Chris
Well-Known Member
Any of you guys ever built one like this? I have built several single RP devices but this is the first time with two and a pressure relief.
Crazy Reduced pressure device.
- Thread starter Chris
- Start date
Help Support Plumbing Forums:
I would say that the reasoning behind that setup would be so you could service one of the devices with out interrupting the water service to the building. We have done that with back flow presenter's but have never seen it with PRV's. The relief valve is in case the PRV's fail.
John
John
Chris
Well-Known Member
That kind of makes sense but one is set for 78 psi and one is 79 psi then the relief valve at 80 psi.
What is it feeding? Sounds like they require very strict water pressure control.
John
John
Chris
Well-Known Member
A 7/11 convenience store.
Beni
Well-Known Member
When using two or more pressure reducing valves in a manifold, its common practice to set the lead at at higher pressure then the lag unit. Many times I might use a 1/3 / 2/3 arrangement with the smaller unit sized for low flow say 10-15 gpm and the lag valve at 50 to 75 gpm. Depending on the building.
If both were set at the same pressure the valves would crack open at the same time and cause wire drawing of the seats and premature valve failure.
That said I would have expected the pressure difference to be about 5 psig. One psi difference is not really enough to prevent wire drawing of the seats at low flow rates. Assuming both are the same size...
With two valves of the same size it would be for redundancy. However the problem unless someones on the ball, the first sign of trouble is when both fail.
The pressure relief valve is in case the valve(s) fail open.
Opps, looked at the diagram and they are using a 1/3 / 2/3 valve arrangement. You get better overall control with two valves between low flow and high flow and no problem with wire drawing. Most of the time the small valve is doing all the work. But when they flush a flush valve toilet or urinal the larger valve opens. It makes sense though I might have specified a single valve to do it all or a pilot actuated valve. Lots of extra fittings and labor for a 7/11.
If both were set at the same pressure the valves would crack open at the same time and cause wire drawing of the seats and premature valve failure.
That said I would have expected the pressure difference to be about 5 psig. One psi difference is not really enough to prevent wire drawing of the seats at low flow rates. Assuming both are the same size...
With two valves of the same size it would be for redundancy. However the problem unless someones on the ball, the first sign of trouble is when both fail.
The pressure relief valve is in case the valve(s) fail open.
Opps, looked at the diagram and they are using a 1/3 / 2/3 valve arrangement. You get better overall control with two valves between low flow and high flow and no problem with wire drawing. Most of the time the small valve is doing all the work. But when they flush a flush valve toilet or urinal the larger valve opens. It makes sense though I might have specified a single valve to do it all or a pilot actuated valve. Lots of extra fittings and labor for a 7/11.
Last edited:
![MEISTERFAKTUR drain snake 2.0 [50 FT] - with drill attachment - Ideal plumbing snake for sink and drain unblocking - Solid drain auger for real DYIs! (50 FT - 1/4 inch)](https://m.media-amazon.com/images/I/41VwmTiOsgL._SL500_.jpg)
Chris
Well-Known Member
Thanks.
So the the pressure of the main line here is 135. No wonder why all these water lines in LA keep blowing apart.
So the the pressure of the main line here is 135. No wonder why all these water lines in LA keep blowing apart.
Wow. That's unreal. Highest it gets in my city (only 1 million people though) is like 80 psi. I guess they must have it so high so it can travel further and still have good pressure. Although technically the higher the pressure is the higher your pressure loss. Either I've never dealt with pressures that high for water
Chris
Well-Known Member
This is the first time I have seen it myself.
If your in a area that is very hilly the higher pressure is needed for the homes in the higher elevations.
John
John
Chris
Well-Known Member
This is in Los Angeles, pretty flat.
Yes, Chris. We Install a lot of those around here on commercial jobs. The smaller bypass will just remain off until it's needed to maintain water supply if the main regulator or strainer need to be serviced.
The norm in my area for water main pressure is anywhere from 70 psi to 200 psi. Topography definitely has an impact on the pressure.
The norm in my area for water main pressure is anywhere from 70 psi to 200 psi. Topography definitely has an impact on the pressure.
200 PSI?!!???!? That is a whole pantload of pressure!
How long does the normal city water main last in your area?
How long does the normal city water main last in your area?
Chris
Well-Known Member
We test to 200 PSI never have I seen a line with pressure like that.
We get a lot of main breaks, but the old cast and ductile iron seems to hold up better than expected for being 100 years old. Many of mains are being replaced with HDPE and the size of the mains are increased to accommodate demand. The main on my street was 2 1/2" iron @ 118 psi and when replaced changed to 4" HDPE and pressure is now @ 70 psi. I live on top of a hill so the people down in the valley may see higher pressure with the elevation change.
I should also add that there are the occasional wooden water mains that are exposed in the city. We discovered one a few years ago, but it was inactive, though it seemed to be in extremely good shape.
Chris
Well-Known Member
I would love to get a section of redwood pipe for my office. There is still some out here but most is abandoned.
