Sizing Backflow Preventers and Valves

[slimart01]

Do any of you use the next size down (from your mainline or lateral) on your backflow preventer or valves? It seems like I have seen this done more then once. Is it a standard procedure to go from 1" mainline to 3/4" for a 3/4" backflow assembly and then back to 1" for the system?

[Lite Headed]

Nope. Why would you restrict the flow and add pressure losses by reducing the size? You can overcome too much pressure if need be.

[Wet_Boots]

There is some logic behind the occasional downsizing you will see. Zone valves are sized more for reliable operation than anything else. For example, a Buckner catalog from way back when pointed out the use of 3/4-inch zone valves on systems that were otherwise one-inch.

Also, backflow preventers are rated to handle flows equivalent to the same size water meter. I have no problem seeing a one-inch Wilkins PVB on a 1-1/2 inch line running 40+ gpm.

Many product lines used identical castings for both 3/4 and 1 inch RPZs, so no big deal if you saw a 3/4-inch RPZ on a one-inch line. RPZs have the additional concern of water-hammer-caused relief-valve venting, so don't be pushing the envelope with them.

[M L Thomas]

Before you do any downsizing learn how to calculate available water and pressure loss from your water source (water main, pond, river, etc. to your sprinklers). And do it on EVERY job to determine what size pipe, valves & BF you need. At some point this will save you money. Trust me, I see too many systems where a contractor "designed the system just like the last one he installed" but failed to notice the longer run from the water main to the POC or some other restriction that caused pressure drop so severe the system is not capable of keeping the plants watered and alive.

Contractors that never learn how to calculate available flow and pressure drop make good contractors lotsa money, providing the customer is smart enough to make sure they don't get screwed a 2nd time.

Having said all that, around my area most everything residential and small commercial is all 1" except some guys save $5 and buy a 3/4" backflow device.

[AI Inc]

I always hated 3/4 pvb,s . My fingers dont fit inside to pull out busted guts.

[Wet_Boots]

I always hated 3/4 pvb,s . My fingers dont fit inside to pull out busted guts.Wilkins 720 series, dude. Same central casting for 3/4 and one inch models.

[Mike Leary]

Every man jack should have, at least, one of these:


www.betterwaterind.com/flowmeter.html

[Wet_Boots]

If you absolutely need a flowmeter to make a sprinkler system work, you are living in Pikerville.

[Mike Leary]

If you absolutely need a flowmeter to make a sprinkler system work, you are living in Pikerville.

Sezz you. Sure has been handy to check after the backflow goes in to make sure the calculation for the design was close. The newer DCVA top loaders with the dweeb small checks have a higher psi loss than the "Y" patterns.

[M L Thomas]

We made one of those or something like it once to measure the output and available water in a drilled well. We measured flow with stopwatch and bucket and use pressure gauge and a gate valve to determine when we were dropping the well.

[Wet_Boots]

Sezz you. Sure has been handy to check after the backflow goes in to make sure the calculation for the design was close. The newer DCVA top loaders with the dweeb small checks have a higher psi loss than the "Y" patterns.They'll always be handy. Not absolutely vital, so long as you have a wristwatch and a water meter. But definitely handy.

[Mike Leary]

They'll always be handy. Not absolutely vital, so long as you have a wristwatch and a water meter. But definitely handy.

Yup, those do-dads are not expensive and could sure save Jr. the embarrassment of the heads not coming up during the walk-through.