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Dirt Boy
08-30-2011, 12:13 AM
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

Wet_Boots
08-30-2011, 12:22 AM
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?

ThanksIt's supposed to vent when there's low pressure.

Dirt Boy
08-30-2011, 09:37 AM
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.

Kiril
08-30-2011, 09:49 AM
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.

Dirt Boy
08-30-2011, 10:27 AM
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.

AI Inc
08-30-2011, 10:40 AM
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.

Wet_Boots
08-30-2011, 10:48 AM
Is there a pressure tank in the supply?

Kiril
08-30-2011, 10:48 AM
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.

AI Inc
08-30-2011, 11:20 AM
or swap the pvb to a dcva and call it done.

Kiril
08-30-2011, 11:25 AM
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.

AI Inc
08-30-2011, 11:27 AM
RPZ,s suck, thats why I didnt recomend it.

Dirt Boy
08-30-2011, 11:27 AM
The flo sensor would probably be the answer, at least according to my thinking.
Yes Boots, there is the "standard" what are they 1/2 - 1 gal tank.
Kiril, I fail to see how adding a master valve or delay in will do anything.
If the controller tells the zone valve to turn on, and it delays 1 sec. or 60 sec. the pressure in the system is going to be the same. Same think with a master valve. The VSP is not going to turn on until the pressure drops, and when the pressure drops, due to the small pressure tank, there is always going to be a "lag" of a second or three before the pressure builds back up in the line.
Perhaps I'm blind to your reasoning, but again, there is no pump start per se, IOW's the sprinkler controller is not kicking on a relay, the relay is being turned on by pressure drop at the very small pressure tank.
Hope that makes sense!
What there needs to be is a flo sensor to activate the pump relay, instead of relying on the pressure switch.

Wet_Boots
08-30-2011, 11:36 AM
If there is a pressure switch and a pressure tank of sufficient size, then the PVB should be staying closed. Of course you would have a master valve, so the tank and switch can function properly.

AI Inc
08-30-2011, 11:37 AM
He already said its not a pressure switch but a constant pressure flow senser if Im not mistaken.

AI Inc
08-30-2011, 11:41 AM
http://www.constantpressure.com/why-constant-pressure.aspx

Wet_Boots
08-30-2011, 11:45 AM
It might be cheaper to let it continue to burp water, than to mess around with it.

Wet_Boots
08-30-2011, 11:57 AM
If it's a constant pressure system, then it isn't doing a heck of a job. Maybe a bigger tank near the PVB would help.

Dirt Boy
08-30-2011, 12:14 PM
Correct AI,
And yes Boots, it really isn't hurting anything, homeowner just asked about it, and if it had to be that way.
Yes a bigger tank would help, but that ain't going to happen.

Kiril
08-30-2011, 12:16 PM
The flo sensor would probably be the answer, at least according to my thinking.
Yes Boots, there is the "standard" what are they 1/2 - 1 gal tank.
Kiril, I fail to see how adding a master valve or delay in will do anything.
If the controller tells the zone valve to turn on, and it delays 1 sec. or 60 sec. the pressure in the system is going to be the same. Same think with a master valve. The VSP is not going to turn on until the pressure drops, and when the pressure drops, due to the small pressure tank, there is always going to be a "lag" of a second or three before the pressure builds back up in the line.
Perhaps I'm blind to your reasoning, but again, there is no pump start per se, IOW's the sprinkler controller is not kicking on a relay, the relay is being turned on by pressure drop at the very small pressure tank.
Hope that makes sense!

A slow opening master valve may allow the system to lose enough pressure to kick the pump on but not cause the backflow to dump.

What there needs to be is a flo sensor to activate the pump relay, instead of relying on the pressure switch.

