US2647590A - Hydraulic elevator - Google Patents

Description

Aug. 4, 1953 c. A. ANDERSON, JR

HYDRAULIC ELEVATOR 2 Sheets-Sheet l Filed Feb. 16, 1951 INVENTR. 614% 4 /Ves/Ja Aug. 4, 1953 c. A. ANDERSON, JR

HYDRAULIC ELEVATOR 2 Sheets-Shea?I 2 Filed Feb. 16, 1951 INVENTOR` wieso/14 l/Q, WMZ/@d HTTOF/VEYS Patented Aug. 4, 1953 UNlTED STATES PATENT OFFlCE HYDRAULIC ELEVATOR Carl A. Anderson, Jr., St. Joseph, Mich.

Application February 16, 1951, Serial No. 211,387

(Cl. IS7- 29) 14 Claims. 1

This invention relates to improvements in hydraulic elevators.

The primary object of the invention is to provide an hydraulic elevator construction which is adapted to operate at high pressure and which is adapted to use a comparatively small cylinder having a piston or plunger provided with a t loose compared to that heretofore required with hydraulic elevators.

A further object is to provide an hydraulic elevator whose cost, from the standpoint of both material or parts and installation, is small compared to previous hydraulic elevators.

A further object is to provide an hydraulic elevator having a cylinder-plunger unit and an hydraulic unit for controlling flow of fluid to and from said cylinder-plunger unit, wherein a flow control valve having a restricted ow capacity is positioned adjacent to the point of connection of the hydraulic system to the cylinderplunger unit so as to restrict the rate of flow in the system and to p-revent the elevator from falling freely in the event a leak develops in the system at any point except in the said valve, in said cylinder-plunger unit, or in the connection between said valve and said cylinder-plunger unit.

A further object is to provide an hydraulic elevator operating at high pressure and adapted for descent by gravity.

A further object is to provide an hydraulic elevator having a novel solenoid-operated, dashpot-restricted valve, or stopping the descent of the elevator.

A further object is to provide a device of this character with means to prevent creeping, and which provides for automatic re-leveling of the elevator in the event of lowering thereof as a result of undesired displacement of fluid in the system, as in the event of the leakage of valves.

A further object is to provide an hydraulic elevator having guides or tracks which position the elevator cage or platform against lateral displacement or play, so that the cylinder-plunger unit cf the device is relieved from lateral distortion or play, and is only required to raise and lower the cage or platform, thereby making possible the use of a cylinder-plunger unit of the high pressure type having lateral clearance between the plunger and the cylinder.

A further object is to provide a novel hydraulic elevator operating at high liquid pressure and having a novel liquid-circulating system and a novel electric circuit for the controllers which regulate the flow of liquid in said system.

Other objects will be apparent from the following specification.

In the drawing:

Fig. l is a schematic view illustrating a typical installation of the elevator operating between. three floor levels.

Fig. 2 is a transverse sectional View taken 0n line 2--2 of Fig. 1. I

Fig. 3 is a schematic view illustrating the liquidcirculating or hydraulic system of the device.

Fig. 4 is a wiring diagram illustrating the electrical circuit of the device.

Fig. 5 is a vertical axial sectional view of the cylinder-plunger unit, taken on line 5 5 ofFig. 6.

Fig. 6 is a transverse sectional view takenon line 5 5 of Fig. 5.

Fig. 7 is an axial sectional View of a solenoidoperated dashpot-controlled valve employed in the device.

Referring to the drawings which illustrate one embodiment of the invention, the numeral I0 designates the iioor of a building which is preferably slightly recessed or lowered at I2 to provide the bottom of an elevator shaft, designated generally at I4. The elevator shaft may be constructed in any manner found suitable and provides a vertical or upright passage through which an elevator cage or platform I6 may travel in passing from the level of the floor I0 to other elevations, here illustrated in Fig. 1 as upper floors I8 and I9 of a building. The elevator shaft may be provided with the usual door openings 20, 2| and 22 at the different levels I0, lyand I9 of the building. Also each of the openings 20, 2I, 22 will be provided with a door closure 24 which may be of any suitable construction. It will be understood that the recess or lower part I2 at the bottom of the elevator shaft is so proportioned as to make possible the lowering of the platform or cage I6 to such a level that the upper surface of its oor is flush with the surface of the building floor I0.

