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    Backflow preventers (15 Posts)

  • Wayco Wayne Wayco Wayne @ 7:59 AM
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    Backflow preventers

    Hey y'all. I need a simple explanation of why backflow preventers are needed on domestic potable hot water tanks. About 4 years ago our area started requiring them along with potable expansion tanks of course. I understand why a boiler system needs them, because boiler water is nasty stuff. But not why a potable water heater? I'm hvac so I'm not so much into the plumbing, but I've seen several systems where the expansion tank pressure has not been maintained and the result is a flooded basement. What problem is being dealt with and is it worth creating the flooding problems? Thanks for your information.
  • Mark Eatherton Mark Eatherton @ 8:30 AM
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    Cross connection potential...

    Wayne, The water authority is required to eliminate any back flow/cross connection conditions that are not covered by the conventional means (air gap).

    This means that if there is a 1 in 1,000,000 chance in a cross connection between water of questionable character (boilerwa) and the potable water, that an approved means of cross connection control be employed.

    Our AHJ's used to require the same thing. We convinced them that we could control cross connections with the use of normally closed EBV ball valves on the heating lines between the boiler and the DHW tank, controlled by a pressure differential controller. If the potable water had more pressure than the boiler water, the valves would close. It was slightly more expensive than BFP on initial cost, but didn't require annual inspections.

    Through education, we have finally convinced them that there really is no need for this protection, because if a heat exchanger fails and cross connects, the water will flow from the potable system (high pressure) TO the non potable (low pressure) system and will show in the form of a leak that can not be ignored.

    To avoid the requirement for a BFP on the boilers make up, we eliminated the make up in lieu of The PIG, which satisfied their needs.

    Commercially, we have to use a RZPBFP even if we are employing our Excess Flow Preventer.

    A little education might go a long was in your case. Many times, they just look at it from the "potential" point of view, and not necessarily from the real world perspective.

    Good luck

    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • icesailor icesailor @ 8:57 AM
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    Backflow:

    Mark,
    All that you say is true and the conventional wisdom of some.
    My concern against is my over riding belief in the laws of intended consequences. That no good deed will remain unpunished.
    In MA, ALL water heater tanks MUST have a approved vacuum relief device installed on the cold water inlet. Because if there is a fire near by, and the guy on the fire truck does not keep an eye on his gauges, he can easily pull a vacuum on the system. Which can collapse a tank. Easily.
    If "AHJ" is "Authority Having Jurisdiction", then the easiest way around these problems is to require all buildings to be backflow protected.
    I'll tell you something I have seen quite often.
    Where I work, they have a public water system. Depending on altitude, the system pressure runs between 45# to 65#. There are many lawn irrigation systems. They all have some sort of a Watts 800 back flow device. When they drain them in the Fall, they blow them out with air. Usually set at 100# with a compressor. There have been a number of occasions where someone did not shut off the right valves and when they air pressurized the system, the air backed out of the building through the underground service, through the mains and went into other houses in the area.
    If something can go wrong, it can.
    And they shouldn't be using 100# PSI air pressure to blow 80#PSI poly irrigation pipe. It makes splits. Seen that.
  • icesailor icesailor @ 8:36 AM
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    Backflow Preventers:

    This is coming from the Feds/EPA. They are trying to protect public water systems from cross contamination. There are many forms of cross contamination. They can come from anywhere. If the potable water system isn't protected from backflow, and there is a breach in the systen where the pressure drops, water can flow back into the systems from any place. System integrety depends on water flowing out, not back in once it left.
    Which can cause the next problem, overpressure. Most fixture manufacturers do not warranty their fixtures when operating over 75#. And a shower head delivering water at 75# hurts. Hence, pressure reducing valves on potable water systems. Less blown washing machine hoses and floods. Then, you need a Extrol like tank for water expansion to go. Like the expansion in a water system from a water heater heating.
    New water systems or old ones, that install meters, will be required to use meter hangers/setters that have built in check valves on the outlet side to stop water from backing out.
    If you install a water softner or any other type of water treatment where anything of an unknown quality is put in to the potable water of a building, it can not, by law, be introduced into the public water system. That is why you can not under any circumstances, have a private well/water system, piped in any way where you can turn a series of valves and switch from public or private water systems. They MUST be physically seperated and inspected.
    And if you have a irrigation system, or any system wherebackflow can occur, you need a special double check system that must be inspected annually for proper operation.
    It is all to protect the public drinking system.
    In the 1960's, over 90 of just over 100 of the Holy Cross college football players came down with infectious hepititis from drinking contaminated water at a drinking fountain. The only players who didn;t get sick had not drank from the fountain.
    Backflows keep you safe and well.
  • TonyS TonyS @ 9:02 AM
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    Seems a little ridiculous

