# RPZ



## Vale (Apr 2, 2011)

Question boys. I'm installing a 2" reduced pressure backflow preventer. Does that mean I also need a pressure reducing valve(regulator). If yes were does the reg go upstream or down stream of backflow?


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## rombo (Jul 17, 2008)

Vale said:


> Question boys. I'm installing a 2" reduced pressure backflow preventer. Does that mean I also need a pressure reducing valve(regulator). If yes were does the reg go upstream or down stream of backflow?


No man just buy a normal pressure backflow and save some money:thumbup:


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## SlickRick (Sep 3, 2009)

Vale said:


> Question boys. I'm installing a 2" reduced pressure backflow preventer. Does that mean I also need a pressure reducing valve(regulator). If yes were does the reg go upstream or down stream of backflow?


If there is excessive pressure, then yes you need a PRV upstream of the RPZ.


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## Airgap (Dec 18, 2008)

Vale said:


> Cool. Tnx. Nothing to do with toilets I just can't figure out where to post my question.


Go to the main page of the forum. Pick the area you think your question will fit best. Click on box at top of page that says new topic. Name your thread and put question or comment in field below, and submit new thread.....


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## SlickRick (Sep 3, 2009)

Relocated


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## skitian (Apr 5, 2011)

Vale said:


> Question boys. I'm installing a 2" reduced pressure backflow preventer. Does that mean I also need a pressure reducing valve(regulator). If yes were does the reg go upstream or down stream of backflow?


The RPZ distinction has nothing to do with the pressure requirements for the BFP, it deals with how the device works. That BFP "should" have a maximum pressure rating of 175 psi, that, the incoming pressure, and code will determine if you need a PRV.


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## Redwood (Sep 8, 2008)

Vale, I'd check these links out....

http://www.plumbingzone.com/f8/commercial-work-13127/#post175749

http://www.plumbingzone.com/f3/why-post-intro-11368/

http://www.plumbingzone.com/newthread.php?do=newthread&f=3

Rick are you sleeping? :laughing:


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## SlickRick (Sep 3, 2009)

Redwood said:


> Vale, I'd check these links out....
> 
> http://www.plumbingzone.com/f8/commercial-work-13127/#post175749
> 
> ...


I guess so. :whistling2:


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## ToUtahNow (Jul 19, 2008)

Vale said:


> Question boys. I'm installing a 2" reduced pressure backflow preventer. Does that mean I also need a pressure reducing valve(regulator). If yes were does the reg go upstream or down stream of backflow?


What is the upstream pressure and what do you want your downstream pressure to be?

Mark


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## Vale (Apr 2, 2011)

ToUtahNow said:


> What is the upstream pressure and what do you want your downstream pressure to be?
> 
> Mark


There is no way of checking upstream pressure there is nothing between the existing backflow and meter. What I do know is that I only have 40psi at bldg and 30psi at boiler on rooftop. That pressure, in combination with bad shower valves are causing crossover in the bldg. So im thinking after I replace backflow device I will then see the true city water pressure and more than likely it will be close to 100psi (Los Angeles ). That's were my pressure reducing valve comes into play. I don't know what comes first after meter, the reg or backflow. I know it's a lot of info but my target pressure after all is done I want it to be 65psi. Tanks Vale.


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## skitian (Apr 5, 2011)

If you're going to have meter, PRV, and BFP in one location, then it should go PRV then meter then BFP. That way the pressure reduces before it goes into the meter, and the meter is protected from back pressure from the building. Also, you should have a valve on both sides of the entire assembly, but that probably depends on code in your area too.


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## Tommy plumber (Feb 19, 2010)

Vale said:


> There is no way of checking upstream pressure there is nothing between the existing backflow and meter. What I do know is that I only have 40psi at bldg and 30psi at boiler on rooftop. That pressure, in combination with bad shower valves are causing crossover in the bldg. So im thinking after I replace backflow device I will then see the true city water pressure and more than likely it will be close to 100psi (Los Angeles ). That's were my pressure reducing valve comes into play. I don't know what comes first after meter, the reg or backflow. I know it's a lot of info but my target pressure after all is done I want it to be 65psi. Tanks Vale.


 



Was the original customer complaint low water pressure? If so, you may be mis-diagnosing the situation. Why don't you take a pressure reading from the #1 test port on the RPZ and see what city pressure is before it goes through the device. Typical loss is about 10 psi through an RPZ.


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## Vale (Apr 2, 2011)

The original complaint is hot water on the cold side of of system. The entire bldg has hot water every where. I can't check the backflow preventer because all valves are frozen in partially closed position and I don't trust readings that way. That's why I want to start by balancing my pressures first. In addition I have also found and confirm about ten shower valves on first floor bad. Meaning the valve body is worn out and is allowing water to cross from hot to cold and vise versa. What do you think am I on the wrong path?


