US2951132A - Pressure responsive device - Google Patents

Description

PRESSURE RESPONSIVE DEVICE Filed March 27, 1958 IN V EN TOR. JAMES M. CUNNIEN United States Patent C i" PRESSURE RESPONSIVE DEVICE James M. Cunnien, St. Paul, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Fired Mar. 27, 195s, ser. No. 724,302

7 claims. (ci. zoo-ss) This invention is directed to a pressure responsive device and more particularly to a pressure responsive switch of very compact design. While the device is very compact it nevertheless possesses characteristics ordinarily associated with devices of greater complexity and size. The invention provides a pressure responsive switch in which the effects of friction are greatly reduced as there are no pivotsin the linkage between the diaphragm and the precision snap switch. Movement is transmitted to the switch by a simple drive rod. This rod is guided in a post carried by the frame, and since there is nol lateral force thereon required for switch actuation, there is practically no frictional drag that may affect the response of the device. As a result the device is highly repeatable in operation.

Repeatability is also aiected adversely if the pressure sensing diaphragm is permitted to deflect through too great a distance. Likewise, the travel of the snap switch plunger must be limited if the use of special overtravel mechanisms is to be avoided. `In addition to adding to the cost, an overtravel mechanism would also add to the size of the device. By providing means tov limit diaphragm movement to a range based on the requirements of the snap switch, the diaphragm is protected from excessive deections that might affect its characteristics, lwhile at the same time preventing injury to the snap switch due to excessive force applied to the operating plunger. lf the diaphragm -were to receive a se due to excessive-travel at high pressure its eiective area and effective spring rate would be changed so that the device would lose its calibration and no longer control at the desired pressures. Life of the diaphragm is also extended by limiting its movement to the required range.

The device provided herein attains these objects in an overall physical size little larger than the diaphragm, loading spring and switch, so that it may be incorporated in compact equipment. At the same time it is capable of adjustment to meet the exact requirements of the equipment being controlled. An idea of the size of a physical embodiment of a device incorporating the invention can be had from the fact that the case of the snap switch is slightly less than two inches long. The device is comparable in size with some simple pressure switches having slow acting contacts and no adjustments. lf differential adjustment were not required, or a smaller capacity switch were satisfactory the device could be made considerably smaller. The pressure sensing portion of the disclosed device has a physical size only slightly larger than the snap switch which it actuatcs.

1n the drawing, Figure l is a sectional view of a pres'- sure switch incorporating the invention, and Figure 2 is a view of the device as seen from the top of Figure l.

The disclosed embodiment of the invention is a pressure switch designed to respond to` changes in pressure in the low-pressure side of a refrigeration system. The power head is of the diaphragm type and is directly loaded by a helical spring. Motion is transmitted directly through a push rod to make or break the switch 2,951,132 le@ Patented Aug. 30, 1960 contacts. Means is provided to limit diaphragm movement to a range determined by the requirements of the `snap switch, thus protecting the switch as well as insuring maximum reliability. f

Control point setting is determined by the load applied to the diaphragm by the loading spring. Differential adjustment is `accomplished by rotation of a dial wheel on the switch. As mentioned above, the novel features of the invention make possible the provision of a high quality pressure switch of very compact conformation, and relatively simple construction.

A frame 10 is built up of two sheet metal sections 1-1 and 12 staked together at 13 (Figure 2) to form a boxlike enclosure for the pressure sensing mechanism. Frame section 12 is formed to provide parallel legs 15 which embrace a precision snap switch 16 which is secured thereto by rivets 17. The legs 15 extend laterally beyond one end of the switch and are shaped to provide mounting ilanges 18.

As seen in Figure l, frame section 11 carries a nipple 20 to which is `secured a diaphragm assembly 21 includ# ing an outer flexible diaphragm disk 22 to which, in turn, is secured an inner diaphragm disk 23. The interior of the diaphragm assembly is in communication with a capillary tube 25 through a bore in the nipple 20. An annular raised portion at the center of the inner diaphragm disk 23 iits within a complementary recess formed in a disk 27, which serves to transfer diaphragm force and movement.

A post St) is situated in line with the axis of movement of the diaphragm and is carried by a portion of frame section 12 opposite the diaphragm. The post terminates at a. point spaced from the disk 27. The post 30 has external yscrew threads in an area intermediate its ends cooperating with internal threads on a control point adjusting nut 32. A helical compression spring 34 bears against the nut 32 and against the disk 27 on the diaphragm. The periphery of nut 32 is provided with rounded teeth to facilitate turning the nut and hence varying the force with which the spring 34 opposes the force of the diaphragm. Frame section 11 has a cut-out 35 providing a window through which the nut 32 can be turned. Obviously, the disk 27 will move toward or from the post depending on the relative forces of the spring and the diaphragm.