    There are plenty of places in a domestic system for crossover...wash machine valves, single handle valves,ect. I dont see the reason.
  • icesailor icesailor @ 9:10 AM
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    Backflow:

    Washing Machines have a air gap built in side. Same with dishwashers. Faucets on fixtures have a air gap usually over 2.5 times the diameter of the outlet pipe. Whirlpool tube with subnerged fillers must pass through a air gap fitting. Trap re-sealers must pass through a air gap fitting.
    Everything in plumbing is to protect the safety of the potable water system.
  • TonyS TonyS @ 5:26 PM
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    icesailor

    you misunderstand. These devices have airgaps to protect the potable water from cross contamination of the water once inside the device but there is nothing to stop cold and hot lines from passing over to each other( there is only hot to a dishwasher..no problem there) even a two handle valve when both handles are open is a direct crossover...pressures will equalize. Wash machines are notorious for this. You never had a customer complain about the cold water being warm and all you had to do was turn off the single handle wash machine valve? Stops on the shower head also allow hot and cold lines to cross connect and equalize unless you install checks on both hot and cold lines before the valve( I doubt that). The check valve installed by Wayne may just be to stop thermal migration of the water tank.
  • Jean-David Beyer Jean-David Beyer @ 9:22 AM
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    other crossovers

    In my darkroom is a "washtub" valve: hot and cold come in, and essentially a hose bib comes out. Screwed onto this is a foot-or-so long flexible hose that can end in a tray of photo chemicals. To make matters worse, this is on the second floor of my house, and the toilet, diswasher, and washing machine are on the first floor, and a hose bib outside is even lower than that. Now if everything downstairs were full on at the same time, this might suck water out of the tray into the water system. I do not know for sure what the water pressure here is, but it is pretty good. On my second floor, it is high enough to pin a water pressure gauge that reads to 30 psi, so it is at least that. To guard against problems, I installed vacuum breakers where the hot and cold water enter my darkroom, so if the supply pressure drops too much,  air will be sucked in in preference to the (possibly contaminated) water.

    I also have a Lawler pressure balancing temperature regulating valve. It comes with a check valve in both the hot and cold supply lines, but those are not likely to be sufficient for health concerns, but they probably keep the hot and cold supplies from mixing. That valve has a vacuum breaker at its output too.

    http://www.lawlervalve.com/index.php?p=product&id=25&parent=5
  • icesailor icesailor @ 11:18 AM
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    Backflow Preventers:

    JBD,
    I am from MA and our codes are very specific about backflows. I don't have a code book with me but darkroom/photo labs are very specific and need special protection. Because you can leave the wash hose in a sink where the end of the hose is "below the flood level of the rim". And that is the key in much of the backflow world. That the water that flows out of the faucet, into a receptable must pass through free atmosphere before it can enter a fixture that COULD be full of water from an unknown source or quality. On photo labs, it may be just a backflow preventer on the hose at the valve, NOT the end of the hose.
    Pull out kitchen sink faucets have vacuum breaker.back flow devices inside them.
    The mix valve for washing should have checks on the hot and cold so you do not get cross flow between the hot and cold water.
    You need a backflow device on outside hose hydrants. If you put a chemical sprayer on the end of your hose, it could end up in your house.
    Come up with any plumbing device and I will try to tell you where the backflow device is or should be.
    Some places are down right nasty. Like mortuarys or dental offices. Slaughterhouses, butcher shops, heating systems with anti-freeze in them. You wouldn't want that stuff backing out and contaminating your or someone else's house.
    It's nasty.  
  • Jean-David Beyer Jean-David Beyer @ 4:29 PM
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    I agree.

    I respect the Massachusetts code,  as I understand it. I have never seen it, but I can tell something about it because the I&M manual for my boiler has one set of drawings for installation, and an additional set of drawings if you are in Masachusetts.

    As far as my darkroom is concerned, I think I am pretty close. The air gaps are missing or too small because of the design of some of the items. The temperature controlled mixer valve has check valves at the input and a vacuum breaker at the output. The "wash-tub"
    valve has neither built in, but I have vacuum breakers just before it. I suppose I could put check valves on the input of that valve, but as a practical matter, the pressure in the hot and cold water lines is very close to the same, so I have never in 34 years noticed hot water coming out the cold. I recognize that this is not the same as obeying a code, if it exists here. I am not a professional, but I have never seen a laundry tub faucet with checkvalves on it. Similarly outdoor hose bibs. I have seen lawn-watering equipment with vacuum breakers.

