US3764763A - Pressure switch - Google Patents

Pressure switch Download PDF

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Publication number
US3764763A
US3764763A US00218718A US3764763DA US3764763A US 3764763 A US3764763 A US 3764763A US 00218718 A US00218718 A US 00218718A US 3764763D A US3764763D A US 3764763DA US 3764763 A US3764763 A US 3764763A
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Prior art keywords
contact
switch
camming
switch blade
pressure
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Expired - Lifetime
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US00218718A
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English (en)
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G Barnes
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Eaton Corp
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Eaton Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H35/00—Switches operated by change of a physical condition
    • H01H35/24—Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow
    • H01H35/26—Details
    • H01H35/2607—Means for adjustment of "ON" or "OFF" operating pressure
    • H01H35/265—Means for adjustment of "ON" or "OFF" operating pressure by adjustment of one of the co-operating contacts
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H35/00—Switches operated by change of a physical condition
    • H01H35/24—Switches operated by change of fluid pressure, by fluid pressure waves, or by change of fluid flow
    • H01H35/26—Details
    • H01H35/2607—Means for adjustment of "ON" or "OFF" operating pressure
    • H01H35/2614—Means for adjustment of "ON" or "OFF" operating pressure by varying the bias on the pressure sensitive element

Definitions

  • Hlh 1/48 housmg a pressure a swtch blade means 58 Field of Search 200/83 WM 83 s movable between first secmd "9" 200/83 SA 81 4 81 337/311 323 able contact means and a contact stop means having first, second and third camming means controlling re- [56] References Cited spectively the first and second contact means and the switch blade means.
  • the camming means may each be UNITED STATES PATENTS a pair of spaced opposed surfaces in the contact stop 3,450,854 6/1969 Simmons 200/83 WM means whereby movement of the contact stop means 2930374 3/1960 controls the positions of the switch blade means and 2 2188.438 l/l940 Judson 200/83 SA movable Contact means so that various levels f fluids may be controlled by the pressure switch.
  • This invention generally relates to fluid pressure responsive circuit makers and breakers and more particularly concerns a fluid pressure switch having a diaphragm which is moved by the fluid pressure to actuate a switch blade means movable between contact with first and second electrically connected contact means.
  • the switch blade and contacts are easily movable by a contact stop means to adjust their position relative to each other so that the pressure necessary to cause actuation thereof may be varied.
  • the relationship of the upper and lower levels is such that the lower level of the fluid or pressure remains constant while the upper level of the fluid or pressure is varied.
  • the constant differential reset level indicates the relationship wherein the difference between the high and low pressure or fluid levels remains constant so that as the upper level is increased or decreased, the lower level remains at a predetermined constant differential therefrom.
  • an increase or decrease in the upper fluid or pressure level causes a proportionate increase or decrease in the lower fluid or pressure level so that, for example, as the upper level increases, the difference between it and the lower level increases proportionately.
  • a particularly advantageous use of the invention herein occurs in automatic clothes washing machines wherein it is desirable that a wide range of fluid levels be easily and accurately maintained by as small, as economical and as fool-proof a switch structure as is possible.
  • these machines have increased in size and hence it is becoming more important that the water level in the machines be controllable over a wider range of enable these higher capacity machines to carry a wide range of loads.
  • the water level selections it is no longer unusual for the water level selections to vary from four inches for a light load to 18 or more inches for a heavy load. Compounding these requirements is a greater emphasis on a higher degree of accuracy, stability, consistency of performance, and a desire for a smaller size pressure switch.
  • the higher motor requirement have increased the electrical load thereby increasing the effects of contact chatter, contact bounce and subsequent contact welding.
  • the many problems of the prior art are overcome by the pressure responsive switch means according to the invention herein in which an easily positionable contact stop means cooperates with a switch blade means movable between contact with a first and second contact means to move the switch blade means and the first and second contact means relative to one another and to limit their extent of movement so that the amount of pressure and hence the fluid level to which the switch means will be responsive to may be simply and accurately varied.
  • the switch means further includes a pressure chamber bounded in part by a diaphragm means with the pressure chamber being adapted to be connected to a variable pressure source.
  • the switch blade means is operatively connected to the diaphragm means and the switch blade means has connected therewith a variable biasing means to vary the force required to move the switch blade means whereby the switch blade means may be movable against the force of the biasing means from the first contact means to the second contact means.
