US1538128A - Power-control device for pneumatic-dispatch systems - Google Patents

Description

May 19, 1925.

J. G. MACLAREN POWER CONTROL DEVICE FOR PNEUMATIC DISPATCH SYSTEMS Filed Jan. 28, 1925 Fig.2 J19 B 5/ 6/53 50 60 I V J? 0 J 3 W67fi0 7 James d-fi'ac'lav'e 7-0 590% @m a m Patented May I UNITED STATES JAMES MACLABEN, OF SYRACUSE, NEW

OF SYRACUSE, NEW YORK, A

YORK, ASSIGNOR TO THE LAMSON COMPANY, CORPORATION OF MASSACHUSETTS.

POWER-CONTROL DEVICE FOR PNEUMATIC-DISPATCH SYSTEMS.

Application filed January as, 1925. sci-m1 No. 5,329.

To all wizom it may concern:

Be it knownthat I, JAMES G. MAon-mEN, a citizen of the United States of America, and resident of Syracuse, in the count of Onondaga and, State of New. York, ave invented new and useful Improvements in Power-Control Devices for Pneumatic-Dispatch Systems, of which the following is a specification.

This invention pertains to power control- 'lers for pneumatic dispatch systems and relates more particularly to automatically actuated controllers of the So-called minimum flow type of which the patent to Libby 968,576, August 30, 1910 furnishes an early example.

Pneumatic dispatch tube apparatus of the minimum flow type as exemplified by said Libby patent, are vacuum systems as distinguished from pressure systems, and are open or continuous current systems as dis tinguished from closed systems in which normally no air current is maintained through the line when the line is idle. Controllers for said open or continuous current vacuum systems of the minimum flow type, comprise, essentially, an air controlling valve located in the exhaust pipe between the transit tube and the air exhauster or vacuum drum, which normally cuts down the air current to a minimum when the line is idle, never wholly cutting it ofi' but at all times permitting a continuous flow of relatively small volume called the minimum flow, and a pneumatic such as a piston or dia phragm which responds to a change of pressure in the line due to the momentary cutting OK or checking of the minimum flow of air by the insertion of a carrier into the tube, and opens the air valve wide to permit a full flow of air for driving the carrier. For convenience and succinctness of description the term pneumatic used as a' noun has herein been employed to designate broadly any pressure or vacuum actuated instrumentality, for example a flexible diaphragm. a piston or abellows, by means of which fluid pressure is converted into mechanical motion.

In the form of apparatus described in said Libby patent an auxiliary diaphragm and valve are used to control the operation of the main diaphragm which opens the air-valveupon the insertion of a carrier into the tube; also a third valve is used to con closed or normal and with the extension 6'which trol the pressures for actuating the auxiliary diaphragm both for its opening and closing function; also a. timingdevice is used for restoring the air-valve to its normal miiiimum flow position after the discharge of the carrier.

The apparatus greatly simplifies apparatus in that of? the present invention the structure of the Libby it dispenses with the auxiliary diaphragm and valve, also the said third valve, and also the timing device for closing the main valve, and leaves the main diaphragm permanently open to the atmosphere at one side and in condition at all times to respond to the pressure variation caused by cutting off the minimum flow, and replaces the timing device with a member instantly responsive to the rushof air which follows the discharge of the carrier, or which is sometimes produced by drop of a carrier through a long vertical run of the tube, for equalizing the pressures on opposite sides of the main pneumatic to permit the valve to return to its normal, closed down position.

' In the accompanying drawings which illustrate one embodiment of the invention,-

Fig. 1 is a fragmentary view showing a portion of the central station apparatus of a pneumatic dispatch system and illustrating one pair of transmission tubes, of which one is'the sending tube and the other the receiving or return tube, and the power control apparatus corresponding to that pair;

Fig. 2 is a fragmentary section to larger scale showing the construction of the power control apparatus, the main valve being in position;

Fig. 3 1s a view similar to Fig. 2 showing the main valve open but just upon the point of closing; and

Fig. 4 is a fragmentary plan view of the power control apparatus showing a form of bafile or air actuated vane forming an element of the device.

Referring to- Fig. 1 the numeral 1 indicates a portion of a central station desk provided with the dispatch terminal 2 forming a part of the sending transmission tube 3 leading to an outlying station. The corresponding return transmission tube 4 is provided with the usual delivery terminal 5 passes down through the top of the desk land is connected'with the power control apparatus '3'.

