US2389962A - Hydraulic remote control system - Google Patents

Description

' Nov. 27, 1945.

L. E. DOUGHERTY HYDRAULIC REMOTE CONTROL SYSTEM Filed July e, 1942 2 Sheets-Sheet 1 eaammmaammmaa li l @im Mwmmum I l 2 6 4 o iff-` l i, l

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INVENTOR' mue/E. DOU/yrfy I l za 7 'v 40 l BY 2 g /z/ /20/ w Nov.27, 1945. L. E. DouGHER'rY HYDRAULIC REMOTE CONTROL SYSTEM 2 Sheets-Sheet 2 `Filed' July e, 1942 Figc 4f.

ATTRNEY Patented Nov. 27, 1945 VUNITED STATES PATENT Aomer:

A 2,989,962 HYDRAULIC REMOTE ooN'raoL SYSTEM Lemnel E. Dougherty, Miami, Fia.

Application July 6, 1942, serial No. 449,942 l 11 claims. '(ol. en -54.5)

This invention relates to an improved hydraulic remote controlo! the type wherein a single tube is used as connection between the controlling station, usually called the transmitter, and the controlled station, usually called the receiver.

Hydraulic remoteA control systems of this type usually consist of a/ cylinder and piston in the transmitter, a cylinder and piston in the receiver, a connecting tube between the cylinders and a hydraulic duid in the tube and cylinders between the pistons. upon the transmitter piston and receiver piston so that the hydraulic uid between the pistons is held under compression. Thus mov( -nent of the transmitterpiston in one direction causes a corresponding positive movement of the receiver piston by transmission of the hydraulic fluid and movement of the transmitter piston in the other direction allowsv a corresponding movement of the receiver piston through the action of its spring.

It hasbeen proposed to provide means `whereby the forces of the springs upon the pistons in transmitter and receiver are maintained substantially equal to each other so that the transmitter and receiver pistons will tend to retain any position into which they may be moved without any tendency on their part to return to a centralized position. However in some installations such as, for instance, the operation of airplane engine controls where the control system is subject to severe vibration and also where the member controlled might have a tendency to assume some other position than that in which it was placed, it is necessary to provide some locking means to hold the control in the desired position. A locking means can of course be provided for the transmitter operating lever to prevent any undesired movement of this part but such a lock requires manual unlocking before the control is moved and relooking after the desired movement has taken place or else depends upon such a high element of friction that excessive force is required to move the control. A further disadvantage of a locking means at the transmitter is that although unauthorized movement of the transmitter piston is prevented any contraction or expansion of the hydraulic fluid in the system will cause a movement oi the receiver piston and thus an undesired movement of the controlled member.

The primary object of this invention is to provide an automatically operating valve apparatus between the transmitter and receiver of a hydraulic remote control system to normally prevent the passage of hydraulic iluid between the Usually springs are provided acting.

transmitter and receiver thereby effectively locking the system and preventing unauthorized movement of the receiver piston due to vibration or other external -force acting upon the receiver.

Another object of this invention is to provide an automatically operating locking valve apparatus which can be located adjacent to the receiver in a hydraulic remote control system to prevent movement of the receiver piston due to expansion or contraction of the hydraulic fluid in any part of the system other than in the receiver cylinder itself.

Another object of this invention is to provide minimum.

Another object of this invention is to provide an automatically operating locking valve apparatus between the transmitter and receiver of a hydraulic remote control system which will eliminate the necessity o balancing the spring forces between the transmitter and receiver.

Another object of this invention is to provide an eiiicient linkage between the spring and the piston in a hydraulic remote control system so as to maintain a constant uid pressure in the system, insofar as the force from the spring is concerned, regardless of the position of the piston throughout its travel in the cylinder.

Other objects and advantages of this invention will be apparent during the course of the following detailed description.

In the accompanying drawings of one apparatus illustrative of this invention,

Figure 1 is a sectional view showing the transmitter assemblage.

Figure 2 is a sectional view of the receiver assemblage.

