Thermal power element with safety lockup

A fusible link is provided in a force transmitting device. Upon reaching a preselected temperature, the fusible link melts causing a cooperating locking member to engage a shoulder on a power piston to secure the same in an extended operating position and effect a lock-open condition for certain critical applications.

This invention generally relates to temperature responsive force 
transmitting devices and particularly concerns such a device featuring a 
safety lockup. 
A primary object of this invention is to provide a new and improved thermal 
power element particularly suited for use with an automatic sprinkler 
system for fire protection services and which will automatically respond 
at a preselected temperature to lock open the system under critical 
conditions. 
Another object of this invention is to provide a new and improved thermal 
power element having a safety lockup feature operable under specified 
critical conditions and which is also capable of effecting a force 
transmitting motion to both activate and deactivate an associated unit 
providing that ambient temperature conditions do not reach a critical 
level. 
A further object of this invention is to provide a new and improved thermal 
power element which is not only quick and easy to economically manufacture 
in production quantities, but is also readily installed in both new and 
existing systems at low cost for reliable performance under demanding 
service conditions. 
Yet another object of this invention is to provide a thermal power element 
having a lock open unit which effects a fail-safe function under critical 
conditions. Included in this object is the provision of a thermally 
actuated safety lockup which restricts a piston from retracting from an 
operating position at a preselected temperature to prevent undesired 
disablement in the event the element may have otherwise been caused to 
fail for any reason, e.g., by exposure to excessive heat. 
Other objects will be in part obvious and in part pointed out more in 
detail hereinafter. 
A better understanding of this invention will be obtained from the 
following detailed description and the accompanying drawings of 
illustrative applications of the invention.

Referring to the drawings in detail, a temperature responsive force 
transmitting device or thermal power unit illustrated in FIGS. 1-3 of the 
drawing is generally denoted by the numeral 10 and comprises a housing 11, 
base cup 12, a piston guide 14, a piston 16 received for linear 
reciprocating movement within the guide 14 and within a resilient boot 18 
which is fitted within the base cup 12 with a neck of the boot 18 
extending into the piston guide 14. The boot 18 may be formed of any 
suitable elastomeric material exhibiting resistance to high temperature, 
aging and swelling. Boot 18 has a radial flange 20 which serves as a 
common seal between piston guide 14 and base cup 12. 
Cup 12 is filled with a temperature sensitive expansible material such as 
wax 22, and the cup 12 itself is formed from a thermally conductive 
material. As is well known in the art, a rise in ambient temperature 
causes the wax 22 within cup 12 to expand, and such wax expansion acts 
through boot 18 to force piston 16 to be driven from a retracted 
inoperative position shown in FIG. 1 to an extended operating position 
shown in FIGS. 2 and 3. Upon cooling, the wax 22 itself contracts and 
piston 16 normally returns to its inoperative position by a spring 
actuated device connected to the thermal power unit 10. 
Base cup 12 has radial shoulder 24 formed about its open end. An annular 
wall 26 extends from the periphery of shoulder 24 and terminates in an 
inwardly turned lip 28. The base of boot 18 depends from its radial flange 
20 which is clamped between flange 30 of piston guide 14 and shoulder 24 
of cup 12. A well 32 is formed within piston guide 14 which tapers away 
from cup 12 toward a central opening 34 of minimum diameter through which 
piston 16 extends toward a conical end 36 which fits within a well 38 of 
boot 18. 
An intermediate portion 40 of piston 16 is of relatively enlarged diameter 
and is received within a piston guide chamber 42 of correspondingly 
enlarged diameter relative to opening 34. Portion 40 of piston 16 extends 
through a disk 44 and into a central opening 46 of a coupling 48 
threadably connected to a valve body 50, e.g., through which fluid flow 
may be controlled by the power element 10. A pair of O-ring seals 52 and 
54 are fitted on opposite sides of coupling 48 in engagement with valve 
body 50 and piston portion 40 respectively. Coupling 48 is mounted within 
an end of housing 11 and has a radial shoulder 55 sandwiched between an 
overlying annular thermal insulator 56 and the underlying disk 44 which is 
formed of thermal insulating material. 
A piston return spring 58 has one end seated on a terminal face of the 
power piston 16 received within a chamber 60 of valve body 50. An opposite 
end of spring 58 seats against screw 62 threadably connected within an 
opening 64 in valve body 50 axially aligned with chambers 42 and 60 to 
selectively adjust the return spring force for driving piston 16 from its 
extended operating position into its retracted inoperative position upon 
cooling of the wax 22. The power piston 16 received within valve chamber 
60 is illustrated as having a reduced diameter portion 66 which upon being 
moved into operating position as shown in FIG. 3 registers with valve 
passages 68, 70. 
