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

is it 1 inch coming into you back flow? It wont hurt to use 1".

Three quarters. Backflow capacities are way beyond those of the pipe sizes they possess, just like water meters.

About as much as it would hurt to use inch-and-a-half. Understand that many backflow preventers of the 3/4" and 1" sizes are actually identical castings, only differing by the size of the pipe thread and valves on the unit.

I'd say use it in good health, but if you haven't figured that out by now, I would be politely inquiring whether you actually know whether this gift backflow preventer is of a type that is actually approved for use in your state/town/whatever ~ A Febco 850 is a Double Check Valve Assembly, and those are not toxic-rated, and are therefore unusable where protection from possible toxic backflow is required. Learn what the plumbing codes/laws are where you live, then make your decision.

Based on what I've learned at www.irrigationtutorials.com, the only thing to consider between a 1" v. 3/4" backflow is pressure losses. Each backflow will have a different pressure loss graph (pressure loss v. flow rate). These graphs are NOT strait line graphs. They actually are very curvy, and frequently have a "sweet" spot where they lose the least amount of pressure. If the flow rate is higher or lower than the "sweet" spot, there will be a greater pressure loss. Now sometimes these pressure losses don't amount to much of anything, and if you've got pressure to spare, then you don't care. If you are borderline in having enough pressure to work with, then you'd want to review these pressure charts. Most manufaturers have them availible on their web sites. Well, I assume they do. When I was looking into WATT back flows, I had no problem finding them, and I THINK I even found Febco at one time too.

I'd have to agree with Wet Boots on this one. Sure would hate for you to install the backflow and then come home and your water was off because it's not the right one for your municipality. Heck, here in Columbus there are at least six different variations on code and enforcement, all based on the municipal code.

Should you decide to go with it, another option is to use 3/4 into the bottom of the backflow and then use a 3/4 sweat x 1" MIPT copper adapter as your transition to 1" on the inlet side, then 1" out.