Figure 3 is a sectional view of the locking valve assemblage.

Figure 4 is a cross sectional view taken substantially on its respective line shown in Figure 1.

Figure 5 is a. sectional view of a modified form of receiver assemblage.

Figure 6 is a sectional view-of a modified form of the locking valve assemblage.

In the drawings, wherein for the purpose of .pherie pressure.

illustration are shown preferred and modified forms of the invention, the letter A may generally designate the entire hydraulic control equipment, which may include a transmitter assembly B; receiver assembly C and locking valve assembly D.

In this description all movements and directions toward the left of the drawings will be considered as forward and all movements and directions toward the right of the drawings will be consid- A ered as rearward.

Referring to Figure 1, the transmitter assemblage B comprises a supporting frame l upon which is mounted a cylinder Il. vA fluid actuating piston I2 is slidable in the cylinder. 'I'his piston is relatively long and includes a piston head I3 having minute transverse openings I4 therein. At its rear end the piston head |3 is provided with a yieldable piston cup |5 of a nature which will prevent now of fluid forwardly but will permit the uid to pass through `the minute openings |4 into the rear end of the cylinder when the pressure in the supply line I6 is greater than that which exists in the rear part of the cylinder. The forward end 25 of the piston I2 is provided with the seal 38 which prevents -leakage of fluid past this end of the piston.

Fluid from a supply tank flows by gravity or other means through the tube I6 and theinlet port 48 into cylinder I I so that the chamber between the front and rear heads of piston I2 is always filled with uid at not less than atmos- A compensatingport 4| is provided to permit fluid in the system, when there is an excess thereof, to return to the supply tank at the most forward movement of the piston when the compensating port 4`| is uncovered, as will be subsequently referred to.

The operating lever 28 is pivoted at '2| upon the frame I0, and at a location between the pivot 2| and the handle 23 the lever is connected by a rod 24 with the end 25 of the piston I2. This connecting rod 24 has a ball and socket connection with the end 25 of the piston I2 and a pivot connection at 2T with the lever 20. A spring supporting rod 3| is suitably pivoted at 32 upon the lever 28 at a location between the pivots 2| and 2T. This rod 3| intermediate its ends is slidably supported within a collar 33. The latter is trunnioned at 34 in the frame I0, as shown in Figure 4 of the drawings. A spring 35, under compression, is supported upon the rod 3| being seated at one end in the collar 33 and atA its other end y being held in compressed relation upon the rod by means of a retaining disc 31 held on therod in adjustable relation by means of a nut 38. It is of course apparent that the compression force of the spring acts through the linkage to maintain the fluid in the rear part of cylinder I under pressure. Movement of the lever increases or decreases the compression of the spring 35, but the leverage and linkage connecting this spring with the piston is so arranged that it exerts a substantially constant force upon the fluid, in the cylinder Stop shoulders 44 and 45 are provided upon the spring rod 3| for contact with the collar 33 in order to limit the travel of the piston I2. The piston I2 of the transmitter is given slightly greater travel than the piston of the receiver, to be subsequently described, so that the compensating port 4| can be uncovered if required.

It will be well to note here the principle of construction of the linkage connecting the spring and the piston so as to maintain a constant fluid pressure'in the cylinder and other parts of the I system.

It is apparent that to maintain a. constant axial thrusting force upon the piston |2 that the rotating moment or torque of the lever 2l at the pivot point 2| varies with the movement of the piston due to change in angular relationship of the rod 24 with the piston and the lever. After establishing the location of the cylinder, the length of the connecting rod and itspoint of attachment to the lever, all in relationship to the pivot point 2| of the lever, the required torque at the point 2| for various positions of the piston can be ascertained. It is now necessary to locate the pivot point 32 of the spring rod 3| so that the force derived from compression of the spring` 35 transmitted through the rod 3| to the lever 28 at pivot point 32 provides a torque about the point 2| substantially equal to that required to maintain the constant force upon the piston, at all points of the piston travel. While exact mathematical balance of these forces can not be obtained for any great angular travel of the lever, proper proportioning and location of the various parts allows a close approximation to an equality of forces so that there will be but ,slight variation of fluid pressure in the cylinder for a considerable angular movement of the lever. In general it may be stated that with the piston in its rearmost position and the spring in its least compressed position, as illustrated in C, Figure 2, the spring rod is at its nearest approach toa perpendicular to the lever; forward movement of the lever, which increases the compressive force of the spring, increases the angular difference of the spring rod with a. perpendicular to the leverl so that the desired torque at the pivot point of the lever is obtained.