  • the first, second and third camming means are each a pair of spaced opposed surfaces receiving therebetween a portion of the first contact means, the second contact means and a switch blade means, respectively, so that movement of the cam stop means controls the position of the switch blade means and the movable contact means.
  • the opposed surfaces of the camming means are each spaced apart a distance to allow movement of the portion of the respective contact means and switch blade means received therein within predetermined limits.
  • the first and second contact means may be biased toward each other and toward intermediate switch blade means and will lie adjacent the innersurface of the first and second camming means re spectivley so that it may move between the opposed camming surfaces in response to contact by the switch blade means whereby the rapid movement of the switch blade means may be brought to a stop with the contact means against the outer camming surface and in abutment with the switch blade means.
  • the controlled movement of the contact means between the inner and outer surfaces of its respective cam means greatly reduces any tendency for the contacts to bounce or chatter. By varying the angle of the arm of the contact means with respect to the switch blade means, any amount of wiping of the contacts can be obtained.
  • control of amount of wiping of the contacts is impor- I tant in that it allows the generation of a force multiplication which will break any contact welds which may have been formed between the contacts.
  • the opposed surfaces of the first and second camming means are arranged generally parallel to each other so that the difference between the high and low pressure of fluid levels remains constant.
  • the opposed surfaces of the second camming means are arranged so that upon movement of the contact stop means the second contact means remains generally in its original position whereas the first camming means diverges therefrom as required to produce a predetermined upper level.
  • the first and second camming means are divergent in a proportional relationship to the movement of the contact stop so that, for example, as the upper level increases, the difference between it and the lower level increases proportionately.
  • first, second an third camming means may be varied to produce practically all relationships or combinations thereof.
  • the pressure switch housing according to the invention herein may be quickly snapped open and a new and/or different contact stop means readily inserted to allow this very wide range of operation.
  • the switch speed is a function of diaphragm speed which will cause the switch making to be bounced free due to a slow speed.
  • the arc generation due to breaking contacts is minimized by being able to control the speed of opening of the contacts whereas a conventional switch will break at a great enough speed to cause high are generation.
  • the camming means on the contact stop means provide positive stops for the contact means as well as the switch blade means for each of an almost infinite variety of positions. This thereby allows ready control of the diaphragm stroke and the curve in a graph of force on the switch blade means versus stroke of the switch blade means is greatly improved by being able to select just the portion of the curve required for each situation.
  • FIG. 1 is a schematic cross sectional diagram of the invention as embodied in a typical washing machine water system
  • FIG. 2 is a schematic cross sectional elevation of an embodiment in a pressure responsive switch means adapted to be used in the system of FIG. 1;
  • FIG. 3 is an isolated view of the contact stop means of FIG. 2 with the switch blade means shown in the normally opened position as opposed to the normally closed position of FIG. 2;
  • FIG. 4 is an isolated view of another embodiment of a contact stop means configured to provide a generally constant differential reset level relationship
  • FIG. 5 is a graph of force versus stroke of the switch blade means indicating the ability to select a desired portion of the curve between upper and lower levels;
  • FIG. 6 is a graph of water level versus adjustment and indicates the ability of the pressure responsive switch means of the invention to provide various fluid level relationships
  • FIG. 7 is another graph of water level or pressure versus adjustment which serves to indicate the examples of the combinations of fluid level relationships which may be obtained with the invention herein.
  • FIG. 1 Referring to the schematic diagram of a typical wash machine water system in FIG. 1 there may be seen a pressure responsive switch means 10 according to the invention having an inlet 12 in communication with a pressure conduit 14 which in turn is in pressure communication with a wash machine tube 20.
  • a pressurized water supply schematically represented by the conduit 22 is opened and closed by a solenoid water valve 24 which in turn is connected by suitable electrical connection means 26 to the pressure switch 10 whereby the solenoid water valve is controlled by the pressure switch 10.
  • the water valve 24 When the water valve 24 is opened water runs into the tub 20 through the conduit 23 to fill the tub to a desired water level.
  • the tub 20 may include the conventional drain means 30 and pump 32 for draining the wash water.
  • the depth of water or range of levels of water in the tub 20 is indicated by the arrow 36 extending between the bottom of the tub 20 and the desired upper water level 37. It is important in a wash machine to control the level of water. at two points, the first is the desired water level 37 at which point the water is cycled or tripped off after filling the tub 20 and the second point is the lower water level limit indicated at 38 at which point the switch is reset and the water is cycled on.
