Hot Topics: What Is the Correct Water Pressure for a House?

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1oldpop Member

Hi, All! I have posted before about the water hammer noise in our home (started with one toilet, then both, then the clothes washer), and the noise has been getting progressively worse. Thought about just buying a water hammer arrestor, but since the sound is getting progressively louder, and after some good advice here, I am looking at the pressure regulator (PRV) at the front of the house. Incidentally, we don't have an expansion tank in our Southern California home built in 2002, but the inside plumbing is all a PEX system.

I put a gate water pressure gauge on the water spigot, which is just before the 3/4 inch pipe goes into the house. Here is where I am a bit confused: what exactly should the water pressure be at? Some say 30 to 50 PSI, some say 40 to 60 PSI. A few YouTube videos made by plumbers say 70 or even 80 PSI is OK. So, which is it?

In our case, I am getting a base pressure of 70 PSI (black needle), and the red needle (MAX pressure) shows 100 PSI. My understanding is that the black needle shows the static pressure, and the red needle shows the most the water pressure PSI has been since it was last reset. Is that correct? If so, does the fact that the max pressure is 100 PSI, even if only for a short time, mean there is a problem with the water pressure? Or is it normal to have pressure spikes and that I should only care about the base pressure?

Finally, if the consensus here is to adjust and, if need be, to rebuild or replace the valve (Watts LFN45B), how do I do that? I know how to adjust the pressure (by screwing in/out the screw), but how do I open up the valve to rebuild it? The rep at Watts gave me the part number (0006960), which doesn't include the diaphragm or big spring—just a black plastic thing with a screen on it, along with two o-rings. However, I don't know if there is a rebuild kit that replaces all the guts inside. Does anyone know if there is one?

Thanks in advance to all who offer help or advice.

Pilot Dane Group Moderator

There is no "right" water pressure. I generally go for a max of 60-80 PSI.

There is no standard for pressure gauges. You will have to look at what you purchased and determine what each color needle is indicating. But, you shouldn't be seeing spikes above your set pressure. Have you spent some time watching the gauge to determine when and why it's spiking?

marksr Forum Topic Moderator

I'd have to dig up my pressure gauge to see which needle is what color, but the gauge will read the current pressure as soon as it's screwed in and the valve is opened. The other needle records the highest pressure while it's in operation.

I live on top of a hill and don't have a pressure reducer valve. My pressure averages between 20 and 40 PSI with nightly spikes up to 60 PSI. It sounds to me like your PRV isn't working correctly. While I've adjusted them, I've never repaired one—only replaced defective ones. They can last decades or crap out in just a few years.

AllanJ Member

Do you have an expansion tank in your water system, usually mounted near the water heater? If not, or if such a tank is worn out, then you can get unusually high pressure in your water system.

1oldpop Member

From the instructions on the water pressure gauge package, the black needle is the base/constant water pressure, and it goes to 70 PSI right when I put it on the front spigot and turn on the water. The red needle shows the highest water pressure and it sits at 100 PSI. We don't have an expansion tank and I have not been out there to see what goes on/off that drives the red needle to 100 PSI. I guess my question is if a PRV should ever let the water pressure jump to 100, even for a short time? If not, then the PRV is defective.

marksr Forum Topic Moderator

You did reset the red needle to zero before you hooked up the gauge, right? It doesn't automatically go to zero like the black needle does.

1oldpop Member

Yup, I've taken it off and put it on several times. I always move the red needle to zero when I start.
I called the local Ferguson store and they put me on with a sales rep. He told me he couldn't give any info on fixing/rebuilding the valve (doesn't know anything about it—just sells them). Called Watts and support tech gave some instructions on installing a rebuild kit, but then said it would be best to replace the valve. $$$ I don't have.
marksr Forum Topic Moderator
PRV aren't all that expensive. We replaced the one on my son's house a couple of years ago and if I remember correctly, the PRV was about $35. Of course, we also had to get some fittings because we had to cut the old pipe it was connected to.
Panacea Member
I had a water pressure issue at my home several years ago. The water softener timer mechanism would self-destruct because of the high pressure. The softener unit was high quality and came with a 10-year warranty. The first time this happened, the repair was taken care of under warranty, no problem. The second time, the repairman told me they would not cover this repair a third time unless I installed a water pressure regulator to reduce the pressure to about 60 LBS. I installed the regulator (he had one in his truck) and had no more problems. I did increase the pressure to about 80, though. With a sprinkler system and four kids, 60 didn't cut it. It's been several years and no more problems with the softener.
Pilot Dane Group Moderator
I never repair PRVs. They are inexpensive enough, so I just replace them. I convert the piping next to the PRV to PEX. The flexibility of the PEX makes it easy to install the new valve without disturbing the old piping. But...it relies on having the tools, which is an added expense if you don't already have them.
1oldpop Member
Well, the guy at Watts agrees on just replacing the PRV and he gave me his suggested replacement of the Watts 3/4 inch valve: LFN55BM1-DU 0009585. When I Google that, they aren't cheap—at least for those of us on a fixed income. Alternatively, Home Depot has one ( Model # 3/4 LFN45BM!-U) for about 56 bucks versus a rebuild kit for what I have of $33.51. I know I can handle rebuilding it, but I have never changed a PRV and it sounds a bit intimidating. But I guess with the double union, as long as I get the same size PRV, it should go in OK. I am just a bit worried because the pipe from the street and the pipe going into the house seem so stiff that it would be hard to remove/replace. Anyone done this before?

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