Note: Descriptions are shown in the official language in which they were submitted.
THERM~L ELEME NT
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B~CK~,ROUND OF THE INVENTIO'.`1
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l'his invention pertains ~o hea-t-responsive
thermal elements usable for actuation of devices such
as fluid control valves which are responsive to temper-
ature of the fluid.
For many years, various types of control de-
vices which are temperature-responslve have been operated
by a thermal element. The thermal element has a casing
1~ carrying a charge or volume of material expandable in
response to heatiny thereof with such material typically
being a wax material~ The thermal element also has motion-
transmitting means for transmitting the foxce created by
the heat-expandable wax to a member to be operated, such
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as the valve member of a fluid valve such as a reliéf
valve and also structure to form an interface between the
, wax material and the motion-transmitting means. Such in-
terfaces have typically utilized either O-rings or other
forms of hollow cylindrical seals. Such prior devices
have required some structural part to impart a radially
outwardly force to form a seal with the casing of the
thermal elernent.
Some of the prior art thermal elernents have
atternpted to prevent flow of a part of the controlled
~luid to a location bet~7een the motion-transmitting struc-
ture and the sealing structure which imposes additional
design requirements for the thermal element.
SUMMARY OF T~IE INVENTION
A primary feature of the invention disclosed
3q herein is to provide a thermal element of new and improved
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constructlon having a minimal number of components in a pencil-
thin, relatively short package, which develops more load and
which is designecl for fully automatic assembly.
The invention in one broad aspect pertains to a heat-
responsive thermal element comprising four parts including a
tubular casing having an open end, a volume of heat-responsive
expandable material positioned in the casing at a distance from
the open end thereof, a motion-transmitting pin within the
casing and having a portion thereof extending through the open
end of the casing, and a generally spherical resilient seal
member compressively positioned with random orientation in the
casing between the material and the pin and free of connection
to the pin for freedom of positioning and orienta-tion to
maintain a seal with the tubular casing. The seal member
defines in each adjusted position an annular zone of maximum
sealing force engagement with the casing substantially about the
center of the seal member.
An additional aspect of the invention is to provide a
thermal element as defined in the preceding paragraph wherein
the pin is loosely fitted within the tubular casing and has a
washer of relatively soft material attached to an end thereof
for engagement against the seal member to prevent extrusion of
the seal member in the space between the pin and the tubular
casing and snugly fit the interior of the casing and hold the
pin against inadvertent movement.
Still ano-ther aspect of the invention is to provide a
thermal element as defined in the prececling paragraphs wherein
the washer is an annular member ~itted on a reduced diameter
section of the pin and secured by an integral part of the pin
and with the washer having means, preferably in -the form of at
least one notch on the periphery thereof, to prevent entrapment
between the washer and the seal member.
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Still another aspect of the invention is to
provide a thermal element as defined in the preceding para-
graphs wherein the spherical resilient sealed member is
formed as a ball of soft material, such as silicone rubber
or the like, and having a diameter greater than the internal
diameter of the tubular casing for compressive deformation
to seal against the interior of the casing while being movable
axially thereof as the heat-expandable material expands and
contracts.
Still another aspect of the invention is to pro-
vide a thermal element having the structure as set ~orth in
the preceding paragraphs which is capable oE simple assembly,
wherein the tubular casing is formed of stainless steel
that may be formed to the desired dimensions and the motion-
transmitting pin is suitably formed of metal or plastic with
a reciuced diameter end to receive the annular washer thereon
with the pin end burnished over the washer to retain it in
association with the pin and at the same time the washer is
notched at the periphery to provide for said flow of lic~uid
therepast in operation. The washer has a snug fit with the
tubular casing whereby once the pin and washer are assemhled
into the casing the parts may be easily transported and
positioned in different ways without any separation of the
parts and with the pin being f~ee of contact of the tubular
casing whereby no close tolerances between the pin and interior
of the tubular casing are required.
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BRIEF DESCRIPTION OF ~HE DRAWING
F'ig. l is a central vertical section of the
thermal element;
Fig. 2 is a fraymentary vertical section, on an
enlarged scale and taken along the lines 2-2 in Fig. l;
Fig. 3 is a fragmentary exploded view showing
several components of the thermal element; and
Fig. 4 is a sec-tional view taken along line 4-4
of Fig l.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
The thermal element is shown in assembled rela-
tion in Fig. l and identi~ied generally at 10. The thermal
element has four primary parts including a tubular casing
indicated generally at ll, a motion-transmitting pin indi-
cated generally at 12, a resilient seal member indicated
generally at 15, and heat~expandable material 16, preferably
in the form of a commercially available wax.
The tubular casing ll is formed from metal, such as
copper or thin wall stainless steel, with the lat-ter being pre-
ferred, and has a closed end 20 and an open end 21. The stain-
less steel has relatively high strength ~nd, tllerefore, the
tubular casing can be made of a thinner wall than copper to
provide for a larc,Jer internal diameter in khe same si~e
thermal element to provide for a greater cross section of
-the heat-expandabLe material 16. 'rhj,s can provide'greater
axial Éorces and loads with the same pressure oE the heat-
expandable wax 16. With the greater force or load pro-
vided with this construction, the thermal element is some-
what less load sensi'tive when used in a structure, SUCil asa relief valve and which has to overcome a preset closing
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pressure on the valve member tha-t is to be opened by the
thermal element upon e~pansion of -the heat-expandable ma
terial. Although stainless steel is considered difficult
to form because it work hardens, a two-step roll-orming
method is usecl to very effectlvely close the end,20 of the
tubular casing with the final sealing of it by use of Tungsten
Inert Gas welding.