A suction tube 8 leads from the power control apparatus to the usual suction drum or header 9 in which vacuum is constantly maintained by means of a suitable exhauster, not shown. A continuous air passage or conduit is thus provided extending from the terminal 2 to the exhauster, that portion of the conduit provided by the tubes 3 and 4 formingthe carrier transmission line.

The power control apparatus 7 which forms the immediate subject matter of the present invention comprises an elongate preferably cylindrical casing 10 having a flange 11 at its upper end to receive the lower end of the extension tube 6 and a flange 12 at its lower end for the reception of the upper end of the suction tube 8. The casing 10 is provided with a lateral ofiset portion 13 of tubular construction which ma if desired be formed as an integral part of the casing '10 or which for conveni-. ence in manufacture may be separately formed and attached in any desired manner. The outer end of the offset portion 13 is closed by a removable cap 14 having an aperture 14 therein admitting atmospheric pressure to the interior of the offset 13.

That portion of the air conduit which is contained in the main body of the casing 10 divided into an inlet chamber or space 15 an outlet chamber or Space 16 by means (if a suitable partition. This partition may if desired consist of a simple septum extending across the casing but as here shown takes the form of a hollow-box-like casing 17 of inverted U-shape disposed within the space-15 and whose interior provides a space 16*, forming a continuation of the space 16. This double partition or casing 17 is provided with opposed substantially parallel walls 18 and 19 having apertures 20 and 21 respectively therein, said apertures being coaxial with the oiiset portion 13 of the cas- 1n a %n common with other devices of this general type a main valve is provided for controlling the passage of air from the space 15 to the space 16. In this instance the main valve is of balanced type comprising the spaced heads 22 and 23 which ceoperate respectively with the apertures 20 and 21. This main valve comprising the heads 22 and 23 is mounted upon a sliding valve rod 24 which is guided in a suitable bearing in a partition 25 which separates the space 15 in the main casing from a chamber 26 within the offset portion 13 of the casing. The valve rod 24 is also guided in a suitable bearing in the cap 14 and projects outwardly beyond said cap.

A rocker 27 is pivotally secured at 28 to the projecting end of the valve rod 24, such rocker being tulcrumed at 29 in a bracket 30 carried by cap 14. The lower end of the rocker 27 is furnished with a r a .stem 01 passing series of spaced openings 31 adapted to receive a rod 32 which may be adjustably secured in any of said openings by means of suitable nuts 33. sion spring 34 is secured to the rod 32. The other end of this spring is furnished with a hook or similar attaching device 35 adapted to engage any one of a series of openings 36 in a bracket 37 depending from the main casing 10. The spring 34 acting through the rocker 27 tends to move the main valve One end of a coiled ten-- into closed position but its movement in this direction is limited by a stop screw 38 mounted in a bracket 39 carried by cap 14. This stop screw engages the upper part of the rocker 27 and is soadjustcd 'that the valve heads 22 and 2-3 .are normally slightly advanced so as to permit a minimum flow of air from the space 15 to the space 16. Manifestly the desired minimum flow may be provided if desired by the employment of a small pipe exterior to the casing communicating at its opposite ends with the spaces 15 and 16 respectively.

A suitable pneumatic is employed for opening the valve. The pneumatic here disclosed consists of a piston 40 arranged to slide with a snug fit within the offset portion 13 of the casing. This piston is free to slide upon the rod' 24 but its movement relatively to the latter is limited in one direction by a stop 43 secured to the rod. Movement of the piston in the opposite direction is restricted by means of a compression spring 41 encircling the rod 24 and bearing at one end against the piston and at its other against a collar 42 fixed to the rod 24. While a piston is here illustrated, it is contemplated that a diaphragm or other form of pressure actuated may if desired be substituted therefor.

The. oiiset 13 of the casing is furnished with an upstanding boss 44 provided with a chamber 45 forming a continuation of the chamber 26. This chamber '45 communicates by means of a valve orifice 46 with the space 15 at the inlet side of the main valve. The capacity of. the orifice 46 is controlled by an adjustable valve 47 having 'a screw threaded stem engaging a threaded opening in boss 44 and which may be adjusted to the desired position by means of a knurled head 48 upon the valve stem.

