US2921595A

US2921595A - Pneumatic system responsive to changes in a variable condition

Info

Publication number: US2921595A
Application number: US490907A
Authority: US
Inventors: Paul F K Erbguth
Original assignee: Daystrom Inc
Current assignee: Daystrom Inc
Priority date: 1955-02-28
Filing date: 1955-02-28
Publication date: 1960-01-19
Anticipated expiration: 1977-01-19

Description

III

Jan. 19, 1960 P. F. K. ERBGUTH 2,921,595

PNEUMATIC SYSTEM RESPONSIVE T0 CHANGES IN A VARIABLE CQNDITION Filed Feb. 28, 1955 4 Sheets-Sheet 1 LOW PRE$$URE\ or M: rm

PAUL F. K. ERBGUTH IN VEN TOR.

Jan. 19, 1960 P. F. K. ERBGUTH 2,921,595

PNEUMATIC SYSTEM RESPONSIVE T0 CHANGES IN A VARIABLE CONDITION Filed Feb. 28, 1955 4 Sheets-Sheet 2 mllllllllfifp IIIIIIIIIA'! PAUL E K. ERBGUTH INVENTOR.

Jan. 19, 1960 P. F. K. ERBGUTH PNEUMATIC SYSTEM RESPONSIVE TO CHANGES IN A VARIABLE CONDITION Filed Feb. 28, 1955 4 Sheets-Sheet 3 H/GH PRESSUR 20/bs. PER .90. IN.

j 520 LOW PRESSURE PAUL EK. ERBGUTH INVENTOR.

A To EY Jan. 19, 1960 P. F. K. ERBGUTH 2,921,595

PNEUMATIC SYSTEM RESPONSIVE To CHANGES IN A VARIABLE CONDITION Filed Feb. 28, 1955 4 Sheets-Sheet 4 PAUL 5K. ERBGUTH INVENTOR.

A O E) United States Patent PNEUMATic SYSTEM RESPONSIVE T0 CHANGES IN A VARIABLE CONDITION Paul F. K. Erbguth, Great Neck, N.Y., assignor, by

mesne assignments, to Daystrom, Incorporated, Murray Hill, N.J., a corporation of New Jersey Application February 28, 1955, Serial No. 490,907 11 Claims. (Cl. 137-85) ments for selectively positioning and/or controlling a remotely-positioned member, etc. Such condition-sensing means include a vane, or baflle, movable between a pair of aligned nozzles across which flows an elastic fluid, generally air, Movement of the vane in the air stream inhibits, more or less, the flow of air from the discharge nozzle to the receiving nozzle resulting in corresponding variations in the air pressure in an air relay connected as the receiving nozzle. The resulting air pressure vari-' ations in the output of the air relay efiects a desired operation such as a control of signal means, or a follow-up of air at low pressure between said nozzles, a device responsive to changes in a variable condition and carrying a vane movable into and out of the air stream, an air relay responsive to the variations in air pressure in the receiving nozzle, and means responsive to the output of the air relay to effect a movement of the vane until a balance is restored in the system.

An object of this invention is the provision of a pneumatic system comprising a discharge nozzle and an axiallyaligned receiving nozzle, means for maintaining a flow of air at'low pressure between the nozzles, a device responsive to changes in a variable condition and carrying a vane movable into and out of the air stream, an air relay responsive to variations in the air pressure in the receiving nozzle as the vane moves further into or out of the air stream, a bellows controlled by the air output of the air relay, and means movable by the bellows to effect a movement of the vane in a direction to maintain the system in balance;'

An object of this inventionis the provision of an electro-pneumatic system comprising axially-aligned disaction effecting return of the vane to, or maintenance of the vane at, substantially its initial position relative to the aligned nozzles. Such operation is accompanied, if desired, by a simultaneous indicating, measuring or recording function. 7

Prior systems of this type are of complex construction and, more importantly, are not adapted for actuation by a condition-sensing means developing only a low torque. 'An object of this invention is the provision of a pneu-1 matic system responsive to changesin a condition-sensing device developing only a low torque and which system provides a measurement, record or control of a variable condition. a

An object of this invention is the provision of a pneumatic system responsive to changes'in a' variable condition andin which a vane is movable between axially aligned air nozzles, said vane being movable by a low torque element such as the pointer of an electrical millivoltmeter.

