Anti-scald feature

Discussion in 'Shower & Bathtub Forum & Blog' started by dx, Sep 8, 2015.

  1. dx

    dx General Contractor

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    Trying to understand how this works. I'm looking at the temp limit adjustment for a Kohler K304 shower valve. Seems it's just a travel stop for the valve. So if I adjust it for 120F max temp under existing conditions, it will be useless when someone changes the temp on the water heater. Am I correct?

    Quick call to Kohler and they say yes, if you increase the temp of water coming in, it can exceed 120F. Are you kidding? So every time the HO changes the setting on the heater, like going on vacation and back, your anti-scald feature is meaningless? I would think a true anti-scald should be absolute, not dependent on the water temp coming in. Do all valves work this way?
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    There are two components to passing the requirements for an anti-scald shower valve:
    - the ability to set a maximum temperature when everything's normal, and yes, this changes based on the season as the cold water temp changes and changes to the hot water coming in.
    - the automatic control of the BALENCE between the hot/cold volumes based on a variation in pressure that might be caused by say, someone flushing a toilet and dropping the cold water pressure, decreasing the cold supply momentarily. This is internal to the valve and adjusts itself.

    There is more than one way to perform that second task, but the more common method is a pressure balance spool valve; a second one, and this may also have a spool valve in addition, is a fast-acting thermostatically controlled valve (there is a maximum time allowed for the protection and not all designs of thermostatically controlled valves can adjust fast enough so some also have a pressure balance valve).

    SO, the max temp adjustment is only part of it, the automatic part comes into play once you've set your desired temp, and then variations caused by pressure issues, prevents it from becoming momentarily hotter because of changes in pressure. It will NOT automatically adjust the outlet temperature warmer as say you start to run out of hot water unless you've chosen a thermostatically controlled valve.
     
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  4. dx

    dx General Contractor

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    Jim, I understand all that. What I don't understand (well, maybe I understand, but I'm surprised at) is this: do all of these valves NOT contain a device /feature that prevents water over 120F from being discharged? Regardless of anything else?
     
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Essentially, the only one that might is a thermostatically controlled valve that was properly calibrated upon install - there, it's looking at an actual temperature verses a balance between hot and cold that could change. Technically, code calls for the outlet of the WH to not exceed 120-degrees F, regardless of how hot it is set except in certain situations. This is done with a tempering valve on the outlet of the WH. In the small city where I live, if you want to pass an inspection, you MUST have one installed to prevent water exceeding 120-degrees from entering the hot water supply lines, so the max setting at the individual valve becomes somewhat moot. It is likely that may become required more and more places in the future.
     
  6. dx

    dx General Contractor

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    Thanks Jim. Good explanation.
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    FWIW, there are tempering valves sized for point of use situations, so you could install one for your tub/shower. Hassle is, it's a wear item, and you'd need access to it to repair or replace. At least with a good thermostatically controlled valve, you can replace all of the required components without going behind the wall.

    [​IMG]

    Tempering valve under the lav cabinet.
     
    Last edited by a moderator: Sep 23, 2017
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