  • both the desired upper water level 37 and the lower water limit 38 may be easily and conveniently regulated to have the relationships of levels 37 and 38 known as constant differential, a proportional differential or constant reset. It is also unique to this invention that variations of these combinations may be possible. These relationships will be explained in greater detail with regard to the operation of the invention.
  • the pressure switch 10 comprises an expandable air chamber 15 communicating at one portion thereof with the conduit 14 and h aving a diaphragm means 16 bounding another portion thereof.
  • a diaphragm means 16 is connected by a translation member 17 to an elongated blade-like switch plate means 40 so that movements of the diaphragm 16 in response to pressure changes in the pressure chamber 15 are transferred to the switch blade means 40 by the translation member 17.
  • a first contact means 50 is positioned on one side at an angle to the switch blade means 40.
  • the first contact means 50 includes a contact 52.
  • a second contact means is situated on an opposite side of the switch blade means 40 and also extends at an angle thereto.
  • the second contact means includes a contact 62.
  • Both the contact means 50 and 60 may comprise flexible, elongated blade members.
  • the contact means 50, the contact means 60 and the switch blade means 40 each have portions engaging respectively a first camming means 55, a second camming means 65 and a third camming means 45 which camming means are located on a contact stop means 70 and control the permissible movement of the respective contact means and switch blade.
  • the contact stop means 70 may be rotatably mounted in a housing 11 of the pressure switch means 10.
  • a tension spring 80 has a first end 81 attached to the switch blade means 40 and a second end 82 attached to an adjustment means 85 whereby the tension in the spring means 80 may be varied.
  • the resilient tension force in the spring 80 acts against the force transmitted through the translation member 17 by an increasing pressure in the pressure chamber 15.
  • the increasing force on a diaphragm 16 as transmitted by the translation means 17 is opposed by the tension means 80 until the force on the translation member 17 overcomes the tension force on the spring means 80 at which point the switch blade means 40 is moved from its normally closed position as shown in FIG. 2 to a normally opened position as illustrated in FIG. 3.
  • Each of the means 40, 50 and 60 includes electrically conductive means so that the switching of the switch blade 40 between the first contact means 50 and the second contact means 60 breaks one circuit and makes another in response to the change in pressure in the pressure chamber 15.
  • the pressure switch means acts as a transducer, converting a hydropneumatic function into an electrical function. That is, the increase in the level 36 of water in the tub 20 as shown in FIG.
  • an air pressure head in the chamber causes the diaphragm means 16 to overcome a predetermined tension in the spring means 80 to thereby move the contact arm 40 from the normally closed contact 50 which is part of a circuit that will activate the solenoid 24 to allow water under pressure in the pipe 22 to be dispensed into the tub through the inlet 23 and move it to the normally closed contact means 60 thereby stopping further flow of water into the tub 20 and to activate the circuit of which contact means 60 may be a part.
  • the diaphragm 16 will be moved in a direction whereby the contact between the switch blade 40 and the second contact means is broken and the contact between the switch blade means 40 and the contact means 50 is made to thereby activate the solenoid 24 and again increase the water level in the tub 20 to the desired selected level 37 at which point the cycle is repeated.
  • the first, second and third camming means 55, and 45 respectively, each comprise a pair of opposed inner and outer surfaces 56, 57; 66, 67; and 46, and 47.
  • Each of the respective camming means 55, 65 and 45 receive between their respective inner and outer surfaces a portion of the respective first camming means 50a, the second camming means 60a and the switch blade means 400.
  • the opposed surfaces of the camming means are each spaced apart a distance to allow movement of the portion of their respective contact means and switch blade means received therein within predetermined limits. As shown in FIGS.
  • the contact stop means may take the form of a generally cylindrically shaped rotatable member wherein the first camming means takes the form of a groove means on the outer surface of the generally cylindrically shaped member and receives the portion 50 a of the first contact means therein.
  • the second camming means 65 will be a groove on the outer generally cylindrically shaped surface of the contact stop means 70 and receives a portion 60a of the second movable contact means therein.
  • the third camming means 45 also is a groove means on a generally cylindrically shaped surface of the contact stop means 70 and receives a portion 40a of the switch blade means therein.
  • the position of the first contact means 50 will vary in relation to the generally constant position of the second contact means 60.
  • This variation in the location of the first contact means 50 has the effect of changing the position of the switch blade means 40 when it is in its normally closed position so that the forces acting on the switch blade means 40 in opposition to the forces acting through the translation member 17 will be varied and hence the trip or upper level position 37 of the fluid will be varied.
  • Suitable gauge and/or indicator means in conjunction with the contact stop means 70 may be provided to allow selection of the desired water level in accordance with common and well known expressions.