In a typical application, the thermal power element 10 may be connected to 
any suitable operated unit, and in the illustrated embodiment the operated 
unit will be understood to be a control valve for a sprinkler system for 
fire protection. Upon an ambient temperature rise, the wax 22 expands to 
drive piston 16 into operating position (FIGS. 2 and 3) to connect valve 
passages 68, 70 across the reduced diameter portion 66 of piston 16 
registering with the passages to permit water flow through valve body 50. 
Providing that the sprinkler system components are functioning effectively 
and the water supply is maintained, the sprinkler system will continue to 
operate so long as power piston 16 remains in operating position. When 
power piston 16 is returned into its inoperative position (FIG. 1), fluid 
passages 68, 70 are closed by the relatively enlarged end portion of 
piston 16 to interrupt operation of the sprinkler head. 
In accordance with this invention, a safety lockup feature is provided 
which, while permitting reciprocating movement of power piston 16 between 
its inoperative and operating positions under the influence of the wax 
motor 22 and spring 58 when the ambient temperature is below a preselected 
temperature, also provides for continual operation of the unit being 
controlled under critical conditions above the specified preselected 
temperature. The safety lockup feature of this invention comprises locking 
means movable into a locking position in cooperation with the piston in 
its operating position and restraining means for securing the locking 
means in locking position at a preselected temperature to effect piston 
lockup. 
The locking means in the embodiment of FIGS. 1-3, comprises a locking ball 
72 received within a side wall opening 74 in piston guide 14 wherein the 
side wall opening 74 is in communication with and extends radially from 
the chamber 42 of piston guide 14. Side wall opening 74 is located in a 
predetermined position axially of chamber 42 such that a locking shoulder 
76 of piston 16 formed by the differential diameter portions of the piston 
16 is disposed for locking engagement with ball 72 when piston 16 is in 
its extended operating position (FIGS. 2 and 3). 
When the piston 16 has reached its maximum stroke in response to a rise in 
ambient temperature and is driven into its operating position by the wax 
motor 22, the locking ball 72 is free to move in and out of guide chamber 
42 without locking the piston 16 providing that the ambient temperature 
has not exceeded a preselected temperature which is the melting point of 
spacer 78 of a restraining assembly 80. In the embodiment of FIGS. 1-3, 
the spacer 78 is formed as a ring of solid material which is fusible at 
said preselected temperature and is mounted within the housing 11 in 
engagement with the insulating disk 44. A cam sleeve 82 of the restraining 
assembly 80 is provided with an end skirt 84 supported on piston guide 14 
for sliding movement and has a radial flange 86 at the opposite end of 
sleeve 82 which is urged into seating engagement with spacer 78 by a 
compression spring 88 mounted within housing 11 in surrounding relation to 
the piston guide 14 and sleeve 82. 
Spring 88 has its opposite ends respectively seated against lip 28 of base 
cup 12 and the radial flange 86 of sleeve 82 and is installed in a 
compressed or loaded condition to a predetermined spring load. Sleeve 82 
has an annular cam shoulder 90 connecting the skirt 84 with a maximum 
diameter portion 92 of sleeve 82 which merges with the outwardly flared 
radial flange 86. 
To effectively secure piston lockup under critical conditions above a 
specified temperature wherein it is desired or imperative that the valve 
passages 68, 70 be maintained in communication to ensure continuous water 
flow, e.g., to the sprinkler head, once the ambient temperature reaches 
the melting point of spacer 78 with the piston 16 in extended operating 
position, the spacer 78 melts and the installed spring load of spring 88 
drives cam shoulder 90 of sleeve 82 over the locking ball 72 and traps it 
in guide chamber 42 against the piston locking shoulder 76 (FIG. 3). When 
the ambient temperature lowers, the return force from spring 58 exerts a 
linear force on piston 16 which tends to wedge ball 72 radially outwardly 
in guide opening 74. However, ball 72 is captured by end skirt 84 of 
sleeve 82 which is maintained by the spring 88 in overlying relation to 
side wall opening 74 of guide 14. Ball 72 is accordingly fixed relative to 
piston 16 in engagement against its locking shoulder 76 preventing any 
return of piston 16 and thereby maintaining the sprinkler head in an 
operating functional condition providing fail-safe operation. 
Accordingly, spacer 78 and sleeve 82 function as an actuator and the sleeve 
is driven by spring 88 into a lockup position (FIG. 3) for securing piston 
16 in its operating position. It will be noted that shielding from heat 
sources other than ambient temperature conditions is provided by thermal 
insulators 44 and 56. 
Turning now to the embodiments illustrated in FIGS. 4, 5 and 6 wherein like 
numerals are used to designate parts identical to those described in the 
embodiment of FIGS. 1-3, actuator assemblies are illustrated as including 
sleeve components 100 similar to sleeve 82 in the first embodiment of 
FIGS. 1-3. The sleeve components 100 each have an external shoulder 102 
serving as a seat for spring 88. 