The chamber 45 may also communicate with the outer atmos here by means of a assagc 49 leading through the wall of the boss 44. This passage 49 is normally closed by an auxiliary valve 50 provided with a loosely through an openin one arm of a lever 53 fulcrumed at 54 upon the main portion of the casing, said stem having a head normally spaced from the upper surface of lever 53. spring interposed between the valve and ing the opposed surface of the lever tends to 1 carrier.

move the lever and valve in opposite directions, while a stop 61 carried by the lever limits approach of the lever and valve. A counterweight 55 mounted upon the outer end of this lever tends normally to hold the valve 50 closed. v i

The lever 53 is provided with a second arm which projects through an opening in the wall ofthe casing 10 and which supports a baflle or vane B arranged concentrically within the space 15. This baflle or vane 15 preferably adjustable in area and comprises a pair of slotted superposed discs. 56 and 57 secured to the end of the lever by means of a pin 58. By rotating these discs relatively to eachother passages 59 of greater or less area may be provided for the movement of air past the dlSCS:

The operation of the device is substan tially as follows, the parts normally, that is when no carrier is being sent, occupying the position shown in Fig. 2. In thisposition a continuousminimum fiow of air is entering through the transmission tube 4 into the space 15 and is passing around the edges of the valve heads 22 and 23 into the space 16 which communicates with the vacuum in the suction drum 9. Under these conditions the tension of spring 34 is sulficient to maintain the main valve in closed position. When a carrier is introduced into the transmission line it acts as a plug and the minimum flow of air is thereby momentarily cut off or restricted; and as air is continuously being exhausted from thespace at the left or inner side of piston 40, while its right or outer side is permanently exposed to the atmosphere through port 14 a difference in pressure upon the oltgosite' cient sides of the piston 40 is produced su to move the latter inwardly or to the left. When the pressure first drops the piston, which is opposed only by the light spring 41,

slides relatively to rod 24 and a very slightdrop in pressure in the transmission line suffices to start the iston into motion. By the time the iston iias collapsed the spring 41 against a utment collar 42, it has acquired an appreciable momentum, which now becomes available to assist the pressure acting upon the piston to open 'the main valve; thus permitting a full or free flow of air through the casing for driving the This flow of air continues until the carrier discharges from the transmission tube. J i

- The counterweight 55 is so adjusted that during the flight of the carrier, although a relatively strong carrier driving current of air is passin the bafile B, the latter is held in substantlallv horizontal position thus maintaining valve 50 closed. When the car rier is discharged from the transmission tube a sudden and accelerated rush of air occurs through the system, which is now her or space 16.

unobstructed either by a carrier or by the air-valve, and this sudden rush, acting upon the baflle B tilts the lever 53 thus opening valve 50. Due to thelost motion between the head of the stem 51 and the upper surface of the lever 53 the latter is permitted to move to some extent before the valve 50 opens, so that very slight and momentary fluctuations in the air current will not cause the valve 50 to chatter.

In Fig. 3 the parts are shown at the very instant the valve 50 opens and before atmospheric air has entered the chamber 26 in quantity suflicient substantially to change the pressure therein. This position of the parts is of momentary duration for almost simultaneously with the opening of valve Thus the action of the device depends wholly upon the introduction and delivery of the carrier and no timing devices of any kind are necessary for its proper operation.

While a main valve of balanced type is herein illustrated it is contemplated that a valve comprising a single head might be employed if desired or that a piston valve or in fact any other equivalent arrangement can be substituted therefor.

As herein shown the space 26 communicates through orifice 46 with the space 15 at the inletside of the main air-valve but it is contemplated that under some circumstances this chamber 26 may alternatively be made to communicate with the outlet cham- As the fluctuation in pressure in the latter space is less when a carrier is introduced into the transmission line than in the space 15 this suggested arrangement is not regarded as being so desirable as the preferred arrangement herein illustrated.

While the invention is herein shown as embodied in a certain specific construction it is to be understood that various change: and modifications, in addition to those abovi specifically suggested, in the shapes, ar rangement and relative sizes of parts may be made as circumstances may warrant with out departing from the spirit of the inven- 3 tion.

