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Parallel Tempering Valve Advice

BigRob Member Posts: 308
My Powers LHMM434-1 tempering valve was oversized by 4 sizes and the thermal actuator seems to be shot. The factory helped me troubleshoot it and they were very helpful. The LHMM431-1 valve body doesn't work with the 434-1 check stops, so that is a bummer that requires me to remove everything. Before the Powers 434 the building had a MX128 that worked well for over 10 years. It was changed when we had a new tank installed because San Francisco hasn't allowed lead fittings for a while now. I called Honeywell and they say there are no plans to make the MX128 lead free.

I'm considering putting two Honeywell AMX102-UT-1LF's in parallel. Thoughts? Should I reverse return them or stage them?

I came up with 113 fixture units for our building using an online guide. 7 units have 2 full baths with tubs w/overhead showers. Five units have 2.5 baths with tubs w/overhead showers. All 12 units have dishwashers and laundry. 113 fixtures units is around 33-38gpm based on some stuff I found online. Using the powers web tool with the apartment/multifamily option and adding 12 laundry units I get 29gpm.

Has anyone created a manifold to favor one valve without using a differential pressure valve? I will add isolation valve, too. I suspect the AMX will be around for a while.


  • icesailor
    icesailor Member Posts: 7,265
    Oversize valves:

    It is my (limited) experience that if you install a oversized mixer in an application like yours, they do NOT work well in your application.

    Your application needs a true thermostatic-pressure-balance valve.

    Look into this one.


    They meet lead free requirements. They have been around for a long time. In a place like yours, a oversize valve will NOT work at little or no flow. The higher the flow, the better the valve works. I dealt with them on a nursing home that had a improper valve installed. I installed their valve over 20 years ago and never once had any issues with parts. Honeywell, Symmons, Watts etc. were NOT in the thermostatic hot water controller business. When I had my issues, all passed me off to Leonard. They have been in the thermostatic control business for a very long time.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Oversize P-T valves do not work well.

    My first hand experience with a very fancy one by Lawler is the basis for my opinion. They used to make such valves for photographic darkrooms where it is desired to hold the temperature to +|- 1/2 degree. And they come in various sizes. Mine is the smallest, and regulates from 1/2 gpm up to about 3 gpm. The ones most used regulate from about 2 gpm to 7 gpm, and larger ones were available. I do not think they make any of these anymore.

    Mine is pretty much like this one, but this one is the next larger size:


    My unit has a check valve at the hot input, another one at the cold input, a vacuum breaker at the valve output. Inside, the hot and cold go to a pressure balancer and from there to the temperature regulator. This has a big knob for you to set the temperature. It goes around about 3 full turns. At the output is a large temperature dial that you can easily read to 1/2 degree. Now when I need accurate temperature, I must run it at 1/2 gallon per minute or a little more, or it does not hold the temperature. the valve (especially the pressure balancer) needs a pressure drop through it to activate that, and and lower flow rates, it does not get it. And if the pressure balancer is too far off, the temperature controller cannot move far enough to compensate. If they made a valve from 1/4 gpm to 1 1/2 gpm, I would be much better off. They still make shower valves.
  • BigRob
    BigRob Member Posts: 308

    Thanks for the advice. Would you guys use a pressure reducing valve to stage two valves or not even bother?
  • icesailor
    icesailor Member Posts: 7,265
    Parellel Piping:


    It matters not one bit to me what you do.

    But look at the site for Leonard Valves I posted. Your question about using reducing valves is already covered by them. If you know what you are trying to do and understand the "issues", you will get the idea of what your obstacles are. Leonard has been doing it for a long time. Buildings like you are dealing with have issues because most of the time the flow is too low for a valve to work properly. So if you use a valve that is "properly sized" for maximum flow, it won't work at low flow. So, use a small valve  and a reducing valve that will open when the pressure drops and then the larger valve starts to work.

    If you read up on their site, you might get an understanding of the concept and how it works. You'll understand why "oversized" valves are so bad. You should size the valve for the maximum flow with the lowest flow and not the other way around. Look at it like a Multi-Zone heating system with zone valves.

    How do I know? Experience.

    Its just the same as a heating system with a modulating boiler or Variable Speed circulator. Same problem, same principle.
  • BigRob
    BigRob Member Posts: 308

    I looked at the Lawler literature and I think you are right - they seem to have a good, if not best design.  The spring/actuator makes a lot of sense in the 800 series.  The 802 looks like a good fit at first glance.  They are not cheap.  Quality rarely is.  Thanks for the suggestion.