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Патент USA US2408875

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oct- 3, 1946-
‘
c. M. OST>ERHELD
2,403,374}
THERMAL RETARDER
Filed May 29, 1944
\‘\
IN VEN TOR.
J
. 0s 7Z'RHEL p
' ATTORNEY
2,408,874
Patented Oct. 8, 1946
UNITED STATES PATENT OFFICE
2,408,874
THERMAL RETARDER
Clark M. Osterheld, Stoughton, Wis., assignor to
McGraw Electric Company, Elgin, 111., a cor
poration of Delaware
Application May 29, 1944, Serial No. 537,941
13 Claims. (01. 219——-39)
1
My invention relates to electric heating and
particularly to thermal retarder control switch
units for electric heaters of domestic hot water
storage tanks.
An object of my invention is to provide a novel
and improved form of thermal retarder heater
control switch unit.
Another object of my invention is to provide
a thermal retarder heater control switch unit in
cluding two dissimilarly thermally-expansible
snap-acting switch mechanisms separate from
2
trated the electric heater 2i generally only, since
heaters of this general kind are old and well
known in the art, the same comments applying
also to the details of construction and assembly
of the tank II.
I provide a lower or main thermally-actuable
heater control switch designated in its entirety
by numeral 25. This switch is also shown gen
erally or schematically only and comprises a tube
El having a closed inner end and having its open
outer end portion secured in a ?uid-tight manner
in an opening in tank ll adjacent the lower por
tion thereof. An expansion rod 29 is positioned
Another object of my invention is to provide a
within the tube 21 and is adapted to be subject
thermal retarder heater control switch unit that
shall be selectively effective to cause energization 15 to the temperature of the water in the tank.
The outer end of rod 29 is adapted to engage
of an electric heater of a domestic hot water stor
with and be disengaged from a small block 3| of
age tank immediately or after a predetermined
electric-insulating material secured to the free
time period of delay in accordance with the
or movable end of a resilient contact arm 33.
amount of cold water in the tank.
Other objects of my invention will either be 20 A contact member on arm 33 is adapted to en
gage with and be disengaged from a contact
apparent from a description of my improved form
member
on a substantially rigid contact arm 35,
of device or will be pointed out in the course
the two contact arms being supported in heat
of such description and set forth in the appended
receiving relation and electrically-insulated from
claims.
one another 'as by blocks 31 of suitable material.
25
In the drawing,
When tube 2'! is positioned in cold water, by which
Figure l is a vertical, sectional view of an ordi
I mean water the temperature of which is on the
nary domestic hot water tank, with which is as
order of 60 to ‘70° F., the length of expansion rod
sociated a device embodying my invention,
29 will be a minimum and contact arm 33 will
Fig. 2 is a front View of my improved thermal
30 then be in engagement with contact arm 35 so
retarder with the cover removed,
that the two contact members supported by the
Fig. 3 is a sectional view on the line 3——3 of Fig.
respective arms will be in electric-conducting en
2 showing the first bimetal bar and contacts in
gagement with each other. When tube 21 is posi
full lines, in position when the tank is filled with
tioned in or surrounded by hot water, by which
cold water so that the thermal retarder is sub
one another.
I mean water the temperature of which is on the
35 order of 150° F., the length of expansion rod 29
Fig. ll is a sectional view on the line 4-4 of Fig.
will be a maximum so that contact arm 33 will
2 showing the second bimetal bar and contacts
have been moved out of engagement with con
controlled thereby in full lines when in open posi
ject tocold water,
tion,
tact arm 35. I have illustrated the thermally
actuable control switch 25 generally only, since
Fig. 5 is a diagram of electric circuits used with 40
I do not desire to be limited to the particular
my improved thermal retarder.
construction illustrated in Fig. l of the drawing,
Fig. 6 is a front View of a pivot plate, and,
but may use any other thermally-actuable switch
Fig. 7 is an end view of Fig. 6.
effective for the same general purposes as above
Referring ?rst of all to Fig. l of the drawing,
described for switch 25.
I have there illustrated a domestic hot water tank
I provide a thermal retarder heater control
H having a lower cold water inlet pipe l3, an
switch unit designated generally by numeral 39
upper hot water outlet pipe 15, and being cov
and mount the same in heat-receiving relation
ered by heat-insulating material [1, which ma
on tank ll intermediate the ends thereof and
terial may be held in proper operative position
preferably at or about the half height of the
around the tank by an outer casing I9.
tank.