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## ToUtahNow (Jul 19, 2008)

Vale said:


> There is no way of checking upstream pressure there is nothing between the existing backflow and meter. What I do know is that I only have 40psi at bldg and 30psi at boiler on rooftop. That pressure, in combination with bad shower valves are causing crossover in the bldg. So im thinking after I replace backflow device I will then see the true city water pressure and more than likely it will be close to 100psi (Los Angeles ). That's were my pressure reducing valve comes into play. I don't know what comes first after meter, the reg or backflow. I know it's a lot of info but my target pressure after all is done I want it to be 65psi. Tanks Vale.


I'm not sure how familiar you are with plumbing but you can test the pressure at the existing RPZ by using one of the test-cocks. Going a little further, the maximum loss through an RPZ is 10 psi. So if you have 40 psi at the building and assuming no change in elevation or friction loss you have 50 psi at the street. I too am in Los Angeles and all you need to do to find out what your pressure is would be to call the DWP.

Mark


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## Vale (Apr 2, 2011)

What's up Mark. I've been doing commercial for eight years. I still don't think that I'll get an accurate pressure reading at the test cock on the RPZ if the isolation valves are stuck halfway closed and frozen that way. I have solved this kind of crossover issues before. I'm just not sure why the preventer reduces pressure. I'll figure it out. The DWP I had nothing but negative experiences with those dudes.


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## ToUtahNow (Jul 19, 2008)

Vale said:


> What's up Mark. I've been doing commercial for eight years. I still don't think that I'll get an accurate pressure reading at the test cock on the RPZ if the isolation valves are stuck halfway closed and frozen that way. I have solved this kind of crossover issues before. I'm just not sure why the preventer reduces pressure. I'll figure it out. The DWP I had nothing but negative experiences with those dudes.


Nothing personal but I really have no idea how much experience you have. Your pressure reading would remain unchanged regardless of the position of the SOVs. Only the volume would change with a partially closed valve.

Now back to the RPZ. If this RPZ is protecting the meter any pressure regulator would have to be after the RPZ. However, I doubt you need a pressure regulator. For USC-CCCHR to approve an assembly it cannot have more than a 10 psi head-loss. If your pressure after the RPZ is 40 psi then the pressure upstream of the RPZ has to be between 40-50 psi. One thing that is a little different in LA is when you are serviced by a reservoir the pressure is based on the elevation of the water in the reservoir. I have seen historic pressure changes in areas of LA as high as 50 psi. 

That is where the DWP comes in handy. When you call the service yard the engineer will tell you the range of pressure over whatever time period you want. It may take a few days to get back to you but they have to provide you with the information.

Mark


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## ToUtahNow (Jul 19, 2008)

Here this will save you looking for it:

http://www.ladwp.com/ladwp/cms/ladwp001582.jsp

Mark


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## SlickRick (Sep 3, 2009)

ToUtahNow said:


> Nothing personal but I really have no idea how much experience you have. Your pressure reading would remain unchanged regardless of the position of the SOVs. Only the volume would change with a partially closed valve.
> 
> Now back to the RPZ. If this RPZ is protecting the meter any pressure regulator would have to be after the RPZ. However, I doubt you need a pressure regulator. For USC-CCCHR to approve an assembly it cannot have more than a 10 psi head-loss. If your pressure after the RPZ is 40 psi then the pressure upstream of the RPZ has to be between 40-50 psi. One thing that is a little different in LA is when you are serviced by a reservoir the pressure is based on the elevation of the water in the reservoir. I have seen historic pressure changes in areas of LA as high as 50 psi.
> 
> ...


Why would the PRV be located downstream of the RPZ or any other device? Lets say you have 200 psi at the meter, and the BFP is rated at 175 psi.


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## ToUtahNow (Jul 19, 2008)

SlickRick said:


> Why would the PRV be located downstream of the RPZ or any other device? Lets say you have 200 psi at the meter, and the BFP is rated at 175 psi.


 
In theory, the water purveyor wants nothing installed between the meter and the RPZ, if the RPZ is for protecting the meter. If you have excessive pressures they would probably wave that but here it sounds like there is only 50 psi from the street.

Mark


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## Tommy plumber (Feb 19, 2010)

Vale said:


> The original complaint is hot water on the cold side of of system. The entire bldg has hot water every where. I can't check the backflow preventer because all valves are frozen in partially closed position and I don't trust readings that way. That's why I want to start by balancing my pressures first. In addition I have also found and confirm about ten shower valves on first floor bad. Meaning the valve body is worn out and is allowing water to cross from hot to cold and vise versa. What do you think am I on the wrong path?


 



Sounds like the shower valves are the problem, I think you're on the right track. Either way, sounds like a nice job. I would also give them a proposal to upgrade the old backflow assembly as well.

With regard to the tub/shower valves, are they single-handle? Or 2-handle? Might be you can replace the stems or cartridges.


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## Vale (Apr 2, 2011)

Shower valves are single handle "mixet". Notorious for crossover. It's the first time I service this bldg. There are a lot of funky stuff going on there. Thanks for all the input.


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