Within the elevator shaft, at opposite sides thereof, are positioned a plurality of rigid brackets 26 which Will be located at different levels, as is well understood, and to which are secured .elongated rigid guide members 28, here illusforces and preventing improper rapplication trated as bars of T-shape in cross-section. The guides 28 are rigid and extend substantially full height of the elevator shaft. The elevator cage I6 is of a size to fit between the brackets 26 and their guides 28 with clearance, and it will be understood that the cage 26 will preferably include side Walls or panels 30 which, at vertically spaced points thereof, carry shoe or slide membersk 32 which have a sliding and guiding engagement with the guide members 28. The brackets 26, guides 28, cage structure 30 and guide shoes 32 are all constructed in any manner found suitable and of such strength as to denne the path of -travel of the cage and to prevent tilting of the cage or lateral play or movement of the cage within the elevator shaft. In other words, these cooperating parts take all stresses which are exerted in connection with the operation of an elevator, except the forces required to move the elevator cage from one level to another, and even cooperate with the lifting Amechanism to the extent of guiding the application of the lifting or unguided application of those forces.

The vertical movement of the cage or elevator platform is effected by means of a cylinderplunger unit which may be of the type illustrated in Figs. 5 and 6. This cylinder-plunger unit includes an elongated metal tube 34 which is positioned vertically in the building or in the earth below and substantially centrally of the elevator shaft I4, as illustrated diagrammatically in Fig. 3, with the major portion of that tube positioned below the level of the top surface of the recessed iioor portion l2. The cylinder 34 will be of a length slightly greater than the total length of travel of the elevator cage I6 through and within the elevator shaft. Thus, for the installation illustrated in Fig. l, the tube 34 will be of a length greater than the spacing between the top surface of the floor l0 and the top surface of the top level or floor I9. The tube 34 will preferably be constructed of steel to possess adequate strength to withstand high fluid pressure without damage or leakage. At its lower end the tube 34 is closed by an end plate 35 which is preferably Welded peripherally to the tube at 38 to provide a continuous bottom sealed joint. The upper end of the tube 34 preferably is externally screw-threaded to receive the internally screw-threaded flange 46 of a cap member 42 having a central aperture therein of a size slightly smaller than the bore of the tube 34. An annular sealing member 44 is preferably mounted in an annular groove open at the bore of the cap 42, said sealing member preferably constituting a flexible annular resilient member, such as a rubber ring of the character commonly known as an O-ring.

A cylindrical plunger member 46, of a diameter slightly less than the diameter of the bore of the cap 42 and encircled in sealing engagement by the sealing member 44, nts within the tube 34. The plunger 46 preferably constitutes a strong metal bar or tube whose outer diameter is less than the inner diameter of the tube 34 so that a substantial clearance exists between the parts 34 and 46. This clearance may be of the order of one-quarter inch. The plunger 46 is of a length substantially equal to the length of the tube 34 and is closed at its lower end by an end member 48 which is preferably peripherally welded at 5D to the lower end of the tube 46 to provide a huid-tight seal. At its upper end the plunger tube 46 receives a cylindrical member 52 which projects lengthwise therefrom and which is peripherally welded to the tube 46 at r54. The block 52 is provided with an aperture 56 which constitutes means to receive a securing member for connecting the upper end of the plunger to the floor of the elevator cage or platform I5 in any manner found suitable and well understood in the art.

