Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS2563295 A
Publication typeGrant
Publication dateAug 7, 1951
Filing dateSep 17, 1947
Priority dateOct 28, 1946
Publication numberUS 2563295 A, US 2563295A, US-A-2563295, US2563295 A, US2563295A
InventorsRoy Westbury
Original AssigneeHobson Ltd H M
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Remotely operated hydraulic servomotor
US 2563295 A
Abstract  available in
Images(3)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

Aug. 7 1951 R. WESTBURY REMOTELY OPERATED HYDRAULIC SERVOMOTOR Filed Sept. 17, 194'? 5 Sheets-Sheet l l l l Aug. 7, 1951 R. WESTBURY REMOTELY OPERATED HYDRAULIC SERVOMOTOR Filed Sept. 17, 1947 5 Sheets-Sheet 2 1951 RWESTBURY 2,563,295

REMOTELY OPERATED HYDRAULIC SERVOMOTOR Filed Sept. 17, 194'? 3 Sheets-Sheet 5 i atenteci Aug. 7, 1951 UNITED STATES PATENT OFFICE w t I 2,563,295 H REMOTELXQPERATED minim-.10 H SERVOMOTOR any West-bury, Laney, near seen-a, England; asfiign'dr t6 II. M. Hobson Limited, London; England, a company of Great Britain A ucauairjseptntr 17, 194i, sem N 774,611 In Great Britain October 28, 1946 11 Claims. o1.1-21=40)- This invention rlates to hydraulically e 'ei ated servomotors', or the kind comprising a serve cylinder and associated piston, a control vane operable by variations in mild pressure estab lishd in a signal line between the contravene and a. sender unit having an operating member which can be adjusted to control the pressure in the signal line, the control valve normally cc: cupying a neutral position in which the servo piston is maintained at rest in its cylinder but moving, in response to variations in pressure in the signal line to allserlativ movement (if the SGI'VO piston andeylinder', Said movement being terminated by return or the COI itrOI Valve to neutral posit-ice when the piston has attained a position in relatin to the cylinder determined by the pressure in the signal line.

Such servoni'otors' have been used for operat-' ing the landing flaps of aircraft, and it is known to provide hydraulic locks for positively locking the flap in the position to which it has been Set; such locks consisting or noneturn valves placed in the pipes leading from the control valve to the servo cylinder and normally arranged" to perm-it liquid to flow only from the valve to the cylinder. Each ii'o'n ret'ur'nvalve is under the control of a small leek piston, and when pres: sure is applied to the pipe line connecting the control valve and one end of the servo cylinder, tending to move the piston towardsthe other end of the cylinder, pressure is also applied to the lock' piston associated with the hon return valve in the pipe, leading from the other end of the cylinder to the control valve. This lock pi -ston is then displaced into position to" hold the non-return vaive open, thus permitting the servo piston to move in its cylin er; v

A hydraulic lock of this kind provides irreversibility and safeguards the aircraft against accidental-rapid movement oith'e' flap: should a rain ure occur inthehpipe line by which operating pressure is supplied from the control valve to the servo cylinder. Being fully automatic, itdoes not, however, guard against afault in thesignal line. Should the sender unit, due to such; afault, fail to select the correctposition of the control valve,-v the non-returnvalves will automatically be opened by .rea'sono'f movementof the cdntrol valve from neutral position, thereby allowing :the flap tomove to the wrong'positi'on. Furthermore; the above .form' of lock is not applicable to the three-linexsystem of servomotor in which the minorside of the s'ervozpiston is always subjected to pressure; the niajor side being corinectedto pressure or exhaust according to the control valve position. I a V vAn object of this invention is to provide ahy draulic servomotor of the above kind in which the servo piston cannot be set to a wrong position in relation to its cylinder by reason of a fault in the signal line, and in which the lock will only open to allow of displacement of the servo piston in its cylinder in response to actuation of the operating member. a p g V A further .object is to provide a hydraulic ser'vfo'motor of the above kind in which hydraulic pressure to free the lock is supplied only on movement from operative position of a retaining de-' vice for holding the operating member in set position. I v p Premature release of the retaining device to allow the same to return to operative position after the operating member has been moved to a position selecting a new position of theservo piston in its cylinder, would release the hydraulic lock and so prevent the servo piston from reach ing the newly selected position. A further object of the invention therefore is to provide for immediate opening of the hydraulic lock on actuation of the retaining device, and toprcventlclosingof thelo'c'k until the servo piston has ceased to move as'a result of return of the control valve to neutral position. k vThe invention will now be described in detail, by way of ei'iampl'e, with reference to the accompany'ing drawings, in which 7 t 4 V Fig. 1 is a diagrammatic detail view of the hydraulic lock, showing the non-return valve and associated lock piston, V r