  • the lands 70b and 700 between the camming means 55, 45 and 65 may be of a width or configuration in accordance with efficient operation and the sizes of the contacts 52, 42, and 62, respectively.
  • the first contact means 50 and the second contact means 60 may be biased by means not shown toward each other and toward the intermediate switch blade means 40 to bear against the outer camming surface 57 and the inner camming surface 66 respectively, when they are free from contact with the switch blade means 40. Accordingly, as the switch blade means 40 snaps into contact with the first contact means 50 it moves the contact means against its inward biasing force and moves the portion 50a into contact with the inner camming surface 56 of the first camming means 55. When the pressure force in the chamber becomes great enough to move the switch blade means 40 and break contact with the first contact means 50 the portion 50a of the first contact means 50 returns to its original position biased against the outer camming surface 57.
  • the switch blade means 40 moves the portion 60a from its position biased against the inner camming surface 66 to a position where it contacts the outer camming surface 67 as is more clearly shown in FIG. 3.
  • the inward bias of the contact means 50 and 60 has the effect of decelerating the switch blade means 40 at the end of its snap-type action movement and also accelerating the movement of the switch blade means 40 at the beginning of its movement. This has the effect of reducing if not eliminating the amount of, bounce of the contacts and also minimizes chatter. Forces between the members 40, 50 and 60 are transmitted through the contact points 42, 52 and 62 so that an excellent contact results with accordant improvement of chatter, capacity and general functioning.
  • the angular relationship of the contact means 50 and 60 to the switch blade 40 and their different relative arcuate movement together produces a wiping of the contacts 42, 52 and 62.
  • This wiping is important in that it allows the generation of a force multiplication which will break any contact welds that may have been formed between the contacts while they were together. This is particularly important with the demands for higher electrical capacity of these switches.
  • the angular relationship of the contact means 50 and 60 with the switch blade means 40 may be varied to vary the amount of wiping of the contacts. By this means the wiping may be reduced to zero and the friction present in the mechanism due to the wiping of the contacts may in theory be eliminated.
  • the translation member 17 may be a resilient springlike member which will act to store energy during initial movement of the diaphragm 16 and prior to the diaphragm force overcoming the resilient spring means 80 so that after the force of the spring means 80 has been overcome the translation member 17 will tend to release its energy and effectively snap the switch blade means 40 between the contact means 50 and 60. It will be understood by those skilled in the art that the resilience of the translation member 17 relative to the spring means 80 and the force on the diaphragm 16 may be designed to vary the movement characteristics of the switch blade 40. Thus, the translation member 17 may vary from being very stiff to being very flexible depending upon the switching characteristics desired. The ease of modification by changing this one part is yet another example of the flexibility and adaptability of the switch means of the invention.
  • fluid levels may be simply and accurately varied.
  • a further illustration of the range of variations which may be effected is the contact stop means 170 in FIG. 4.
  • the first contact means 50 is received in a first camming means 155
  • the second contact means 60 is received in a second camming means 165
  • the switch blade means 40 is received in a third camming means 145.
  • the camming surfaces 156, 157 of the first camming means 155 and the camming surface 166 and 167 of the second camming means 165 are parallel to each other to produce what is known as the constant differential level wherein the difference between the upper and lower levels remains constant as they are varied.
  • contact stops may be designed to produce all fluid level relationships which can be foreseen. Further, the variation and flexibility is readily effected. For example, by means of lateral protrusions 172 in the third camming means 45 and 145 respectively, the switch blade means may be manually urged against the normally closed first contact means to thereby override the automatic pressure responsiveness. Clearly, other and different variations will be apparent to those skilled in the art having knowledge of my invention.
  • FIG. 5 there may be seen a graph of force transmitted to the switch blade member 40 by the translation member 17 versus the displacement of the switch blade means 40 to illustrate the ability of the invention herein to allow selection of a particular portion of a normal toggle curve.
  • the normal toggle curve is illustrated at 90
  • the upper level or trip line is indicated at 92
  • the reset or lower level is indicated at 94.
  • the line indicates that the pressure will build up on the switch blade means 40 at the normally closed stop until the trip point 96 at the trip level 92 is reached at which point the switch blade will move and the force will decrease until the normally opened contact means 60, in FIG. 2 is reached. At this point the force will again increase as indicated by the line 97.
  • the lines 95 and 97 indicate the limits of movement of the switch blade means 40 and hence allow selection of any portion of the curve 90 as represented by the portion 98. Moreover, the selection may be simply and accurately effected.
  • FIG. 6 there may be seen a graph of the water level versus adjustemnt of the contact stop means which will allow the various relationships of the upper and lower levels.