The upper end portion of the tube 34 has 2- bore portion 58 of a diameter slightly greater than the bore diameter of the maior portion of said tube, thereby providing a shoulder GB. A ring 62 bears upon said shoulder and encircles the plunger tube 46. A packing bears upon the ring 62 said packing being of any character Suitable and being here illustrated as composed of a plurality of annular packing members 64 formed of asbestos and cloth and impregnated with graphite, which are preferably of V-shape in cross-section and so arranged that the apex of the V is positioned upwardly. The bottom packing ringr 66 is preferably of triangular crosssection so that the lower ring 64 may bear thereon in a nested or locked arrangement. .A

gasket follower or compressor ring 68 ts upOn the upper or outer end of the pipe or stack of rings 64 and is adapted to be pressed upon by the cap 42 as the latter is threaded upon the tube 34. It will be understood that the plunger tupe 46 has a sliding fit within the lower ring 62 and the follower ring 68, and that the packing rings 64 and G6 are pressed so that each firmly and continuously engages the plunger tupe 46 at its inner periphery and the wall Of the tube 34 at the enlarged bore portion 58 thereof.

A guide flange 'lil of annular' construction is carried by the plunger tube 4G at its lower end, as by means of snap rings T2 received in annular slots formed in the outer wall of the tube in a manner well understood in the art. The slide 1D has a sliding guide fit within the bore of the tube 34 and is notched at 'i4 at a plurality of circumferentially spaced points so as to accommodate the free flow of fluid therepast.

At its upper end portion, and preferably at a point slightly below the shoulder 69, the tube 34 is provided with an aperture into which extends a conduit 76, preferably welded at i3. The inner end of the conduit 16 preferably terminates substantially flush with the inner surface of the tube 34 and clear of or spaced outwardly from the tube 46. A valve Si) is mounted upon the tube 'I6 adjacent to the tube 34, as illustrated, to control the fiow of liquid in the tube '16. The valve 86 may be of any type found suitable, that is, it may be a plug valve, a gate valve, or any other type of valve, and has a handle 82 by means of which it may be set or adjusted so as to control the rate at which liquid may fiow therethrough. For purposes of convenience, therefore, I elect to call the valve 36 a flow control valve or a safety valve. The tube 34 will preferably be positioned so that the safety valve Bil is accessible at the bottom of the elevator shaft, that is, above the floor or recess l2 as illustrated in Fig. 3, and it will be apparent, therefore, that the uppermost portion of the tube 34 will project above the level of the recessed floor part i2, as

1' illustrated in Fig. 3.

The hydraulic system of the elevator, which communicates with the cylinder-plunger unit under the control and through the medium of the valve Si), is best illustrated in Fig. 3. This system is positioned externally of the elevator shaft and may constitute a compact unit which can be preassembled and installed as e. unit. This system comprises a tank or reservoir 84 which has a storage capacity dependent upon the size,

-, that is, the and length, of the tube 34.

This reservoir communicates through. a conduit 86 with the intake of an hydraulic pump 88. The pump 88 will preferably be of a character capable of pumping liquid at high pressure, for example, in the range between 300 pounds per square inch and 1G00 pounds per square inch cr more. The pump i8 is preferably mounted upon a base S6, and this base also mounts an electric motor S2 or other prime mover. The shaft 94 of the motor is connected by a coupling 96 with the shaft of the pump 88 so as to provide a direct drive between the motor and the pump.

A conduit 98 is connected with the outlet of the pump 88 and has interposed therein a oneway valve or check valve H16 of any suitable type, and preferably of the type which will permit adjustment or regulation of the rate at which fluid may now therethrough. A conduit |62 extends from the valve 163 to a manually control valve or vent |04. The valve i514 is preferably positioned adjacent to the safety valve 80 and is connected thereto by a conduit |06. The vent or valve |04 is preferably of the type which can be operated or opened to bleed air from the system if such air becomes entrapped in the system. It will be understood that the position and location of the conduits, as illustrated in Fig, 3, is illustrative and schematic and that the parts, and particularly the line |02 illustrated in Fig. 3 as extending in the path of the elevator cage |6, will be so positioned as by extending the same through passages or grooves in the building structure, that it will be clear of the cage and will not be in a position to be injured by the normal operation of the cage.

A conduit |06 branches from the conduit |02 between the valve |00 and the vent |04. A solenoidoperated shut-off valve ||0 is connected to the conduit |08 and a conduit |I2 extends from said valve I0. A check valve or ilow control valve ||4 is connected with the conduit ||2, the same preferably being of the type which is adjustable to control the rate of flow therethrough, that is, being of a type comparable or similar to the valve |00. A conduit ||6 is connected to the valve I|4 and communicates with the conduit 86.

