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aerodan1

Active Member

1

Sunday, August 16th 2015, 10:06pm

Friction loss calculation

Hi, I wanted to run my friction loss calc. for the upcoming irrigation system I'm putting in by the members of this forum. Any feedback would be greatly appreciated, thanks! My static pressure is very consistent at 67-68 psi (will use 67 to figure design operating pressure).

The first question relates to the friction loss in the service line running from city main to the water meter, since I couldn't find friction loss tables for this pipe. It is a 1" cement-lined black iron pipe (ductile iron). To be conservative I'll use the losses for the 3/4" (since the cement lining is perhaps 1/8" thick, which would reduce the inside diameter by 1/4") schedule 80 (as opposed to sch. 40) steel pipe. Zones are designed for 10-11 gpm flow, so I've used 11 gpm for all calculations.

Water main to POC
Corporation stop and curb stop (total 16 equiv. ft.): 1.3 psi
approx. 55 feet ductile iron pipe from water main to meter: 4.5 psi
2 90 degree elbows (6 equiv. ft.): 0.5 psi
6 foot (best guess, I live in Mass.) elevation from water main to ground: 2.6 psi

From POC to PVB
3/4" water meter: 1.9 psi
10 ft. 1" Type L copper: 0.4 psi
elbows, tees, etc.: 3 psi
Febco 765-1 PVB: 4 psi

From PVB to zones
Master valve (ICV-101G): 3 psi
Each zone valve (ICV-101G): 3 psi
Each head funny pipe / swing assembly: 1 psi

Base friction loss: 25.2 psi
Base operating pressure: 41.8 psi

I'll be using 1" SIDR 19 or 15, 4710 poly pipe for the mains and laterals; psi loss is 3.24 psi per 100 ft for 3408 PE pipe, not sure if the psi loss is different for the 4710, per charterplastics.com:

"Charter PE4710 NSF Irrigation pipe is made from high performance PE 4710 resins. It is made to the same dimensions as the PE 3408 pipe, but offers higher pressure ratings".

Front yard zones 1 and 2, which would be about 60 - 90 ft. of pipe, for loss of 2 - 3 psi, figure about 39-40 psi working pressure; plan is for rotor zones with radii at 25-32 feet, either PGPs, MPR 3000 or Rainbird 3500.

Left side yard zones 3 and 4, which would be about 70 - 140 ft. of pipe, for loss of about 2 - 4.5 psi, figure about 37 - 40 psi; plan is for spray zones with radii at 15 - 18 feet, probably Rainbird 1800 SAM PRS - my understanding is these heads regulate pressure to 30 psi, so these zones appear fine.

Back yard zones 5, 6 and 7, which would be about 165, 240 and 300 ft. of pipe to farthest heads, about loss of 5 - 10 psi, figure about 36, 34 and 32 psi for these zones; plan is for rotors, generally 30 - 32 ft. radii, again either PGPs, MPR 3000/3500 or Rainbird 3500 / 5000. The concern is whether I really have enough pressure to operate rotors for each of these zones. I could probably knock down the distance (currently 300 ft.) to the farthest head on zone 7 at least a little bit.

Right yard zone 8, which would be about 240 feet to farthest head at most, about loss of 8 psi, figure about 34 psi; plan is for rotors / rotators, radii about 26 - 30 ft., either PGPs, MPRs or Rainbird.

Right side front yard zones 9 and 10, which would be about 270 - 300 ft, about loss of 9 - 10 psi, figure about 32 - 33 psi; plan is for sprays, radii about 15 - 24 ft, Rainbird 1800 SAM PRS spray. I may not need much pressure regulation for these zones but am ok spending a few extra dollars for the PRS - it doesn't appear there is a minimum pressure differential needed for the heads to function properly, I could be wrong though.

A special consideration for zones 8, 9 and 10 is that it looks like the property line is about 7 feet in from the next door fence (I maintain the lawn up to this fence), so I need to water up to the fence but don't want to place any laterals on the neighbors property, so I figured a 7 foot run of funny pipe for the heads on this edge of the lawn would be the best solution. It looks like the the inside diameter of funny pipe runs about 1/2", but looking at this thread it doesn't appear that any additional pressure loss would be a big deal. http://www.lawnsite.com/showthread.php?t=37618

Thanks again for anyone willing to read through my long winded post,

Dan

This post has been edited 4 times, last edit by "aerodan1" (Aug 16th 2015, 10:23pm)


Wet_Boots

Supreme Member

Posts: 5,222

Location: Metro NYC

2

Monday, August 17th 2015, 5:48am

You should make your supply connection and plumb it to the outdoors, and then do a "bucket test" to confirm your flow-and-pressure estimate.

aerodan1

Active Member

3

Monday, August 17th 2015, 2:47pm

Thanks for the response. I don't currently have the PVB installed and was trying to see whether the calculation appeared correct / reasonable in the meantime so I can keep moving ahead while waiting for the plumber / permits.