Fig. 2 is a diagram showing the application of the hydraulic lock toja four line remote control system -for an air'craft flap,

Fig. 3 is a diagram showing the application of thehy'draulic lock to a three line remo'te control-system for an aircraft flap, and

Figs'n l and 5 are respectively sections through the. control valves of the servomotors shown in Figs. 2' and 3.

Like reference numerals designate like parts vent liquid from flowing out of the'servocyl} inder through a conduit [2, a lock piston: l3which' isf'inovableto the leftasf seen in Fig. 1, to open the ball valve lffl 'when lockcontrol pressure" is applied to its right hand endthrough' a conduit 14. Liquid can then flow, in the case of 'the'lo'ck on the outlet side of the servo cylinder, through the open ball valve l and a pipe ||6 into a cylinder l surrounding the piston l3. Forward movement of the piston to open the ball valve causes a large diameter section I6 of the lock piston, fitting this cylinder [5, to open communication between the rear end of this cylinder and an annular space H communicating with a pipe I8 leading to the servo control valve. Free movement of the servo piston is thus permitted.

On release of the lock control pressure on the v right hand end of the lock piston l3, the ball valve l0 cannot close, so long as liquid is flowing from the cylinder l5 to the annular space H, since the pressure difference across the larger section l6 of the lock piston will retain the same in position to maintain open the communication between the cylinder and annular space. When however the flow of liquid ceases, due to closing of the control valve, the ball valve ID will reseat under the pressure of its spring M, an orifice It! being provided in the larger section l6 of the lock piston to allow of leakage of liquid from one side to the other as it is returned by the ball valve spring H to the initial position illustrated in which it cuts off communication between the cylinder l5 and annular space H.

A look of this character possesses therefore the desirable property that the non-return valve |0 will not close immediately the lock control pressure is relieved, unless in the meantime the servo piston has reached the end of its permitted travel. The non-return valve remains open until the servo piston movement has ceased.

Fig. 2 shows the application of the hydraulic lock of Fig. 1 to a four line system for the remotely controlled operation of an aircraft flap.

In this figure the servo cylinder is shown at 20, the servo piston is shown at 2|, and a link 22 transmits the movement from the servo piston, in conventional fashion, to the flap, not shown. 23 is a control valve which is movable in known manner to connect pipes |8 alternatively to pressure and exhaust lines 24, 25 respectively, The control valve 23 is remotely controlled from a pilots lever 26, movable over a quadrant 21, by a fluid pressure operated remote control system of the kind described in British patent specification No. 483,049. This system embodies a sender unit operable under control of the lever 26 to establish a variable signal pressure in a line 42 shown in Fig. 4. The sender unit of the remote control system is not shown in Fig. 2 but may be of the same type as sender unit 4| of Fig. 3. As shown in Fig. 4, the valve member 223 of control valve 23 normally occupies the neutral position illustrated, in which its lands 51 interrupt communication between the conduits l2, the pressure line 24 and the exhaust line 25. The right hand end of the valve member 223 is connected to a capsule 55 exposed to the pressure in the signal line 42 and connected at its other end, by a follow-up link 58, to the piston rod of the servo piston 2|. If the pressure in the signal line 42 increases, the bellows 55 collapses drawing the valve member 223 to the right, and so connecting to pressure line 24 the conduit |2 leading to the right hand end of the servo cylinder and connecting the other conduit |2 to exhaust line 25. If the change in pressure in signal line 42 is due to a fault, the non-return valves ID will remain closed and the servo-piston 2| will be unable to move in its cylinder despite movement of the valve member 223 away from neutral position. Provided, however, the change in pressure in signal line 42 arises as the result of operation of the pilots lever 26 to select a new flap position, the non-return valves ID will be opened, as later described, and in response to the above-described movement of the valve A member 223 to the right the servo piston 2| will move to the left in its cylinder until the followup link 58 has moved the valve member 223 back to neutral position. It will be readily seen that on movement of the pilots lever 26 to a position selecting a lower signal line pressure, the bellows 55 will expand, moving the valve member 223 to the left and causing the servo piston 2| to move to the right in its cylinder until the follow-up link 58 has returned the valve member 223 to neutral position.

