cbass Posted January 28, 2011 Report Posted January 28, 2011 Can someone shed some light on whey there would be three PRV's on this water heater? Click to Enlarge 51.41 KB
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Obviously because, if one is good, three must be better. - Jim Katen, Oregon
Brandon Whitmore Posted January 28, 2011 Report Posted January 28, 2011 So when water shoots out, it hits you in the face from multiple locations.
hausdok Posted January 28, 2011 Report Posted January 28, 2011 Hi, Because you don't have three PRV's; you have two plus a Watts 210 automatic gas shutoff valve because that's a basement installation. They've been installed in an alternate configuration because there aren't any side tappings on the tank. A gas pipe is supposed to be plumbed to both sides of the 210 - the one with the green reset button - and that TPR on top of the tank should be in that line to the left of the 210 and it's hole on top of the tank plugged. Then the discharge lines from both TPR's should terminate near the floor. Look at figure two of the attached document. Download Attachment: Watts210Installation.pdf 640.08 KB ONE TEAM - ONE FIGHT!!! Mike
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Hi, Because you don't have three PRV's; you have two plus a Watts 210 automatic gas shutoff valve because that's a basement installation. They've been installed in an alternate configuration because there aren't any side tappings on the tank. A gas pipe is supposed to be plumbed to both sides of the 210 - the one with the green reset button - and that TPR on top of the tank should be in that line to the left of the 210 and it's hole on top of the tank plugged. Then the discharge lines from both TPR's should terminate near the floor. If a Watts 210 valve still requires a pressure relief valve that drains onto the floor, what's the point of the Watts 210? Why not just use a TPR that drains to the floor? - Jim Katen, Oregon
hausdok Posted January 28, 2011 Report Posted January 28, 2011 Hi Jim, The watts shuts off the gas and prevents an explosion. However, if the watts fails, they have the other two TPR valves there and they will activate. ONE TEAM - ONE FIGHT!!! Mike
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Hi Jim, The watts shuts off the gas and prevents an explosion. However, if the watts fails, they have the other two TPR valves there and they will activate. ONE TEAM - ONE FIGHT!!! Mike As I understand it, the Watts 210 only requires a single pressure reducing valve, not two TPRs. At least that's what the document you posted shows. (The Watts 210 only responds to heat, not pressure, so you still need a separate safety valve to guard against high pressure.) But what I'm wondering is why someone would use a Watts 210 instead of simply using a TPR and then put a pressure reducing valve down near the water heater where it would have to drain to the floor anyway. (Or, in this case, onto someone's face.) A TPR valve will prevent an explosion just as well as the Watts 210. If you don't want to use a TPR because it might spill water all over the basement floor, why use a Watts 210 and install a PRV in a location that will spill water all over the basement floor anyway? Seems to me that the PRV should be way up high so that it can drain by gravity to the backyard or somewhere similar. - Jim Katen, Oregon
hausdok Posted January 28, 2011 Report Posted January 28, 2011 Hi Jim, Your response has me a little confused. You repeatedly refer to a pressure reducing valve and say that the document specs one. Either I'm suffering from dementia or there is nothing on that document that specifies a pressure reducing valve and only pressure relief valves are specified. I agree, the document only requires one pressure relief valve. The diagrams for various options all show a 210 used with a pressure relief valve and show an alternate location that can be used for the pressure relief valve. In that photo posted by the O.P.,I think that someone was trying to copy those diagrams and didn't realize that the second relief valve shown in the diagram is an alternate location; possibly because they'd become confused because the second and third drawings are labeled alternative installation. I think they also didn't realize that a pressure relief valve and a TPR aren't the same device. The whole idea of the 210, as you've stated, is to shut off the gas and a pressure relief valve is required in addition to the 210. Because the tank is in a basement, they don't have any way to drain a TPR valve via gravity to the outside so the alternative is to kill the flame and allow the tank to cool. The 210 is set to open at 210°F. If it doesn't function they still need to relieve the pressure that's inevitably going to occur. I agree, it makes more sense to put it up high so that it can drain to the outside, but it's a last chance fail safe anyway. Around here, plumbers skin that cat differently. They install a TPR high on the line that will activate at 125 pounds instead of the normal 150 pounds. The discharge pipe plumbed from that valve goes outside or to some kind of receptor. They then leave the original TPR that activates at 150 pounds on the tank and end the discharge pipe just above the floor (usually). I think the idea is that the TPR high in the line will vent at 125 pounds regardless of temperature. They know that the temperature sensing aspect of that valve can't function correctly up high on the pipe, but it's only functioning as a pressure relief valve anyway so they aren't concerned with that aspect. However, if that lighter spec TPR doesn't activate at 125 pounds they still have the original TPR which will activate at either of 150 pounds or 210°F whichever occurs first. If that happens, the valve is going to dump hot water all over the basement regardless; unless the discharge goes to some kind of receptor. I suppose if the lighter spec valve fails and the other vents into the home they might justify that by pointing out that they'd done everything that the could under the circumstances, by installing a safety device on the system that was plumbed outside as required by code, but that it had failed and the second device, although it allowed some damage to occur, prevented a catastrophic explosion. After seeing so many critical structural members hacked up by plumbers without any sign that they'd informed anyone about it so that alternative framing could be constructed around the plumbing in question, I've given up trying to figure out plumbers' thought processes. ONE TEAM - ONE FIGHT!!! Mike
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Hi Jim, Your response has me a little confused. You repeatedly refer to a pressure reducing valve and say that the document specs one. Either I'm suffering from dementia or there is nothing on that document that specifies a pressure reducing valve and only pressure relief valves are specified. . . Ah yes, I was thinking pressure relief valve but typed reducing. I understand the strategy behind the valve. I just think that the Watts 210 solution is a useless exercise in complication unless you can get the pressure relief valve to drain to another location. Aside from their normal operation, these valves sometimes leak. (I've seen two leakers in the last month.) It just seems that, if you don't want water on your floor, you shouldn't be plumbing discharge valves there.
kurt Posted January 28, 2011 Report Posted January 28, 2011 Don't you guys put drain pans under the water heaters?
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Don't you guys put drain pans under the water heaters? Sure but some of our basements lack drains for the catch pan to dump into. Without a drain, the pans can only hold a few gallons of water.
kurt Posted January 28, 2011 Report Posted January 28, 2011 Bilge pump in the pan, just like a condensate pump for a furnace. Small problem is, most (all) marine bilge pumps operate on 12 volts; you need a transformer. This confuses people.
Jim Katen Posted January 28, 2011 Report Posted January 28, 2011 Bilge pump in the pan, just like a condensate pump for a furnace. Small problem is, most (all) marine bilge pumps operate on 12 volts; you need a transformer. This confuses people. Can a bilge pump keep up with a TPR valve that's stuck wide open? - Jim Katen, Oregon
Firm Foundation Posted February 24, 2011 Report Posted February 24, 2011 Bilge pump in the pan, just like a condensate pump for a furnace. Small problem is, most (all) marine bilge pumps operate on 12 volts; you need a transformer. This confuses people. Can a bilge pump keep up with a TPR valve that's stuck wide open? - Jim Katen, Oregon Yes.
gpdewitt Posted February 26, 2011 Report Posted February 26, 2011 Violates code here in CA to plumb the tpr line into the pan under the WH. In fact, it must terminate outside 6-24" from the ground. When this is an expensive safety upgrade, I recommend a Watts. Looks like an old vent on a newer WH, there's a good chance it doesn't meet the manufacturers installation requirements.
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