While for simplicity of illustration in the drawings the piston and spring are shown both connected to the same lever, it is apparent that, if desired, they may be connected to different levers, said levers being connected together by a shaft, gears or other means, Without departing from the principle or spirit of this invention. Also that while only one spring is shown, a plurality'of springs may be used to obtain the desired force. Referring to the receiver C, the same is in many respects similar to the transmitter assemblage. It is provided with a frame 50 which supports the cylinder 5I having a piston 52 slidable therein. This piston is provided with a sealing cup 53. A lever 54 is pivoted at 55 upon the frame 58; this lever having suitable openings 56 therein for the connection of control rods, etc.,

all of which are well understood by those skilled in the artto which this -invention relates. The piston 52 is connected by the rod 51 to the lever 54 at pivot point 58 in spaced relation to the lever pivot 55. The details of the spring assemblage of this receiver are substantially the same as that of the transmitter. The spring rod. 59 is pivoted at 60 upon the lever 54 intermediate the pivot points 55 and 58. The rod 59 is slidable in the collar 82 which is trunnioned upon the frame 50, the same as the collar of the transmitter as shown in Figure 4. A spring .63 under compression is supported upon the rod 59, being seated at one end in the collar 62 and at the other end by the retaining disc 65 adjustable upon the rod 59 by means of a nut 66. The stop shoulders 'I0 and 1| upon the rod 59 limit the travel of the piston 52 by seating against the collar 62.

,While the cylinder and piston ofthe receiver are different from those of the transmitter, inasnuc'h as. the transmitter contains a fluid ccmlpensating means, the linkage and spring arrangements of transmitter and receiver are substan- V tially the same.

with the proper quantity of a hydraulic fluid,4

movement of the handle 23 rearwardly causes a rearward movement of the transmitter piston I2 and a corresponding 'forward movement of the recelver piston 52, and lever 5'4, by transmission of the hydraulic fluid.' After such movement has taken place, forward movement of the handle 23 causes a corresponding rearward movement of lever 54 through the action of the receiver spring 63. As the springs of transmitter and receiver exert a substantially 'equal and constant pressure force upon the fluid in the system, regardless of the positions of their respective pistons in the cylinders, it is a substantially balanced system with notendency on its own part to assume a position other than where moved. As explained heretofore, in certain positions there maybe a slight unbalance of forces between the springs of transmitter and receiver but it is insufficient to overcome the friction of the system and cause any movement.

Compensation for loss, expansion or contraction of the hydraulic iluid is accomplished by movement of the transmitter piston I2 to its foremost position, with the stop 45 against the collar 33, at which point the compensating port 4I is uncovered and is open into the pressure part of the cylinder rear of the piston sealing cup I5.

If thereY is an excess of iluid in the system, rearward movement of receiver piston 52 will continue until it has reached its rearmost position with the stop 10 against the collar 62 and the excess of fluid will escape through the compensating port 4| into the supply tank. If there is a deficiency of fluid in the system, the receiver pislton 52 will reach its rearmost position before the transmitter piston I2 has reached its, corresponding forward position. In this case, further forward movement of the transmitter piston, by exertion of force on the handle 23, will cause the fluid pressure in the rear part of cylinder I I to fall below that in the front part which is connected to the supply tank. Therefore fluid will flow through the openings 4|, around the sealing cup I5 and into the rear part of the cylinder thus reestablishing the proper quantity in the system. In either case of an excess or deficiency of fluid in the system, if the operating lever 20 is moved to its foremost position, with the stop 45 against the collar 33, and then released the transmitter piston Will return to its normal position closing the compensating port 4| through action of its spring 35 and the pistons will be re-established in proper relation.

