SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

Every backflow we install has a drain on it. Twin Cities' winters demand it.

There is a line of thinking that is sometimes reflected in codes, that a blowout valve upstream of a backflow preventer is a cross-connection opportunity. If that is the case in your locality, then you don't see the usual blowout valves in the optimum location at a low point where they can be left open during the winter. This is all relating to above ground backflow preventers fed from a supply pipe exiting the house foundation above grade.

Redundant....Yes, but makes blowing out the system easier. We typically install a "T" fitting below the PVB on the supply line that exits the foundation of the home. Supply line comes into the "T", PVB installed above the "T", and a 3/4" threaded plug on the third side of the "T". By removing the plug in the fall, all the water in the supply line inside the house drains out. Plus, this threaded portion of the "T" gives you your blow out point.

Quoted from "Central Irrigation"

Redundant....Yes, but makes blowing out the system easier. We typically install a "T" fitting below the PVB on the supply line that exits the foundation of the home. Supply line comes into the "T", PVB installed above the "T", and a 3/4" threaded plug on the third side of the "T". By removing the plug in the fall, all the water in the supply line inside the house drains out. Plus, this threaded portion of the "T" gives you your blow out point.

Yes, this will make blow-outs easier, but it does go against the instructions of every manufacturer of every backflow prevention assembly to not run pressurized air through the assembly.

Install a drain and shut-off inside the home before the assembly, install a hose-bibb after the assembly for hoses and fall blow out.

Or do it your way, I make a lot more money doing backflow assembly repairs in the spring when people turn on their irrigation systems after they have had someone blow through it in the fall. On second thought, disregard what I said about the drain installation.

Mick

I have seen far more freeze damage to a drained backflow than I have ever seen to one that has had air put through it. It is borderline impossible to completely drain a backflow of all water, after all, its designed to prevent water flowing back into the house. I do agree that the air puts added stress on the parts, but I believe it does a far superior job of preventing any damage to the backflow assembly, supply pipes, and ball valves. Just my two-cents.

Because of the opportunity of cross contamination, every municipality does (or should) forbit the instilation of a blowout connection before the backflow preventer. Doing so risks the possibility of pumping "stuff" (think compressor oils and the like) into the potable water source.

Drain valves I would suspect to be ok in most locations because it only allows draining the water, not the connection of a pump to push water back through the valve.

If freezing of remaining water in the backflow preventer is a concern, I would think you would set up the backflow preventer on unions (assuming local building codes allow) so that you can just plain remove the back flow preventer during the winter.