This is really off topic, but maybe I can get some help here,
or from some one, or from some one some one of you may=20
know who knows how things work. It has to do with the=20
oven gas valve in my old '50's vintage Kenmore range.

The oven worked unreliably, and finally would not ignite.
Examination revealed everything apparently in order, with a
good pilot flame centered in the element which it heats. But
the "thermostat", which appears to be a sealed wire-wound
potentiometer, did not feel right, and did not test consistently
with an ohm meter. Function was restored by drifting in TV
tuner cleaner and exercising the control. Which is to say that
the oven now works like new. When the oven is off, there is
infinite resistance across the "thermostat" terminals. On, there is
a low variable resistance.

Sears has been famous for supplying parts for its stuff, but has
let us down monumentally in recent years. Needless to say,
parts for this old range are not available.

My problem is this -- I do not have the faintest idea how this
system works. There are two skinny cylinders, which are
connected to the main valve by narrow copper tubing, and
the pilot also, which heats one of the cylinders. The other=20
cylinder senses oven temperature at the exhaust vent. And
there are the two wires to the above-mentioned potentiometer.
Although the range has a light and a clock, there is no electrical
power to the oven gas valve.

I can imagine a resistive bridge circuit between the potentiometer
and the heat sensor, assuming it is a thermocouple, maybe driven
by power generated by the device heated by the pilot flame, assuming
it is a thermocouple. However, in my experience, such-looking things
have sometimes turned out to be hydraulic devices containing mercury.
In any case, I cannot begin to guess how the force to open and close
the gas valve is generated.

Please, if you can help me to understand my gas valve, REPLY BY EMAIL,=20
as this is not a topic of general interest. (There does not seem to be
much about this valve on the Internet. It is one where the pilot flame
does not increase when the oven is started.)

For those of you who may wonder why I continue to wonder after
the fault is removed, be informed of the guiding principle:

When and if you do something right, you should always try to find out
how that happened. (Even taking notes!)

--=20
Dick Adams
<firstname> dot <lastname> at bigfoot dot com
___________________
Sourdough FAQ guide at=20
http://www.nyx.net/~dgreenw/sourdoughfaqs.html

Dick Adams wrote:

> Please, if you can help me to understand my gas valve, REPLY BY EMAIL,
> as this is not a topic of general interest.

I tried (yes, to <first> dot <last> at bigfoot dot com), but my email
was apparently bounced, due to my ISP being blocked. I'll retry from a
different account...

Dave

Dick, I give up on mailing you!

See if your hypersensitive ISP will let you *browse* to the text:
http://advanceassociates.com/DickAdams.txt

Dave

A while back I asked for help with an oven thermostat problem.
Some persons kindly provided some support.
But I misreported the case.
I fix that now:

Finally, I detached and opened the "thermostat", which is a device
located at the top of my 50's (60's?) Kenmore gas range. It has
two wires coming out, and a copper capillary tube (which I did
not previously report because I did not see it).

The problem had been that the oven gas did not turn on reliably.

The capillary copper tube is to the oven temperature sensor. In=20
the "thermostat" it goes to a bellows. Presumably the oven-
temperature sensing system is filled with an expansible fluid like=20
mercury. The "business end" of it is a narrow cylinder which senses=20
the oven temperature at the exhaust duct of the oven.

The "thermostat" is a cam which decides when the bellows will open
a switch. That switch, with little doubt, sends the output of the pilot
sensor (which, with little doubt, is a thermocouple) to the oven gas
valve, which is located in a box below the back of the oven/broiler
burner..

At the low end of the thermostat rotational travel, the contacts are
fully open, by a considerable increment.

I learned from one correspondent that this system is called a "millivolt
control" presumable because of the lowness of the pilot-sensing=20
thermocouple electrical output.

Now that I see what it is, I really like it. It seems to have lasted =
more
than a half-century with no more trouble than dirty switch contacts.
But time must yet tell that cleaning the contacts (with crocus cloth)
fixed the problem. Today's stoves may have electronic ignition. =20
So far the electronic ignition devices I have come across did not
distinguish themselves by their high reliability. In any even, in =
stoves,
they take mains power, which, with terror (terrorism!) we can count
on less nowadays.

I must apologize to the persons to whom I reported that the "thermostat"
seemed to be a rheostat. It is not. Actually, the thermostat is the =
entire
system which controls the oven heat. The "millivolt control" is =
probably
among the simpler systems, if not the simplest. Simplest tends usually
to be the most reliable.

The old Kenmore range detaches from gas with a union under the stove
top at the level of the burners. So you just raise the top, uncouple =
the
union and pull the stove out, after turning off the gas in the basement.
New stoves have the connections at different places, apparently=20
involving that you should pull out the stove slightly, and send a midget
in to do something with a flex line, assuming you have a stove which
is enclosed on both sides and the back by walls and counters like
we do.

So I hope that my repair, consisting of cleaning the contacts in the
"thermostat", will work out. Otherwise, it is a new stove, and a =
plumber,
I guess, since Mrs. Adams does not trust my gas-fitting skills, and=20
since I have not figured out how to do an installation with a flex line
without a midget. But, in the meantime, I am looking for a cheap
range with "millivolt control" for the oven, and stainless-steel burners
ignited by pilot flames. Those are good because you can pull them
out a soak the out in the dishpan when they get dirty. Presumably
such things are still made for 3rd-world people who cannot not afford
the kind of complexities which make our lives very expensive.

--=20
Dick Adams
(Sourdough minimalist)
<firstname> dot <lastname> at bigfoot dot com
___________________
Sourdough FAQ guide at=20
http://www.nyx.net/~dgreenw/sourdoughfaqs.html

Dick Adams wrote:
> A while back I asked for help with an oven thermostat problem.

> Now that I see what it is, I really like it. It seems to have lasted more
> than a half-century with no more trouble than dirty switch contacts.
> But time must yet tell that cleaning the contacts (with crocus cloth)
> fixed the problem. Today's stoves may have electronic ignition.
> So far the electronic ignition devices I have come across did not
> distinguish themselves by their high reliability. In any even, in stoves,
> they take mains power, which, with terror (terrorism!) we can count
> on less nowadays.

> The old Kenmore range detaches from gas with a union under the stove
> top at the level of the burners. So you just raise the top, uncouple the
> union and pull the stove out, after turning off the gas in the basement.
> New stoves have the connections at different places, apparently
> involving that you should pull out the stove slightly, and send a midget
> in to do something with a flex line, assuming you have a stove which
> is enclosed on both sides and the back by walls and counters like
> we do.

Old plumbing design, now deprecated, since it is difficult to hook up
and replace (as you find), and with the valve in the basement, very
dangerous in case of an earthquake or other emergency disconnect
situation. Some jurisdictions would also require an aotomatic cutoff
valve that shuts down upon loss of line pressure. (Excessive flow)

> But, in the meantime, I am looking for a cheap
> range with "millivolt control" for the oven, and stainless-steel burners
> ignited by pilot flames. Those are good because you can pull them
> out a soak the out in the dishpan when they get dirty. Presumably
> such things are still made for 3rd-world people who cannot not afford
> the kind of complexities which make our lives very expensive.

That's the on;y supply you're likely to find, as the pilotless designs
are legislated most places in the US, for energy efficiency.

Dave