Back Flow Preventer

Blackoakbob

forever until I settled on piping it: shut off, rpz, tee, check valve, tee with a ball valve and bypass back to the first tee, fill valve, and then the system. I use the bypass for annual testing and find that the check eliminated the rpz dribbling due to rise and fall of system pressure. It's like setting up steam trap testing cocks, you can either spend a few dollars up front, make service and testing easier or you can fight with it everytime you do service. I appreciate it every time I have to check a trap that I can actually watch the function of it and make a swift diagnosis to repair,replace or know that it is working, for sure. Best Regards.

Tony_25

Back Flow Preventer.

I sometimes go on boiler jobs that have a Back Flow Preventer before the feed valve that leak. I know they are just doing there job preventing a back flow. They are costly to replace and if you have to charge a customer for one on a boiler that you installed recently , you know what they say. Its better than cutting it out or plugging it. Could it be possible to install one after the feed valve instead of before it. It should do the same thing.

JK_3

not really

By putting the backflow prenentor after the feed valve it would be affected by thermal axpansion. meaning that when the boiler pressure risses above the set pressure the backflow would open.

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Brad White_9

I agree

that Thermal Expansion may be a factor here. If your city water pressure is above 30 psig (it could be close to 80 of course) you would see relief valve dripping sooner than at the BFP. If the dribble is continuous it may be some crud under the seat too. Always good to check your expansion tank size and your pressure when run to limit just to be sure.

Steverino

BACKFLOW

I think the BFP's require 25 psi to "open". System pressure is normally 12 psi. With the fill valve 1st in line I don't think you're going to get any water past the BFP and into the boiler.

Brad White_9

Conventional

units like the Watts 900 series perhaps. But the residential/light duty Watts 9D will open with pressures in the single digits I believe. Certainly works on any residential system running about 12 psig.

JK_3

I beleive

Ibeleive that the watts 9d which is the most common back flow prevnter in my area works on single digit pressures as brad stated. If your fill valve is set to 12 lbs the 9d will dump water at any boiler pressure above that which is why it should be put before the fill valve then it wont dump unless your supply water pressure drops below the boiler pressure. In many casses this happens when the house main is shut off and drained without first shuting the boiler supply valve.The backflow is then doing its job off not allowing cross containation.As brad stated also if this occures you may get debris from the boiler in the seat of the backflow causing it to not close properly when the house pressure is restored. hope this helps.

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Steverino

sorry...

maybe I misred ad the question. I thought the intention was to install the fill valve, the BFP, then the boiler. I figured the fill valve didn't have enough pressure to get past the BFP. Watts says 25 psi to open.

Jerry_15

I agree with you on that one. I like to put them up-stream side so I can still work on the boiler/prv without cutting pressure to the bfv. Seems like every time they trip for any reason they never re-seat. But then I put in a y-strainer too. Good luck.

Weezbo

the reason for the back flow...

isnt to regulate boiler pressure. by having the regulator then the backflow then the t at the ponp what would happen with a pressure loss before the regulator?

it would require another check valve on the regulator , to keep the feed water from operating in reverse right?the diaphram in the regulator would essentially become a vaccum pump in reverse backing off the available pressure on the BFP.

the right way would at least check the flow against the supply side of the regulator.

Jerry_15

Sorry Brad - the back flow preventer doesn't give a damn about the system pressure, unless it's too low or cuts out. when they go off they may not re-seat. See my note below. These things are a royal pain, in SF you have to get them inspected and approved by the health dept every year. I kid you not.

Mr. Blonde

soft seat check

If your talking about intermittent spitting of water then this is normal. Anytime you get a change in water preasure, like opening a faucet or flushing the stool the backflow is affected by it which causes this. The easy fix is to install a soft seat check valve in front of it so its isolated from these preasure changes and unaffected. If your seeing a steady stream of water coming from it then one or both of the check valves are fouled with debris and it will need disassembled and cleaned. There should be a strainer installed before the backflow to help keep it free of debris.

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Unknown

I agree

I agree with Jerry, these backflow preventor are a real PITA.. 9 out of 10 will "dry stuck" closed...and when u really needs to add water into the system, have to take them out to unstuck and reinstalls the unit...after that, they leaks... Then u replaces them and customers blamed me for "ruining" them... IMHO, pressure reducing valves been working fine all these years and I have not seen them leaky water out... How I know this... During boiler replacments, first thing I do before draining the system.. I disconnect the supply between the shut off and pressure reducing valve.... Nothing comes out... Been working fine all these years.... Its those plumbing inpectors trying to keep their jobs....