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The last 7 posts

Monday, April 30th 2012, 12:52pm

by Wet_Boots

In a zone, downstream of a valve, with nothing but heads to consider, excess water velocity only matters as a reason for pressure loss. That is our OP's situation, and his concern is misplaced. Damaging water velocity, where it can actually cause physical wear, is at levels far greater than what we can create in a lawn sprinkler system.

7.5 fps is a number that appears on most backflow preventer pressure loss charts. Remember that these devices are rated for flows way beyond actual usage.

For best behavior of zone valves and especially RPZs, slower water velocity is better. Designing with 5 fps or less upstream of zone valves makes good sense.

Monday, April 30th 2012, 10:25am

by GatorGuy

Wet-Boots,
5 fps is considered max for PVC in most designs.
Hunters, Rain Bird, etc will design to that max.
Allows for safety factor.
In the licensing test the state of Texas will fail your design if you exceed that limit.
Galvanized is another matter.

Sunday, April 29th 2012, 7:15pm

by seansy59

Valves for 70-75 psi? Hunter PGV with flow control. They are rated for 150 psi and has flow control to limit flow to each zone. I just ordered 6 of these (flow control was not needed for me)

Hunter PGV with flow Control

Sunday, April 29th 2012, 5:44pm

by Central Irrigation

After giving it some thought, a pressure regulator would decrease your flow by a 1 or 2 gpm. I'm still not sure if your concern is with fogging heads or excessive velocities.

Sunday, April 29th 2012, 5:14pm

by Wet_Boots

Since when is 6 feet per second too high a water velocity?

Sunday, April 29th 2012, 5:00pm

by Central Irrigation

The Toro P-220 or the Hunter Pressure Regulator in combination with a Hunter PGV valve would work. You could also consider installing an adjustable pressure regulator before the backflow at a lower cost, you would lose any adjustability per zone, however.

Click the valve name for the link.
Take the readings you get at the backflow and subtract 5 psi. This will take into acct. the valves pressure loss and any loss from pipe friction. Taking the reading at the head would give you your most accurate readings, though, but this is difficult to do. Most Tech's would calculate pressure losses based on flow and zone layout.
15 gpm through 1" PE pipe is not the end of the world, though. It's 1 gpm higher than what is recommended velocity. If you're concerned with velocities, limit your flow. What I don't know is if a pressure regulator would do that for you.

Sunday, April 29th 2012, 3:16pm

by mrweiss52

Hunter control valve for high pressure application?

I live in Elk River, MN. My turf irrigation system is 13 years old. The system consists of a Hunter SRC 9-zone control, Irritrol 2500T 1" valves, Hunter PGP-ADJ rotors, and Hunter PSU04 sprays with adjustable nozzles. The water is supplied via municipal water service (with a static pressure of 70-75 psi) thru 1" type k soft copper service from the street through a 1" water meter and 1" type M hard copper distribution. The 1" branch for the irrigation system is the first takeoff after the water meter which flows through a 1" pressure vacuum breaker and into 1-1/4" polyethylene. I live on a cul de sac so our yard is pie shaped (very narrow front yard and very wide back yard), so the valves are located in individual boxes around the yard instead of having a valve manifold. The branches from the 1-1/4" poly to the valves and then to sprinkler heads are all 1" poly. I know that the irrigation contractor did NOT do a pressure / flow test prior to the installation, and probably used the "rule of thumb" method that most contractors use around here - 5 (but no more than 6) rotors per zone. Awhile back I did do a pressure / flow test and found that at 50 psi I can get over 15 gpm, but the velocity is over 6 feet per second which is too high! When I put a pressure gauge on the system after the pressure vacuum breaker the pressure is between 55 and 60 psi depending on which zone is running. The addition of some hard landscaping is forcing me to add / alter some zones. While I'm doing the preceding I'm thinking that I might replace all the valves. Does anybody have a recommendation for a Hunter (or other manufacturer) valve that will allow me to reduce the pressure at the sprinkler heads to acceptable levels? And where is the correct spot to measure the pressure? At the vacuum breaker, at the valve, or at the sprinker head? Thank you!