Having explained the construction and operation of the transmitter and receiver assemblages and their functioning in the system I will now describe the automatic locking means associated therewith. Referring to Figure 3, the locking valve assemblage D consists of a casing Ii containing the valves |03 and |04 supported respectively by the diaphragms and |06. A common spring |01, under compression; is seated at its opposite ends upon the diaphragms, so the tendency of said spring is to normally seat valve times.

transmitter cylinder.

|03 .and unseat valve |04. A suitable vent hole is provided in the casing so that the chamber .between the diaphragms is open to the atmosphere. A passage |09 in the Ycasing connects the 5 outer sides of the valves y |03 and |04 and is connectedat |0| with the tube or duct 84 which leads to the receiver cylinder. It is thus apparent that fluid pressure from the receiver is present at the outer sides of the valves at all The fluid chambers ||0 and are provided in the casing at the outer sides of the diaphragme |05 and M06 respectively, these chambers being connected by the passage |08 which is connected at |02 with the tube leading to the Thus fluid pressure from the transmitter is present at the outer sides of the diaphragms at all times, the reaction of said fluid pressure against diaphragm |05 tending to open valve ,|03 and the reaction of said fluid pressure against diaphragmy |06 tending to close valve |04. f

In considering the force's acting upon the valves it is apparent that fluid pressure in chamber I I I acts against the diaphragm |06 to close the valve |04 and also acts upon the exposed inward side of said valve in the opposite direction; so that what will be called the effective. area of the diaphragm is equal to the exposed area of the diaphragm less the exposed area of the valve on which the pressure force acts in the opposite direction. To some extent a similar condition may exist in regard to diaphragm |05 and valve. |03, so what will be considered the effective area of diaphragm |05 will be equal to the exposed area of the diaphragm less any area of valve |03 0n Which the fluid pressure in chamber ||0 imposes a force in the opposite direction. Forces acting to open valve |03 are the fluid pressure from the transmitter acting upon the effective from the receiver acting upon the outer side of the valve head. 'Ihese vparts are so proportioned that the total force acting to open said Valve are normally slightly less than the oppositely acting force of spring |01 so that said valve isv normally held closed. It is apparent that an increase of fluid pressure from the transmitter will `increase the force tending to open the valve.

against the spring |01, so that the valve will openand permit fluid to flow from the transmitter to the receiver. The parts are so proportioned that only a small increase of fluid pressure from the transmitter will cause opening of the l' valve; but as the area of the valve head is relatively small in regard to the area of the diaphragm, a much greater increase of fluid pressure from the receiver is required before the valve willl open.. Force from the spring |01 acts to open valve |04; but this valve is normally held* closed by the fluid-pressure from the transmitter acting upon the effective area of the diaphragm |06 plus the fluid pressure from the receiver acting upon the outer side of the valve head. A decrease in fluid pressure from the transmitter will thus decrease the force tending to hold valve |04 closed, against the force of spring |01, so the valve will open and permit fluid to ow from the receiver to the transmitter. The parts are so proportioned that only a slight decrease in fluid pressure from the transmitter will cause opening of the valve; but as the area of the valve headvis relatively small in regard to the area of the diaphragm, a much greater 'decrease in fluid pressure from the receiver is required beforethe valve will open.

area of diaphragm |05, plus the uid pressure It is thus seen that the valves are normally closed and effectively lock the system by preventing flow of fluid between the transmitter and re" ceiver or vice versa; but when force is applied by the operator to move the transmitter operating lever 20 the resultant increase or decrease of iluid pressure in the transmitting end of the system causes the appropriate valve to open and allow flow of fluid, and transmission of motion, between the transmitter and receiver. This in effect provides an irreversible control system, as slight force applied at the transmitting end oi' the system causes a corresponding movement at the receiving end; but that force applied at the receiving end, within the limits of the individual design, will cause no movement.

