[RE-wrenches] SWH - mixing valves

Kelly Keilwitz, Whidbey Sun & Wind kelly at whidbeysunwind.com
Thu May 20 09:12:11 PDT 2010


Hi Bill,
The valves are the AM-1 series. I wasn't aware that these incorporate  
check valves. In fact, we have had problems in some systems having HW  
recirculation with the hot circulating back through the cold supply,  
causing us to install separate check valves in the cold lines (which  
we install as standard practice, now). The specifications say, "Check  
valves, as indicated, may be installed, to prevent migration of hot  
water into the cold branch, and cold water into the hot branch through  
the SparcoMix Valve". The "indicated" check valves on the spec  
schematics are external to the AM-1 mix valve. Are integrated check  
valves a relatively new feature? My specs are old, and we haven't  
installed any new valves within the past year or so.

I have seen the "crossover" problem on some systems. I don't think  
that is the cause, here. I have (calibrated) temp gauges on the hot  
and the mix lines right at the mixing valve to see what's going out. I  
suspect THAT is the problem - I can SEE that it's not working right,  
whereas most people don't know and just adjust the temp at the  
faucet......

-Kelly
Kelly Keilwitz, P.E.
Whidbey Sun & Wind
Renewable Energy Systems
kelly at whidbeysunwind.com
360-678-7131


On May 20, 2010, at 4:29 AM, Bill Loesch wrote:

>
> Hi again, Kelly,
>
> You mentioned backflow issues in your post, which I should have  
> addressed
> with my previous reply.
>
> If the Honeywell valve you are using is a Honeywell AM-1  
> Thermostatic Mixing
> Valve it incorporates dual check valves on the inlets. Those check  
> valves
> are removable and those check valves are also susceptible to scaling  
> if the
> water quality is deficient. (See previous post.) The AM-1 has a Teflon
> coating which would delay the effects of scaling, but would ultimately
> succumb. The integrated check valves as well as the mixing valve  
> itself,
> will also produce a pressure reduction in the system.
>
> A phenomena known in the plumbing trade as "plumbing crossover" and  
> perhaps
> more descriptively labeled as plumbing bypass, is the situation where
> (typically) the cold water flows into the hot water side. This can be
> illustrated with the homebrew shower where the throttling valves on  
> the hot
> and cold lines are supplemented with a third valve to allow the mixing
> (throttling) valves to remain preset and the shutoff is downstream  
> of the
> two mix valves. This is an excellent written illustration and  
> relatively
> obvious. Unfortunately, what is much more common is the not so  
> obvious,
> widespread use of  single handle faucets. Once the seals on the  
> cartridge,
> module, insert (terminology dependent on manufacturer) become worn,  
> the same
> situation exists with the single handle faucet as described with the
> homebrew three valve shower.
>
> The easy test for this condition is to stop the flow of hot water at  
> the
> source, then open all hot water faucets. _Any_ flow, at any faucet,  
> after a
> delay to allow gravity drainage to occur, would indicate a plumbing
> crossover/bypass _somewhere_ in the system.
>
> Some single handle faucets also incorporate dual check valves into  
> their
> construction. Again, poor water quality can render those inop in  
> either or
> both directions.
>
> Thanks for your interest in getting a solution to this pesky problem.
>
> Bill Loesch
> Solar 1 - Saint Louis Solar
>
>
>
> ----- Original Message -----
> From: "Kelly Keilwitz, Whidbey Sun & Wind" <kelly at whidbeysunwind.com>
> To: "RE Wrenches listserve" <re-wrenches at lists.re-wrenches.org>
> Sent: Wednesday, May 19, 2010 1:14 AM
> Subject: [RE-wrenches] SWH - mixing valves
>
>
>> Thermal wrenches,
>> I'm having an ongoing issue with mixing valves in my own system not
>> keeping a steady mix domestic HW temperature as the tank temperature
>> varies with solar heating. If I set it for (say) 122˚F mix when the
>> tank is 135˚, it seems to hold that differential at all tank temps -
>> i.e. when the tank is hotter the mix is too hot (sometimes  
>> dangerously
>> so), and when colder the mix is too cold for a comfortable shower.
>> Thus, I need to change the setting all the time.
>>
>> I'm now using a Honeywell valve with a 100˚ - 145˚ range. This is a
>> replacement for a valve with a wider range that acted the same way.
>> Any ideas,  suggestions for better valves, or....?
>>
>> This has me wondering how many of our SWH customers are  
>> experiencing a
>> similar thing, but just aren't bothered enough to say anything. We
>> seem to have encountered many plumbing situations where the mixing
>> valve allowed weird backflow or siphoning situations to mess with
>> system operation, especially with HW recirculation. I thought I had
>> all such causes eliminated on my system, but maybe not.
>>
>> Thanks for sharing your experience with such matters.
>> -Kelly
>>
>> Kelly Keilwitz, P.E.
>> Whidbey Sun & Wind
>> Renewable Energy Systems
>> kelly at whidbeysunwind.com
>> 360-678-7131
>>
>>
>>
>>
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