The solenoid-operated valve I I0 may be of any type found suitable, but preferably is of a type which is equipped with a dashpot for restricting the rate of adjustment thereof. A valve of this type is illustrated in Fig. 7 and has a tubular housing ||8 with which an inlet port |20 and an outlet port |22 communicate at diiferent levels. Annular resilient sealing members, such as O- rings |24 and |25, are carried by the casing ||8 and encircle a valve plunger member |28 positioned axially in the tubular casing I|8 and having a slight clearance therein. The plunger |28 has an annular enlarged valving shoulder |30 which is adapted to be positioned in the bore of the tubular casing I I8 between the inlet and the outlet |26, as illustrated in Fig. 7, for the purpose of stopping the ilow of liquid between the inlet and the outlet of the valve. The plunger |28 is formed of magnetic material and constitutes the core of a solenoid having a coil |32 which is preferably mounted upon the upper end of the casing |I8 in concentric relation thereto. The electrical arrangement of the parts is such that, when the coil. |32 is energized, the core |28 is drawn upwardly, thereby raising the valving shoulder |30 to an open position. The rate at Awhich the solenoid-operated valve may function is determined by a dashpot, here illustrated as a cupshaped housing |34, secured to the lower endof` the tubular housing 8 in concentric relation thereto and sealed therefrom by means of an annular gasket |36 which encircles the plunger |28. The plunger |28 extends into the cup-shaped member |34 with clearance, as illustrated, and mounts at its lower end a cup leather or like seal |38 which engages the inner wall surface of the dashpot cup |34. At its lower end the casing V|34 may have a small bore |40 formed therein and provided with a spring-pressed valve I 42 which is constructed to be opened upon downward movement of the plunger |28 for the purpose of evacuating any liquid or air within the bottom portion of the dashpot cup |34. It will be apparent that as' the core |28 is raised upon operation of the coil |32, the movement of the core |28 is resisted or retarded by the suction effect at the bottom of the dashpot. A similar dashpot effect upon out flow can be provided by restricting the size of the bleed opening in theplug |44 at the outer end of the port I 40 against which the spring urging the ball valve |42 to seated position, normally bears.

The electrical circuit of the device is illustratedr in Fig. 4. Line conductor |50 has connected thereto conductor |52 in which a springpressed switch |54 is interposed, said switch |54 preferably being spring-pressed to open circuit `position as illustrated. In the event a multiple number of levels are provided, there may be a switch |54 for each level, said switches and the conductors |52 in which they are interposed being connected in parallel to one another and each tapped at |55 to a conductor 56. The conductor |56 has a switch |58 interposed therein, said switch |58 being of the spring-pressed type and normally engaging terminals |66 in the conductor |56. 'Ihe conductor |56 also has a top limit switch |62 interposed therein. The conductor |56 leads to a solenoid |64 which actuates the switch |66 for the motor 92. A conductor |68 leads from the solenoid |64 to the line I 10.

A second lead |12 branches from theline |50 to extend in parallel to the lead |52. The lead |12 preferably has a plurality of safety switches |14 interposed therein. These switches may constitute the door switches atthe various levels of the elevator shaft so positioned to be operated by the door for closing of the switches when the doors are closed and opening of the switches when the doors are opened. A lead |16 is connected to lead |12 and is connected to the leads |52 and |56 at the tap |55. A spring-pressed normally open switch |18 is interposed in the lead |16. A lead branches from the conduit |12 in parallel to the lead I 16. A pair of switch terr minals |82 are interconnected in the lead |80 and are adapted to be spanned by the switch 58 when the same is depressed against the action of its spring. A lower limit switch |84 is also interposed in the lead |80. The coil |32 of the solenoid-operated valve illustrated in Fig. '1 is also interposed in the lead |80, and said lead extends to the line |10, having also interposed therein contact mechanism |86 on the pump starter. The switches |58 and |18 are preferably located in the cab of the elevator to be` controlled by the user of the elevator, the switch |58 being the switch for down, and the switch |18 being the switch for "up.