The heat-expandable material 16 is preferably in
the form of a commercially available wax and has a working
range of 195-~17F., i.e., a transition point at 195F. At
this temperature it starts to turn from a hard and brittle
solid to a plastic-like substance and expansion begins. At
217F., it starts turning to a li~uid and expansion is con-
siderably slowed.
After forming of the tubular casincJ 11, as described
above, the next step lS to fill the tubular caslng with liquid
wax at some temperature between 230F. and 260F. followed by
-~ a~xamming at 190F. The ramming is reqiiired to remove solid wax
from the wall of the ~ubular casing and to create a uniform
wax length within the tube.
The r~silient seal member 15 is a spherical or ball-
shaped member of relatively soft silicone rubber selected to
provide optimum performance at temperatures encountered. For
exarnpl~, the tempexatures encount~red in a valve application
could be ].~0F, to 180F. with higher test temperatures, The
rubher ball lS has a diameter greater than the int~rnal dia
eter of the tubular casincJ 11, as shown in Fig. 3, and is
positioned by squeeziny into the bore oE the tubular casiny.
I-ts shape permits considerable stored eneryy or memory and
the ball does not have to be oriented for assembly or for
proper function inside the element. In addition, the
ball provides more latitude in dimensional control,
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without losing sealing capability or creating excessive
sidewall pressure. Additionally, it has been found that
the ball seals very ~ell over an internal weld seam in the
tubular casing if the tubular casing is made with a raised
weld seam.
After placing of the wax within the tubular
casing, as described above, the tube is evacuated by apply-
lng a vacuum and the seal member 15 is lnserted within the
casing against the upper level of the wax 16.
The motion-transmitting pin 12 is a cylindrical
member and of a diameter less than the internal diameter of
the tubular casing 11 in order that the major part 25 of the
pin has a loose fit therein. This enables free movement of
the pin relative to the tubular casing.
The pin has an upper end 26 of reduced diameter
extending beyond the open end 21 of the casing for engagement
wlth a structure, such as the structure associated with the
valve member causing opening thereof as the pin 12 moves up-
wardly, as viewed in Fig. 1.
An annular washer 30 of relatively soft materlal is
fitted on a reduced diameter lower end 31 of the pin 12 and
held thereto by a flattened sec-tion 32 of the pin formed as
by burnishing whereby the washer 30 moves with the pin. This
washer has a snug fit within the tubular casing 11 to prevent
inadvertent fall-out of the pin from the casi.ng if the casing
is inverted and also to prevent extrusion of the seal member
15 into the space between the pin section 2S and the interior
of the tubular casing.
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The washer 30 has an annular groove formed, as by
machining for example, to provide a relatively thin flexible
section 33 for contact with the tubular casing. This reduction
in contact width of the washer enables flexing thereof and
greater tolerances for the washer and tubular casing without
undue sliding friction therebetween.
As shown particularly in Fig. 2, the washer section
33 has a pair of notches 35 and 36 at the periphery thereof
to prevent the washer frorn forming a fluid seal with the tube.
With the notches 35 and 36 in the washer, a leak path for
flow of liquid across the washer in both directions is pro-
vided to avoid trapping of liquid, rather than trying to pre-
vent leakage past the washerO Without the notches, it would
~be possible for a condition to exist where the pin 12 would
extend out from the casing 11 a distance sufficient to space
the washer 30 from the seal member 15. Over an extended
period of time, water under pressure could seep into said
space. When the wax 16 expands rapidly, this water would be
trapped and act as a solid fill.
In design of the motion-transmitting pin 12, the
pin must be of sufficient strength to withstand some small
amount of bending and the tensile loads developed by loads
i.n the valve, such as a spring load which resists opening
- of the valve mcmber. Preferably, this pin is oE brass, al-
though stainless steel and certain plastics could be used.
In forming of the pin, the pin i.s machined to the configura-
tion shown and the washer 30 is installed with the flat-tened
end being formed by burnishing in the machine which machines
the pins and at the same time the notches 35 and 36 are formed
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in the washer. The washer is also machined to form the
flexible sec-tion 33. The assembled pin is then placed
within the tubulax casiny and is retained in position
during additional handling of the thermal element by
the snug fit between the annular washer 30 and the
tubular casing.
Use of plastics for the pin 12 would enable
- the pin and washer to be a one-piece molded or machined
part.
lQ The thermal element disclosed herein results
in an extremely simple structure having the four primary
elements and without requiring springs and plugs and extra
plastic spacers. The disclosed thermal element results in
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reduced assemhly time and costs. The use of the spherical
seal member 15 avoids the requirement for some additional
part of the unit to impart radially outward forces on an
; 0-ring for example in order to impart a siae wall squeeze
against the tubular casing. The notched washer 3~ permits
leakage therepast with no adverse effects on operation of
the unit since the leakage fluid can flow across the washer.
Alternatively, the washer can be formed of a hexagonal or
octagonal shape to provide the same functional results
as the annular, notched washer.