I provide preferably, but not necessarily, a
The thermal retarder switch unit '39 comprises
single electric heater 2 l , which, when only a. single
a
casing M having a cover 43 thereon, which
electric heater is provided, is positioned around
cover may be held in proper operative position
the tank adjacent the lower end thereof and may
be positioned in a tunnel member 23. I have illus 55 on casing M as by a clamping screw 45. Casing
3
2,408,874
4| is made of heat-conducting material and may
be made of aluminum.
I provide a pair of heateconducting brackets
41 and 49, which brackets are of substantially
L-shape and are secured .to say the top wall of
easing 4|. Bracket 41 has ?xedly secured there
to one end of a bimetal bar 5| as by rivets 53
or in any other suitable manner. The thickness
of bar 5| may be on the order of .025”, although
4
secured thereto at its inner end, which is also
adapted to be engaged by contact bridging mem
ber 19. Contact bridging member 63 is adapted
to engage with and be disengaged from a pair of
contact members 9| and ‘33. Contact member
9| is adapted to be electrically connected to con~
tact terminal 85, and contact member 93 is elccv
trically connected to contact terminals 31 and
88.
this is given for illustrative purposes only and 10
Contact terminal 39 is connected by a col actor
may be varied. The movable end of bimetal bar
95 to one terminal of heating coil 91, which is
5| is provided with a central longitudinal slot 55,
insulatedly mounted on bimetal bar 11 of the
and the two spaced end portions have each
second switch of the thermal retarder switch unit.
mounted thereon a pivot plate 51 (Figs. 6 and
The other terminal of coil 91
connected by a
'7), which pivot plate is of substantially U-shape, 15 conductor 99 to contact terminal 85. I may here
having a rounded or circular intermediate por
point out that if coil 91 is made of resistance
tion having an indentation therein for a purpose
material so that the flow of current the 'ethre 1:11
which will presently appear. The two straight
will generate heat, the total resistance of coil 51
end portions of pivot plate 51 are ?xedly secured
is relatively high so that the amount of heat
to the outer end of the side portions of bimetal 20 generated in heating coil 31 will be relatively very
bar 5|.
small so that the rise of temperature of the bi
I provide further a second bimetal bar 59, hav
metal bar 1| will be relatively slow, and
will
ing a central longitudinally~extending slot 6|
require a length of time on the order of ?ve or
at its inner end, the two side portions of bar 59
six hours to raise the temperature of bimetal bar
being of V-shape so that the sharpened ends 25 1| to a value on the order of 250° F. or over, at
thereof may ?t into the indentations in the pivot
which temperature snap~acting movement of the
plates 51. I provide a contact bridging member
normally open switch will occur with resultant
63 on the outer end of the second bimetal bar
engagement of contact bridging member 19 with
59 which is insulatedly mounted on a support 65,
the contact members on terminals 85 and 81.
which is of substantially T-shape, with a main 30
A stop member for the two separate and disstem thereof extending through an opening in
tinct thermally-actuable snap-acting switches in
the outer end of bimetal bar 59 and held there
cludes a member |0| which is of Z~shape, having
by a cotter pin 61. An over center spring 69 is
one end portion secured to the base of casing 4|,
positioned in slots 55 and BI, the ends of this
while the other end portion is of elongated lat
spring being suitably connected to the bimetal 35 eral dimensions and has adjustable stop screws
bars 5| and 59 at points thereof just beyond the
I03 therein adapted to be held in any adjusted
slots 55 and 6|. The two bimetal bars 5! and 59
position by lock nuts P85.
in combination with the over center spring 69
In order to vary the operating temperature of
constitute a snap-acting device of the toggle arm
the two pairs of bimetal bars, the respective
type, as is now well known in the art.
40 brackets 41 and A9 are provided with a manually
I provide a second bimetal bar 1|, having one
adjustable screw I81, the inner end of which ex
end thereof connected to the bracket 49 as by
tends through the oifset outer portion of brackets
rivets 13. The outer end portion of bimetal bar
41 and 49, the end thereof being in engagement
1| is provided with an elongated slot or recess
with the individual bimetal bars supported by
15, and the two side end portions of bimetal bar
these brackets, while the outer end portion ex
1| are provided with pivot plates 51 of substan
tends through a suitable opening in the covering
tially the same kind as used on bimetal bar 5|.