It will be noted that a hydraulic lock of the kind shown in Fig. 1 is shown in Fig. 2 between each of the pipes H3 and the associated conduit l2, the parts of the hydraulic locks in Fig. 2 being denoted by the same references as in Fig. 1 can be readily identified. In parallel with each hydraulic lock is a non-return valve I00 which opens to allow pressure fluid to flow directly from pipe |8 to conduit I2, when the associated pipe I8 is connected to the pressure line 24 by the control valve 23. Each valve [00, however, remains closed when fluid is flowing from the servo cylinder 20 through the associated conduit l2.

The pilots lever 26 has a ratchet tooth 23 which engages one of a number of notches 30 in quadrant 21 to retain the lever 26 in adjusted position. When a button 3| is depressed to release the ratchet tooth 29, a switch 32 is closed to complete a circuit from battery 33 to a solenoid 34. Energisation of the solenoid causes a normally closed valve 35 to lift, against a spring 36, to allow lock pressure to flow to the inlets I4, from pressure line 24, over line 31. A line 38 then supplies lock pressure to the hydraulic locks associated with a flap on the other wing of the aircraft. As already explained, the lever 26 may be moved rapidly to its new position and despite the return of the ratchet tooth 23, by a spring (not shown) to engage the newly selected notch 30, and consequent opening of switch 32, deenergisation of solenoid 34, closure of valve 35 and removal of lock pressure from the inlets l4, the non-return valve III will not close until the servo piston 2| has ceased to move in its cylinder by reason of its having attained its new position and closed the control valve 23 through the agency of the follow-up link. The plunger I35 of valve 35 is loose in the solenoid 34 so that liquid may flow from line I4 to exhaust line 25 after the valve 35 has closed.

Fig. 3 shows the application of the hydraulic locks to a three line system of the kind described in United States application Serial No. 685,594. The pilots lever 26 operates, through link 39, on the control lever 40 of a sender unit 4| which, according to the position of lever 26, establishes as described in said application a variable signal pressure in a signal line 42 communicating with a receiver unit I23. The pressure inlet to the sender unit is shown at 43 and the exhaust outlet at 44. The line ||8 normally connects the minor side of the servo piston 2| to pressure, since the associated non-return valve |0|l will normally be 'open. The line 2! leading to the other end of the servo cylinder is connected alternatively to the pressure line 24 or the exhaust line 25, on movement from neutral position, of a control valve in the receiver unit I23 in accordance with variations in the signal pressure in line 42, all as fully described in United States application Serial No. 685,594. The follow-up linkage, for returning the control valve to neutral position, when the servo piston 21 has assumed the selected position, is constituted by a lever 45, pivoted centrally at 46, a link 31 and a lever 58.

The receiver unit 523 is shown in Fig. but will be described but briefly herein as-it is fully described in U. S. application Serial No. 635,594. It comprises a piston 56, balanced against the pressure in the signal line 42 by a Spring 59, a control valve for the servomotor constituted by a pistonvalve 60 and associated sleeve 6!, and a relay valve 62. As fully described in the above-noted application, movement of the piston 56 in response to variations in signal line pressure effects, through a link 63, movement of a relay valve 62 in the same direction to connect a conduit 64 either to exhaust or to signal line pressure. If the signal line pressure increases, the relay valve 62 moves to the left to supply, via conduit 64, signal pressure to the left hand face of a piston I60 fixed to the piston valve 66, moving valve 60 to the right against a spring 65. This connects line 218 to the exhaust line 25 and causes movement of the servo piston 2| to the left as seen in Fig. 3. The follow-up link 48 (Fig. 3') rotates a pinion 66 (Fig. 5) coacting with a rack B7 on the sleeve 6|, moving the sleeve 61 in the same directionas the valve 50 to cut-off line 213 from the exhaust line 25 when the servo piston 2i has reached the newly selected position. When the pressure in the signal line 42 is reduced, the relay valve 62 connects the left hand face of piston ISO to exhaust, and the piston valve til is moved, by its spring 65, to the right. This connects line 2 E8 to the pressure line 24 and causes servo-piston 2 I- to move to' the right as seen in- Fig. 3, the movement ceasing when the follow-up gear has moved sleeve 61 (Fig. 5)- sufliciently to the left to cut oil line-2 I Efrem the pressure line 2 5.

