 1/2" pipe for the outdoor hose bib. I just can't understand why there are so many opinions on different testing methods (e.g. bucket test, flow-pressure bucket test from existing pipe, simple chart, 3 rule test, flow-pressure bucket test after backflow preventer installed) and acceptable safe velocities (5 ft./sec, 7 ft./sec, 7.5 ft./sec., 9 or 10 ft./sec.). I know the safe velocities vary with pipe size and material but even among a single size/material there is no universally agreed upon amount.

Wet_Boots

Supreme Member

Posts: 5,287

Location: Metro NYC

5

Monday, July 27th 2015, 5:31pm

How about you just make the connection first. Then measure the flow and pressure. Then design the sprinkler system.

That way you don't get into trouble.

Also, the presence of galvanized steel pipe in the supply is a wild card you do best to take out of the picture, by not having to make assumptions about it

aerodan1

Unregistered

6

Tuesday, July 28th 2015, 2:47pm

Thanks for the feedback Wet Boots. That sounds logical to me, not sure why this approach isn't advocated across the board.

I'm not sure what you meant by the galvanized pipe being a wild card, could you please explain? Thanks

Dan

Wet_Boots

Supreme Member

Posts: 5,287

Location: Metro NYC

7

Tuesday, July 28th 2015, 4:42pm

galvanized steel pipe can accumulate a layer of rust on the inside, sometimes building up to the point of the pipe needing replacement - you can look up numbers on performance charts for all sorts of pipe materials, but heavy rust buildup in old steel pipe isn't on those charts (hence calling that sort of pipe a wild card)

aerodan1

Unregistered

8

Tuesday, July 28th 2015, 10:42pm

Got it, that makes sense, thank you for making me aware of this.

Dan

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