I do like the idea I saw on another thread to make a test manifold that would just have the master valve, a zone valve and a couple of heads attached, with a hose bib on the end to measure the working pressure with the heads flowing to the desired gpm for the planned zones (e.g. 11 gpm).

Instead of a test manifold noted above, would it get me to basically the same place (not counting the additional pressure loss in the master / zone valves in the above test manifold) if I did the bucket test using my desired flow rate of 11 gpm and then measured pressure at another bib to get my "base" operating pressure at that point in the system? I know there are special pressure - flow gauges (e.g. by Toro) that exist to help calculate the working pressure and flow, not sure if they still make 'em and if it's even needed in this case, since I have other bibs to grab the pressure off of. Thanks

Wet_Boots

Supreme Member

Posts: 5,222

Location: Metro NYC

4

Tuesday, August 18th 2015, 5:27am

As long as your wide-open supply connection is brought outside, you can do a proper test of flow combined with pressure. The idea here is that you have a pressure gauge on the discharge, with a valve you can partially close downstream of the gauge. Those two items make up the heart of a flow-and-pressure tester. Run flow tests at various pressure gauge readings, and chart the results. You can determine flow by filling a pail while timing it with a watch, or you can read from the water meter instead.

aerodan1

Active Member

5

Tuesday, August 18th 2015, 10:44pm

Thank you for the follow up, much appreciated. When the PVB is installed, I will have a boiler drain valve upstream of the PVB and a hose bib downstream of the PVB - would I be correct to assume the pressure gauge should go on the boiler drain and the bucket under the outside hose bib for the bucket test? I also have two existing outdoor hose bibs but those are running off the domestic meter (I'm having a separate irrigation meter put in).

For the PVB install, although I'm running 1" copper Type L with a 1" PVB and 3/4" meter, some of the fittings (i.e. shut-off valves, nipples, boiler drain) are 3/4" in size; should I consider upsizing so that all of the fittings and couplings are 1" to avoid additional friction loss? I would think this wouldn't make much of a difference but not sure. I included the parts list the plumber gave me, already have all parts on hand. Three of the shutoff ball valves (the 1/2" sweat, 3/4" sweat and maybe one of the 3/4" threaded would be for the existing domestic supply I think). Thank you again

(1) 3/4" water meter tailpiece w/ washer
(2) Watts 8D threaded vacuum breaker
(1) 3/4" brass IPS tee
(1) 3/4" x 3" brass nipple
(2) 3/4" x close brass nipples
(2) 3/4" threaded ball valves
(1) 3/4" sweat ball valve
(1) 1" sweat ball valve
(1) 1" C x 3/4" F 90°
(1) 3/4" C x F 90°
(1) 1" x 10' C tubing "L"
(6) 1" C 90°
(2) 1" C street 90°
(2) 1" C x Male adapters
(1) 1" C x Female adapter
(2) 1" C x 1/2" Female tee
(1) 1" x 1/2" C tee
(2) 1/2" ball valve boiler drains
(1) 1/2 sweat ball valve with drain nut
(2) 1" C split ring hangers
(2) 3/8" C hanger plates
As long as your wide-open supply connection is brought outside, you can do a proper test of flow combined with pressure. The idea here is that you have a pressure gauge on the discharge, with a valve you can partially close downstream of the gauge. Those two items make up the heart of a flow-and-pressure tester. Run flow tests at various pressure gauge readings, and chart the results. You can determine flow by filling a pail while timing it with a watch, or you can read from the water meter instead.

Wet_Boots

Supreme Member

Posts: 5,222

Location: Metro NYC

6

Wednesday, August 19th 2015, 8:43am



A simplified diagram of a bucket test. In your case, the hose bib labeled "first tap" is replaced by the plumbing you bring out from the basement.

By the way, your list of parts should be amended to include a gate valve for the outside sprinkler plumbing. It will be right next to the outside wall, and shuts off everything downstream. Very useful for maintenance and service.

aerodan1

Active Member

7

Wednesday, August 19th 2015, 4:16pm

That's a neat setup, I hadn't thought of that configuration. Hadn't thought of the additional outdoor gate valve for convenience when servicing the system. I would already have ball valves on the inlet / outlet of the PVB but I assume the gate valve would be better to more slowly turn the water on and prevent unnecessary extra wear and tear on the PVB valves. Thanks

Dan

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