When the button 3i (Fig. 3') is depressed, it rocks an arm as clockwise about a pivot 5% to depress the tappet 5-! of a pilot valve 52, thereby moving down a ball 68 against the action of a spring 63-. This allows pressure fluid to flow from the pressure line 2 5-, through lines 53, 5 to apply lock pressure to the inlets l4. When the pressure on button 3| is released, and the ratchet tooth- 29. engages a new notch 36-, the spring 69- in the valve 5 2 lifts tappet 5i and arm 49 to their initial positions and the ball 68 is likewise lifted to cut off the lock pressure. As already explained' the non-return valves it do not, however, close until the servo piston 28- has completed its movement.

When the lever 26- is moved so as to cause the control valve I23 to connect line 218 to the pressure line 24 theassociated non-return valve H30 opens to apply pressure to the left hand face of the-servo. piston 2|. As the servo piston moves to theright, thenormally open non-return valve I00 associated with line H8 closes. However, before lever 26-can be so moved, the button 3i must have been depressed so supplying, through valve 52, pressure to line 54 to the inlets it to open both non-return valves H) as already described. Notwithstanding, therefore, that the right hand nonreturn valve Ill} closes as the servo piston 2|- moves to. the right, the right hand non-return valve i=0: remains. open. to allow liquid: to be ex-- pell-edrfrom therighthand end of the cylinder totline; M8; already noted, this. valve. misunable to. close despite release of pressure onthe;

button 3!, until the movement of the servo piston ceases. The valve Hi0 reopens when the movement of the servopiston has ceased, thus once more connecting. theminor side of the servo piston to pressure. Similarly, when the lever 25 is moved to cause the control valve I23 to connect the line 2I8 to the exhaust line 25, the left hand valve [00 will close as liquid seeks to flow out of the left hand end of the cylinder to'line 2 8:8 as the .piston 21 tends to move to the left under the pressure supplied to it from line H8 through right hand valve H30. Left: hand valve I0 is open at this time, due to the application of lock pressure to line 54,'so allowing liquid to flow out of the cylinder to. line 218, and remains open, as already explained, until the movement of the piston 2t ceases. .1

While the locking devices according to the invention have been primarily described with reference to hydraulic servomotor for operating flaps, they are equally applicable in any other installatfons in which a remotely located hydraulic servomotor is controlled from a distant sender unit by variations in pressure in a pipe line connecting the sender unit with a receiver unit associated with the control valve of the servomotor.

What I claim as my invention and desire to secure by Letter Patent is:

1. In. a hydraulic servomotor comprising a servo cylinder, a servo piston in the cylinder, an output member operable by relative movement of the servo piston and servo cylinder, a control valve responsive to fluid pressure in a signal line, a remote manual operating member for establishing a variable fluid pressure inv the signal line, said control valve normally occupying a neutral position, in which it prevents movementof the servo piston in relation to the cylinder, but responding tochange in said variable fluid pressure tocause relative movement between said servopiston and cylinder to move the output member to a position determined by the pressure in the signal line, the combination with hydraulic locks for normally preventing relative movement of the servo piston and servo cylinder, of a fluid pressure operated remote control system controlled by'said operating member and independent of said signal line, said remote control system operating, on actuation of said operating memher to change the fluid pressure in said signal line, to release said hydraulic locks.

2-. Ina hydraulic servomotor comprising a servo cylinder, a servo piston in the cylinder, a control valve responsive to fluid pressure in a signal. line, a remote manual operating member for establishing a variable fluid pressure in the signalv line, said. control valve normally occupying a. neutral position, in. which it. prevents movement of. the servo piston in relation to the cylinder, but responding to change in said: variable fluid; pressure to cause sympathetic movement of said servo piston in relation to said servo cylinder to an extent determined by the change in said variable fl uid pressure, the combination with a pair of' non-return valves each controlling and normally closing a conduit constituting the sole outlet for liquid from one end of the servo cylinder, of a lock piston associated with each nonreturn valve, a pressure conduit independent of the signal line and avalve operating, on. actuationof. the. operating. member to change the fluid pressure inv said signal line, to. supply lockereleasing: hydraulic pressure .throughrsaid; pressure;

conduit to both look pistons to cause. them to open their associated non-return valves.

