Need help: branching off from incoming water pipe

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JasonY

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The street water pressure is 110 psi, and I then installed the PRV, gauges, and expansion tank with the help from this forum. Part of the design is to branch off from the incoming water pipe before the PRV, so that I can feed the outside spigot with high (street) pressure. See the picture below.

Upon finishing installing it, the main branch (going to PRV) is functioning as designed. However, when I open the outside spigot, I got a bad pulsating of water flow. I used a Tee (3/4x3/4x1/2) for the branch off, see picture. the pipe is reduced to 1/2 for the outside spigot. I think the problem is when outside spigot opens, it somehow created a low pressure at the Tee, and water back flowed from the branch that feeds the PRV/expansion tank. The pulsating is so bad it actually broke the pressure gauge.

PRV is set at 65psi, same at tank (set when empty).

Is the branch off just a bad idea or I simply did it wrong? What is the proper way to branch off in this scenario?
Thanks,

-Jason
 

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wwhitney

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Is your outside hose bibb quarter-turn or multi-turn? Multi-turn has the advantage of opening more slowly, so it is less likely to induce dynamic effects.

Otherwise, I'm stumped. If it is easy for you to temporarily remove the PRV and cap that branch, you could confirm that the phenomenon is due to interaction with the PRV, but I'm not sure where you'd go from there.

Cheers, Wayne
 

JasonY

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the spigot is a multi turn...

Thanks for your insight... I confirmed that it is the PRV pulsating. It does it when I open the spigot just a bit. If I fully open the spigot to have full flow, pulsating stops. I am assuming the PRV is reacting to upstream pressure fluctuations created by a partially open spigot, but I don't understand why. Any thoughts/solution would be highly appreciated. Thanks.
 
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James Henry

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I would turn the regulator all the way down and turn on the hose bib then slowly turn the regulator up and see if the water pressure difference has an effect. Stop at 35 PSI, turn off
the hose bib and check the pressure going into the house.
 
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JasonY

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James, thanks. I lowered the PRV to 55 psi, still pulsating. Will try to lower it further when I find a good time when family members are away from home. I tried to just crack the spigot just a little tiny bit, just a trickle of water, and I can hear the pulsation. This is really odd. It's with the very slow movement of flow. but maybe this is the normal operation of PRV. but further slight opening will quickly amplify the pulsation and I can hear the banging of pipes.

Anyone has done this kind of setup? maybe it's not such a good idea...

This is a picture of the entire setup, followed by a shot of the branch for outside of the house.
 

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JasonY

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Here's the outside hose bib... I tried to open it wide after I close the ball valve on this branch first, and then tried to slowly crack open the ball valve and open the ball vale rapidly, there was no pulsation... do you think it's the hose bib that's causing the problem?
 

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James Henry

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shut off the supply to your hose bib and take the guts out of your hose bib then open the valve. that will rule out a bad hose bib.
I've even heard of faulty toilet flush valves causing water hammer.
 

Reach4

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I would turn off the first blue-handled valve, and see if you get the pulsating. If no, try closing just the second blue-handled valve. I am not a plumber.

What is the gadget under the right-most tee?
 

JasonY

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further investigation..... when it vibrates, the source seems at the spigot end, not at the PRV end. As James suggested, I removed the bonnet of the spigot, see what I found. The washer is loose, because the screw has eroded away, long ago by the look of it. Now when I open the shut-off valve slowly, there is no vibration.

What are the odds, as it did not vibrate in the old setup, in which the spigot was teed off of the nearby 3/4 in line with a short distance. The new routing has increased the length of pipe and as a result it has become more flexible. What are the odds that the new pipe natural frequency would match the vibrate frequency of the spigot to result in a resonance!

I can either repair the spigot, or replace it with a frost-proof silcock. Either way, case closed. Thanks for the discussion, and a shout-out to James. Rejoyce!
 

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