An object of this invention is the provision of a pneumatic system in which low pressure air, not exceeding 3" of water, passes from a discharge nozzle to an axially-. aligned receiving nozzle unlesscut off by a vane movable between the nozzles inlresponse to changes in a variable condition, the variation in the air pressure in the receiving nozzle effecting the operation of suitable mechanisms to provide a measuring, recording or control function.

An object of this invention is the provision of a pneumatic system in which the position of a pair of axiallyaligned nozzles may be adjusted with respect to an intercepting vane inorder to effect a desired operation of the yste An object of this invention isthe provision of a pneumatic system comprising a discharge nozzle and an axiallyeligned receiving nozzle, meansfor maintaining a flow charge and receiving nozzles, means maintaining a flow of air at low pressure between the nozzles, an electrical instrument responsive to changes in an electrical quantity, a pivotally-mounted arm mechanically-coupled to the pointer and carrying a vane movable in the air stream in response to displacement of the pointer, an air relay responsive to changes in the air pressure in the receiving nozzle as the vane moves further into or out of the air stream, a bellows movable by the air output of the air relay, a second pivotally-mounted arm mechanicallycoupled to the bellows, and resilient spring means coupling together the said .pivo'tally-mounted arms, the

arrangement being such thata movement of the vane effects an operation of the system to restore the vane substantially to its initialposition. v

These and other objects or the advantages of the invention will become apparent from the following specification when taken with the accompanying drawings. It will be understood, however, that the drawings are for purposes of illustration and are not to be construed as, defin ing the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.

In the drawings wherein like reference characters denote like parts in the several views: i Figure l is a diagrammatic view of the electric and pneumatic circuits in an instrument embodying my invention; Figure. 2 is a diagrammatic view similar to Figure l but showing another embodiment of this invention;

Figure 3- is a diagrammatic view corresponding to the left hand end portion ofrFig urc 2 but showing a modifi cation; l p,

Figure'4 is an enlarged axial sectional view of the cooperating nozzles of a preferred shape, viewed as on the line IV-'-IV of Figure l, in the direction of the arrows; Figure 5 is a sectional view on the line VV of Figure 4, in the direction of the arrows;

Figures 6 and 8 are axial sectional views of nozzles as in Figure 4 but showing modifications;

Figures'7 and 9 are, respectively, a transverse sectional view on the line VIIVII of Figure 6, in the direction of the arrows and an end elevational view of the form of Figure 8;

Figure 10 illustrates a practical embodiment of my invention; V

Figure 11 is a perspective view of a portion of the mechanism of Figure 10; and I Figure 12 is a diagrammatic view of the electricand bearings 27. Each'of

thejpivots

25 and 26 has secured thereto aspiral hair spring, :28 and 29, resiliently causing the coil 24 to occupy a given position with respect to thepoles of anassociatedpermanent magnetinot shown)- until electric current is passed therethrough. Such current may be generated by ai -thermocouple 31, which from, as by means of a weight 47 carried by a pan 48 may se'rveas a temperature-sensing element as, forexam ple, in the'furnace 40 shownin'Figure 12.

-; A pair of axially-aligned nozzles 32 and33; forming apneumatic couple, are: positioned so that the leading edge of the vane 21 is normally disposed therebetween. The vane 21 is desirably as illustrated, that is, formed of thin'metaland has an edge beveled, or formedbya diagonal plane, to provide aknife edge to thereby facilitate the movement of the vaneinto an air stream, The

nozzle 32 is connected to a source of elastic fluid, under' pressure, such as a compressed air supply, through a tube 34. The tube '34 has a flow wrestrictor 35 therein to cause the air-to pass from the discharge nozzle 32 at a low pressure, say-about 1 of Water and no more than 3 of water, whichis apressure of about 1l.lb. .per.

suspended from one end of the lever 22a.