3. A hydraulic servomotor as claimed in claim 2, wherein each lock piston comprises a portion of smaller cross section to receive the hydraulic lock-releasing pressure, and a portion of larger cross section movable in a housing forming part of the associated outlet conduit from the servo cylinder and located in said outlet conduit beyond the associated non-return valve, each lock piston being normally retained by its non-return valve in position to seal said outlet conduit but being movable, when subject to hydraulic lock-releasing pressure not only to open its associated nonreturn valve, but also to permit of restricted flow of liquid through said housing past its larger portion, said restricted flow of liquid past said larger portion of said lock piston maintaining said lock piston in moved position, notwithstanding removal of said lock releasing pressure, until said flow of liquid has ceased.

4. A hydraulic servomotor as claimed in claim 2, comprising a retaining device for retaining said operating member in any position to which it has been moved, and means controlled by said retaining member and operable, on movement of said retaining member to position to free said operating member, to open said valve to supply hydraulic pressure to said pressure conduit.

5. A hydraulic servomotor as claimed in claim 2, comprising a retaining device for retaining said operating member in any position to which it has been moved, a solenoid operatively associated with the valve for supplying hydraulic pressure to said pressure conduit, and a switch operable by movement of the retaining device to the free position to energise said solenoid and thereby to open said valve.

6. In a fluid pressure operated remote control system comprising a servo cylinder, a servo piston in said servo cylinder, a pair of conduits, each allowing liquid to flow to and from one end of said servo cylinder, a non-return valve in each of said conduits which normally prevents liquid from flowing out of said cylinder through its conduit, a control valve normally occupying a neu-.

tral position in which said control valve seals. both said conduits, a remote operating member, a signal line, a sender unit for maintaining in said signal line a fluid pressure corresponding to and determined by the position of said operating member, said control valve being movable in response to changes in the fluid pressure in said signal line to establish in said conduits a diiferential hydraulic pressure and thereby to cause relative movement of said servo piston and servo cylinder in a direction determined by the direction of movement of said control valve from neutral position, said control valve returning to neutral position on arrival of said servo piston at a position in relation to said servo cylinder determined by the fluid pressure in said signal line, the combination with said non-return valves of a pair of lock pistons, one associated with each of said non-return valves, a lock pressure conduit for supplying operating fluid pressure to said lock pistons, a valve normally closing said lock pressure conduit and mechanism operable by said.

operating member to open said valve to apply pressure through said lock pressure conduit to said lock pistons and thereby to open said nonreturn valves.

'7. In a hydraulic servomotor, comprising a servo cylinder, a servo piston in said servo cylinder, an output member operable by relative movement of said servo piston and servo cylinder, a control valve which normally occupies a neutral position in which it prevents said servo piston from moving in relation to said servo cylinder, a manual operating member which is operable to displace said control valve from neutral position and thereby to cause relative movement of said servo piston and servo cylinder to move said output member to a position determined by said operating member, the combination with locks for normally preventing movement of said servo piston in relation to said servo cylinder of a manually operable retaining device for retaining said operating member in any position to which it has been moved, and lockreleasing means, operable by movement of said retaining device into position to release said operating member for movement, to release said locks to allow movement of said servo piston in said servo cylinder.

8. In a hydraulic servomotor comprising a servo cylinder, a servo piston in said servo cylinder, an output member operable by relative movement or" the servo piston and servo cylinder, a control valve responsive to fluid pressure in a signal line, a remote manual operating member for establishing a variable fluid pressure in the signal line, said control valve normally occupying a neutral position, in which it prevents movement of the servo piston in relation to the cylinder, but responding to change in said variable fluid pressure to cause relative movement between said servo piston and cylinder to move the output member to a position determined by the pressure in the signal line, the combination with a pair of non-return valves each controlling and normally closing a conduit constituting the sole outlet for liquid from one end of said servo cylinder, a pair of lock pistons one associated with each of said non-return valves, each lock piston being operable by hydraulic pressure to open its associated non-return valve, a pressure conduit, a source of hydraulic pressure, a valve normally shutting off said source from said pressure conduit so that said lock pistons are deprived of lockreleasing pressure, a manually operable retaining device for retaining said operating member in any position to which it has been moved, and an operative connection between said retaining device and said valve operable, by movement of said retaining device to free said operating member, to actuate said valve to connect said pressure conduit to said source.

