US2614754A - Thermostatic control device - Google Patents

Description

Oct. 21, 1952 J CAPARQNE 2,614,754

THERMOSTATIC CONTROL DEVICE Filed July 9, 1949 INVENTOR. (9108954 J. Cameo/m.

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Patented Oct. 21, 1952 THERMOSTATIC CONTROL DEVICE Michael J. Caparone, Arcadia, Calif., assignor to Robertshaw-Fulton Controls Company, Greensburg, Pa., a corporation of Delaware Application July 9, 1949, Serial No. 103,820

This invention relates to thermostatic control apparatus and, more particularly, to snap-action controls operated by thermally responsive hydraulic power elements.

\ Elements of the described type may have the filling fluid always under compression and at an internal pressure greater than atmospheric. In such event, the control device which such elements operate does not move to its safe position should the fluid begin to leak. It has been proposed to counteract this unsafe feature by utilizing' a liquid filled power element which, upon contraction of its liquid, exerts a pull force on the control device to cause it to assume a fuel flow position. Should a leak develop in the system, then the liquid is not able to exert a pull force to produce a fuel flow condition nor maintain such a position if fuel is already flowing.

An object of the present invention is to. improve such so-called fail-safe thermostats by insuringpositive operating characteristics in con-.

junction with the fail-safe feature.

.Another object of the invention is' to render the thermostatic control devices operable under a variety of temperature ranges.

I Another object of the invention is to permit variations in the force opposing the power element without affecting the normal operation thereof.

Another object of the invention is to facilitate changes in the temperature rangeof the thermostat by minor changes in the power element.

Another object of the invention is'to reduce the size of the power element to a minimum.

Other objects and advantages will become apparent from the following description taken in connection with the accompanying drawing wherein: I Fig. 1 is a section through a portion of a thermostatic control apparatus showingthe essential features of the invention, and "Fig. 2 is an enlarged view, partly in section, of the power element.

Referring more particularly to the drawing, the control apparatus is shown in Fig. l as comprising a casing I having an inlet opening I2 and an outlet opening M for fuel. The inlet l2 and outlet 14 communicate with a valve chamber I5 provided in the casing and having an annular valve seat It carried therein. A valve member 20 is positioned in the valve chamber 16 for reciprocable movement relative to the valve seat 18 between openand closed positions. The valve member Zilis normally biased toward the valve seat l8 and thus to its closed position by means 1 Claim. (Cl. 236--48) action mechanism 26 for overcoming the bias of the spring 22 and causing movement of the valve z r i of a coil spring 22 which is operative between the valve member 20 and a cover plate 24 carried by the casing Ill and forming a closure for the valve chamber l6 therein.

Snap action means, designated generally by numeral 26, are positioned coaxial with and for operating the valve member 20 between its open and closed positions. The snap-action means 26 cooperate for this purpose with a valve stem "28 which projects from the valve member 20 through the valve seat 18 for slidable movement in a guide support 3!] formed in the casing'IO. The valve stem 23 is adapted for operative engage ment with a clicker mechanism comprising a pair of opposed fulcrum levers 34, a fulcrum button 36 and a clicker disk 38, all of which are housed within a recess it! formed in the casing Iii beyond the guide support 30. The clicker disk 38 is adapted to be operatively engaged by an annular thrust element 42 which is slidably mounted in. the recess in overlying relationship with the clicker disk 38 and carries an upstanding collar 44 provided with a reduced stem portion 46 projecting exteriorly of the casing ID. As snap action devices of the type briefly described herein are well known, further description is deemed unnecessary, except to point out that suitable provision is made, such as by a gasket and gland 41', for sealing such mechanism against escape of fuel from-the casing ll as .well known to those skilled in the art. In the absence of force applied to the thrust element 42, it is to beunderstood that the valve member 20 is held in closed position under bias of the spring 22.

Means are provided for operating the snapmember 20 from closed to open position. To this end, a thermally responsive hydraulic powerele-. ment is utilized in conjunction with lever means for transmitting movement of the power element through the snap action means 26 to the valve member 20. The power element of this invention includes an expansible or bellows member 48, a capillary tube 50 and a bulb element 52 connected in a closed system as is customary in such devices. The bellows member 48, as more clearly shown in Fig. 2, is hermetically sealed to a plug .insert 54 suitably tapped for reception of one 3 between. The opposite end of the-adjusting stem projects exteriorly of the casing I8 adjacent the cover plate 24 and is also threaded for cooperation with manually operable means in the form of a knob 62 which bears against the casing I8. Hence, rotation of the knob 62 causes the stem 56 to be reciprocated in the casing l 8 on an axis substantially parallel with that of the snap-action means 26. Consequently, the bellows member 48 moves toward or away from the casing [8 depending on the direction of rotation of the knob 62.

As is apparent from Fig. 2 of the drawing, the bellows member 48 has its inner wall spaced from the plug insert 54 to provide. a space therein for a filling fluid 64. In this embodiment, the filling fluid 84 is a non-metallic liquid, such as xylene or aniline, or metallic, such as mercury, and is maintained under pressure always above that which would permit vaporization throughout the range of temperatures that are to be .controlled by the thermostatic apparatus.