A pair of aligned nozzles 32a and 33a forming a pneumatic couple are positioned so that the leading edge of the vane 21a is normally disposed in the air stream between the nozzles. Thisvane is desirably formed of thin metal and has an edge beveled to a knife edge to thereby facilitate the movement of the vane into the air stream. The nozzle 32a is connected to a source of air under -.pressu.re through tube 34a, which'tube'has'a flow restrictor 35:2 therein to cause the to-flow from. the nozzle 32aat a low pressure, say about apressure of :1 and no more than a pressureloffi" of water. The receiving nozzle 33a is connected to the chamber of the relay 36a by 'tube37'a.

When the vane 21a is. moved, a variable amount of air flows into the receiving nozzle 33a, thereby causing a; movement of the air relaydiaphragm 38a. Assuming thatsuch vane movement results in an increase inthe quantity of air flowing .to thereceiving nozzle 33a, there results an increase in air pressure Within the air relay chamber. The diaphragm 38a,-therefore, moves upward- 'ly thereby rotating the. connected member, suchas the pivoted lever 39a, in a counterclockwisedirection. The free endof the lever 39a carries .aflapper 51 cooperating with a nozzle. 52 that is connected to the source of air pressure by the tube 53 containing a flow restrictor 54 therein. 7 q 1 7 It may .be pointed out that the pressure ofithe .air suppliedto thenozzle 52 maybe relatively high, that is, in the order of pounds per squareinch and the actual airpressure in the tube 53 dependsupon the spacing of the flapper '51 fromthe nozzle 52. Onthe other" hand,

the pressurelof the air suppliedto the discharge nozzle 32ais veryilow, the order of a fraction of a pound per square,inch,.thereby reducing to an insignificant degree the reaction eflects between the airstream 'flowingacross the change in air. pressure within the chamber moves the air relay diaphragm 38, thereby moving a connected member, such as the pivoted lever'39 of a switch 41, so that itmay engage one or theother of the upper and lower stationary contacts .42 and 45. The engagement of the movable member with either of the contacts'42,- completes a circuit for energizing one or the other of the lamps 43, '46 from the battery 44.

Y 'From-the foregoing descriptiomlit will be seen that l have devised a system whereby movement of the pointer ance point effects a desired control of 'signal lamps so that when the vane changes position between the nozzles one lamp is de-energized and another energized. It will be noted that in this arrangement there isno follow-up action,[that is, there is merelya change in thesignal indi cation as the vane moves to either side tion between the opposed nozzles.

" Those skilled in this-art will understand that; theprese't position of the vane'edge in the air stream may be altered of a preset posialigned nozzles 32a, 33a and the .vane, 210:. This is im portant .sincemy systems are adapted for use with con- 40' dition-sensing devices producing very low torques, such as sensitive electricalinstruments, sensitive balances, etc,

:When the, air relay diaphragm moves the flapper '51 a greater distance away from the associated nozzle 52 there is effected a corresponding decrease in the air pressure in the bellows assembly 55 (connected to the output 'tube 53) causing a partial collapse thereof. 'In the particular. arrangement illustrated in the drawing, the bellows 55 ar'ebiased by a compressed spring 56 disposed between the upper surface of {the bellows and a fixed surface 57.

-A connecting wire 59 is wrapped around the drum. 58, one end of the wire'be'ing secured to the drum and the respect to thejshaft .2,6r z, jan'd normally held resilientlyin a'certainfp'osition as' byrmeans of a hair spring 63; The

inner endof the springf63is connected to the shaft 61 and as by adjusting the'normal zero position of th'e'in'strumen't pointer or "by a physical setting of the aligned nozzles along" the arcuatepath of travel of the vane.21.'