9. A hydraulic servomotor as claimed in claim 8, wherein said operative connection comprises a solenoid associated with said valve and a switch, operable by movement of said retaining device to the free position to energise said solenoid and thereby to actuate said valve.

10. A hydraulic servomotor as claimed in claim 8, wherein each lock piston comprises a portion of smaller cross section to receive the hydraulic lock-releasing pressure, and a portion of larger cross section movable in a housing forming part of the associated outlet conduit from the servo cylinder and located in said outlet conduit beyond the associated non-return valve, each lock piston being normally retained by its non-return valve in position to seal said outlet conduit but being movable, when subject to hydraulic lock-releasing pressure, not only to open its associated nonreturn valve, but also to permit of restricted flow of liquid through said housing past its larger portion, said restricted flow of liquid past said larger portion of said lock piston maintaining said lock piston in moved position notwithstanding removal of said lock-releasing pressure, until said flow of liquid has ceased.

11. A hydraulic servomotor, comprising a servo cylinder, a servo piston in said servo cylinder, conduits communicating with opposite ends of the servo cylinder, a control valve movable in opposite directions from neutral position to connect said conduits alternatively to pressure and exhaust and thereby to effect relative movement of the servo piston and cylinder, a non-return valve in each conduit orientated so as to normally prevent liquid from flowing out of the cylinder through the conduit, a lock piston associated with each non-return valve and operable to open said non-return valve when subject to hydraulic lock pressure, each lock piston comprising a section of smaller diameter to receive the hydraulic lock pressure and a section of larger diameter movable in, and normally preventing the flow of liquid through, a cylinder forming part of the associated conduit and located on the side of the non-return valve remote from the servo cylinder, each of said lock pistons moving to open its nonreturn valve and also to alloy flow of liquid REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 486,095 Elmes Nov. 15, 1892 2,236,467 Clench Mar. 25, 1941 2,336,808 Simon Dec. 14, 1943 2,378,409 Joy June 19, 1945 FOREIGN PATENTS Number Country Date 218,963 Switzerland Apr. 16, 1942

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US486095 *Mar 12, 1892Nov 15, 1892 Fluid-motor
US2236467 *Mar 11, 1939Mar 25, 1941Automotive Prod Co LtdLiquid pressure remote control system
US2336808 *Nov 21, 1941Dec 14, 1943Globe Hoist CoHydraulic hoist
US2378409 *Mar 18, 1942Jun 19, 1945Joy Joseph FHydraulic elevating mechanism
CH218963A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2633102 *Dec 18, 1950Mar 31, 1953Weston Hydraulics LtdIrreversible hydraulic pressure power actuator
US2984985 *Feb 16, 1959May 23, 1961Macmillin Hydraulic EngineerinHydraulic operating and control system
US3020705 *Oct 21, 1959Feb 13, 1962Walter P Hill IncPositioning system including a prime mover and locking means therefor
US3093116 *Apr 7, 1960Jun 11, 1963Gen Motors CorpHigh-low speed hoist valve
US3942325 *Nov 30, 1973Mar 9, 1976David Franklin HowethHydraulic throttle actuator
US4242942 *Mar 19, 1979Jan 6, 1981G. L. Rexroth GmbhHydraulic positioner with feedback device
US5014824 *Jan 19, 1990May 14, 1991Otis Elevator CompanyHydraulic elevator control valve
US5082091 *Sep 28, 1990Jan 21, 1992Otis Elevator CompanyHydraulic elevator control
US6131610 *Nov 19, 1997Oct 17, 2000Smc Kabushiki KaishaSpeed controller with pilot check valve
US6293180Jul 21, 2000Sep 25, 2001Smc Kabushiki KaishaSpeed controller with pilot check valve
US6296015Jun 8, 2000Oct 2, 2001Smc Kabushiki KaishaSpeed controller with pilot check valve
Classifications
U.S. Classification91/360, 91/387, 92/181.00P, 91/417.00R, 91/365, 91/454, 91/461, 91/447, 91/374
International ClassificationF15B9/12, F15B9/00
Cooperative ClassificationF15B9/12
European ClassificationF15B9/12