In the embodiment of FIG. 4, a fusible link is provided at 104 in the form 
of a fastener made of a solid material fusible at a preselected 
temperature and serving to secure the sleeve 100 in fixed relation to 
piston guide 14 under ambient temperature conditions below a specified 
preselected temperature. The fusible fastener 104 connects a ring member 
106 to underlying sleeve 100 with ring 106 being maintained in engagement 
against insulating disk 44 within housing 11 under the biasing force of 
spring 88. Upon ambient temperature rising to the specified preselected 
temperature which is equal to the melting point of fusible fastener 104, 
the sleeve 100 will cam ball 72 into piston guide chamber 42 and end skirt 
84 will overly guide opening 74 thereby trapping ball 72 in a safety 
lockup condition. It is to be understood that the wax motor, not shown, 
will always drive power piston 16 into its operating position (such as 
shown in FIGS. 2 and 3) during an ambient temperature rise before that 
ambient temperature reaches the specified preselected temperature or 
melting point of fusible link 104. 
In the embodiments of FIGS. 5 and 6, the actuator sleeve 100 is shown as 
being substantially identical to that illustrated in the above described 
embodiment of FIG. 4 while the fusible link is respectively illustrated as 
a solder joint securing the actuator sleeve 100 in fixed relation to 
piston guide 14. The solder joint 104A in FIG. 5 is secured to an 
overlying sleeve 106A surrounding the actuator sleeve 100 and urged 
against insulating disk 44 by spring 88. In FIG. 6, the actuator sleeve 
100 is directly soldered by fusible link 104B to an outside surface of 
piston guide 14. In both embodiments, upon the ambient temperature 
reaching the melting point of the solder joints 104A and 104B, the 
actuator sleeve 100 will be driven by spring 88 from its normal position 
illustrated in FIGS. 5 and 6 against the insulating disk 44 when piston 16 
is in its operating position to effect the safety lockup as previously 
described in connection with the embodiment of FIGS. 1-3. 
In FIGS. 7 and 8, a flat spring 110 of U-shaped configuration is provided 
forming a locking means mounted within housing 11 in registration with a 
side wall opening 112 in piston guide 14. The side wall opening 112 is in 
communication with chamber 42 of the piston guide such that locking 
shoulder 114 of piston 16 is disposed for locking engagement with arm 110A 
of spring 110 when piston 16 is in its operating position (FIG. 7). Spring 
110 is formed of a suitable material having a resiliency which 
continuously urges its spring arms 110A and 110B toward one another. A 
groove 116 formed in guide 14 provides for retaining arm 110B in position. 
The preferred embodiment shows a spacer 118 extending between free ends of 
spring arms 110A and 110B, the spacer 118 serving as a restraining means 
to maintain spring 110 in a normal ready position illustrated in full 
lines in FIGS. 7 and 8 when the ambient temperature is below a specified 
preselected temperature. The temperature specified may be preselected at a 
prescribed melting point of spacer 118 or a fusible link portion of the 
spacer such as illustrated at 120 in FIG. 7. When the ambient temperature 
rises to the melting point of the fusible portion or link 120 of spacer 
118, the link 120 melts and arms 110A and 110B are released such that the 
resiliency of the spring material drives spring arm 110A from normal ready 
position shown in full lines in FIGS. 7 and 8 into a locking position 
illustrated by broken lines in those figures. As in the above described 
embodiments, the melting point of the fusible link 120 of spacer 118 is 
above that required for the wax motor to drive power piston 16 into its 
operating position such that its locking shoulder 114 is disposed for 
locking engagement with spring arm 110A upon its snapping into locking 
position when spacer 118 is effectively destroyed to activate the safety 
lockup. 
The fusible link of the safety lockup of this invention may be provided by 
any suitable solid material which has a melting point at a specified 
temperature to secure the piston 16 in operating position under extreme 
conditions. Tin which has a melting point of about 450.degree. F. has been 
found to perform satisfactorily as a fusible link, as has a eutectic alloy 
comprising 97.5% lead, 1.5% silver and 1.0% tin having a melting point of 
about 588.degree. F. Another alloy which may be used comprises a solid 
fusible material formed of 92.5% lead, 5.0% tin and 2.5% silver having a 
melting point at about 536.degree. F. The wax motor 22 will normally 
operate to stroke power piston 16 through its maximum stroke into 
operating position at about 140.degree. F. 
In accordance with the teachings of this disclosure, it will be seen that a 
compact low-cost thermal power element is provided which is capable of 
reliable operation under demanding conditions and which effects a safety 
lockup particularly useful for automatic sprinklers for fire protection 
services. 
As will be apparent to persons skilled in the art, various modifications, 
adaptations and variations of the foregoing specific disclosure can be 
made without departing from the teachings of this invention.