Referring now to the embodiment of my invention illustrated in Figure 2, there is shown a modified pneubut in which a followup action is provided to return the vane to a throttling position between the aligned nozzles, such vane position being precisely that position. in which the entire system is in balance. .In this embodiment I show a pneumatic force-balance system which may measure, record or control forces such as weight, torque or humidity. In this instance, the vane 21a 'is'carried by a balance arm 22a that is secured to a pivoted shaft 26a, rotatable in the bearings 27a'and normally held'in one position by a hair spring 74. "The lever 22a, therefore, 'tends to' stay in the position illustrated until movedtherethe outer end "thereof is connected to" a fixed abutment 64. The shaft6l has'a rigid angular member 65 extending'towardfthe,'first vshaft 26a andtothe'end .of which the'outer portion of the hair spring 74is connected, as indicated at '66.. .Consequently, a partial collapseof the bellows 55 effects a rotation of the shaft 61 to'act on the hair spring '74 and tend to restore the vane'Zla to its throttling position between the aligned nozzles 32a and 3301, thereby restoring the system to a new balance point.

It will now be apparent that mean pressure in the lzagllows 55 is a meature of theforce applied to the lever a.

I In addition to the restoration of the shaft 22ato its throttling position, the movement of the bellows may be measured by a carried pointer 67, movable overacalibrated scale fitl to thereby-indicate themagnitu de of the particular weight I 47. This factor may also .be recorded on a chart 69, "carriedlby 1a rotatingshaft 71, :as by apen 72 carried by an arm 73 extending from-the shaft 61 and into engagement with the chart. I

Referring now to the embodiment of the invention illustrated in Figure 3, there is shown instead of the lever 22a, the pointer 22b of an electrical measuring instrument such as a millivoltmeter. The vane 21a is attached to the pointer and is movable between the aligned nozzles 32a, 33a to effect operation of the system in response to a change in the electrical quantity controlling rotation of the instrument movable coil 24 as, for example, the thermocouple 31. The remainder of the apparatus may be the same as illustrated in Figure 2.

As an alternative, however, the tube 37a may be connected directly to a bellows, such as indicated by the reference character 55 in Figure 2, the pressure being indicated on a gauge 75. However, if this embodiment is adopted, it is necessary that the bellows, like 55, be relatively large because of the low operating pressure of the air within the tube 37a. Forthis reason, it is generally better to operate the bellows from an air relay such as that designated 36a in Figure 2.

Referring now to Figures 4 and 5 there is shown one form of the

nozzles

32 and 33, and the-vane 21 which may be employed in any or all of the described embodiments of my invention. To facilitate manufacturing thereof, these

nozzles

32 and 33 are formed as tapered members having apertures 76 smaller than the bore of the air-carrying

tubes

34 and 37, so as to form a stepped construction. The cutting, or leading, edge of the vane 21 is desirably beveled, as indicated at 30. In other words it has an approximately 60 degree knife edge, as indicated. 7

' The direction of movement of the vane 21, further into the air stream, from what may be the normal position illustrated in Figures 4 and 5 wherein the vane cuts off part of the air stream, is in the direction of the arrow 50. The full-line position of the vane is normal to the direction of air fiow, from right to left as viewed in Figure 4. However, to further facilitate the cutting of the air stream by the vane 21, the plane of the vane may be turned slightly at an angle to the position illustrated by the dotted lines in Figure 4.

Referring now to Figures, 6 and 7, there is shown a modified form of nozzle 33c wherein the aperture at the tip, instead of being circular, is transversely elongated as indicated at 76 in Figure v7. This elongation in the tip portion 77 is formed by flattening the end of the tube. When nozzles of this form are used the vane may move in a direction either longitudinally of the elongated aperture, transversely thereof, or any intermediate relation. In the first instance, the cut off action is much more gradual and less sensitive than in the second instance, as will be understood.

Figures 8 and 9 illustrate an embodiment in which the nozzle aperture 76a, elongated or circular as desired, is formed in a cap or tip portion 77a, which is in turn connected to the carrying tube 37 by solder or other suitable means.

