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New Member

Posts: 5

Location: Denver


Sunday, April 21st 2019, 11:10pm

Need some design help with irrigation valve box & freezing/drainage


I need a little help with my irrigation valve layout and drainage and
preventing freezing or at least reduce the need for sprinkler blow out, vs gravity drain. I'm located in the Denver area, with frost line

How should I lay out my two (17x23) control
boxes to prevent freezing to city water supply for house (green line,
about 33" below grade), well supply line to house (just above and
parallel to the green line and about the same elevation), and manage

#1-4 & D (in the photo) are maybe 14" below grade (D maybe 1" lower
than the others) and based on a water test, I think they go up slightly
as they head away from the pit area.

How do I handle drainage, if I'm trying to
avoid having to blow out sprinklers seasonally? Originally I thought D
would be a gravity drain to the spigots, but testing with water, I think
it must slope up a little first and so there is not natural escape for

In the photo I have:

A: City water supply for BFP

B: Downstream of BFP, where copper will drop to a threaded el

C: Well

D: Blue 1" Poly leading to three seasonal spigots, each with a drain
valve about 18" under ground... they are arranged so one end spigot is
at the highest point, and one end spigot isat the lowest point. This
area is between the first two spigots.

X: Ignore

1: One zone, 1" Poly

2: One zone, 1" Poly

3: One zone, 1" Poly

4: One zone, 1" Poly

5: One drip zone, 3/4" Poly

6: One new drip zone, 1" Poly

7: One new drip zone, 1" Poly

8: One new drip zone, 1" Poly


Supreme Member

Posts: 5,326

Location: Metro NYC


Monday, April 22nd 2019, 9:57am

"How do I handle drainage, if I'm trying to avoid having to blow out sprinklers seasonally?"

You don't. Just set up normal drainage in your supply, with the idea that an open drain in the winter can keep water from entering the breakable sprinkler plumbing.

Trying to set up gravity drainage is likely to cost more than an air compressor you'd use for winterizing.


New Member

Posts: 5

Location: Denver


Monday, April 22nd 2019, 8:13pm

Thanks Wet_Boots. I guess the key words you mentioned were 'breakable parts'. Yeah, the long-time prior owner said he had never blown out the system, and the valves are about 20 years old. So, I was just trying to see how this could be managed with similar success. I figured there was gravity drain to the spigots, but it seems not entirely so.

Can I ask you a couple questions about about what you posted here about manifolds?

- Do you use Schedule 40 slip fittings for the rest of the manifold?

- You've mentioned elsewere to use the machined version of the TOE, and I
noticed there is a molded version of the TOE... is the machined notably
stronger? I'm assuming that the molded TOE is smooth enough for

- For the manifold supply, which would likely be 160 or 200psi poly,
what style fitting do you use to join that to the manifold without
having a female fitting?

- For the 1" barb-to-MPT fittings from valve to poly, are brass or PVC
better? I also have a similar fitting underground (as well as a barbed



Quoted from "Wet_Boots"

The best pro-built manifolds are made from all-slip PVC fittings and
schedule 80 TOE nipples (TOE = threaded one end) - pros learn soon
enough about a female-threaded-side-outlet sch 40 tee being a problem
waiting to happen.

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