I thought you said there was no pump relay? :dizzy:

Wet_Boots
08-30-2011, 12:38 PM
some PVBs will not take to the continual re-pressurizing - the poppet washer will wear out prematurely

Kiril
08-30-2011, 12:56 PM
This is an issue of both pressure and time .... pressure drop downstream of the PVB and time required to fill the irrigation mains & laterals. Let's assume he is using a Febco PVB, which starts to dump when downstream pressure falls below 5 PSI (i.e. the air inlet poppet requires 5 PSI to seal properly) and will fully open at 1 PSI downstream pressure per specs. The goal here is to maintain downstream pressure above 5 PSI until the pump kicks in.

In addition to a slow opening master valve (or as a possible alternative), another way you could potentially do this is to maintain a "leak proof" system by first making sure you aren't getting any low head drainage (i.e. use sprinklers and drip lines with check valves). The more water/pressure you can keep in the irrigation mains and laterals between irrigation events, the less water/pressure and time it will require to bring the downstream lines back up to operating pressure and flow.

Wet_Boots
08-30-2011, 12:58 PM
this problem isn't solved until we nick the homeowner for an additional thousand dollars :)

Dirt Boy
08-30-2011, 01:06 PM
A slow opening master valve may allow the system to lose enough pressure to kick the pump on but not cause the backflow to dump.



I thought you said there was no pump relay? :dizzy:

Don't mean to confuse you, there is a pump relay, but it is not turned on by the sprinkler controller. It is turned on by the pressure switch at the very small pressure tank.
Thus, by the time that pressure switch "sees" low pressure and activates the pump, the main line pressure has dropped significantly and the PVB pops open.

Wet_Boots
08-30-2011, 01:13 PM
what are the pressure switch settings?

Dirt Boy
08-30-2011, 02:10 PM
Not sure, it just has settings you can choose 40, 50, etc. right now it's at 60

stebs
08-30-2011, 03:05 PM
What if you had a very small zone such as a small drip zone or just a couple heads as the first station in the lineup? Just enough to slowly bleed down the pressure and get the pump running, but big enough to keep the pump running.

Dirt Boy
08-30-2011, 03:43 PM
What if you had a very small zone such as a small drip zone or just a couple heads as the first station in the lineup? Just enough to slowly bleed down the pressure and get the pump running, but big enough to keep the pump running.

Thought of that, basically doing what Kiril suggest, just different way:laugh:

bcg
08-30-2011, 06:07 PM
You guys sure are devoting a lot of effort to fix a PVB that's working exactly as designed. As long as the PVB was installed correctly (somewhere that the dumping water isn't an issue), leave it alone. This reminds me of NASA spending millions of dollars to develop a pen that would work in zero gravity while the Russians chose to use a pencil. Sometimes the pencil is really the better solution.

FIMCO-MEISTER
08-30-2011, 06:28 PM
On a subject similar to this. How would a well on a pressure tank cause water hammers at startup and during zone changes? All the piping allows for 5fps. It cycles every 45 seconds if that means anything.

AI Inc
08-30-2011, 06:32 PM
Pete, if its cycling every 45 seconds , its not using enough water. Between the cycling and the water hammer I would guess that ya have bucu water and are not using all that much of it.

FIMCO-MEISTER
08-30-2011, 06:34 PM
Okay I'll post the whole scenario and see what you guys think. Not a well man. Think I mentioned that before.

FIMCO-MEISTER
08-30-2011, 06:38 PM
The original post
I had a customer tell me I was unprofessional because I could not gurantee getting rid of the water hammer in a existing system with a well pump. About 50 psi and roughly 10-12 gpm

Entire system was 3/4 schedule 40. Zones were exceeding 13 gpm. They did not want to spend the money for a new system. I removed 46' of 3/4 from the poc, installed 1" and 1"pvb. I renozzled the heads to get to 10 or less gpm, which increased his arc to get head to head coverage. It minimized the hammer. I then added 180' of 1" to get to the other side of the house and installed his existing valves for the already installed zone pipe and spray heads. I renozzled the sprays, a very small area and he didn't like the way water came out of the 5 half nozzles. He wanted more water in the area. Needless to say, he told me he was happy the hammer was nowhere near as bad as it was, however the wife sung a different tune the next day when I went to get paid.

