Water pressure questions, static is 130, running is 45


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Old 05-07-08, 09:29 PM
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Water pressure questions, static is 130, running is 45

Im somewhat confused after reading a bunch of threads I searched. Trying to find out how one properly measures water pressure. I have a gauge on my laudry bib and it reads about 130 or so if the water faucets have not been used for say about 2-3mins, if I turn one on, it drops to about 45 or so, turn it off, it sits around 50 and then continues to rise slowly to about 130.

Is this normal or does this kind of show that there is a possibly problem with the pressure regulator valve where its leaking, I know they dont last forever, and this house was built in 1998.

Reason Im checking is that I just installed a new waterfall faucet in my remodelled master baths and the water pressure seems too high, it basically shoots it out to the point where it hits the overflow hole in the china sinks and splashes water all over the granite vanity.

Dixit
 
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Old 05-08-08, 03:40 AM
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No, 130 is twice what you should be seeing at static. Running water always drops pressure. You should adjust your pressure regulating valve to about 65-70 lbs max. Do it soon, as your connections may not can take a really high pressure for long. If you are unable to regulate the pressure, your prv may need replacing, which is another story. Let us know how it goes.
 
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Old 05-08-08, 05:14 AM
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Sounds like your pressure regulating valve has a leak and letting the presure build after the flow is stopped.
 
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Old 05-08-08, 07:36 AM
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Originally Posted by joed
Sounds like your pressure regulating valve has a leak and letting the presure build after the flow is stopped.
Thats where Im leaning toawards the more I think about it because I cant remember getting surge/high water pressure for 5secs when I bought the house 2yrs ago.

Now almost every faucet shower has a surge if the water hasnt been used for 5-10mins.

Will see if I can rebuild this PRV or just replace it.

Dixit
 
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Old 05-09-08, 04:14 AM
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Good morning all

First I need to know a few things.

Are you on city/town water?
Do you have a water heater vs. a tankless coil in a boiler?
Do you have a pressure reducing valve on your water main?

These are classic symptoms of "thermal expansion".

Thermal expansion is caused when water is heated. You cannot compress water but you can compress air. So a tank with an air charge is installed so when the hot water heats it will give the water an environment to expand into without effecting your water pressure. If you have a boiler for your heating, it will also have an expansion tank. DO NOT GET THEM CONFUSED.

Usually if you are getting pressure readings in excess of your normal operating pressure then it is usually caused by either thermal expansion or a faulty pressure reducing valve.

If you have no thermal expansion tank installed someplace on your domestic water (main water line), it can be anyplace on the water main, usually either around the hot water heater or near the water meter, one should be installed if a tank type water heater. If you already have one, the tank may be waterlogged and need replacement.
The tank pressure should be set at 3lbs under the normal operating house pressure(NOP), and is sized by NOP and capacity of the hot water tank. The chart will be in the tank box. Bring this info with you when purchasing an expansion tank.

Usual tell tale signs of thermal expansion is water leakage of the relief valve on the water heater. If you are reaching pressures of 130psi then your relief valve has probably not leaked yet. Water heater relief valves are set to open at 150lbs

Another way to check if it is your water heater or pressure reducing valve causing the problem is, turn off the water heater and run some water to cool off the water in the tank and release any excess pressure in the lines, wait 1/2 hour and then check your water pressure. if it is normal, go for the expansion tank, if has risen to 130lbs look for a pressure reducing valve.

Good luck, Let us know the outcome, Mark
 

Last edited by plumbingods; 05-09-08 at 04:17 AM. Reason: Typo
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Old 05-09-08, 05:51 AM
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plumbingods is onto something....

Check with the water heater off and cool before we go any further.

Let us know how this turns out....
 
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Old 05-09-08, 07:30 AM
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Thanks plumbingods. I read a few more things a day ago and tested that theory. I recently replaced the waterheater myself and decided to put a valve on both sides. So I turned off both valves and then tried the test. The water pressure while running is around 38 or so, and as soon as I turn it off, it just go to 50 and within 10secs climbs back to 120. It climbs much faster without the hot water involved.

And to answer some of his questions, yes Im on county water lines, I do a 50ga hot water heater that I just replaced, and I have a Watts U5-Z3 PRV right off the water main valve.

Dixit
 
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Old 05-09-08, 09:36 AM
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Your pressure reducing valve (PRV) is definitely leaking through.

While rebuild kits are available the cost of the kit is not that much less than a new PRV. Add to the cost of the kit and the time (and trouble) of rebuilding the PRV I suggest a new one.
 
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Old 05-09-08, 03:11 PM
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Hi again,

I was just looking at you last post and started thinking, WOW that is some high water pressure. Do you live next to your town reservoir? I think the highest I ever tested was around 100psi. You really want to get that fixed as soon as possible because you have a potential time bomb here just waiting for a weak soldered joint or water heater to blow.
 
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Old 05-09-08, 03:38 PM
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Originally Posted by plumbingods
or water heater to blow.
speaking of that, what is a typical pressure relief valve designed to release at? I would guess less than this 130. If so, OP may be running water out the relief valve nearly continually, Gonna make for a heck of a water bill if it is.
 
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Old 05-09-08, 03:47 PM
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hello,

typically water heater relief valves are set to blow at 150psi.
When you get into commercial w/h's that may change
 
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Old 05-09-08, 05:51 PM
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Its been more than thirty years since I lived or worked in Seattle but back then pressure in excess of 100 psi was not uncommon.

We had about 105 at the house where I grew up and 130 at Lake Union where I worked at several different places. I think that the former steam-electric generating station (at the county airport) that is now an historical museum still has in excess of 125 psi.

The main office building of the electrical utility was 11 stories high and had no booster pumps. The pressure was a little low, maybe around 30-35 psi on the tenth floor.

None of these places had pressure reducing valves on the domestic water.

Seattle color-coded the fire hydrants by painting the tops a different color than the body; red was less than 30 psi, yellow was 30 to 60 psi and green was over 60 psi.


I think that the "normal" municipal water pressure being 40 to 60 psi is a relatively recent thing.
 
 

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