You are not logged in.

1

Friday, July 3rd 2015, 3:33pm

PBV leaking when zone starts up

I believe I have a Wilkins 720a backflow valve and it has sporadic issue. Quite often, when it turn on a zone, water will cascade from under the plastic bell housing cover. Sometimes it will stop on it's own, other times I have to turn the zone back off and it will recover. Then I start the zone again and it will most likely work as expected.
I am wondering if I need to adjust the size of the pipe? I have a 1.25" feed off my well, then it jumps to 1.5" to pass through my house wall to the backflow valve and continuing with 1.5" to the valve manifolds where it drops to 1". The reason it makes the jump from 1.25" to 1.5" is because I was re-using an existing hole in my house wall. Probably not the best idea, but it seemed like the right decision at the time.
Thanks for any advice.
-Joel

Wet_Boots

Supreme Member

Posts: 5,245

Location: Metro NYC

2

Friday, July 3rd 2015, 7:26pm

You may need to program a delay between zones, so that the pressure can build back up before the next zone activates. The 720A is reacting to the drop in pressure.

3

Saturday, July 4th 2015, 6:24am

I am not describing what happens when I am switching between zones, this happens when nothing has been used for a couple of days or more. I thought might be related to a pressure drop, but given the time that it happens I don't know what I could to prevent it?

Wet_Boots

Supreme Member

Posts: 5,245

Location: Metro NYC

4

Saturday, July 4th 2015, 7:09am

It's incumbent upon you to not let the water supply pressure drop to the point where the PVB will dump. Start by adjusting the pressure switch. What is its current range?

5

Saturday, July 4th 2015, 7:28am

I have a continuous pressure setup on my well. The pressure would be 60 PSI when the zone valve opens. I don't know what it drops to. Is that the pressure switch you are referencing?

Wet_Boots

Supreme Member

Posts: 5,245

Location: Metro NYC

6

Saturday, July 4th 2015, 9:10am

You probably want 40 psi minimum at all times in the water supply. The design of the 720A gives it a higher vents-water pressure than many other PVBs, but the same design allows it to recover and seal back tight better than other PVBs.

7

Thursday, July 9th 2015, 7:24am

Is there a device that I can install down stream of the PVB that would ensure that it never drops below 40? My assumption is that when the zone valve opens, the pipe beyond is empty enough to drop the pressure below that.
Thanks for the responses.

Wet_Boots

Supreme Member

Posts: 5,245

Location: Metro NYC

8

Thursday, July 9th 2015, 7:47am

How large is your pressure tank? You may have an undersized one. The constant-pressure devices tout their ability to protect a well pump without needing a large tank, but your sprinkler system doesn't care about the ad copy. It needs a good-sized surge of water to fill a zone and bring it up to pressure, and that surge will come from the pressure tank.

What are your pressure switch settings? If you don't have a pressure switch, just what do you have? Make and model. Photo of your set-up. Some anti-cycling devices (and it is the prevention of pump cycling that these devices are about) might have a running-water pressure regulation of 60 psi, but they still allow a small flow that will charge a pressure tank higher than 60 psi.

As an alternative to increasing pressure tank volume, you could replace or modify every last sprinkler head so that they have check valves in them, and by doing so, retaining as much water as possible in the sprinkler zone plumbing.

9

Wednesday, January 20th 2016, 10:44am

Time to start thinking about this again. Re-reading your last post, I have the standard Grundfos 2 gallon tank connected to my well manifold. If I understand your statement on drawing water, are you saying that I can install say a 20 gallon pressure tank on the feed line to the irrigation system? Would that tank need to be before the PBV or after it? If it before, would a check valve be necessary to keep my house from drawing from this additional tank?

Wet_Boots

Supreme Member

Posts: 5,245

Location: Metro NYC

10

Thursday, January 21st 2016, 11:29am

Upstream of the PVB you need a pressure tank large enough to surge out enough water to fill a zone. I expect 20 gallons is way too small. Remember that only a portion of the tank contents actually flows out during the time a pressure switch controlling a pump has the pump power off.

It may be that you have a constant pressure setup that is not really compatible with a sprinkler system, and that more than a pressure tank is required to make everything work. But you do need a pressure tank to effectively run that system in any event, so you might as well begin with that item. I would recommend as a very minimum a 40 gallon tank, with the idea that you are sizing the tank to work in a conventional pressure-switch-controlled arrangement. (with the idea that the tank can feed all water needs all by itself for at least a minute or two)

Rate this thread