    I just looked at my relatively new kitchen sink pull out squirter and see no evidence of any check valves, backflow preventers, or air gaps. The nearest thing is a little valve, that they call a "diverter" that senses that I am calling for water at the sprayer, and sends the water that way. It might be code, but I would not consider that thing very reliable, an would never consider it suitable  for hygenic safety. It is a Kohler K-8763 valve.

    My outdoor hose bib has no check valve, no vacuum breaker, and no anti-backflow valve. I imagine the neighbors are safe from my darkroom, my boiler (that has an anti-backflow valve), and some other appliances, but not from the outside hose bib, my hot water tank, and probably the kitchen sink sprayer. I am not so sure about the Gerber toilet. The gap is there for the shower, the bathroom sink, and the kitchen sink main outlet. I suppose the next time I have a plumber around here, I could have an anti-backflow installed where the water enters the house. I would have to add an expansion tank, and maybe a vacuum breaker there as well. When the plumbing inspector was here last, all that stuff was in plain sight, and he said nothing.
  • icesailor icesailor @ 10:39 AM
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    Backflow checks:

    JDB,
    Lets see if I can cover it all.
    Your darkroom may have a Symmons valve. I believe they have internal checks. Because they are known to be :on" all the time, they need to have the checks to not allow hot and cold pater to flow through other.
    Laundry tray usually have a cheap faucet that had a 3/4" male hose fitting so you can but a short piece of hose on it to fill a bucket. The problem arises when you put a male hose on the outlet with a shut off sprayer fitting and don't shut off the hot and cold on the laundry sink. You now have a direct closed loop connection between the hot and cold. The same you would have on your photo mixer without the checks. The pressure between hot and cold isn't equal because it only takes a 7.5 degree rise in temperature to cause circulation.
    The check valve on your Kohler faucet is in the spray hose or the handle/spray. You probably noticed that there isn't a lot of pressure in the faucet. If you unscrew the spray handle and turn on the water, and the strainer thingey isn't there, you have a lot more pressure. Look into the inlet of the handle. You will see that something covers most of the hole. That is the check valve. If you remove it (it isn't easy) you will see a remarkable improvement in water flow.
    As far as outside faucets with back-flow protection, if you have a frost proof design, it will be on top, behind the handle. If it doesn't have it, there will be no plastic cap behind the handle. If you do not remove the hose in winter, freezing weather, the cap and check assembly may blow off. The ones without the device with the hose on will just break inside the wall in the house and when you turn it on in the spring to use it, you will have very little pressure and the water will be flooding the inside of the house. Remove the hose.
    The old kinds do not do this. But, they have a screw on device that goes on the end with a screw you must tighten to keep from removing it. It breaks off flush when you get it tight. They are a PITA because my place in Florida had them on it when we bought the place and they both leaked. I had to cut them off because the hose bibs were soldered in to the copper pipe rather than use adapters that you could change.
    There is stuff around that you don't even know about. It is set in our codes. Like GFCI  in bathrooms and grounded outlets. Some things we take for granted but we don't know what they are. Like being safe.
  • Jean-David Beyer Jean-David Beyer @ 1:00 PM
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    Backflow checks.

    "Your darkroom may have a Symmons valve. I believe they have internal
    checks. Because they are known to be :on" all the time, they need to
    have the checks to not allow hot and cold water to flow through other."

    I I just looked up Symmons valves They are different from mine in that none of the ones I could find included a pressure-balancing stage before the temperature controlling stage. This probably does not matter much for the present discussion. Mine is Lawlor, and it has check valves as separate (but supplied with the valve) components.They may leak slightly so a slight amount of hot water could leak into the cold. I am not sure because the first thing the hot and cold water get to is a pressure balancing stage so the water delivered from there is at the same pressure (hot and cold) before it enters the temperature controlling stage of the valve. In the second stage, the pressures of the hot and cold water are the same, so there should be no net flow through the valve between hot and cold. If the output of the valve is shut off is about the only time mixing of hot and cold could take place. I  hope the check valves that are definately installed there would take care of this. But as far as I can tell, the pressures of the hot and cold water up there are the same.

