PRV question

[SGkent]

I asked other questions on PRV's before but this is a new question directed at folks who install and who have them. The PRV in question is a Zurn / Wilkins model 70. The outside pressure is about 80 - 85 PSI. The PRV is now set to 70. When a large flow is initiated, like the washing machine, or the irrigation system, the pressure falls from 70 to about 45 - 50 then as the PRV acts to regulate it, it rises upwards to the fall off pressure - say 55 - 60 PSI. Last time the valve was rebuilt was about 3 years ago. I still have plenty of rebuild kits but I like to save them for when the PRV really fails. Is the wild swing normal under a large sudden demand like the washing machine or irrigation? I would think the PRV should react quicker but this is the only one I have ever monitored. Usually when the springs rot away they fail in the open position. I am having trouble understanding why the pressure falls so far and so fast, then recovers. Is it possible there is a city water device acting up in my line near the meter?

 

[Geofd]

You would think the pressure drops when the washing machine fills or irrigation then gradually returns to were you set it, you say the last time you rebuilt it was three years ago, if it's on unions maybe you could valve it off, spin it upside down fill it with vinegar,and let it sit for a bit and the flush it out to see if it cleans it

 

[SGkent]

I am pretty sure one side is soldered in. I will rebuild it probably later today when the laundry is completed. It is only a 20 minute process. I just hate replacing it is the behavior is standard because I have a limited number of kits and they are like $40 each now when one can get them.

 

[Geofd]

I am pretty sure one side is soldered in. I will rebuild it probably later today when the laundry is completed. It is only a 20 minute process. I just hate replacing it is the behavior is standard because I have a limited number of kits and they are like $40 each now when one can get them.

Can you remove both nuts and spray the internals with vinegar,and see what happens

 

[SGkent]

I'll try to get a video. Basically when high demand is made the pressure falls a lot more than I think it should then recovers. It is like the PRV That delay causes the house pressure to fall so much that when it recovers it is like hammering the whole house.

 

[SGkent]

I am going to just rebuild it and move on. I don't even think that many professional plumbers come here because no one seems able to answer the question, "how much lag time does a residential PRV have? This one is about 1/2 to 2 seconds before it opens and lets the set pressure back in. It may even be something in the water meter that was installed 20 years ago when Congress mandated them. If you looked at a graph you would see the water pressure setting steady at the PRV pressure quite consistently, Open a small faucet and it would hold steady where set, but open a large demand like the solenoid in the washing machine and the pressure would drop 15 - 20 pounds for about a second and a half to two seconds then recover and hold steady. That causes the whole system to softly hammer and stress. It is a Wilkins / Zurn 1" Model 70. The insides are clean.

 

[Twowaxhack]

80 psi is the limit. I wouldn’t use a PRV in your system. Technically 85psi is too much but I’d live with the extra 5psi rather than dealing with a PRV

Your PRV is operating correctly.


Have a beautiful Monday

 

[molson]

Agree with @Twowaxhack, all makes of traditional direct acting PRVs exhibit similar fall-off pressure behavior: some more pronounced than others. The "bounce back" of 10psi you are experiencing does seem a little high, but is the momentary low building pressure really a noticeable problem?

Zurn has recently introduced a new direct acting PRV said to have little fall-off pressure. 500XL3 I believe, but I suspect it's pricey at the moment.

Wash machines, irrigation and other fast acting solenoid valves are tough on rubber diaphram valves type valves like you are experiencing. Water hammer pressure spikes are stressful. Consider using a valve that is designed to withstand spikes. The Caleffi 536 HP series uses a metal piston in place of a diaphram. Looks like a match for your situation.

Hope this helps

 

[Geofd]

Just looked it up direct acting seat type is 2-5 minutes,spool type, 10-30 mins, there are also anti shock prv's

 

[SGkent]

conclusion - the valve was sticky and took a lot of effort to move the core once it was out. With a new kit the PRV responds almost instantly now. The lag was caused by the sticking internal valve. I know how they work, just did not know if a lag is normal - it is not. In my experience the guts last 4 to 7 years for those who are unfamilar with them. This one still worked but was beginning to deteriorate at 3 years. We have quite soft water so there were no deposits. It was just hard to move. The screen was clear. Now the bad news, I paid like $9 a kit when I bought 25 years worth 20 years ago but now they are $60 - $80 each, and the brass and stainless ones hard to find now. RK1-70. The plastic ones for RK1-70XL are around. My stock is getting low.

 

[Twowaxhack]

The new one will wear a little and not regulate perfectly. It was fine, it’s not a precision instrument.

 

[SGkent]

It was fine,

no, the old one was not fine. The valve was quite stiff, almost un-moveable by hand, and the pressure swing as a result caused a very large drop in pressure before the valve responded. Now the drop is only 7 - 10 psi and holds steady when the washer comes on. It was 20 - 25 PSI with a several second lag. In fact when the sprinklers came on the whole house banged due to the pressure dropping so much then recovering suddenly.

 

[BlueSkyHigh]

I have a question regarding PRVs and I admit that I am ignorant on this point. My internal logic engine, my noggin, says that if there is no flow through the PRV then there would be no drop in pressure from the inlet side to the outlet side and the outlet side pressure would build to that of the inlet side.

Can someone put into layman's terms how a PRV actually works? BTW, Google didn't help me.

 

[MicEd69]

A normal house water Pressure Regulating Valve has a diaphragm and spring to regulate the pressure on the downstream side. When there is no flow, the spring has closed the valve at the set point maintaining the set point pressure in the house. When water is needed by something in the house, the downstream pressure is reduced as flow starts, and the PRV opens and maintains the set point pressure in the house. Then when flow stops, the PRV spring closes and maintains the set point pressure in the house.

Note that house PRVs are not precise devices, and the downstream pressure does vary some depending on the flow rate, duration of flow, and how fast the flow is stopped.

Now there will be a time when what you are thinking will happen. That's when the PRV needs to be replaced or rebuilt. I replace faulty PRVs, but SGkent seems to have good luck in rebuilding them. Good for him!

 

[BlueSkyHigh]

Thanks MicEd69. Now I get the picture.

 

[molson]

@BlueSkyHigh , adding to @MicEd69 , this is a good illustration on what takes place inside a PRV
https://idronics.caleffi.com/article/31/2-plumbing-system-pressure-concepts

 

[SGkent]

- whether they can be rebuilt depends on whether parts are available and the price. It also depends on the quality of the water. Here we have water from annual snow runoff in the Sierra Nevada Mountains. It is not mineralized like some water is so there is very little damage to the valve body. This valve body is soldered on one side and a union on the other. It is in a tight space and is more of a pain to replace than rebuild.

In answer to the question how they work. They try to keep pressure in the house near a set point. There is a graph that shows what is called fall off pressure - meaning that as more demand is made, the pressure falls below the set point. So - if say the city has 120 PSI water pressure, that is not good on the house plumbing system. A PRV would drop it to a set pressure - say 60 PSI. Then as more and more demand is made on the system the pressure will fall from that 60 PSI to maybe 45 PSI. Each type valve has a different fall off pressure based on flow. Mine was falling almost instantly from 55 PSI to 30 PSI then suddenly rebounding back to say 50 PSI two or three seconds later. It was pounding everything in the house. I didn't know if that was normal. It is not, the valve was sticking and needed replacement. A new Zurn/Wilkins 1" Model 70XL is $170. The Model 70XL repair kits run about $75. The new kit has a plastic valve. The old one, which was not lead compliant was brass.