43, so that the owner of the hot (Water tank or
Bimetal bar 1| is preferably made of a thicker
a representative of the electric utility company
piece or strip of bimetal.
can easily and quickly adjust the same. As is
I provide a second cooperating bimetal bar 11,
well known, adjustment of stop screw i531 on
which may be similar to bimetal bar 59 as to
bracket 41 to permit the free end of bar 5| to
thickness and dimensions. I provide a contact
move away from the base of the casing and to
bridging member 19 on the outer end of bimetal
ward the cover, will increase the temperature to
bar 11, which is loosely supported on bimetal bar
which bimetal bar ill will be subject before open
11 in the same manner as was hereinbefore set
ing movement of the switch to the position shown
forth for the contact bridging member 63 mount
by broken lines in Fig. 3 of the drawing will take
ed on bimetal bar 59. I provide an over center
place. This, therefore, provides a means for ad
spring 8|, which is positioned in the slots in the
justing the control switch of the heater to cause
adjacent ends of bimetal bars 1| and 11, the ends
an increase in temperature of the water in the
of spring 8| being connected with bars 1| and
tank before deenergization of the heater is ef
11 adjacent the ends of the slots therein. The
fected, as will hereinafter be described. Refer
combination of the two bimetal bars 1| and 11
ring to the second normally open switch, in which
and the over center spring 8| provides a snap
the bimetal bar 1| has a heating coil thereon,
acting thermal switch, which is of lesser thermal
adjustment of screw H31 in bracket 49, so that
expansivity than the ?rst named switch com»
the free end of bimetal bar 1| will be moved closer
prising bars 5! and 59.
to the base of the casing, will increase the tem~
I provide a block 83 of porcelain or other
perature to which bimetal bar 1| must be heated
electric-insulating material at the lower end of
before it will be moved from its normally open
casing 4| and mount thereon a plurality of corn
position, shown by the full lines in Fig. 4, to its
tact terminals 85, B1, and 89. Contact terminal
closed position, shown by the broken lines.
85 is connected, or has secured thereto, a contact
While I have hereinbefore described the heat
terminal which is adapted to be engaged by con—
ing coil 91 as operating to raise the temperature
tact bridging member 19, supported by bimetal
of bimetal bar 1| by heat generated in coil 91, I
bar 11. Contact terminal 81 is of substantially
do not desire to be limited thereto, since if the
straight bar shape and has a contact terminal 98 75 bimetal bar 1| is of a magnetizable material, the
1.
2,408,874
5
coil 91 may carry an alternating current which
will cause heating of bimetal bar 1| by hysteresis
and eddy current losses, as is well known in the
art.
Referring now to Fig. 5 of the drawing, I have
there shown a diagram of connections which may
be used with the thermal retarder illustrated in
Figs. 2, 3, and 4 and hereinbefore described. A
pair of supply circuit conductors I09 and III
on the order of ?ve or six hours, when the tem
perature of bimetal bar ‘II will have become su?i
ciently high, say on the order of 250° F., or slightly
over, with resultant snap-acting closure of the
second switch of the thermal retarder switch unit
comprising particularly the bimetal bars ‘H and
11. The ?rst switch of the thermal retarder
switch unit comprising bimetal bars 5| and 59
was subject to the temperature of hot water, with
are provided, which may either be energized con 10 the result that this switch was in open position
so that heater 2| was deenergized until an en
tinuously during a twenty-four hour day, or in
ergizing circuit therethrough was closed by snap
the circuit of which there may be included a
acting movement of the second switch compris
time control switch of any kind now used by elec
ing bimetal bars ‘H and 11.
tric utility companies in the control circuits for
If, for instance, enough hot water was With
domestic hot water tank heaters. Supply circuit 15
drawn from the tank during the hour of '7 a. m. to
conductor I69 is connected by a conductor “3
8 a. m., energization of heater 2| would be de
' to contact terminal 85, while supply circuit con
layed until around 12 noon or 1 p. m., which is
ductor III is connected by a conductor H5 to
generally a time of low demands for electric en
the resilient switch arm 33 of the lower thermal
switch 25. Switch arm 35 is connected by a con 20 ergy on the circuit. Further, if such relatively
small amount of hot water was withdrawn from
ductor H‘! to one terminal of electric heater 2|,
the tank during the early evening hours, or say
the other terminal of which is connected by a
between 5 p. m. and 7 p. m., energization of
conductor HQ with contact terminal 81. It will
the heater 2| would not be eifected until mid
be noted that I have shown only the ?rst bimetal
night or 1 a. m, which is the usual off-peak period
bars El and ‘H in Fig. 5 of the drawing, but it is
of the late night hours. Thus if only relatively
to be understood that the second bimetal bars
small amounts of hot water were withdrawn from
59 and ‘H are included, the showing of only one
the tank, the energization of the electric heater
of the pair of bimetal bars for each switch being
of the tank would be delayed until such time when
for purposes of simpli?cation only.