In the normal operation of the device, assuming that the elevator doors are closed and other parts of the device are functioning properly so the safety switches |14 are closed, and assuming that the elevator is at the bottom of the shaft and it is desired to raise it to an upper level, the switch button |18 is depressed to closed circuit position. Under this circumstance current from line |50 passes through lead I 12, the closed safety switches |14, lead |16, up switch |18 to lead |56, switch |58 closed across terminals |60, top limit switch |62 and the relay coil |64 for operating the motor control switch |66. Current from the coil |64 flows through lead |68 to the line |10. The energizing of the coil |64 of the relay which controls the switch |66 causes the motor -92 to operate for the purpose of actuating the pump 88 and forcing a flow of liquid from the reservoir 84 into the cylinder 34 so as to displace the plunger 46 upwardly and thus raise the elevator cage I6.

The pump 88 operates at high pressure, preferably a pressure in the range from 750 p. s. i. to 1000 p. s. i. The rate at which liquid flows from the pump throughthe conduit 98 is controlled by the check valve |00. This valve may be adjusted to permit flow at the rate desired, which preferably is a rate slightly less than the rate at which liquid is permitted to flow through the valve 80. During the operation of the pump, the valves I Iii and |4 serve as means to prevent the circulation of liquid in the conduit |08. In other words, the valves and ||4 function to limit the flow of liquid from the pump 88 except through the conduits 98, |02 and |05 to the cylinder 34. When the elevator reaches the desired level, the switch |18 is opened and flow in the system stops. In the event the operator fails to open the switch |18 when the uppermost level is reached, then the top limit switch |62 positioned in the path of the cage I6 above the uppermost level will serve as a safety stop to open the electrical circuit and stop the operation of the motor 92 and the pump 88.

Whenever the elevator cage is at rest, the valves |00, 0 and I4 serve to prevent now and thereby to lock or hold the elevator at its rest position. Thus, assuming that the elevator cage is at an elevated position in which the pressure of the cage is acting on the plunger 46 and tending to displace the liquid in the lower part of the cylinder 34 back through the conduit system, the following Valve action serves to prevent such return ow. The valve ||0, being a check valve, permits iiow only from the pump 88 to the conduit 98 into the conduit |02. Flow in the conduit |02 toward the conduit 98 is stopped at the valve |00. The valve ||0 is positively closed by its control solenoid, and ow therepast is consequently prevented. In some instances, as in the event of leakage of the valves which results lowering of the elevator cage or platform to an extent sufficient to operate and close switch |54, the elevator is operated to return to its desired level. Thus, the circuit for this purpose is from line |50 through lead |52, switch |54, lead |58, switch |58 spanning terminals |60, to the solenoid coil |64 and thence through lead |68 to line |10. The energization of the coil |64 serves to close the switch |66 to the motor 92, whereby the pump 88 is caused to operate. As soon as the pump |38 is operated sufficiently to raise the elevator cage I6 clear of the switch |54, 'that switch is re-opened and the circuit is opened. Thus it will be apparent that by proper 'positioning of the switch |54, the elevator is provided with a safety factor such that, inthe event of leakage in the system, the elevator cage, nevertheless, will be automatically restored to a position at vthe desired level.

Assuming that the elevator at an elevated station is to be lowered, the switch |58 is depressed against the action of its spring to span and close the same across terminals |82. The circuit then established is from line through lead |12, closed safety switches |14, lead |80, through the switch |58 across the terminals |82, thence through the bottom limit switch |84 to the coil |32 of the valve operating solenoid |30, and thence to the line |10. The coil |32 of the solenoid opens the valve to permit .flow from port |20, which is connected with the conduit |08, tc the port |22 which is connected with the line or conduit ||2. The openingof the valve |30 permits flow from the bottom of the cylinder 34 through the conduit 15, the Valve 80, the line |65, the valve |04, the lines |02 and |08, thence through the valve |0 and the line I l2, the valve ||4 and the lines H5 and 86 to the reservoir 84.