My response
Looks like you got everything below 5fps. If nothing else a shock absorber at the washing machine connection might help a little more. Griswold valves claim to avoid water hammer issues. As a MV it might help. Is the hammer at startup or when zones change? I'd try to deal with the husband obviously.

OP response
at start and between zone changes. I also recommended switching valves as I know dv100 are fast closers. I was dealing with the husband until I went to the house to get paid, I gave him a time I'd be there and I passed him on my way to his house. I know who wears the pants in that house.

My response
I'm getting curious now. My troubleshooting gene is kicking in. Which controller are you dealing with? Is there any chance the pump is shutting down between zone changes? Is a pressure activated pump?

OP response
There is no relay for the timer. The timer the homeowner installed is Hunter x-core. The pump has a pressure tank which cycles according to the well tech. every 45 seconds. I did recommend installing a flow switch and pressure switch for the system to have continual even flow no matter if they were irrigating or using house water. The rid-o-rust tank is connected to a pump relay.

Then I came here

AI Inc
08-30-2011, 06:47 PM
weird, actualy a hunter closes a lot faster then a 100 dv.

bcg
08-30-2011, 06:48 PM
So the pump is short cycling every 45 seconds or so? If so, the first thing I'd do is install a Cycle Stop Valve to fix that problem. Odds are that fixing the short cycle will also help a great deal with the water hammer. Honestly though, with a pressure tank, it should be absorbing a lot of the hammer so it would be a good idea to also check the air pressure in the tank and recharge it if needed.

Wet_Boots
08-30-2011, 06:56 PM
echo the Texan - stop the cycling and check the pressure tank



...and don't piggyback on other threads - you piker

FIMCO-MEISTER
08-30-2011, 06:56 PM
I passed that on. THKS Always open to more though.

Mike Leary
08-30-2011, 07:17 PM
...and don't piggyback on other threads - you piker

Ouch!.....the MAN makes a true statement.:clapping:

FIMCO-MEISTER
08-30-2011, 07:23 PM
Only on well stuff. No piggybacking other than that. It gives me a chance to learn a few things.

Sprinkus
08-30-2011, 10:03 PM
Is it a VFD drive or a pressure switch?
The small pressure tank make me think that it's using a VFD or a cycle stop valve/pressure switch combination.
If it' a VFD then the settings could possibly be able to be changed to fix the problem.
Pictures would be helpful.

FIMCO-MEISTER
08-30-2011, 11:07 PM
Can't answer that. I think he had a falling out with the customer so we may never know.

Dirt Boy
08-31-2011, 01:09 PM
Is it a VFD drive or a pressure switch?
The small pressure tank make me think that it's using a VFD or a cycle stop valve/pressure switch combination.
If it' a VFD then the settings could possibly be able to be changed to fix the problem.
Pictures would be helpful.

Who are you asking? The piggybacker?

If you're asking me, then its a VFD setup. I will have to apologize if the VFD method doesn't use a pressure switch. I just "assumed" :hammerhead:that that is what was used.

bcg
08-31-2011, 01:11 PM
VFD uses some fairly high-end electronics to control the pump. I think a pressure tank CSV combo is better because there is less complexity and fewer failure points but either way, I still wouldn't worry about a PVB doing what it's designed to do.

AI Inc
08-31-2011, 01:11 PM
No, its actualy a flow senser.

Sprinkus
09-01-2011, 09:15 AM
VFD uses a pressure transducer, or pressure transmitter as called in this VFD lesson (http://www.danfoss.com/NR/rdonlyres/8ADD5B52-74B5-4AC7-805F-00E490681D7F/0/waterlesson1.pdf).

AI Inc
09-01-2011, 09:21 AM
Thanks for posting