US2821592A - Pressure actuated switch - Google Patents

Description

Jan. 28,v 1958 P.'B`. SAGAR PRESSURE ACTUATED SWITCH Filed Feb. 20, 1956 INVENTOR. PAUL B. SAGAR BYr A T'ORNEK? United S'tates Patent() This invention relates to a pressure actuated switch and Imore particularly to a simple and inexpensive switch which is capable of being actuated by slight pressure diterentials and which can be accurately adjusted so as to be actuated by a predetermined pressure differential. The switch of the present invention has particular utility in air conditioning and heating systems for sounding an 1 alarm when air filters become clogged but also has utility u in any environment where it is desired to sound an alarm or actuate a control when a predeterminedpressure diierentialhas been reached between two different gas or air lled spaces.

Pressure yactuated switches of the prior art which are suciently sensitive to be actuated by very small pressure l differentials, have either included diaphragms of large area connected to switch elements through complicated linkages or have included pivoted vanes or plates of large size with the switch element carried by a projecting pivot shaft or connected thereto by a linkage mechanism. Such switches have required diaphragms or vanes of relatively large size since relatively large actuating forces were necessary to overcome friction and to insure proper functioning of the switch.

In accordance with the present invention, a mercury switch element is mounted directly on a plate member or vane positioned in the passage between spaces containing 1 gas or air at different pressures, the plate member substantially closing the passage when in normal position and being pivoted about an axis extending transversely of the passage and eccentric to the pressure areas of the plate member. A simple pivot structure may be employed imposing substantially no friction forces resisting movement of the plate member by such diierential pressure. A biasing force may be provided by a suitable mechanism, such as a weight or a spring, for holding the plate member in a normal position but a preferred structure includes a permanent magnet adjacent the plate member. By adjusting the distance between such magnet and the plate member when the plate member is in its normal position, a simple structure is provided having a rapid action when the forces due to the pressure differential exceed the magnetic force on the plate member.

` The value of the pressure differential required to actuate the plate member and thus tip the mercury switch to open or close, a circuit can be adjusted by varying the distance between the plate member and the permanent magnet and the pressure ditferential required to hold the plate member in its actuated position is less than that required to initially actuate the plate member.

It is therefore an object of the invention to provide an improved pressure actuated switch which is operative by small pressure diierentials and which is simple and `reliable in operation.

Another object of the invention is to provide a pressure actuated switch which is simple and inexpensive in construction and which will open or close an electric circuit to Sound an alarm or initiate the actuation of a control when subjected to a predetermined pressure dilerential.

A further object ofthe invention s to provide a pressure actuated switch in which a plate member is positioned in a passage in a housing and pivoted about aneccentric axis extending transversely of the housing and carries a mercury switch element mounted directly upon the plate element so that pivoting of such element by a predetermined pressure dilerential causes actuation of the switch.

A still further object of the invention is to provide a switch mechanism in which a mercury switch element is mounted directly upon a pivoted plate member subjected to a pressure differential and in which the value of such pressure differential required to tip said plate and actuate the switches may be adjusted by varying the distance between a permanent magnet and an edge of the plate member.

Other objects and advantages of the invention will appear in the following description given in connection with the attached drawings of which:

Fig. 1 is a vertical section taken approximately through the center of a switch in accordance with the present invention and showing the switch structure mounted in the wall of anv air or gas chamber or conduit.

Fig. 2 is a front elevation of the switch of Fig. 1;

Fig. 3 is a rear elevation of the switch of Fig. l;

Fig. 4 is a view similar to Fig. 1 with the wall of the conduit or chamber omitted and showing a modified form of switch;

Fig. 5 is a fragmentary rear elevation of the lower portion of the switch of Fig. 4; 4

Fig.v 6 is a view similar to Fig. 4 showing a further modified form of switch; and

Fig. 7 is a diagrammatic view showing one type of system in which the switch of the present invention can chamber or duct but it is apparent that the housing can extend to the exterior of such chamber or duct. The

' passage 17 through the housing 10 has a plate member 18 positioned therein so as to extend across and substantially fill such passage. In Fig. 1 the plate member 18 is shown as being pivoted adjacent its upper edge. Such plate member has a pair of laterally spaced apertures 20 near its upper edge which receives hook members 22 formed on the downwardly bent forwardly projecting edges of a support member 24 secured to the upper interior portion of the housing 10 by a screw 26.