The valve H4 is adjustable to control the rete CTI at which liquid may flow in the path just clescribed, and the valve ||4 is preferably adjusted to permit a rate of flow less than the rate which is permitted past the valve 89. The restriction of the valve ||4 controls the rate of descent of the elevator which occurs by gravity, that is, which occurs as the result of the forces of gravity applied and acting upon the elevator cage i5 as limited by the control vaive H4.

The speed at which the solenoid |32 can open and close the valve |30 is determined by the setting of the dash-pot mechanism |34, |38, |40, |42, |44. Thus when the operator releases the switch |53 to disengage the terminals |82 to dcenergize the coil |82, a sudden stop of the elevator is prevented by the dashpot action which restrains the rate at which the valve element can move from its open toward its closed or sealed position. In the event the operator neglects to open the switch |58, |82 when the lowermost level is reached, then the cage trips the bottom limit switch |84 and automatically opens the circuit to the solenoid, thereby closing the valve |30.

One of the primary advantages of the device is the provision of the valve 80. This Valve is adjustable and preferably is set to have a iiow capacity just slightly exceeding the flow capacities of the valves |00 and ||4 so as to avoid interference with the rate of flow determined by the setting of the valves |00 and |4. The difference between the rate of liow permitted by the valve 30 and that permitted by the valves |00 and ||4 is small. Consequently, in the event a failure should occur in the system externally of the cylinder 34 and the valve 80, which results in leakage of liquid from the system, or ow of liquid in the system, the rate at which liquid can be discharged from the cylinder is limited by the adjustment of the valve 30. This settinT is such that the flow past the valve is only slightly greater than the rate of flow permitted by the valves |00 and H4. Consequently, the rate at which the ele vator cab lowers is held to a safe rate or speed and danger of .injury or damage, as might occur incident to free fall of the elevator cab, is avoided. It will be understood in this connection that the use oi the valve 80 is not limited to a high pressure system, and a valve 8G could be used to good advantage in a system designed to operate at low pressures as well.

rlhe use oi' a high pressure system has a number of advantages. Principal among the advantages is the eliniination of large cylinders and large diameter piping which entail high initial cost oi material and labor.

Another advantage is that standard high pressure cylinder-plunger units can be employed, which are characterized by a clearance or loose fit between the cylinder and the plunger. Clearance in the order of one-quarter inch is not detrimental in a high pressure system of the character mentioned. These clearances are not possible in a low pressure system, and in fact, very close fits of piston and cylinder are necessary in low pressure systems. The fits are of such character as to require lapping or other expensive finishing of the surfaces of the intertting parts. Lapping operations are time-consuming and, therefore, costly, and, consequently, their elimination through the use of a cylinder-plunger unit having substantial clearance is highly advantageous from the standpoint of cost.

Another advantage of this construction and the feature which makes possible the use of a high pressure system having a substantial clearance between the cylinder and plunger of the hydraulic unit, is the use of the guides 28 for the cab. These guides, which take all laterally applied stresses, prevent chatter and vibration of the elevator in its operation and release the cylinder-plunger unit from any requirement that it guide or position the elevator cab. In low pressure systems it has been customary to rely upon the close fit of the cylinder and the piston as the means for guiding the cab and preventing lateral play. In the present construction where the guides it are employed, a loose or rree iit of the cylinder-plunger parts is permitted, and the hydraulic cylinder-plunger unit is relied upon only for raising and lowering purposes.

Another advantage of the construction resides in the descent of the cab by gravity, coupled with the use oi a dashpot controlled solenoid valve to control the stopping of the cab. The dashpot prevents sudden or jarring Stops by cushioning the stopping action, and avoids imposition of A sudden or excessive strains upon the hydraulic mechanism. It will be understood that, while the construction herein described is preferred, changes may be made therein in accordance with the appended claims without departing from the spirit of the invention.

I claim:

1. An hydraulic elevator comprising an hydraulic unit adapted to operate at high pressure and including a cylinder and a plunger fitting in said cylinder with clearance, an elevator member supported by said hydraulic unit to be elevated and lowered thereby, rigid vertical guides, slide members on said elevator member and engaging said guide to prevent lateral displacement of said elevator member, an hydraulic system communieating with said hydraulic unit and including a reservoir, a high pressure pump for supplying' liquid from said reservoir to said hydraulic unit, a check valve in said system for preventing liquid iiow from said hydraulic unit to said pump, and a valve controlled by-pass for accommodating ilow oi' liquid frein said hydraulic unit to said reservoir.