Referring now to the embodiment of this invention illustrated in Figures 10 and 11, there is shown a practical instrument embodying preferred features shown diagrammatically in the preceding embodiments. The mechanism for sensing changes in a variable condition is here an electrical measuring instrument, such as a millivoltmeter or milliammeter, generally designated 23d. This instrument is more or less conventional so the parts are not described fully. Sufiice it to say that the part 78 is a soft-iron yoke or housing having an axial bore in which rotates a coil 24d mounted on pivots operating in suitable bearings such as the upper jewel screw 25d shown in the drawing. Each of the pivots has a conventional spiral hair spring (not shown) resiliently causing the coil 24d to stay in a given position with respect to the poles of the permanent magnet core M until electrical current is passed therethrough. Such current may be generated as described in connection with the preceding embodiments. The pointer secured to the coil is designated by the reference character 22d, the end of said pointer moving over a scale 79 and between suitable limiting stops 81 and 82.

The pointer 22d has a tail 83 extending away from the scale 79 and which engages a lever 84 secured to a shaft 85 journalled in the

bearings

86 and 87 forming part of a supporting frame 88 (see particularly Figure 11). The upper end of this shaft 85 has a knurled setting wheel 89, secured thereto as by means of a screw 91. The setting wheel 89 carries a disengaging rod 92 for the lever 84 and a stop rod 93 for limiting turning movement of itself, as by engaging the frame 88. The shaft 85 corresponds with the shaft 26b of Figure 3, in that it is operated by a shaft 94, corresponding with the shaft 61 in Figure 2, so that it effects turning of the shaft 84 by means of a shaft extension 95, the free end of which is connected to the outer end of a hair spring 96 carried by the shaft 94. In the present instance also, the lever 84 carries a vane 21d.disposed between the aligned

nozzles

32d and 33d, rather than having the vane carried directly by the pointer 22d of the instrument as in the previously-described embodiments.

The shaft 94 carries an arm 97 having a wheel 98 movable by a lever 59d, the latter corresponding to the wire 59 of Figure 2, in that it effects turning of the shaft 94. This lever is pivoted at 99 and operated by a bellows device 55d corresponding with that designated 55 in Figure 2, but in this case by a link 60 connected between the lower end of the bellows and a point intermediate the ends of said lever 59d, instead of by a wire wrapped around a drum. There is also an air relay 36d, corresponding with that designated 36a in Figure 2, in which the diaphragm 38d is moved (when the vane 21d moves in the air stream between the aligned

nozzles

32d and 33d) in response to a change in air pressure in the tube 37d, thereby operating the lever 39d pivoted at 49d, so as to move the free end thereof further from the nozzle 52d and thereby correspondingly decrease the pressure in the output tube 53d.

The operation of the apparatus illustrated in Figures 10 and 11 is similar to that of the apparatus illustrated in Figures 2 and 3. However, the apparatus illustrated in Figures 10 and 11 is more than merely diagrammatic. In this latter apparatus, air is received from the main supply tube 101 through a shut-off valve 102 where it passes to a manifold or box 103, such air being normally at a pressure of 20 lbs. per square inch, as is commonly available. From the manifold 103 there extends a pipe 104 to the high-pressure gauge 105, from whence air passes to a manifold or box 106.

From the manifold 103 there extends a tube 34d to the discharge nozzle 32d, the pressure of the air in this tube being very low, as has alreadyv been described. Thus, the operation of the apparatus, here disclosed more in detail, corresponds with the operation of the apparatus of Figure 3, in that the vane 21d is movable between the aligned

nozzles

32d and 33d by corresponding movement of the pointer 22d, although not directly by said pointer.

In other words, the pointer tail 83 which extends in a direction opposite to the scale 79, engages an angular extension 107 on the lever 84 and, on upscale movement of the pointer, moves it counterclockwise, as viewed in Figures l0 and 11. This effects a corresponding movement of the vane 21d further into the air stream between the aligned

nozzles

32d and 33d. When the vane cuts further into the air stream, the pressure in line 37d is reduced, thereby causing a corresponding collapse of the air relay diaphragm 38d. The lever 39d, therefore, moves toward the nozzle 52d, thereby correspondingly increasing the pressure of the air in the output tube 53d and bellows system 55d, and causing the lever 5911 to rotate counterclockwise. This rotation effects turning of the vane 21d from'the air stream to its initial throttling,

position, wherein the forces of meter torque and the. air system are. in balance. The foregoing description presents the functional operation of the apparatus, but those skilled in this art will understand that. the vane is always.

partially in the air stream (see Figures 4' and 5)., that is, inthe throttling position when the actuating pointer is in the mechanical 'zero position. Consequently, any slight movement of the pointer results in an immediate change 7 ingthe relay output and a corresponding rebalancing force is applied to said pointer.

