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
ke...@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" <ke...@whidbeysunwind.com>
To: "RE Wrenches listserve" <re-wrenches@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
ke...@whidbeysunwind.com
360-678-7131
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