The plate member 18 has an aperture 28 therein of suftcient size to receive the body portion of a mercury switch element 30, such switch element substantially filling the aperture 28. The switch element is held in position by a spring clip member 32 having a body portion suitably secured to the plate member 18 and provided with spring arms 34 engaging the switch element 30 and holding it firmly against a rearwardly bent portion of the body portion of the spring clip member. The plate member 18 is of magnetic material and a small permanent magnet 36 is positioned adjacent the lower edge of the plate member 18, that is, opposite its pivotal connection to the support member 24. The permanent magnet 36 is secured to the housing 10, by a screw 38 which extends through an aper- 'assises ture in the magnet and also securesin position Va. bracket 40 receiving an adjusting stop screw 42 which engages the surface of the plate member 18 to set the normal distan'ce between the vplate member 18 and the magnet 36.

vIt will be apparent that the plate member V18 is held v.against movement in a direction toward vthe magnet 36 bya stop serieu/42 but that itis fre'e topi'vot away from the magnet 36 until its lower end strikes another'stop screw 44. Suitable tiexibleel'ectrical conductors 46 ex- Y tend from the mercury switch element 30 to terminal members 48 lmounted upon a terminalstrip 50 of electrical insulating material secured to a bracket SZinturn secured to the interior of the housing by the screw 54.

The operation of the switch of Figs. 1 to 3"sl1`ould be apparent from theabove description.y The plate member l 18`may move from its normal position, shown in Fig. 1,

about its-"pivotal support on 'thel member 24 to a second position in whiclrthelowe'r edge of the plate member engages against the stopscrew 44. It is held in the normal position, shown in Fig. l, by the force of gravity'and also by magnetic forces provided by the permanent magnet 36. The amount of the latter forces can be adjusted by rotating the stop screw 42 to vary the distance between the lower edge of theplate member 18 and the magnet 36. A pressure differential, of a predetermined mag nitude, on opposite sides ofthe plate member 18 and in a Vdirection urging the plate member from the normal position shown towardv a position against the stop 44 will cause such movement of the plate member to tip the mercury switch element 30. The switch 'can be calibrated to operate at pressure differentials over a considerable range by adjusting the stop screw 42. Tipping of the plate element carrying the switch element causes closing of the electric circuit through the mercury switch element 30 but it is obvious that such element can be l reversed and the terminal strip 48 placed at the other end the inlet side thereof so that a slight partial vacuum is produced in the chamber by the fan 56,. As the filter 58 becomes progressively clogged, the vacuum in the chamber 55 increases, that is, the pressure in the duct or chamber lowers to increase the p1'essure-differential across the switch 8. At a predetermined differential pressure determined by the position of the stop screw 42, the switch operates to sound an alarm 60, which may be an electric bell energized from a step down transformer 62, the bell 60 and switch 8 being in series in the secondary circuit ofthe transformer. Thepressure differential between the interior and exterior of the chamber 55 will ordinarily bel of the order of a few inches of water, even when the filter S8 is sufliciently clogged that it should be changed, so that the force available for actuating the plate member 18 vof the switch' is of the order of a few ounces. The

' switch of the present invention, however,l consistently operates at a definite pressure differential within the range indicated, which pressure differential can be preset by adjusting the stop screw 42.

The switch of Figs.'4 and 5 is similar to that of Figs.

l to 3,except that the modified plate member 64 is pivotedA at the bottom edge instead of at its top edge. Thus, the plate member 64 may have notches 66 in its lower edge I y'received in notches in forwardly extending, downwardly bent edge portions of a pivot support member 67 secured to'the housing68. A mercury'switch element 30of the jsame' type yemployed in theV switch of Figs. l to 3 is likewise positioned in an aperture 28 inthe plate member 4and Held imposition b`y"a 'spring' clipunernber 32. The

remainder ofthe structure of the switch of-Figs. 4 and 6 may be identical to that of the switch of Figs. 1 to 3, except that the stop screw 44 is omitted. That is to say, the switch of Figs. 4 and 6 may include the permanent magnet 36, bracket 40 and stop screw 42 and may also include the terminal strip 50 and bracket 52, the bracket 52 serving as a stop for the plate member 64 instead of the stop screw 44 of Fig. `l. e

A further modified switchis shown in Fig. '6 which may be the same as theswitch shown in Figs. 4 and 5, except that a bl weight 70, which is adjustably secured on a bar 72 extending substantially at right anglesto the plate member 74, is employed to bias vthe plate member 74 toward its normal position instead of a permanent magnet. The operating pressure of the switch of Fig. 6 can be adjusted by moving the weight along the bar 72 and the switch ofl Fig. 6 is satisfactory for certain purposes, although in general', its operating pressure cannot be so accuratelypredetermined as the switches of Figs. l to 5, inclusive.