A push rod 36 is reciprocable axially in post 30 and has a portion of hexagonal section guided in a hexagonal opening `in post 30 at its mounted end. The post 30 is vinternally threaded at its opposite end to receive an externally threaded'plug 33 which serves two purposes. lt has an axial bore which forms a bearing surface to guide a cylindrical portion of rod 36, and is adjustable axially to determine the distance it extends beyond the end of the post The outer end of ping 3S acts as an abutment cooperating with disk 27 to limit expansion of the diaphragm '21. The plug 3S has a hexagonal internal portion adjacent the bore to receive a .tool to turn it and hence adjust its axial position in post 30. This adjustment is made prior to insertion of the rod 36, and is accomplished by first bottoming the diaphragm and then backing off the number of angular degrees necessary to provide the desired diaphragm travel. The right hand end of rod 36 is internally threaded, as seen in Figure 1, to receive a switch actuating screw 40, having a head 41 that engages `a plunger 43 reciprocable in the plastic housing of the snap switch 16.

The switch 16 is generally of the type described in McGall Patent 1,960,920 except that its diiferential is adjustable. The inner end of plunger 43 is provided with an insulating portion 44 that engages a snap spring 45. The free end of snap spring carries a movable contact 47 which is adapted to cooperate with a stationary Contact 48. Movement of the snap switch away from closed cir cuit position is limited by the inner end of a screw 50 which is turned by an external knob 52. The position of the screw 50 determines the operating diierential of the switch as reflected in plunger travel required to move the switch between on and of positions. Since the stationary contact remains fixed, this adjustment changes only the position of the plunger at which the switch is actuated to closed position. A stop 53 on knob 52 engages a boss 54 on the switch case to limit adjustment of the knob.

Since the greatest plunger travel is required when the switch is adjusted for maximum differential, the effective length of the push rod is adjusted for that condition.

This is done by-adjusting the screw 4@ in the push rod so that the switch will snap to` closed position a small distance before the disk 27 engages the plug 38. This may be readily accomplished by applying suticient pressure to the diaphragm so that disk 27 engages plug 38, turning the screw until the switch snaps to closed position, and then turning the screw through an additional number of angular degrees to provide the desired amount of overtravel. Some overtravel is necessary to assure reliable switch operation, but overtravel must be held below a value that Vwould cause injury to the switch. The switch is provided with terminals S6 and 57 for external wiring connections.

The disclosed pressure switch may find application in controlling a refrigeration machine in response to pressure on the low pressure side of the pump. When the refrigeration system is shut down for an appreciable time, the high and low pressures will equalize, resulting in a much higher pressure being applied to the diaphragm of the controller than the normal control pressure. In the above described design the diaphragm is prevented from expanding suiciently under these conditions to adversely affect its operating characteristics.

The novel features of the invention make possible a very small controller of high quality. it will be appreciated that the source of actuating pressure might be a temperature sensing element in which pressure varies as a function of temperature.

The scope of the present invention should be determined -from the following claims.

I claim:

l. A pressure responsive device comprising, a frame, a diaphragm carried by said frame, a switch carried by said frame and having an operator disposed on the axis of expansion of said diaphragm, a post secured to said frame adjacent said switch and extending toward said diaphragm, a rod carried by said post and reciprocable therein and extending beyond said post to engage saidl diaphragm and said switch, a nut threaded on said post, a compression spring acting between said diaphragm and said nut, and a plug carried by internal screw threads inthe end of the post adjacent said diaphragm and adapted to be adjusted to extend beyond said post to engage said diaphragm to determine the limit of expansion thereof.

2. A pressure responsive device comprising, a frame, -a diaphragm carried by said frame, a switch carried by said frame and having an operator disposed on the axis of expansion of said diaphragm7 a generally tubular post secured to said frame adjacent said switch and extending toward said diaphragm, a rod carried by said post and reciprocable therein and extending beyond said post to engage said diaphragm, said rod having a portion axially adjustable thereon to vary the eifective length of said rod and adapted to engage the operator of said switch, a nut threaded on said post, a compression spring acting between said diaphragm yand said nut, and a plug carried by internal screw threads in the end of the post adjacent said diaphragm and adapted to be adjusted to extend beyond said post to engage said diaphragm to determine the limit of expansion thereof.