As has been explained, fluid pressure from the receiver is present at the outer side of valve |03; therefore if the receiver piston 52 is at the forward extent of its stroke and thermal expansion of the fluid takes place, when the fluid pressure increases to a predetermined point the valve |03 will open and allow escape of the excess fluid to the transmitter, thus preventing a destructive iluid pressure from arising in the system. Also fluid pressure from the receiver acts on the head of valve |04 as a component of the force tending to hold this valve closed. Therefore if the receiver piston 52 is at the rearward extent of its stroke and thermal contraction of the iluid takes place the resultant loss of fluid pressure will releaking into the system around the sealing cap In Figure 6 is shown a modified form of locking valve assemblage D'. In principle and. operation it is very similar to the locking valve as` semblage D in Figure 3, the main difference being v that individual springs are provided for the valves and means provided for adjustment of said springs. The casing |20 supportsthe diaphragms |24 and |25 which flexibly support thevalves |26 and |21 respectively. The spring |30, under compression, is seated at one end upon diaphragm |24 and at the other end on the cap |35' which is adjustable in the spring barrel |36. The spring |3|, under compression, is seated at one end upon diaphragm |25 and on the other end on cap I 34 which is adjustable in the spring barrel |31. Fluid chambers |28 and |29 are provided in the casing below the diaphragms |24 and |25 respectively, said fluid chambers being connected by means of passage |23 with a fluid connection to the transmitter at |2|. The passage |40 in the casing leads from below valves |26 and |21 to a iluid connection to the receiver at |23, Unlike th at shown in D, Figurej3, where a common spring is used to activate diaphragms of different area, in this, form of locking valve assemblage the diaphragms may be of equal effective area, if desired in which case the spring |30 is stronger thanspring |3I. normallyheld closed by the force of the spring |30 being greater than the forces of the transmitter iluid pressure acting against the diaphragm |24 and the receiver iiuid pressure against the under side of said valve. The valve |21 is normally held closed by the forces of the transmitter fluid pressure acting against the diaphragm |25 and the receiver fluid pressure act- Valve |28 iS- ing against the under side of said"v|a.lv\4 being greater than the force of spring ISI, An increase in fluid pressure from the transmitter will cause valve |26 to open, against the force of sparing |30, and allow flow of fluid from the transmitter to the receiver. A decrease in fluid pressure from the transmitter will allow the spring |3| to open valve |21 and allow flow of fluid from the receiver to the transmitter, It is apparent that the other provisions of this locking valve assemblage are the same as those described in detail for the assemblage as shown in D, Figure 3. The main advantage of this form of construction is that it allows individual adjustment oi' the springs and thus the pressures at which the valves operate.

In Figure 5 is shown a modified form of receiver assemblage C; The cylinder 80 is pivotally mounted at 8| in a suitable bracket 82. The piston 01 is slidable in the cylinder and is provided with the sealing cup 80, The spring barrel 03 extends from the cylinder and at its outer end is provided with a sleeve or collar as a guide means for the piston rod 89. Said rod is rigidly attached at one end to the piston and at the other end may be suitably connected to the controlled member. As an example, it may be connected directly to the throttle arm of a carburetor, in which case the cylinder mounting bracket 02 could be attached directly to said car` buretor at a convenient point, The pivotal mounting of the cylinder allows a direct connection of the piston rod to a crank arm or lever to be controlled. The spring 9|, under compression, acts directly upon the piston, being seated at one end on the piston and at the other end in the spring barrel 83. A flexible tube, or hose, 85, provides fluid connection to the transmitter and allows movement of the cylinder at the pivot points.