I claim:

l. A pressure actuated switch comprising a housing having apassage therethrough, a plate having a normal positi'onin which vsaidplate extends across and substantially closes said passage, said plate beingpivoted about an axis extending transversely of said passage and adjacent one edge of said plate, a stop preventing movementof vsaid plate in one direction past said normal position, said plate being movable in the other direction about said axis between said normal position and a `second position, a mercury switch element mounted directly on said plate adjacent said axis for closing an electric circuit when said plat'e'is in one of said positions and opening said circuit when said plate is in the other of said positions, said plate being of magnetic material, a permanentr magnet supportedl in said housing adjacent the other edge of said plate and positioned to'urge said plate in said one direction against said stop, means to. adjust said stop and said magnet relative to each other to vary the distance between said magnet and said plate when said plate is in-said normal position so that said plate is moved from said normal position to said second position when the pressure differential in said other direction between opposite sides of said plate reaches a predetermined value depending upon said distance.

2. A pressure actuated switch comprising a housing having a passage therethrough, a plate having-a normal position in which said plate extends across and substantially closes said passage, said plate being pivoted about an axis extending transversely of said passage and ad- Y jacent one edge. of said plate, a stop preventing movement of said plate in one direction past said normal position, said plate being movable in the other direction about said axis between said normal position and a second position, said plate having an opening therethroughk adjacent said axis, a ,mercury switch element mounted in and` substantially filling said opening, said switch element closing an electric circuit when said plate is in 4one of saidfpositions and opening said circuit when said plate is in the'other ofsaid positions, saidplate being of magnetic material, a permanent magnet supported in'said housingadjacent the 'one edge of said plate and positioned to lurge said plate in said lother direction against said stop, said stop being adjustable to vary the distance between said magnet and said plate when said plate is in saidnormal position so that said plate is moved from fsaid normal'p'osition to said second yposi-- tion when 'the' pressuredifierential in said other direction between opposite sides of said plate reaches a predeteri mined value' dependinguponthe positionof said stop.

3. A pressure actuated `switch comprising a housing having apassage therethrough; a` plate having a normal v`position Vinv which :said plate extends across and substantially closes said passage, said vplate being pivoted about xanaxisextendingtraiisversely ofsaidpassageand adjacent one edge of said plate, a stop preventing movement of said plate in one direction past said normal position, said plate being movable in theother :direction about said axis between said normal position and a second position, said plate having an opening therethrough, a mercury switch element mounted in and substantially filling said opening, said switch element closing an electric circuit when said plate is in one of said positions and opening said circuit when said p-late is in the other of said positions, said plate being of magnetic material, a permanent magnet sup ported in said housing adjacent the other edge of said plate and positioned to urge said plate in, said one direction against said stop, said stop being adjustable to vary the distance between said magnet and said plate when said plate is in said normal position so that said plate is moved from said normal position to said second position when the pressure differential in said other direction between opposite sides of said plate reaches a predetermined value depending upon the position of said stop.

4. A pressure actuated switch comprising a housing having a passage therethrough, a plate having a normal position in which said plate extends across and substantially closes said passage, said plate being pivoted for movement about an axis extending transversely of said passage, a stop preventing movement of said plate in one direction past said norm-al position, ,said plate being movable in the other direction about 4said axis between said normal position and a second position, an aperture extending through said plate, an elongated mercury switch tube mounted in and substantially lling said aperture in said plate, said tube extending transversely of said plate and projecting lateral-ly thereof on both sides so that the mercury therein may occupy alternate positions beyond the plane of the plate, said switch element closing an electric circuit when said plate is` in one of said positions and opening said circuit when in the other of said positions, bias means urging said plate in said one direction against said stop, said axis being eccentric of said plate so that said plate is moved from said normal position to said second position when the pressure differential in said other direction between opposite sides of said plate reaches a predetermined value.

References Cited in the tile of this patent UNITED STATES PATENTS 1,292,334 Larsen Jan. 21, 1919 1,398,892 Dorsey Nov. 29, 1922 1,653,177 Herz Dec. 20, 1927 1,693,309 Mettler Nov. 27, 1928 2,214,092 Uhlorn Sept. 10, 1940 2,470,553 Gudmnndsson May 17, 1949 2,679,731 Zearfoss June 1, 1954

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