System design question. - LawnSite.com™

GrazerZ · #1 11-25-2007, 06:36 PM

Here is the situation. I have a job that we were told that the service line was 1 1/4" but turns out to be 1" poly which changes everything. Heres why:
service line 1" poly 550' long from street.
5/8 meter
Delivery line 3/4"
3/4" dual check
static pressure is 45psi with regulator. belived to be 55 wide open.

Heres my question. I would like to run safely from 5-10 gpm.
I know that I can do about 4-5 but it would be marginal. The calculations I did tell me that at 12 gpm I would get a wooping 21 psi. How would you go on this one? its a 45 head system at aprox 30' spacing. I'm considering adding a pump to the system to insure its right but would like to avoid. I'm worried that either way I will be restricted because of the 550' poly service line. Any advice is welcome. This is a bit diferrent than what I've incountered so far. Thank you in advance.

Wet_Boots · #2 11-25-2007, 07:08 PM

Bypass the regulator. Cut the system into bite-size pieces. Use R-50's. (oops!)

Better yet, make a connection very near the street, somewhere in that supply line, and use a second meter for the system.

GrazerZ · #3 11-25-2007, 08:18 PM

I'm going to have the connection to the line made before the regulator. Another connection in the service line is not an option. My issue is with the dynamic pressure.

Wet_Boots · #4 11-25-2007, 08:29 PM

With a 550' service line, the question arises about how large a property is this, and whether there is enough flow to cover the property.

GrazerZ · #5 11-25-2007, 08:48 PM

I think thats valid. I do belive I will be ok. The property in relatively shaded with good water retaining soil. We also need less water here in Maine as a rule as well. 1" a week is good for most turf. I plained on reducing the gpm usage for each zone so that the 1" will be ok. heres what I came up with from a design calculator:

Pressure at point of connection: 55 psi
Dynamic pressure at point of connection: 26.2 psi
Design capacity at point of connection: 12.3gpm
Estimated pressure available for sprinkler opperation: 21psi

what do you think? What would you do?
Would you use only lets say 5gpm to conserve pressure? Or would you go straight to a booster pump as I'm inclined to do? I've been looking at these pressure mate set ups, just for the irrigation system.

Wet_Boots · #6 11-25-2007, 11:49 PM

A booster pump will have a good chance of creating negative pressure in the supply line, or the house, if you aren't boosting the entire home's pressure. That would take you part of the way to a 'backflow event' ~ A poly line is not designed for vacuum service. Don't use any 'set-up' if you go booster. A one-third horsepower jet pump is probably the safest fit for a dinky water supply. Even if you have to pay more for the 1/3 HP, in comparison to a 1/2 HP, while getting less of a boost, you don't want a pump that can pull more than the water supply can push.

GrazerZ · #7 11-26-2007, 09:17 PM

Thanks wet boots for the replys. Would love to hear from someone else as well though. I have a appointment with a plumber on wensday to crank out the pressure regulator and then spec out for the backflow and stub out. Guess we will see what happens.