The force of the spring 9| on the piston 01 varies with said pistons position in the cylinder; so the pressure of the fluid in the cylinder also varies with the pistons position. If this form of receiver is used in thel system, replacing that shown as C in Figure 2, and the spring 9| so designed that with the piston at the mid point of its travel the fluid pressure in the cylinder 00 is equal to the constant iluid pressure in the transmitter cylinder, the system is balanced at this central point, but at no other point in its range of movement, However, as has been shown, the locking valve apparatus prevents ilow of fluid, and movement oi' the control, even though a greater or lesser fluid pressure exists in the receiving end of the system. It is therefore apparent how this form of receiver will operate satisfactorily in the control system and the control will remain locked in any position to which it is moved. The advantages of this form of receiver are that it is relatively light and compact; also, as previously mentioned, is adaptable to direct pivotal connection to a crank arm or lever without additional connecting members.

Various changes in the shape, size, arrangement of parts and details of construction may be made to the forms of the invention herein shown, without departing from the spirit of the invention or the scope of the claims.

I claim: y

1. A locking valve assemblage for hydraulic remote control systems having a tranmitter con- .nected to a receiver comprising a casing, a pair of valves mounted in said casing, a fluid pressure actuated diaphragm attached to each of said valves for the operation thereof in one sense,

spring means acting upon each of said valves for operation thereof in the opposite sense, uid chambers in said casing adjacent to one side of each of said diaphragms and said valves, a passageway in said casing connecting said uid chambers with a fluid connection to the trans. mitter, a passageway in said casing connecting the opposite sides of said valves from said fluid chambers with a Iiuid connection to the receiver, said chambers and passageways being so arranged that iiow of iiuid can take place between the fluid connection to the transmitter and the duid connection t9 the receiver if either one of said valves is open but no ow can take place if both of said valves are closed.

2. A locking valve assemblage 4for 4hydraulic remote control systems comprising a casing, a pair of valves mounted in said casing, spring means acting upon each of said valves tending to close one valve and open the other valve, fluid pressure actuated diaphragms attached to each of said valves normally tending to open one valve and close the other valve forcesfrom said spring means and diaphragm means acting upon each of said valves in opposite directions, uid passages in the casingd associated with said diaphragms and valves and normally closed by said l valves, and said diaphragms being of unequal area, the larger diaphragm being attached to the valve normally held closed by fluid pressure, so that a decrease in fluid pressure acting upon the diaphragms causes the opening of one valve and an increase in said fluid pressure causes the opening of the other valve.

3. A locking valve assemblage for hydraulic remote control systems comprising a casing, a pair of valves mounted in said casing, springs acting upon each of said valves one spring tending to close one valve andthe other spring tending to open the other valve, fluid pressure actuated diaphragms attached to each of said valves normally tending to open one valve and close the other valve, forces from said springs and diaphragms acting upon said valves in opposite directions, fluid passages in the casing associated with said `diaphragms and valves and normally closed by said valves, and said springs being of unequal force, the weaker spring acting upon the valve normally held closed by fluid pressure, so that a decrease in iluid pressure acting upon the diaphragms causes the opening of one valve and an increase in said uid pressure causes opening of the other valve.

4. In a locking valve assemblage for hydraulic remote control systems having a transmitter connected to a. receiver the combination of a valve, spring means acting upon said valve to hold it normally closed, a diaphragm attached to said valve, means whereby iluid pressure from vthe transmitter acts upon said diaphragm tending to open said valve, means whereby iiuid pressure from the receiver acts upon the head of said valve tending to open said valve, the area of the diaphragm being such that a slight increase in fluid pressure from the transmitter will open said valve, and the area of the head of said valve being such that a relatively large increase in fluid pressure from the receiver will open` said` remote control systems having a transmitter connected to a receiver the combination of a valve, springs means tending to open said valve, a dlaphragm attached to said valve, means whereby fluid pressure from the transmitter acts upon said diaphragm tending to close said valve, means whereby Iiluid pressure from the receiverV acts upon the head of said valve tending to close said valve, the combination of forces from the transmitter iiuid pressure acting upon the diai phragm and the receiver uid pressure acting upon the head of the valve being suicient to normally hold the said valve closed against the force of the spring, and the diaphragm being of such area that a slight decrease in uid pressure Ifrom the transmitter will cause opening of transmission of two-way pressures, valve means' in the conduit for controlling the connection between the transmitter and the receiver, said valve means having differentially exposed areas, one of said areas being relatively large and the other of said areas being relatively small, the transmitter being connected to the largearea and the receiver being connected to the small area, the transmitter and the receiver acting upon said areas in the same direction, whereby the valve means is actuated in response to normal transmitter pressures and to abnormal receiver pres sures. p