Let it now be assumed that the tank H has 30 the demands for electric energy were not as heavy
as during the other parts of the day and energi
been ?lled with cold water preparatory to start
zation
of the heater 2| would continue until the
ing the operation and use of the control system
tube 2? of the lower switch 25 is again subject
embodying particularly my improved thermal re
to hot water, with attendant opening of switch
tarder. Since both of the thermally controlled
25 and deenergization of the electric heater 2|
35
switches of the thermal retarder switch unit are
and of thelow wattage heating coil 91.
in heat-receiving relation relatively to the tank,
Let it now be assumed that during any part of
it will be obvious that bimetal bar 5|, as well as
a twenty-four hour day a much greater amount
bimetal bar ‘II, will be subject to the tempera
of hot water is withdrawn from the tank, this
ture of cold water in the tank, with the result
amount being sufficient to cause the thermal re
that the ?rst switch, comprising bimetal bars
tarder switch unit to be subject to cold water.
5| and 53, will be moved immediately to closed
This would cause immediate closure of the
position, as shown by full lines in Fig. 3 of the
?rst thermal retarder switch comprising bimetal
drawing. Since the lower thermally-actuable
bars 5| and 59, with movement of the switch con
switch 25 is also subject to cold water, it also
will be in closed position, the positions of the parts 45 trolled thereby into closed position and resultant
energization of heater 2|. The ?rst switch op
being that shown in Fig. 5 of the drawing. En
erated by bimetal bars 5| and 59 will remain in
ergization of electric heater 2| will therefore be
closed position until enough water has been heat
effected, and heating of the water in the tank
ed in the tank | | to subject the thermal retarder
will take place. When a single electric heater is
positioned around the outside of the lower end 50 switch unit to hot water, when the ?rst switch
will move to open position. The closed switch 25
portion of tank | i and is energized, the tempera
will
effect energization of heating coil 91 with
ture of the water in the tank will be substan
resultant closure of the second thermal retarder
tially uniform throughout the length thereof and
switch after a predetermined time delay period,
will increase gradually from 60° or 70° F. to a
temperature determined by the adjustment of
when closure of the second switch will occur and
reenergization of heater 2| will take place, which
energization continues until opening movement
of the lower thermal switch 25 takes place, as
that these two switches are adjusted so that they
hereinbeiore described.
will move to open position when subject to a tem~ 60
The thermal retarder heater control switch
perature on the order of 150° F. Thus when the
unit hereinbefore described is therefore e?ective
water in the tank has been heated to a tempera
to maintain a tank substantially half full of hot
ture on the order of 150° F., both said switches
water at all times, and further to cause the tank
will move to open position, whereby the heater
to be ?lled with hot water during oil-peak peri
65
2| is deenergized.
ods of the day. The thermal retarder heater
Let it now be assumed that ‘not water is with
control switch unit embodies two separate
drawn from the tank during say the early morn
switches, each connected in parallel with the
ing hours, the amount of hot water thus with
other and so designed, constructed, and adjusted
drawn being sufficient only to cause the tube 2'!
of the lower thermal switch 25 to :be subject to 70 that the ?rst switch will be closed when subject
to cold water and will be open when subject to
cold water. This causes closing of the lower ther
hot water, While the second switch will be open
mal switch 25, which causes closure of a circuit
when subject to cold or to hot water in the tank
through heating coil 91, which will cause slow
and will be closed when the temperature of the
rise of temperature of bimetal bar 1|, this rise
bimetal‘member has been raised to a relatively
of temperature continuing for a vperiod of time
the lower thermal switch 25 and of the ?rst switch
of the thermal retarder switch unit comprising
the bimetal bars 5| and 59. Let it be assumed
2,408,874
7
high temperature, which temperature is above
that of hot water in the tank.