The; motion. transmitting means between the bellows member 48 and the snap-action mechanism 26 takes the form of an angular lever member '68 having one end overlying the bellows member 48 and being fastened thereto by a stud T8. carried by the bellows member 48 and having a nut. 12 for securing the lever 68in position thereon. The opposite end of the lever 68 is provided with a recess 14- for the reception of the end of an adjusting screw 16 to provide a pivotal mounting. The adjusting screw 16 is carried in a housing 18 for thelever 58 which also encloses the bellows member 48 and is secured by any suitable means (not shown). to the casing Ill. The lever member 88 is fulcrumed intermediate its ends on the upstanding collar 44 of the thrust element. 42 and for this purpose. is provided with an aperture 88 through which the. stem 46 extends. To secure substantially lineal. engagement of the lever member 68 with the collar 44 on the thrust element 42, a depressed portion 82 is formed on thev lever 68 adjacent the aperture 80 therein for providing such engagement.

In the operation of the control apparatus described, the open osition of the valve member 28 as shown in Fig. 1 of the drawing, is the normal position of this member whenever the temperature as sensed by the bulb element 52 is below that for which the knob 62 has been set.v Thus, assuming that the snap-action mechanism 26 is normally in position to overcome the bias of the spring 22 on the valve member 20 and the temperature afiecting the bulb element 52 increases, then the liquid filling 64 expands and causes corresponding expansion of the bellows member 48. As the bellows member 48 is held bodily in its adjusted fixed position by the adjusting stem 56, the .expansive movement results in a movement of the stud 18 away from the casing l causing a counterclockwise pivoting movement of the lever member 68 about the adjusting screw 16. The collar 44 on the thrust element 42 follows the counterclockwise movement of the lever 88 and causes the clicker disk 38 of the snap-action mechanism to move to its retracted position. The bias of the .valve spring 22 is then exerted to cause closure of the valve member 28 relative to the valve seat l8. Consequently, flow of fuel between the inlet l2 and the outlet l4 ceases.

In the event that the temperature sensed by the bulb element 52 decreases, then the liquid 84. will contractand the bellows member 48 will exert a pull on the lever member 68 causing it to rotate clockwise on its pivot I6 toward the casing I0. Such motion of the lever 68 will be transmitted to the thrust element 42 of the snap-action mechanism 26 which overcomes the bias of the valve spring 22 and causes the valve member 20 to be moved to its open position as shown in Fig. 1 of the drawing. As so. far described, the opening and closing movements of the valve member 20 due to operation of the snap-action mechanism follows that of any thermostatic control apparatus constructed as described and regardless of the internal pressure used. in the power element. However, should the power element of this invention become punctured. or otherwise develop a leak, then the tension. of the liquid 64 is relieved and the internal pressure will increase to the atmospheric pressure. existing externally of the power element. Consequently, the return snap force of the clicker disk 38 will be exerted to mechanically expand the bellows. 48 and. cause operation. of the. lever 88 in a counterclockwise direction. .As. previously explained, the bias of the valve spring 22 can then be exerted to cause closure of. the valve member 28 relative to itsseat I8. It is apparent, therefore, that the control element of this. invention always fails in a safe condition, due to immediate closure of the valve member 20 when such failure occurs.

It will further be apparent that the bellows member 48 is normally maintained in tension, but is adapted to expand solely by volumetric. changes in the liquid 64 upon sufficient variation in the temperature condition sensed ,by the bulb element 52. The volume of liquid 64 contained in the power element does not change appreciably for very large changes of. pressure. Liquids. offer. great resistance to changes of their volume while gases or vapors ofier very little resistance. The coefficients of compressibility of the non-metallic liquids, xylene and aniline, are about .000074 and, .000043, respectively. Hence, negligible change in linear expansion of the bellows member 48 is experienced. The apparatus, therefore, exhibits great advantages over those utilizing power elements with liquid under compression or involving vapor pressure changes. In the disclosed-embodiment, a normally closed snap mechanism is combined with the fail-safe power element to reduce the internal fluid pressure of the latter and obtain the desired safe failure.

Many changes may be made in the details of construction and arrangement of parts within the scope of the appended claim as will be apparent.

I claim:

A thermostatic control apparatus comprisinga casing having inlet and outlet openings for fuel, a valve seat intermediate said openings, a valve member reciprocable relative to said seat between open and closed positions and being biased to said closed position, a valve stem carried by said valve member and projecting toward said seat, snap-action means mounted in said casing coaxial with said valve member on the opposite side of said seat, said means including spring means adapted for operative engagement with said valve stem for overcomin said bias and causing movement of said valve member to said open position, an expansible bellows member positioned in said casing for movement on an axis substantially parallel with said valve member, a lever pivoted at one end in said casing and overlying said snap-action means and. said mitting a biasing force from said spring means to said bellows member for urging said bellows member toward elongated condition, a bulb adapted to be exposed to variation in a temperature condition, a capillary tube connecting said bellows member and bulb in a closed system, liquid under pressure less than atmospheric completely filling said system for nomially maintaining said bellows member in tension but being adapted for causing expansion thereof solely by volumetric changes in said liquid upon sufiicient variation in said temperature condition, an adjusting stem carried by said casing for supporting said bellows member for bodily movement relative to said snap-action means, and manually operable means projecting exteriorly of said case ing for actuating said adjusting stem to overcome said bias and hold said valve member in i open position in the absence of said or leakage in said system. r

i MICHAEL J. CAPARONE.

expansion REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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