Precision Plumbing Products P1-500 Automatic Trap Primer Valve

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QuietCanuck

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Hi there. Can anyone tell me how the "Precision Plumbing Products P1-500 Automatic Trap Primer Valve" works?

Specifically:
1) From what I have gleaned off the Internet, it appears as though it is supposed to drip or spray a small amount of water every time the water pressure drops ~10 psi. Have I sussed this correctly, or am I off base?
2) Can anyone explain what the adjustment screw on the side of the valve actually does (does it adjust the pressure drop amount that activates it, or does it adjust the amount of water that it sends out each time it activates, or something else entirely)?
3) Is it supposed to spray water each time it activates, or just drip a bit?
4) Can any one explain how it's internal workings work (this last question is just plain curiosity on my part)?

Thanks in advance.
 

hj

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1. That is how they are SUPPOSED to work, but whether they actually do or not depends on one of three conditions. A. The piping has to be small enough to induce that 10psi pressure drop when a faucet is turned on, OR B. the faucet has to open rapidly before the flow can overcome the water's inertia, OR C. with larger sized mains the flow has to be large enough to create the necessary pressure drop. In many cases NONE of these conditions occur and the trap primer does not operate.

2. Most are NOT adjustable, but when they are the adjustment is to set the static pressure. You adjust the screw until the primer starts to drip and then back off a touch.

3. It just drips a few drops while the pressure in the main is stabilizing.

4. I have never taken one apart, but it is probably like a pressure reducing valve, which opens when it senses a drop in the incoming pressure.
 
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QuietCanuck

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Thanks for the reply hj.
I was afraid it worked that way. My house has 3/4" piping all the way to where the P1-500 valve Tees in, and then some good ways beyond, so the odds of getting a 10psi pressure drop when I turn on a tap or flush a toilet seems rather unlikely. This may explain why in the 10 years I have been in the house, I have never seen the P1-500 Automatic Trap Primer Valve ever emit even one drip. At least it solves the mystery for me.

Thanks again.
 
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