I claim 1. Pneumatic dispatch apparatus con prising a conduit and an exhauster con nected therewith, a controlling valve located in the conduit, a minimum flow of air through the conduit being permitted when .the valve is in closed position, a pneumatic to the pressure exposed at one side said pneumatic being the opposite side to atmospheric pressure, adapted to open the air controlling valve when the pressure within the conduit is reduced due to the checking of said minimum flow by introducing a carrier into the conduit, and means responsive to increased flow of air through the conduit such as occurs when the carrier is discharged for equalizing the pressure upon opposite sides of the pneumatic to permit the valve to close.

2. Apparatus for use in a pneumatic dispatch system of the minimium flow. "acuum type having an air conduit, a normally closed main valve controlling the flow of carrier impelling air current through the conduit, a minimum flow of air through the conduit normally being permitted, a pneumatic sensitively responsive to pressure change in the conduit, one side of the pneumatic being constantly exposed to full atmospheric pressure, mechanical means transmitting movement from the pneumatic to the valve sage of carrier impelling to open the valve when the pressure in the conduit varies from normal due to introduction of a carrier into the conduit, and means sensitively responsive to increase in velocity of air in the conduit beyond a predetermined velocity for equalizing the pressure upon opposite sides of the pneumatic to permit the valve to close.

3. Apparatus for use in a pneumatic dispatch system of the minimum flow, vacuum type having an air conduit and an exhauster connected with the conduit, said apparatus comprising a valve for controlling the pasair flow through the conduit, means normally holding the valve in closed position, a passage being provided to permit a minimum flow of air from one side of the closed valve to the other, a pneumatic constantly exposed at its outer side to atmospheric pressure and exposed at its inner side to the pressure obtaining in the conduit, an operating connection between the pneumatic and valve, the pneumatic operating to .open the valve when pressure in the conduit drops below normal due to introduction of a carrier into the conduit, a normally closed valve adapted whenopened to expose the inner side of said pneumatic to atmospheric pressure and a va-ne exposed to the air flowing through the conduit adapted to open said last named valve when the carrier is discharged from the conduit.

4. Power controlapparatus for a pneumatic dispatch system of the vacuum minimum flow type having a conduit communicating with an exh'auster, said apparatus comprising a valve normally closed to prevent a carrier propelling flow of air through the conduit, a minimum flow of air through the conduit being permitted, a pneumatic to attuate the valve for opening the latter when a carrier is introduced into the conduit, one side of the pneumatic being constantly exposed to full atmospheric pressure and the opposite side normally being exposed to pressure conditions obtaining conduit and means operating automatically upon deliver of a carrier from the. conduit to admit ful atmospheric pressure to act upon the latter side of the pneumatic.

5. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type having a transmission tube and an exhauster connected to the tube, said apparatus comprising a valve for controlling air flow through the tube, a minimum flow of air through the tube being permitted when the valve is closed, a pneumatic constantly exposed upon its one side to atmospheric pressure and normally exposed upon its other side to the pressure obtaining in the transmission tube, means connecting the valve to the pneumatic, and means operative upon the delivery of a carrier from the transmission tube to admit atmospheric pressure to act upon the inner side of the neumatic.

6. Power control apparatus for use in a pneumatic dispatch system of the minimum flow type having a transmission tube communicating with an exhauster, said apparatus comprising a casing having a passageway connecting the transmission tube with the exhauster, a normally closed valve controlling said passageway, a minimum flow of air past the closed valve being permitted, a pneumatic connected to the valve for moving the latter, one face of the pneumatic being constantly exposed to the atmosphere and the other face of the pneumatic forming a movable wall for a chamber within the easing",'the pressure in said chamber normallv be'lng below that of the atmosphere, and means exposed to the air flowing through the transmission tube and actuable thereby to admit atmospheric pressure to said chamber.

7. Power control apparatus for a pneumatic dispatch system of the vacuum, minimum flow type having a transmission tube communicating with an exhauster, said apparatus comprising a hollow casing communicating with the transmission tube and provided with an apertured partition-separating spaces in which the air pressure fluctuates, a valve controlling the passage of air through the aperture in said partition, an open passage being provided to permit a minimum flow of air from one of said spaces to the other, a pneumatic connected to the valve, the inner side of said pneumatic being exposed normally to the pressure obtaining in one of said spaces and the outer side being always exposed to full atmospheric ressure, and means responsive to sudden increase in velocity in air flow in the within the transmission tube and actua-ble thereby to admit atmos heric inner side 0 the pneumatic.

8. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type having a transmission tube, said apparatus comprising a casing connected to the transmission tube and having a passage connecting the transmission tube with an exhauster, a valve controlling the passage I through the casing, a pneumatic connected to the valve, one face of the pneumatic being freely exposed to atmospheric pressure and the opposite face of the pneumatic forming a movable wall for a chamber within the casing, the ressure in said chamber normally being be ow that of the atmosphere, a port for admitting air at atmos pheric pressure to said chambe posed to the air flowin in the transmission tube and movable there y, and an auxilia valve actuable by the vane, said latter valve normally closing said air admission port.

9. Power control apparatus for a pneumatic dispatch system of the minimum flow type having a transmission tube," said apparatus comprising a casing, an apertured wall within the casing separating spaces in which air pressure fluctuates, a main valve controlling the flow of air through the aperture in said wall, a continuous minimum flow of-air from one space to the other being provided for, the casing having an offset portion, a movable wall dividing said ofi'set portion into two chambers, one of said chambers being freely open to the atmosphere and the other communicating with one of said spaces, an orifice for admitting air at atmospheric premure to the" last named chamber, an auxiliary valve normally closing said orifice, means automatically actuable upon discharge of a carrier from the transmission tube to open said valve, and means for transmitting movements of the movable wall to the mam valve.

10. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type havinga transmission tube communicating with an exhauster, said apparatus comprising a hollow casing provided with a main portion and an offset portion, an apertured partition dividing the interior of the main portion of the easing into two spaces, one of which communicates with the transmission tube and the other with the exhauster, a main valve normally closing the aperture in said wall, a continuous minimum flow of air fromvone space to the other being permitted, a movable wall divid ing" the offset portion of the casing'into two chambers, one of said chambers communicating freel with the atmosphere and the other chain r communicating by a restricted passage with one of the spaces in the main part Of the casing. the latter film pressure to act upon the r, a vane ex- I controlling an orifice in said chamber d ber having an orifice its wall for admitt ng air at atmospheric pressure, an auxilione being constantly exposed mechanically face of thepiston at all times 12. Power control apparatus for a pneu-' matic dispatch system of the vacuum miniflow type having a transmission tube, apparatus comprising a casing-having a chamber therein communicating with the transmission tube, a normally closed valve the wall of said chamber, a pneumatic resiliently connected to the valve, said pneumatic being exposed upon one side to atmospheric ressure and having its opposite side normal y exposed to. a pressure substantially the same as that existing in saidchambe said pneumatic opening the valve upon variation in pressure in ue to introduction of a carrier into the transmission line, and means of airflowmg through the transmission tube for initiatin the main valve upon delivery 0 the carrier from the transmission line.

11. Power control apparatus for a pneuto atmospheric pressure and the closure of 13:. Power control apparatus for a pneumatlc dispatch system of the vacuum minimum flow type having a transmission tube and a suction tube, said apparatus comprising a casing connected to the respective tubes and having a main portion and a secondary portion, an apertured wall terior of the main portion into two spaces communicating respectivelywith the trans mission tube and the suction tube, a valve controlling the passage of air' through the aperture in said wall,.a movable wall dividing the secondary portion of the casing into two chambers, a partition dividing one of said chambers from the space in the main casing which communicates with the transmission tube, a rod passing through an opendividing the inthe for the passage of air from one side of .the partition to the other.

14. Power control apparatus for a pneumatic dispatch system of the minimum flow vacuum type having a transmission tube communicating with anexhauster, said apparatuscomprising a casing connected to the transmission tube and having a passageway communicating with the tube, annain valve controlling said passageway, a minimum flow of air through the tube being permitted when the valve is closed, a piston sliding in a cylindrical guide disposed laterally of said passageway, means connecting piston to the main valve, a spring tending to close the main valve, a partition separating the space to one side of the main valvefrom a chamber of which the piston forms one wall, a continuous passage connecting said space and chamber, a port leading to the chamber, an auxiliary valve normally closing said port, and an air actuated vane disposed in the transmission tube and connected to the auxiliary valve for opening the latter.

15. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type having a transmission tube, said apparatus comprising a casing having a hollow body portion forming a continuation of the tube and providing a passageway for air, a main valve for controlling the flow of air from the inlet end to the outlet end of said passageway, a minimum flow of air through said passageway being permitted when the valve is closed, a hollow arm projecting from the casing, a partition separating the interior of said arm from the inlet end of the main body of the casing, a

neumatic in the hollow arm, means connecting the pneumatic to the main valve, a restricted channel leading from the inlet end of the passageway in the casing proper to the space between said partition and the pneumatic, adjustable means for varying the capacity of said channel, a port of relatively large capacity leading from said space to the open air, an auxiliary valve normally closing said port, and an air operated device for opening said auxiliary valve.

16. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type havi g a transmission tube, said apparatus comprising a casing having a substantially cylindrical body portion and a hollow arm projecting laterally therefrom, a septum separating the interior of the body ortioninto an inlet chamber and an outlet chamber, respectively, ing the inlet chamber from the interior of the hollow arm, a main valve controlling an orifice in the septum, a minimum flow of air from one side of the septum to the other being permitted when the valve is closed, a piston rod extending from the valve through matic being a partition separatthe partition into the hollow arm, a piston sliding within' the hollow arm, means for transmitting movement of the piston to the rod, a spring tending to hold the valve closed, the space partition being connected to the inlet chamber by a restricted passage, :1 port connecting said space with the outer air, an auxiliary valve normally closing said port, an air operated 'bafile for opening said valve, and means providing for lost motion be.- tween said baffle and auxiliary valve.

17 Power control apparatus for a pneumatic dispatch system comprising a conduit and an exhauster connected therewith, a valve for controlling the flow of carrier impelling air current through the conduit, a pneumatic for moving the valve, the pneu matic bein sensitively responsive to pressure variations in the conduit, and lost motion connections between the pneumatic and valve permitting the pneumatic to acquire momentum before its movement is trans mitted to the valve.

18. Power control apparatus for a pneumatic dispatch system comprising a conduit and an exhauster connected therewith, a valve for controlling the flow of carrier impelling air current through the conduit, a pneumatic for moving the valve, the pneusensitively responsive to pressure variations in the conduit, and connections for transmitting movement of the pneumatic to the valve, saidconnections comprising an abutment fixed relatively to the valve, and means for transmititng movement from the pneumatic to the abutment after a predetermined initial movement of the pneumatic.

19. Power control apparatus for a pneumatic dispatch system comprising a conduit and an exhauster connected therewith, a valve for controlling the flow of carrier impelling air current through the conduit, a pneumatic for movin the valve, the pneumatic being sensitive y responsive to pressure variations in the conduit, and a valve rod for transmitting movement from the pneumatic to the valve, said rod being fixed to one of said parts and sliding relatively to the other, and resilient means for transmigting movement of the latter part to the r0 20. Power control apparatus for a pneumatic dispatch system comprising a conduit and an exhauster connectedtherewith, a valve for controlling the flow of carrier impelling air current through the conduit, a pneumatic for moving the valve, the pneumatic bein sensitively responsive to pressurevariations in the conduit, and connections for transmitting movement from the pneumatic to the valve, said connections comprising a valve rod fixedly secured to the valve, an abutment fixed to the rod, and

between the piston and the i, i tau a van 1i abutment and pneumatic.

21. Power control apparatus for a pneumatieh dispatch system comprising -a conduit and an exhauster connected therewith, a valve for controlling the flow of carrier impelling air current through the conduit, a pneumatic for moving the valve, the pneumatic being sensitively responsive to pressure variations in the conduit, a valve rod fixed to the valve, a collar secured to the rod, and a spring surrounding the rod and hearing at one end against the collar and at its other against the pneumatic.

22. Power control apparatus for a pneumatic dispatch system of the vacuum minimum flow type having}; a transmission tube, said apparatus comprising a casing commui matting at one end with the tuhe, and atthe other end with an exhauster, a partition separating the interior of the easing into an inlet and an outlet chamber, respectively, a valve controlling an orifice in said partition, a minin'ium flow of air past the valve being permitted when. the valve is closed, a valve rod connected to the valve, a piston free to slide upon the rod, a spring opposing relative movement of the piston and rod in one dir ction, a fixed stop limiting relative movement of the piston and rod in the other direction, and resilient means tending to move the rod in a direction such as to close the valve.

Signed by me at Syracuse, this 26th day of January, JAMES G. MACLAREN.

New York,

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