2. An hydraulic elevator comprising an hydraulic cylinder-plunger unit, a reservoir, a conduit connecting said unit and said. reservoir, a pump connected in said conduit for pumping liquid from said reservoir to said unit, a second conduit branching from said first conduit to connect said unit and reservoir and oy-pass said pump, a valve in said by-pass conduit, and a checlc valve in said first conduit between said pump and said lay-pass conduit said pump being of the type developing a high pressure, said cylinder-plunger unit being of the high pressure type in which a plunger lits loosely in a cylinder, and an elevator guide means for restraining lateral play of an elevator and of said cylinder and plunger.

An hydraulic elevator as dei-ined in claim 2, wherein valve means in each conduit serve to restrict the rate of liquid flow in said conduits.

4l. An hydraulic elevator as defined in claim 2, wherein a dow-restricting valve is connected in said nrst conduit adjacent to its connection with said cylinder-plunger unit.

5. An hydraulic elevator as defined in claim 2, wherein a flow-restricting valve is interposed in said by-pass conduit.

6. An hydraulic elevator as deined in claim 2, wherein valve means in each conduit serve to restrict the rate of liquid ilow in said conduits, and a flow-restricting valve is connected in said first conduit adjacent to said cylinder-plunger 10 unit and between said cylinder-plunger unit and said by-pass, said last named valve having a flow capacity slightly greater than said restricting valves.

1. An hydraulic elevator control system for regulating the flow of liquid between a reservoir and an hydraulic cylinder-plunger unit, comprising a conduit network connecting said unit and reservoir and providing two paths of flow therebetween, valve means in said network for controlling the rate of liquid flow in each path at a predetermined value and controlling the direction of liquid flow in said paths whereby iiow to said unit occurs only in one path and flow to said reservoir occurs only in the other path, a pump connected in the path oi low to said unit, and a shut-oil? valve connected in the path of flow to said reservoir.

8. An hydraulic elevator control system as defined claim '1, wherein additional now-restricting means are interposed in a portion of said network adjacent to said unit and common to both of said paths of flow.

9. An hydraulic elevator control system as defined in claim *1, wherein electrical means selectively actuate said pump and said shut-off valve.

lo. in hydrauli'a elevator control system as defined in claim '7, wherein said shut-off Valve is power actuated and a timing device controls the rate of speed of actuation of said valve.

1i. An hydraulic elevator control system as defined in claim 7, wherein a solenoid actuates said shut-ont` valve, and a dashpot regulates the speed of operation of said valve by said solenoid.

12. An hydraulic elevator as dened in claim 2, wherein said pump operates to develop a liquid pressure greater than 30G pounds per square inch and wherein said cylinder-plunger unit has a small cross-sectional size and a clearance therein accommodating free longitudinal flow of liquid between the cylinder and the plunger.

13. A control system for an elevator having a liquid pump controlling ascent thereof and a valve for controlling descent thereof by gravity, comprising a circuit having a pair of parallel branches, an electrical pump controller in one circuit branch, an electrical valve actuator in the other circuit branch, each circuit branch having a pair of terminals therein, said terminals constituting parte or" a manually actuated switch including a spring-pressed switch member normally spanning the terminals in one circuit branch, and a normally open manually actuated switch in the circuit branch which is normally closed by said first switch.

14. A control system of the character defined in claim 13, wherein said pump controller is connected in the circuit branch whose terminals are normally closed by said iirst manual switch and said valve actuator is connected in the other circuit branch, and a lead connected in said circuit to shunt said last named manual switch, and a spring pressed normally open switch connected in said shunt lead and adapted to be actuated by the elevator cab at a selected position thereof.

CARL A. ANDERSON, JR.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,319,125 Grote May 11, 1943 2,359,112 I-Iymans Sept. 26, 1944 2,565,880 Pettingill et al Aug. 28, 1951

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