# pressure reducer valve and backflow preventer



## bluebird5 (Jan 24, 2011)

Is it necessary to have a backflow preventer in front of a preasure reducer valve? is so could you please explain why?


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## Daniel Holzman (Mar 10, 2009)

A pressure reducing valve and a backflow preventer do very different things. A pressure reducing valve reduces the pressure on the outflow side of the device. A backflow preventer restricts flow to one direction only. Typically the pressure reducing valve is used when the pressure is too high on one side, for example boilers typically operate at about 15 psi, while house pressure is typically around 60 psi, so you need a pressure reducing valve on the cold water inlet to your boiler.

Backflow preventers are used when you need to prevent process water from coming into contact with potable water. For example, you generally do not want to drink boiler water, so you put a backflow preventer on the cold water makeup line feeding your boiler. Similarly, you do not want to drink stagnant water from your hose, so you typically put a backflow preventer on a garden sprinkler system.

As you have provided no information about the specific purpose of the pressure reducing valve, it is not possible to say if you also need a backflow preventer.


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## bluebird5 (Jan 24, 2011)

well i am going to need to re run the incoming line into my house bc it is very old galvanized and the preasure is not goo bc it has become restricted and was looking at watts preasure reducer valve and on the instructions it said to install a backflow preventer infront of it and i was wondering why i thought it was to get steady preasure coming into the preasure reducer but i see what you are saying about the outdoor cocksills. is a boiler the same thing as a waterheater? would you recommend backflow preventers on the cocksills and on the cold water lie coming into the waterheater? would it be bad to drink water from the waterheater?


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## Daniel Holzman (Mar 10, 2009)

A boiler is a water heater designed to generate warm water to heat your house. A water heater generally means a device to generate warm water to bathe or cook with. You don't want to drink boiler water or water heater water, as they may be contaminated with chemicals from the heating unit.

But back to your pressure reducing valve. If you have low pressure, adding a pressure reducing valve will not help you. A pressure reducing valve reduces pressure, it does not raise it. As for the Watts valve you were looking at, it may be designed for use on the cold water inlet side of a boiler, in which case you do need a backflow preventer along with the pressure reducing valve.


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## bluebird5 (Jan 24, 2011)

no you misunderstood me. i am replacing the incoming line. my neighbor had the same issue and replaced the line but when he did he said his preasure was too high and he had to put a preasure reducer valve. so i am going to put a new line and a preasure reducer valve on the new line and i was just wondering about whether i need a backflow preventer. the house was plumbed in 1965 and right now there are no backflow preventers on anything. so i think i will put one before the preasure reducer valve and on the cold waterline going into the waterheater. sound good? can these valves become clogged? is there anything that i should do to chck them every now and then?


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## Homerepairguy (Aug 1, 2010)

bluebird5 said:


> so i am going to put a new line and a preasure reducer valve on the new line and i was just wondering about whether i need a backflow preventer.


You need to check with your city to see if they currently have a requirement for backflow preventers on the main line. In the old days, backflow preventers were not required but they are slowly being adopted by some cities as a requirement now.

FWIW, when I installed our Watt's pressure regulator a couple of years ago, it did not mention a requirement for a backflow preventer in the supplied documentation. But that might be because our city does not require one per code right now unless one has additional plumbing that can introduce backflow into the system like lawn sprinklers.

HRG


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## ratherbefishing (Jan 13, 2011)

We had the incoming line from the street replaced last year for the same reason. Replaced the galvanized with soft copper. A new PRV was part of he deal. Then the county replaced the meter. The new meter has a backflow preventer built in, so I'm told. Not long after that, I noticed the water pressure seemed very high when first opening the tap. A thermal expansion tank was needed and fixed the problem.


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## Docwhitley (Jul 19, 2010)

BFP, PRV, and ET are all based on local codes. I prefer to install all three at the time I do a new water service along with 2 new shut off valves... Why 2? It allows me to shut down the water and not drain the house down if either the PRV or BFP are leaking. Again... Just my preference and I have them set up in my warehouse before I even get to the job. Nice and tight and all of the dope has set in


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## TheEplumber (Jul 20, 2010)

bluebird5 said:


> no you misunderstood me. i am replacing the incoming line. my neighbor had the same issue and replaced the line but when he did he said his preasure was too high and he had to put a preasure reducer valve. so i am going to put a new line and a preasure reducer valve on the new line and i was just wondering about whether i need a backflow preventer. the house was plumbed in 1965 and right now there are no backflow preventers on anything. so i think i will put *one before the preasure reducer valve and on the cold waterline going into the waterheater.* sound good? can these valves become clogged? is there anything that i should do to chck them every now and then?


2 PRV's? Why? One on the service will do


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## secutanudu (Mar 15, 2009)

If you put a backflow preventer on your main water line, you will need an expansion tank on your water heater.


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## bluebird5 (Jan 24, 2011)

what is that and why?


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## bluebird5 (Jan 24, 2011)

TheEplumber said:


> 2 PRV's? Why? One on the service will do


 not 2 prv's 2 backflow preventers one for the water heater and one where the line enters the house


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## secutanudu (Mar 15, 2009)

Water expands when it is heated. If you have all faucets off, when your water heats up, it normally expands back into the water main a little. If you put a backflow preventor, this can no longer happen, and your pressure relief valve can leak. The expansion tank gives the water somewhere to go when it expands.


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## Daniel Holzman (Mar 10, 2009)

You should check with your town about the pressure coming in to your house, you may not need a pressure reducing valve. I can understand how a corroded inlet line would reduce flow, but it would not reduce static pressure at your house when there is no flow. Of course, you may already know the static pressure, and if it is too high, then of course you are going to need a pressure reducing valve.


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