Water pulses and "knocks" using manual pool filler pipe

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Wizard19

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Mar 22, 2011
21
Austin, TX
We have a "y" connector to the external water bib at the back of house. I I can turn off the water flow to each side of the "y" connector. One side of the "y" is connected to my garden hose. The other side is connected to a valve and pipe that goes underground to the other side of the pool, and comes out of a small wall about a 18" above the water level, and is what is used to top of the water level. When I turn the water on at the bib, to top of the pool, and open up the valve, the water starts pulsing and knocking about 2-3 times per second. You can hear it inside the house also. It will go away if I close the valve about half way. If I just fill the pool with the garden hose, there is no problem. Any thoughts on what might be causing this?
Thanks.
 
When you close the valve some you reduce the water pressure and stop the knocking.

What size is the pipe leading to the pool compared to the pipe feeding the spigot?

From...

What Can I Do About the Knocking/Banging Noises in My Pipes? – Plumbing Today

Frustrated by the loud knocking noises coming from your pipes? What’s most likely causing the problem depends on when you hear the knocking sound.
plumbingtoday.biz plumbingtoday.biz

High water pressure. The scientific explanation for why high pressure creates knocking noises is that when the water’s flow rate in the pipe is above a certain level (which varies based on the diameter of the pipe), the flow goes from laminar (flowing in even, parallel layers) to turbulent (chaotic).

In plain English: when water flows through a pipe too fast, it begins to bounce of the sides and into itself, which shakes the pipe. The shaking pipes can rattle against walls and other pipes, making the knocking noise you hear.
 
Attached is a picture. The faucet/valve on the right connected to the PVC pipe going to the pool is the one that when the "pulsing" starts, I turn it down about half way and the pulsing stops. The hose is 1.5" and the pvc is 1".
 

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Maybe a bad anti siphon valve.

Try a different garden hose from a different spigot to see if the knocking is from the anti-siphon attached to the spigot or if it's coming from the fill line somewhere.
 

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My experience is that with that type of anti-siphon valve, they can be very loud. I took one of mine off because it was freaking out the dog but I do not use that bib with a hose so siphoning is not an issue. You have potential siphoning occurring so you really should have one on that bib. There are hose bibs with an anti-siphon valve built in. It may be less noisy but I have no experience with that type.

Amazon.com: Anti-Siphon Hose Bibb, 1/2 In, Brass : Patio, Lawn & Garden

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mas985 said:
. There are hose bibs with an anti-siphon valve built in. It may be less noisy but I have no experience with that type.

Amazon.com: Anti-Siphon Hose Bibb, 1/2 In, Brass : Patio, Lawn & Garden

Buy Anti-Siphon Hose Bibb, 1/2 In, Brass: Faucets - Amazon.com ✓ FREE DELIVERY possible on eligible purchases
www.amazon.com
Click to expand...

I have one of those that gives me water knocking at certain flow rates. I have three others that have no knock and one that knocks. Just the way the plumbing was done to that location.
 
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