    "Laundry tray usually have a cheap faucet that had a 3/4" male hose
    fitting so you can but a short piece of hose on it to fill a bucket.The problem arises when you put a male hose on the outlet with a shut
    off sprayer fitting and don't shut off the hot and cold on the laundry
    sink. You now have a direct closed loop connection between the hot and
    cold."

    I know that. That is why I put vacuum breakers on the input to the darkroom, so if the supply pressure drops, air is sucked in in preference to siphoning stuff into the water system. That is to handle sniffing stuff out of a try back into the water system. I never have a shut-off there. They seem to work, though after about 25 years I had to replace the vacuum breakers because they were not working as well as when they were new. Feeling lazy, I asked a plumber to replace them, and he said they were not made any more and that a check valve would do. I suppose putting an anti-backflow valve in both the hot and cold water supply would work, but not the swing type check valve he proposed. That was crazy, so I got them myself and replaced them. The laundry valve has no path from hot to cold if either of the faucets is turned off. In normal use, the output is always open, though possibly under an inch or two of water. There is no shutoff on the output of that, as you say, cheap laundry faucet. I tried to get a better one, but they do not seem to make good ones.

    "The same you would have on your photo mixer without the checks. The
    pressure between hot and cold isn't equal because it only takes a 7.5
    degree rise in temperature to cause circulation."

    I had been thinking about greater pressure differences, but you are certainly right. On the other hand, there is an 8-foot drop for the hot and cold water before it could get from my darkroom to the rest of the water pipinig. It might take more than 7.5 degree drop to get the hot water to go down that far in the cold water line. I was more concerned if someone flushed the toilet lowering the cold water pressure more than the hot, and getting flow that way.

    "The check valve on your Kohler faucet is in the spray hose or the handle/spray."

    I suppose you are right. Hard to tell by looking. There are three copper tubes coming out of the valve, one for hot, one for cold, one for sprayer. Everything happens in the machined casting or in the open end of the sprayer hose. And the diagram offered by Kohler is too small to see how the gizmo in the valve actually works. It must notice when the sprayer is open and route the mixed water there instead of the normal spigot. There is nothing in the hose itself. There may be something in the assembly where the sprayer is.

    "As far as outside faucets with back-flow protection, if you have a frost
    proof design, it will be on top, behind the handle. If it doesn't have
    it, there will be no plastic cap behind the handle. If you do not remove
    the hose in winter, freezing weather, the cap and check assembly may
    blow off. The ones without the device with the hose on will just break
    inside the wall in the house and when you turn it on in the spring to
    use it, you will have very little pressure and the water will be
    flooding the inside of the house. Remove the hose.

    The old kinds do not do this."

    I have the old kind. When the original hose bib crumbled due to old age, I got a plumber to replace it (because the inside shut off also failed, as did the main valve to the house). He put in a frost-proof one that the handle outside turns off the valve inside. But no back flow protection that I can see. No plastic anything. I always turn that off just before Halloween, and take the hose into the garage. Vandalism reduction.

    "There is stuff around that you don't even know about. It is set in our
    codes. Like GFCI  in bathrooms and grounded outlets. Some things we take
    for granted but we don't know what they are. Like being safe."

    I know what ground fault interrupters are.  I have them all over the house. One for my darkroom, three for my kitchen, even one for the outlet next to my boiler as a favor for the technician working on it.

    As far as codes are concerned, I have nothing against them. In fact I am in favor of them. But in my 1950s house, who knows what the codes were when it was built? Who knows if it was ever inspected. My old hot water boiler had no pressure relief valve. It had no low water cutoff. It had no anti-backflow valve. My domestic water still has no anti-backflow valve even though the plumbing inspector looked at everything (sort-of) when I had my old boiler replaced.
  • TonyS TonyS @ 9:16 PM
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    What type of backflow preventer

    are they calling for?
  • Wayco Wayne Wayco Wayne @ 7:32 AM
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    In my case

    The crossover would be the heat exchanger in an indirect water heater. I've been told if the HX had a breach the boiler water could get in to the potable water, if the house water was drained for some purpose. Seems far fetched to me. The most likely scenario is if you had a failed HX the water house pressure would be alive and would most likely be much higher than the boiler water pressure. It would fill the boiler side with the higher pressure and pop the 30 psi T and P valve alerting the home owner to the problem. Like I said in the original post, it causes more problems than it solves. I think there is a larger chance of monkeys flying out of my butt, but I don't wear crotchless underwear in case it happens. :) 
  • Gordan Gordan @ 7:45 AM
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    So if you don't wear crotchless underwear for that reason...

    ...what is the reason? :-)
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