While I have illustrated and described a ther
mal retarder switch unit in which both switches
are subject to the temperature of hot water and
in which the thermally-actuated members are
dissimilarly thermally-responsive, it is evident
8
thermal responsivity and adapted to be in open
position when subject to cold water and to hot
water in the tank and a heating coil for said
second mechanism adapted to be energized by
power from said circuit irrespective of the posi
tions of said switches to heat said second switch
mechanism to a temperature higher than that
that it is not necessary to mount the second
of hot water and cause movement thereof to
normally open switch in heat-receiving relation
closed position after a predetermined time period
to the water in the tank. This second switch
of delay.
could be positioned anywhere within reasonable
4. A thermal retarder switch unit for control
distance of the tank and out of close thermal
ling a hot water storage tank heater circuit, com
communication with the tank, in which case the
prising a ?rst bimetal snap-acting switch mech
temperature at which it would move to closed
anism including a pair of pivotally connected bi
position might be reduced appreciably as by 15 metal
toggle arms of high thermal responsivity
making the bimetal bars thereof substantially of
having two opposite operative positions adapted
the same dimensions as those for the bimetal
bars of the ?rst switch.
Various modifications may be made in the de~
vice embodying my invention without departing
from the spirit and scope thereof, and all such
modi?cations coming clearly within the scope of
the appended claims are to be considered as cov
ered thereby.
I claim as my invention:
,
1. A thermal retarder switch unit for con
trolling a hot water storage tank heater circuit,
comprising two bimetal snap~acting switch
mechanisms, each comprising a pair of pivotally
connected bimetal toggle arms, each pair having
a diiferent thermal expansion than the other
pair, a heat-conducting casing for said mecha
nisms adapted to be mounted in heat-receiving
relation on a tank, the ?rst switch mechanism
to be mounted in heat-receiving relation on a
tank. and to be in closed position when subject to
cold water in the tank and to be moved to open
position when subject to hot water in the tank,
a second bimetal snap-acting switch mechanism
including a pair of pivotally connected bimetal
toggle arms of low thermal responsivity adapted
to be in open position when subject to cold and
to hot water in the tank and a heating coil for
said second bimetal mechanism adapted to be
energized by power from said circuit irrespective
of the positions of said switches to cause clo
sure of said second mechanism after a predeter
mined time period of delay.
5. A thermal retarder switch unit for control
ling a hot water storage tank heater circuit, com‘
prising a heat-conducting casing adapted to be
being adapted to be in closed position when sub" 35 mounted in heat-receiving relation on a tank, a
?rst bimetal snap-acting switch mechanism, of
ject to cold water in the tank and to move into
high thermal responsivity, in said casing and sup
open position when subject to hot water in the
ported thereby, said ?rst mechanism having two
tank, the second switch mechanism being adapt~
opposite operative positions and adapted to be
ed to be in open position when subject to cold
in closed position when subject to cold water in
water and to hot water in the tank and a heating 40 the tank and to be in open position when subject
coil for said second mechanism adapted to heat
to hot water in the tank, a second bimetal snap
the same and cause closure thereof at a predeter
acting switch mechanism, of low thermal 1'e—
mined higher than that oi hot water tempera
sponsivity, in said casing and supported thereby,
ture.
said second mechanism adapted to be in open po
2. A thermal retarder switch unit for control
" sition when subject to cold and to hot water in
ling a hot water storage tank heater circuit, com
the tank and a heating coil carried by said sec
prising two bimetal snap-acting switch mecha
ond switch mechanism adapted when energized
nisms having their switches connected in parallel
to heat the second mechanism to a temperature
with each other, a heat-conducting casing for
higher than that of hot water and cause it to
said mechanisms adapted to be mounted in heat Ch C move into closed position after a predetermined
receiving relation on a tank, the ?rst switch
time period of delay.
mecl':.&i'lisn1 being of high thermal responsivity
and adapted to be in closed position when subject
to cold Water in the tank and to move into open
position when subject to hot water in the tank,
the second switch mechanism being of low ther
mal responsivity and adapted to be in open posi
tion when subject to cold water and to hot water
in the tank and a heating coil for said second
mechanism adapted to heat the same to a tem
perature higher than that of hot water and cause
closure thereof after a predetermined time period
of delay.
3. A thermal retarder switch unit for control
ling a not water storage tank heater circuit, com
6. A thermal retarder switch unit for a hot
water storage tank heater circuit, comprising a
pair of dissimilarly thermally-responsive bimetal
snapsacting switch mechanisms adapted to be
mounted on a tank in heat-receiving relation
thereto, the high-responsive mechanism being
normally closed and adapted to move to open
position when subject to hot water in the tank,
the low-responsive mechanism being normally
open and adapted to move to closed position at a
predetermined temperature higher than that of
hot water in the tank and a heating coil for the
low-responsive mechanism adapted when ener
gized to cause closing of said low-responsive
prising two bimetal snap-acting switch mecha
switch mechanism after a predetermined time.
