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New Member

Posts: 3

Location: No. Virginia


Friday, August 5th 2011, 3:04pm

Designing a system in a frost area

Just found this site after looking through TOH & youtube . . . excuse me for being research tired, but have some questions.

In N. Virginia/Wash DC area with 3 months of freezing temp nights. Front landscape is browning out from semi-dought conditions in the summer so need irrigation (spouse is the current irrigation and she's irritated by all of this).

Topography is difficult: on a down slope, and also sloped on 2 sides for slopes on all 4 sides. Our trees and plants/shrubs are in several areas. I would like general comments on my "design":

(1) My main municipal supply pipe is not easily accessible. Thus, I intend to tap irrigation water from a hose bib (and in the back, tap from an inside copper pipe). My house cutoff is in the basement, and the main pipe looks over 1 feet buried in my front soil.

What are the parts to connect from a hose bib to a valve manifold ? use 3/4" polypipe w/ brass MHT (if available) ? OR use a 3/4" sprinkler hose, and attach to valve manifold with barb 3/4" adaptor w/ 3/4" MPT ?

(2) It looks like I need to use Polypipe (not PVC) for zone and lateral, plus drains at low points and at the sprinkler barb because I have severe enough winters.

(3) Valve manifold -- one valve will be for 2 sprinkler heads watering 2 lawn areas of 20x10 (I am thinking a nozzle for 9x18 square) -- another valve for 2 of the same sprinkler nozzles on the other side to provide head-to-head coverage (it seem best to keep head-to-head on 2 different zones so they don't throw water at each other at the same time).

A separate drip value (w/ a 30 constant pressure inline device) to provide drip irrigation - I have about 15 plants/shrubs -- would one zone and several emitters (each 4-6 bibs) be OK, or do I need to have 2 zones to serve 15 plants/shrubs ?

The valves will be in a value box on a low side of a slope while the lawn/plants/shrubs are about 5 feet higher on the slope.

(4) Is it necessary to use funny pipe to connect to the barb fitting to a sprinkler on a polypipe lateral -- maybe a swing arm instead. It seems unnecesary to use a 3rd type of pipe (3/4" poly for main, 1/2" poly for lateral and 1/2" funny).

(5) How should a 3/4" poly distribution pipe be terminated ? should I use an el that reduces 3/4" to 1/2" and lateral it to a sprinkler head or an drip emitter ??

(6) What is the proper winterization . . . can I rely on drains only ?

(7) How deep to trench ? I intend to use 4" popup sprinklers (9x18 square nozzle) and drip emitters that can be above ground any height. Do I need to go below 6 inches or deeper to get below the frost line ?

Thank you.


Advanced Member

Posts: 67

Location: South Jersey


Saturday, August 13th 2011, 10:17am

Wow, lots of questions here. I'm not a pro but will only give you suggestions to questions that I feel I can.

1) Not the best idea. You will suffer from a severe restriction in flow rate and thus pressure if you try to run heads off a hose bib. More importantly, you will need backflow prevention on both of those connections. You will spend more in BF protection devices for two water sources, than piping if you have one single source of water.

I forget what the terminology is for the thread on a garden hose. It is different than the thread on NPT pipe. You would need to adapt it. They do make them though.

2) Yes, poly pipe is probably the easiest for a beginner to use and manage. Drain valves are largley not recommended since they wind up eventually clogging and must be installed at the lowest point in the zone with a bed of crushed stone so they can drain.

4) No. But it's probably a lot easier. There is a company "Dawn" that makes a 3/4" poly to funny pipe tee fitting. I think they also make a 1" to funny pipe tee. These are what I used. They made life much easier and reduced the number of connections.

5) I don't know the exact answer to this one but I used a 3/4" barb to 3/4" FMT and then connected a 3/4" MPT to funny pipe barb to that for the ends of my lateral lines. At the time, I couldn't find a 3/4" barb to funny pipe fitting.

6) I wouldn't. I installed a drain port at the lowest point in my system. In my case this point was just after the shut off valve for the sprinkler system supply line in my basement. This allows me to open the bleeder on the inlet side of my PVB and drain the pipe down. On the outlet side of the PVB I can connect an air compressor to the bleeder and blow out the lines. You will always have some moisture inside the pipes but you don't want standing water. Standing water can freeze and easily break the pipe. If you don' want burst pipes you will need to blow it out.

7) I'm in NJ and I tried to stay at least 10"-12" below the surface. I would definitely recommend going deeper than 6". If not to help protect against freezing but to avoid you or someone else hitting the lines later on when putting up a tent, sticking an oscillating sprinkler in the ground or digging.


Advanced Member

Posts: 90

Location: Eastern WA


Saturday, August 13th 2011, 4:26pm

Have you seen by any chance? I would strongly recommend reading through it as it will answer most of your questions.
As ReddHead noted using hose bib is not generally advisable.
I will be starting my sprinkler system next week and I have supply line and water meter in the basement as well and that's where I'll be tapping in.
3. Why rectangular pattern? I think you will be better off with 6 spray heads (10' radius) or MP rotators.

6. Drains manual or automatic? If they installed correctly it should be fine?

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