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Senior Member


Thursday, June 22nd 2017, 7:44pm

PVC vs Poly (Under concrete walkaway/frost)

As I continue building my irrigation system (I now have 5 zones covering 15,000 sq ft:)), I have a situation where in my front lawn, I have to dig a tunnel underneath our front walkaway path that leads to our main front door. It's a 3 feet wide path, about 3 inches of concrete on top of it is a 1 inch tick masonry stone (just for visual looks). Below the 3 inch concrete, is about a foot of rocks as well as filler marble (medium size). I actually digged this tunnel today (did take me 3 hours).

Why I am posting here is, after installing three 1" poly pipes (100 psi), I started to worry about whether poly is a good idea in that section due to the weight of the concrete or any situation I am not fully understanding.

My entire system is made off of 1" poly tube (100 psi). The only exception to this will be the 1" copper pipe running from my water meter to the front and back yards as well as the area where the shutoff valves and backflow preventers for each zone is installed. So past the shut off valves, everything is 1" poly tube. I understand its a bit overkill, but I wanted to play safe, but the main reason is frost. We do get frost here a lot (at least 3-4 months of the year is around 32F and sometimes we have extreme weather such as -10F) and I simply couldnt bring myself to install PVC.

The question I have is, should I be using PVC for this 3 feet long tunnel and then just connect to poly again on each side as soon as I exit the tunnel? The concern with PVC is it will crack in freezing temperatures (the tunnel is about 1.5-2ft below ground) and I dont want to dig that tunnel one more time. The counter argument is, poly is too flexible and it may crush and not hold up the pressure of the concrete above (or is this actually true? because the tunnel is carrying the weight of the concrete above not the tubes, but what do I know:)).

My static water pressure is 75-80 psi whereas dynamic water pressure is 50 psi. I have 11 GPM flow all around. When all said and done, I will have about 18 zones:)

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