To illustrate the control function of my invention, reference is now made to Figure 12, wherein there are shown the components required for the control of tem-' perature in a furnace. 40. The relay and" chart .components correspondwith the form ofv my invention illus-' trated in Figure 2, and described inv connection there,- with, but the condition-sensing device-is an electrical millivoltmeter as shownin- Figure Such'instrument deflects in accordance with the voltage fdeveloped'by the thermocouple 31 which in turn depends upon the: temperature of the furnace 40. v

The pressurecontroller 108, here .used, has an operating pressure range generally equal to the air pressure range of the airrel ay 36a, that is, 3-15 pounds pe'rlsquare. inch. The air relay tube 53is connected-to the controller by a tube 116'. Relatively highpressure airis-supplied to' the controller-through the tube 109 and thecontrolled air passes through the tube -1-11-to the control-valve"1=12 inserted in the fuel line 113 of the furnace. The inputand' output air pressures of the controller-are-indicated-by the air supply pressure gauge 90and the controlled air pressure gauge 100. i

The, systemoperates in the following manner; With an increase or decrease of furnace temperature, the electricaloutput of the thermocouple. in the furnace changes. This change is sensed by the moving coil 2i-(Fig ure"3) and motion is transmitted to the vane 21a by pointer zib. The movement of this vane, as previously described, properly alters the position of the air relayflapper51 relation to the associated nozzle 52, thereby resulting in a corresponding movement of the bellows 55' and. the recorder pen 72. V I ,In addition to these indicatingand recording funetions,

I the air pressure change ,in the tube 53 is transmitted throughthe tube 110 to thelsensing mechanism of-the controller 108. The controller senses this airfpressure change and corrects the openingoftheavalve 112 toreturn the furnace temperature to thedesired value. H Those skilled in this art will understand-thatthe desired-;oper ating temperature ofsthe furnace may be setby rotating: the knob 144 of the controller-sensing mechanism to -.the proper value as indicated byan associated-scale -105calibrated "in terms of temperature. It'is here pointed out that my system does not depend uponthe particulartype of pressure, .controllerused. The particular controller used will depend upon the particular application and may be one of numerousconventional types such as asimple on-ofi, high sensitivity, full throttling, reset, or=etc.

changes and modificationsasha i 1 W t h S p d spirit of the inventionaifiSl'Iqqilcdl in the following claims.

'Iclaimz. v a 1. A pneumaticsystem comprising in combination, a sensing member movabledn "response to Ch g in variable condition, a. discharge n z an ia ly receiving nozzle. spaced from the discharge nozzle, means normally maintaining a. low pressur H air stream between the said nozzles, a vane movable in the. air stream in response to movement of the sensing member and thereby to vary the amount of airpassing into-the receiving nozzle, a tube connected to a high pressure air supply, an air relay connected to the receiving noajzle and responsive to variations in the air pressure Within the receiving nozzle to produce corresponding variations, in air pressure within the said tube, a bellows movable in response to variations in the air pressure within said tube, and mechanical coupling means connected between the bellows and the sensing member and arranged to move the vane in a direction opposite to that brought about by a change in the sensing member. i

2. The invention as recited in claim 1, wherein the sensing member is a balance arm carried by a rotatable securedto the bellows.

shaft and said mechanical coupling means includes a second rotatable shaftco-axial andv in t ndem with respect.

to the first shaft, means coupling the two shafts together, spring means normallybiasing the. shafts'to a predetermined position, and meanscoupling the second shaft to the said bellows to effecta turning of the shaft in response to'collapse or expansion ofthe bellows. a v

3. The invention asrecited .in claim *2, wherein the means coupling the second shaft to the bellows comprises a drum carried by the second shaft and a filamentary member entwined about the drum, said filamentary member having one end securedto thedrum and the other end 4. The invention as recited in claim 1, wherein the sensing member is an electrical instrument having a pointer to which the vane is attached.