` 7. In. a hydraulic remote control system, a. transmitter, a receiver, a single conduit connecting said transmitter and said receiver for the transmission of two-way pressures, valve means in the conduit for controlling the connection between the transmitter and the receiver, said valve means being normally eiective to disconnect the receiver from the transmitter, said valve means having differentially exposed areas, one of said areas being relatively large and the other of said areas being relatively small, the transmitter being connected to the large area and the receiver being connected to the small area, the transmitter and the receiver acting upon said areas in the having diierentiallyl exposed areas, one of said areas being relatively large and the other of said areas being relatively small, the transmitter being connected to the large area and the receiver being connected to the small area, the transmitter and the receiver acting upon said areas in the same direction, whereby the valve means is opened in response to normal transmitter pressures and to abnormal receiver pressures.

9. In a hydraulic remote control system, a 4

transmitter, a receiver, a single conduit connecting said transmitter and said receiver for the transmission of two-way pressures, a plurality of valve means in the conduit for controlling the connection between the transmitter and the receiver, each of said valve means including differentially exposed areas,` one of said areas in other of said areas being relatively small, the

transmitter being connected to each of the large areas and the receiver being` connected to each of the small areas,'the transmitter and the receiver acting upon said areas in the same direction, whereby said iirst valve means is actuated in response to normal increase in transmitter pressure and abnormal increase in receiver pressure and whereby said second valve means is actuated in response to normal decrease in transmitter pressure and to abnormal decrease in receiver pressure.

10. In a hydraulic remote control system, a transmitter, a receiver, a single conduit connecting said transmitter and saidv receiver for the transmission oi' two-way pressures,a plurality of valve means in the conduit for controlling the connection between the transmitter `and the receiver, each'of said valve means being normally effective to disconnect the receiver from the transmitter, means whereby one of said valve means is rendered ineffective in response to increase in pressure, means whereby the other of said valve means is rendered ineffective in response to decrease in pressure, each of said valve means including differentially exposed areas, one of said areas in each valve means being relatively large and the other of said areas being-relatively small, the transmitter being connected to each of the large areas and the receiver being connected to each of the small areas, the transmitter and the receiver acting upon said areas in the same direction, whereby said first valve means is rendered ineffective in response to normal increase in transmitter pressure and abnormal increase in receiver pressure and whereby said second valve means is rendered ineffective in response to normal decrease in transmitterpressure and to abnormal decrease in receiver pressure. 11. In a hydraulic remote control system, I transmitter, a receiver, e. single conduit connecting said transmitter and said receiver for the transmission of two-way pressures, a plurality of valve means in the conduit for controlling the connection between the transmitter and the receiver, each of said valve means being normally closed to disconnect the receiver from the transmitter, means whereby one ol.' said valve means is opened in response to increase in pressure, means whereby the other of said valve means is opened in response to decrease in pressure, each of said valve means, including differentially exposed areas, one of said areas in each valve means being relatively large and the other of said areas being relatively small, the transmitter being connected to each of the large areas and the receiver being yconnected to each of the small areas, the transmitter and the receiver acting upon said areas in the same direction, whereby said first valve means is opened in response to normal increase in transmitter pressure and abnormal increase in receiver pressure and whereby said second valve means is opened in response to normal decrease in transmitter pressure and to abnormal decrease in receiver pressure.

LEMU'EL E. DOUGHERTY.

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