  • the constant reset level relationship is illustrated by the lines 100 and 103;
  • the constant differential reset level is illustrated by the lines 102 and 103;
  • the proportionate reset level relationship is illustrated by the lines 101 and 103.
  • the line 103 represents the trip or upper level and lines 100, 101 and 102 represent the reset or lower level.
  • FIG. 7 another example of possible variations in the trip and reset levels are illustrated by the lines 1 10 through 117.
  • lines 110, 111 illustrate one alternate trip level configuration whereas line 112'represents an alternate trip level.
  • lines 113 through 1 17 represent individual alternate variations of relationships.
  • an electrical switch means having a switch blade means movable between electrical contact with a first and second movable contact means
  • a contact stop means including a first camming means controlling said first movable contact means, a second camming means controlling said second movable contact means, a third camming means controlling the position of said switch blade means relative to said first and second movable contact means, said camming means being coaxial, and a common actuator therefor to effect a variation in the point of contact between said switch blade means relative to said first and second movable contact means.
  • a switch means according to claim 1 wherein said first, second and third camming means are each a pair of spaced, opposed annular surfaces on said contact stop means whereby movement of said cam stop means controls the position of said switch blade means and said movable contact means.
  • a switch means according to claim 2 wherein said opposed surfaces of said first camming means receive a portion of said first contact means therein, said opposed surfaces of said second camming means receiving a portion of said second movable contact means therein, said opposed surfaces of said third camming means receiving a portion of said switch blade means therein, said opposed surfaces of said camming means each being spaced apart a distance to allow movement of the portion of the respective contact means and switch blade means received therein within predetermined limits.
  • a switch means according to claim 3 wherein said opposed surfaces of said first and second camming means are generally parallel to each other whereby a constant differential reset level relationship is produced.
  • a switch means according to claim 1 wherein said switch blade means is connected with a pressure responsive means whereby pressure changes may cause movement of said switch blade means in generally opposite first and second directions, a resilient biasing means connected with said switch blade means to oppose movement of said switch blade means by said pressure responsive means in said first direction and to assist movement of said switch blade means in said second direction.
  • a switch means according to claim 5 wherein the force exerted by said resilient biasing means may be adjusted to vary the amount of pressure necessary to cause movement of said pressure responsive means.
  • a switch means according to claim 5 wherein said pressure responsive means is a diaphragm which bounds a pressure chamber, said pressure chamber being adapted to be operatively connected to a variable pressure source, said diaphragm being a polyurethane film.
  • a switch means according to claim 3 wherein said opposed surfaces of said camming means are spaced apart a distance to allow movement of said first and second contact means, said first and second contact means being biased toward said switch blade means, said contacts between said switch blade and said contact means being arranged so that said switch blade means overcomes the bias of the contact means it is engaging and moves said contact means from one opposite surface of its respective cam means to the other opposite surface.
  • a switch means according to claim 1 wherein the contact means and the switch blade means are positioned relative to each other at an effective angle of inclination, said effective angles of inclination being variable by said camming means on said contact stop means whereby the amount of wipe of the contacts may be varied.
  • a switch means according to claim 1 wherein said first and second movable contact means and said switch blade means each have protruding contact points thereon, said contact points providing the points of engagement of the switch blade means with the respective contact means whereby the opposing forces in the switch blade means and in the contact means are transmitted directly through the contact points.
  • an electrical switch means having switch blade means movable between electrical contact with a first and second movable contact means
  • the improvement comprising a contact stop means in the form of a generally cylindrical rotatable member, having a first camming means extending thereabout controlling said first movable contact means, a second camming means spaced from said first camming means for controlling said second movable contact means, and a third camming means controlling the position of said switch blade means relative to said first and second movable contact means
  • said first, second and third camming means each comprising a pair of spaced opposed camming surfaces extending about said cylindrical shaped rotatable member andforming first, second and third camming grooves, said first groove receiving a portion of said first contact means therein, said second groove receiving a portion of said second movable contact means therein, and said third groove receiving a portion of said switch blade means therein, for varying the positions of said movable contact means and said switch blade means relative to each other upon turning movement of said cylindrical member.