5. The invention as recited in claim 1, wherein the sensing member is an electrical instrument having. a pointer, and the vane is carried by a rotatablc arm having an end lying in "the path of travel of the pointer.

6. An electro-pneumatic system' comprising an elec: trical instrument having a pointer, a rotatable arm ha ing an end disposed in the path of travel of the pointer, a vane carried by said rotatablearm, a discharge nozzle disposed on one side of the vane and'connected to a. low:pressure air supply, an axially-aligned receiving'nozzle' disposed on the other side of the vane and receiving air from the discharge nozzle ex cept as cutoff-by the vane, vanIair relay operated by the variation inair ipressurewithin' the receivingnozzle, an output tube connected to a source of air pressure, means operated by said air relay ,to varythe air pressure in said'output -t ube, a bellows movable in response to variations in the air pressure in said'output tube, and means coupling the bellows to the said rotatable arm carrying the'vane.

7. The invention as recited in claim 6, including. means adjustable to space the said rotatable arm 'a predetermined distance fromthe pointer when the latteris'in its normal zero position.

8. The invention as recited in claim 6, wherein the means coupling the bellows 'to the rotatable arm comprises a shaft rotatable about the rotational axis ofthe said rotatable arm, a lever pivoted at one end and con nected to thebellows at a pointintermediateof. its ends, a rigid arm secured to the said'shaft and engaging the said lever,.a resilient spring having one end secured to the said shaft, and a rigid rnember secured to theother ,end ofthespring and to the saidrotatable arm. 7

9. An electro-pneumatic system comprising an electrical instrument including a pointer cooperatingwith a calibrated scale, a rotatable arm having an end lying in the path of travel of the pointer tail, axially-aligned discharge and receiving nozzles, a tube connecting the discharge nozzle to a constant pressure air supply having a pressure not exceeding three inches of water, a vane carried by the rotatable arm and movable between the nozzles to vary the quantity of air flowing from the discharge nozzle to the receiving nozzle, an air relay having a chamber closed by a diaphragm, a first tube connecting the receiving nozzle to the said chamber whereby the diaphragm will move in response to changes in the quantity of air passing into the receiving nozzle, a second tube connected to a source of air pressure exceeding one (1) pound per square inch, means operated by the said diaphragm to vary the air pressure in the second tube in accordance with the variation of air pressure in the said chamber, a bellows movable in accordance with the air pressure variations in the said second tube and means coupling the said bellows to the rotatable arm carrying the vane.

10. The invention as recited in claim 9, wherein the means coupling the bellows to the rotatable arm comprises an extension carried by the said rotatable arm, a lever pivoted at one end engaging the said extension and a link connected between an end of the bellows and a point intermediate the ends of said lever.

11. A pneumatic system comprising in combination, a discharge nozzle connected to a source of low air pressure, an axially alined receiving nozzle spaced from the discharge nozzle so that air from the latter tends to flow thereinto, a vane element with an edge portion beveled to provide an approximately knife edge at a portion normally lying in the air stream between said nozzles, and the plane thereof turned slightly so that the flow of air thereagainst has a component aiding said vane element in cutting into the air stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,352,150 Schneider Sept. 7, 1920 1,369,568 Smoot Feb. 22, 1921 2,058,642 Sperry Oct. 27, 1936 2,408,603 Braithwaite et al. Oct. 1, 1946 2,529,875 Howard Nov. 14, 1950 2,599,159 Breedlove June 3, 1952 2,651,317 Heinz Sept. 8, 1953 2,651,326 Ray Sept. 8, 1953 2,655,408 Williams Oct. 13, 1953 2,667,886 Brewster Feb. 2, 1954 2,669,247 Olah Feb. 16, 1954 2,706,084 Gess Apr. 12, 1955 FOREIGN PATENTS 1,022,236 France Dec. 10, 1952 673,159 France Jan. 11, 1930 689,814 France Sept. 11, 1930 831,161 Germany Feb. 11, 1952