nisms having their switches connected in paral
'7. A thermal retarder heater circuit control
lel with each other, a heat-conducting casing for
switch unit for hot water tank heaters, compris
said mechanisms adapted to be mounted in heat
ing two separate circuit switches, two pairs of
receiving relation on a tank, the ?rst switch 70 bimetal toggle arms of different thermal expan
mechanism being of high thermal responsivity
sivities adapted to be subject to tank water tem
and adapted to be in closed position when sub
perature and to actuate said respective switches
ject to cold water in the tank and to move into
with a ‘snap action, the high-expansion pair of
open position when subject to hot water in the
arms being adapted to hold their switch in closed
tank, the second switch mechanism being of low 75 position until subject to hot water in the tank,
2,408,874
the low-expansion pair of arms being adapted to
hold their switch in open position until subject to
a temperature higher than that of hot water and
means for heating the low-expansion arms inde
10
12. A thermal retarder switch unit for a hot
water storage tank heater circuit, comprising a
?rst pair of pivotally connected bimetal toggle
arms, a contact on the outer end of one of said
pendent of the tank water temperature and of
the position of said switches.
arms, said toggle arms being adapted to be sub
ject to heat exchange with water in a tank and
means for heating one of the low-expansion arms
said contacts.
13. A thermal retarder switch unit for a hot
Water storage tank heater circuit, comprising a
adapted to move said contact into circuit closing
8. A thermal retarder heater circuit control
position with a snap action when subject to cold
switch unit for hot water tank heaters, compris
water in the tank, a second pair of pivotally con
ing two separate circuit switches, two pairs of hi
metal toggle arms of diiferent thermal expansivi 10 nected bimetal toggle arms, a contact on the outer
end of one of said arms, said second pair of
ties adapted to be subject to tank water tempera
toggle arms being adapted to be subject to heat
ture and to actuate said respective switches with
exchange with water in a tank and adapted to
a
action, the high-expansion pair of arms
move said contact into circuit opening position
being adapted to hold their switch in closed po
with a snap action when subject to cold water
sition until subject to hot water in the tank, the
in a tank- and heating means for exchanging
low-expansion pair of arms being adapted to hold
heat
with one of said second pair of bimetal arms
their switch in open position until subject to a
independent of the tank and of the positions of
temperature higher than that of hot water and
directly independent of the tank water tempera
fire and of the position of said switches to a
temperature higher than that of hot water,
?rst pair of pivotally connected bimetal toggle
arms, a ?rst contact insulatedly mounted on the
A thermal retarder heater circuit control
outer end of one of said arms, a ?rst ?xed con
switch unit for hot water tank heaters, compris
ing two circuit switches connected in shunt cir 25 tact connected in said circuit and adapted to be
engaged with and disengaged from said ?rst con
cuit with each other, two pairs of dissimilarly
tact, said toggle arms being adapted to be sub
thermally-expansible toggle arms to actuate said
ject to heat exchange with water in a tank and
respective switches and adapted to be subject to
adapted to move said ?rst contact into engage
tank water temperature, the high-expansion arms
ment with said ?rst ?xed contact with a snap
holding their switch in closed position when sub
action when subject to cold water in a tank, a
ject to cold water in the tank and in open posi
second pair of pivotally connected bimetal toggle
tion when subject to hot water in the tank, the
arms, a second contact on the outer end of one
low-expansion arms holding their switch in open
of said second pair of arms, a second ?xed con
position until subject to a predetermined tem
perature higher than that of hot water in the 35 tact connected in said circuit and in parallel
with said ?rst ?xed contact and adapted to be
tank and an electric heating coil for causing heat
engaged with and disengaged from said second
ing of one of the low-expansion arms to said
positions of said switches.
contact, said second pair of toggle arms being
adapted to be subject to heat exchange with water
10. A thermal retarder switch unit as set forth
in claim 3 and including means adjustable from
the outside of the casing for varying the tem
perature at which said ?rst switch mechanism
moves to open position.
11. A thermal retarder switch unit as set forth
in claim 1 and including means adjustable from
the outside of the casing for varying the tem
perature at which said second switch mechanism
moves to closed position.
tact out of engagement with said second ?xed
contact with a snap action when subject to cold
and to hot water and an electric heating coil
insulatedly supported on one of said second pair
of toggle arms for causing heating of one of said
second pair of toggle arms independent of the
tank and of the positions of said movable con
tacts.
CLARK M. OSTERHELD.
predetermined temperature irrespective of the
in a tank and adapted to move said second con
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