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  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Switches Operated By Changes In Physical Conditions (AREA)
US00218718A 1972-01-18 1972-01-18 Pressure switch Expired - Lifetime US3764763A (en)

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US21871872A 1972-01-18 1972-01-18

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US (1) US3764763A (it)
DE (1) DE2302278A1 (it)
ES (1) ES410696A1 (it)
FR (1) FR2168497A1 (it)
IT (1) IT978236B (it)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3984650A (en) * 1974-07-18 1976-10-05 General Electric Company Fluid pressure diaphragm switch having plural adjustment mechanisms
US4128747A (en) * 1975-08-16 1978-12-05 Danfoss A/S Hinge for a pivotable arm of an electric snap switch
US5198631A (en) * 1991-09-11 1993-03-30 General Electric Company Pressure responsive control device
US5530215A (en) * 1993-11-05 1996-06-25 Furnas Electric Company Pressure switch
US6346681B1 (en) * 1995-09-28 2002-02-12 Ronald S. Joyce Pressure switch
US20090057125A1 (en) * 2007-08-30 2009-03-05 Honeywell International, Inc. Pressure switch with adjustable differential setting

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2188438A (en) * 1937-05-07 1940-01-30 Honeywell Regulator Co Switching mechanism
US2930874A (en) * 1958-07-28 1960-03-29 Gen Electric Adjustable temperature responsive control for electrical devices
US3450854A (en) * 1967-03-30 1969-06-17 Mallory & Co Inc P R Control means for pressure responsive switch

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2188438A (en) * 1937-05-07 1940-01-30 Honeywell Regulator Co Switching mechanism
US2930874A (en) * 1958-07-28 1960-03-29 Gen Electric Adjustable temperature responsive control for electrical devices
US3450854A (en) * 1967-03-30 1969-06-17 Mallory & Co Inc P R Control means for pressure responsive switch

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3984650A (en) * 1974-07-18 1976-10-05 General Electric Company Fluid pressure diaphragm switch having plural adjustment mechanisms
US4128747A (en) * 1975-08-16 1978-12-05 Danfoss A/S Hinge for a pivotable arm of an electric snap switch
US5198631A (en) * 1991-09-11 1993-03-30 General Electric Company Pressure responsive control device
US5300741A (en) * 1991-09-11 1994-04-05 General Electric Company Pressure responsive control device
US5524333A (en) * 1991-09-11 1996-06-11 General Electric Company Method of assembling a pressure responsive control device
US5530215A (en) * 1993-11-05 1996-06-25 Furnas Electric Company Pressure switch
US6346681B1 (en) * 1995-09-28 2002-02-12 Ronald S. Joyce Pressure switch
US20090057125A1 (en) * 2007-08-30 2009-03-05 Honeywell International, Inc. Pressure switch with adjustable differential setting
US7605336B2 (en) 2007-08-30 2009-10-20 Honeywell International Inc. Pressure switch with adjustable differental setting

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DE2302278A1 (de) 1973-07-26
ES410696A1 (es) 1975-12-01
FR2168497A1 (it) 1973-08-31
IT978236B (it) 1974-09-20

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