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  #1  
Old 08-29-2011, 11:13 PM
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Dirt Boy Dirt Boy is offline
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PVB question

Have an installation with an variable speed pump - capacity 25 gpm with an 1 1/2" Watts PVB.
Problem is that due to low/no back pressure at pump startup, PVB will due a short flush until valve seats. Hope that makes sense.
Is there a solution to this?

Thanks
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Old 08-29-2011, 11:22 PM
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Quote:
Originally Posted by Dirt Boy View Post
Have an installation with an variable speed pump - capacity 25 gpm with an 1 1/2" Watts PVB.
Problem is that due to low/no back pressure at pump startup, PVB will due a short flush until valve seats. Hope that makes sense.
Is there a solution to this?

Thanks
It's supposed to vent when there's low pressure.
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Old 08-30-2011, 08:37 AM
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Dirt Boy Dirt Boy is offline
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Yes, and it does exactly that.

But, is this normal for system to behave like this? I would have to surmise that I am losing the back pressure in the mainline. IOW's system is running, valve shuts off, all is OK, system sits for a period of time, controller tells it to start again, valve opens, system (main line) loses pressure ... i.e. starts to run, there is a small delay while the pressure tank pressure decays, VSP starts running, but that lag time, opens up the PVB, thus the "flush" action until pressure builds up and seals PVB.

It doesn't do this between stations, just at startup of new cycle, since the lag time is small.
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Old 08-30-2011, 08:49 AM
Kiril Kiril is offline
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You need a controller that has the option to delay valve opening. It typically is called a master valve/pump to zone delay or something similar. Many modern controllers have this capability, but some hide the feature.
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Old 08-30-2011, 09:27 AM
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Dirt Boy Dirt Boy is offline
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OK, so the valve delays opening, I guess I don't see that making any difference. The system does not have a pump relay switch. It's one of these VSP (not sure if thats the correct term) electronic units that are common now adays.
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Old 08-30-2011, 09:40 AM
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I think your talking about a constant pressure switch. It dosnt wait for pressure to drop before turning on but instead works off a flo senser.
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Old 08-30-2011, 09:48 AM
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Is there a pressure tank in the supply?
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Old 08-30-2011, 09:48 AM
Kiril Kiril is offline
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Originally Posted by Dirt Boy View Post
OK, so the valve delays opening, I guess I don't see that making any difference. The system does not have a pump relay switch. It's one of these VSP (not sure if thats the correct term) electronic units that are common now adays.
As long as you can introduce a delay between the pump start and your first zone valve opening it should help. If that requires adding a master valve, then that is what you should do.
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Old 08-30-2011, 10:20 AM
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or swap the pvb to a dcva and call it done.
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Old 08-30-2011, 10:25 AM
Kiril Kiril is offline
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or swap the pvb to a dcva and call it done.
If you are going to recommend replacing the backflow, then at least recommend one that is actually rated for high hazard backflow protection please ..... and in that case .... it won't solve the problem.
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