3. A pressure responsive device comprising, a frame, a diaphragm carried by said frame, a switch carried by said frame and having an operator disposed on the axis of expansion of said diaphragm, a generally tubular post secured to said frame adjacent said switch and extending toward said diaphragm, a rod reciprocable in said post and having a portion extending beyond said post to engage the center of said diaphragm, said post being formed at the end thereof adjacent said switch to provide a first bearing surface for said rod, said rod having a portion axially adjustable thereon to vary the effective length thereof and adapted to engage the operator of said switch, a nut in threaded engagement with the outside of said post, a compression spring disposed coaxially with respect to said diaphragm and acting between said diaphragm and said nut, and a plug in threaded engagement with an inner surface of said post adjacent said diaphragm, said plug being thereby adjustably extensible beyond the end of said post to act as an abutment to determine the limit of expansion of said diaphragm, and said plug having an axial aperture therethrough providing a second bearing surface for said rod.

4. A pressure responsive device comprising, a frame, a diaphragm carried by said frame, a snap switch carried by said frame and having an operator disposed on the axis of expansion of said diaphragm, said switch being operable between on and ofi conditions by movement of said operator between two spaced positions, a generally tubular post carried by said frame extending axially of said diaphragm from a point adjacent said switch to a point adjacent said diaphragm, a rod reciprocable in said post and having a portion extending from said post to engage said diaphragm, said post being formed at the end thereof adjacent said switch to provide a rst bearing surface for said rod, said rod having a portion axially adjustable thereon to vary the efiective length of said rod and `adapted to engage the operator of said switch, a nut i-n threaded engagement with the outside of said post, a compression spring disposed coaxialiy with respect to said diaphragm and acting between said diaphragm and said nut, and a plug in threaded engagement with an inner surface of said post at the diaphragm end thereof, said plug having an axial aperture therethrough providing a second bearing surface for said rod, and said plug being adjusted to extend beyond the ends of said post to act as an abutment to limit movement of said diaphragm to a range greater than the distance between the two operative positions of said switch, the adjustable portion of said rod being so positioned on said rod that the range of movement of said switch operator by said rod includes the two operative positions of said switch.

5. A pressure responsive device comprising, a frame, a pressure sensing element carried by said frame, a switch carried by said frame and having an operating portion disposed on the axis of expansion of said element, a post secured to said frame adjacent said switch and extending toward said element, `a rod carried by said post and reciprocable therein and extending beyond said post to engage said element and said switch, a nut threaded on said post, a spring acting between said element and said nut, and a member in threaded engagement with said post adjacent said element and adapted to be adjusted to extend beyond said post to engage said element to determine the limit of expansion thereof.

6. A pressure responsive device comprising, a frame, a pressure sensing element carried by said frame, a switch carried by said frame and having an operating portion disposed on the axis of expansion of said element, a post secured to said frame adjacent said switch and extending toward said element, `a rod carried by said post and reciprocable therein and extending beyond said post to engage said element and said switch, a nut threaded on said post, a spring acting etween said element and said nut, and la plug carried by internal screw threads in the end of said post adjacent said element and adapted to be' adjusted -to extend beyond said post to engage said element to determine the limit of expansion thereof.

7. A pressure responsive device comprising, a frame, a pressure sensing element carried by said frame, a switch carried by said frame and having an operating portion disposed on the axis of expansion of said element, a post secured to said frame adjacent said switch and eX- tending toward said element, a rod carried by said post and reciprocable therein and extending beyond said post to engage said element and said switch, said post being formed at the end thereof adjacent said switch to provide a first bearing surface for said rod, a nut in threaded engagement with said post, a spring acting between said element and said nut, and a member in threaded engagement with said post at the end thereof adjacent said ele- 15 2,790,043

6 ment and adapted to be adjusted to extend beyond said post to engage said element to determine the limit of expansion thereof, and said member having an axial aperture therethrough providing a second bearing surface for said rod.

References Cited in the file of this patent UNITED STATES PATENTS 1,938,327 Green Dec. 5, 1933 2,086,264 Gorschalki July 6, 1937 2,376,634 Tellkamp May 22, 1945 2,552,746 Steider May 15, 1951 2,628,296 Dillman Feb. 10, 1953 Clason Apr. 23, 1957

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