US2913070A - Automatic elevator control - Google Patents

Description

Nov. 17, 1959 M. N. NYBERG AUTOMATIC ELEVATOR CONTROL 2 `Sheets-Shlee'c 2 Filed Feb. 26, 19,58

United States Patent O 2,913,070 g AUTOMATIC ELEVATOR CONTROL Magnus N. Nyberg, Oceanside, N.Y., assignor to Hydraulic Elevator & Machine Co., Inc., Brooklyn, N.Y., a corporation of New York Application February 26, 1958, Serial No. 717,688

15 Claims. (Cl. 187-29) This invention relates to hydraulic elevator systems and more particularly to the control of such systems.

Many existing hydraulic elevator systems are mechanically controlled by means of cables and pulleys which activate the valving mechanisms associated with the hydraulic ram that drives the elevator cab. The cables must be manipulated by a skilled operator. In addition, such controls, besides being cumbersome, are slow operating.

It is, accordingly, a general object of the invention to provide improved controls for hydraulic elevator systems.

It is another general object of the invention to provide electrical controls for hydraulic elevator systems.

It is amore specific object of the invention to replace the mechanical controls, such as the cables and pulleys of a hydraulic elevator system, with electrical controls which are both fast operating and compact.

It is another specific obiect of the invention to replace the mechanical controls which require a skilled operator by electrical controls which may be operated by unskilled persons.

Still another specic object is to provide hydraulic control means in conjunction with a hydraulic elevator system whereby such system is conditioned for automatic control by a modern electrical control system.

Other objects and various other features of novelty and invention will be pointed out or will occur to those skilled in the art from a reading of the following specication in conjunction with the accompanying drawings. In said drawings, which show for illustrative purposes only, preferred forms of the invention:

Fig. 1 schematically shows a hydraulic-elevator system incorporating control means in accordance with the invention;

Fig. 2 shows, in accordance with one embodiment of the invention, electrical-signal-operated valve means and hydraulic-control means, as employed in the organization of Fig. l, the valve means being in longitudinal section;

Fig. 3 shows electrical control means, as used in the combination of Fig. 1;

Fig. 4 is a diagram similar to Fig. 2 and showing another embodiment of the electrical-signal operated valve means and hydraulic-control means of Fig. l.

Briefly, the invention contemplates electrical control apparatus for a hydraulic elevator system, as of the type wherein the elevator cab is driven to different levels by a hydraulic ram. The apparatus for controlling the operation of the hydraulic ram comprises a plurality of oor selectors for generating electric control functions indicating the selected oors. Level indicating means are included for generating other electric control functions indicating the actual level of the elevator cab. A control means which is responsive to both the floor selectors and the level indicating means generates electrical control signals related to the relationship between the oor selected and the level indicated. An electrical signal operated valving means is responsive to the control means the actual level of the elevator cab 10.

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to control a hydraulic control means which regulates the movement of the hydraulic ram.

Referring to Fig. 1, a hydraulic elevator system is shown wherein an elevator cab 10 is positioned up and down a shaft by a hydraulic ram 12. As the elevator cab 10 moves from door to oor, a synchro generator 14 which is coupled to the counterweight-pulley shaft 16 feeds back to a synchro motor 18 signals indicating the instantaneous elevation of the elevator cab. When an operator Wishes to move the elevator to a different floor, he depresses the push button associated with that oor on the floor selector panel 20, which generates a signal characteristic of the selected floor.

At the same time, the synchro motor 18 in response to the synchro generator 14 transmits a signal indicating These two signals are compared in the electrical control means 22 and if the selected floor is below the present position of the elevator cab, the down valve means 24 is energized, causing the hydraulic control means 28 to bleed iluid from the hydraulic ram 12. When the elevator cab reaches the selected floor, the electrical control means 22 de-energizes the down valve means 24 and the hydraulic ram stops.

If, on the other hand, the selected oor is above the actual level of the elevator cab, the electrical control means 22, in a similar manner, energizes the up valve means 26. The hydraulic control means 28 feeds iluid to the hydraulic ram 12, and the elevator cab starts on an upward motion. This upward motion continues until the selected iloor and the indicated iloor are the same. At this time, the up valve means 26 is de-energized and the hydraulic ram stops.

Fig. 2 shows the down valve means 24, which includes the normally closed solenoid operated valve 24a and the normally open solenoid operated valve 2411; the up valve means 26, which includes the normally closed solenoid operated valve 26a and the normally open solenoid operated valve 26h; and the hydraulic control means 28, which includes themain valve 30 and the pilot valve 32. During the rest period, all valve solenoids are de-energized, and the main valve 30 and pilot valve 32 are in the neutral positions shown.

When the elevator cab is to move downward, a signal on the line 25 opens the solenoid operated valve 24a and closes the solenoid operated valve 24b. The fluid sink is coupled via the valve 24a and the pipes 37, 34 and 35 to the fluid chamber 36. Since the area of the piston 38 is greater than the area of the cup 39, the Valve stem 40 is driven upward. The valve element 62 is correspondingly displaced, and fluid from the hydraulic ram 12 enters the port 64 and leaves via the port 66 to the uid sink, thus allowing the elevator cab to descend.

At the same time, the stem 48 of the pilot valve 32 is moved downward because of the mechanical linkage 50, and a connection is established between the pilotvalve ports 52 and 56. Since the normally open solenoid operated valve 24b is now closed, this connection at present has no effect on the valve system. When the elevator cab reaches the desired oor, the signal on the line 25 terminates, causing the closure of the solenoid operated valve 24a and the opening of the solenoid 0perated valve 24b. lFluid from the fluid source passes through the now-open solenoid operated valve 24b, the pipe 68, through the ports 56 and 52, and the pipes 57 and 35 to the fluid chamber 36. The main-valve stem 4t) starts falling and the valve stern 48 rises. This action continues until the connection between the ports 52 and 56 is closed. At this time, the main and pilot valves have returned to their rest positions, and the hydraulic ram 12 stops.

. When the elevator -cab is to be moved upward, a signal on the line 27 energizes the normally closed solenoid operated valve 26a and the normally open solenoid operated valve 26b.v Fluid is fed to the iuid chamber 36 from the uid source via the now-opened ysolenoid operated valve 26a and the pipes 33-35. The main-valve stem 40 moves downward, drawing the valve element 62 with it. The port 64 connected to the hydraulic ram 12 is coupled to the fluid source via the port 44. Fluid enters the hydraulic ram l2 and the elevator cab ascends. At the same time, there is an upward movement of the stem 48 in the pilot valve 32, resulting in a connection between the ports 52 and 54; since at present, the solenoid operated valve 26h is closed, the existence of a connection between ports 52 and 54 has no immediate eiect on the valve system. However, when the desired oor is reached, the signal on the line 27 terminates, and the solenoid operated valves 26(a-b) are de-energized. Fluid from the iiuid chamber 36 passes Via the pipes 35 and 57, the ports S2 and 54, and the pipes 58 through the now-- opened solenoid operated valve 26b to the fluid sink.

The main-valve stem 40 is driven upward with accompanying downward movement of the pilot-valve stem 48, which continues until the connection between the ports 52 and 54 is closed. At this time, the hydraulic ram stops, since there is no longer any connection between the ports 44 and 64 of the main valve 30.

The electrical control means 22, which controls the down valve means 24 and the up valve means 26 in response to signals from the Hoor selector panel and the synchro generator 14, is shown in Fig. 3. Associated with each oor is a cam-operated switch 80, a level relay 82, and a drive control relay 84. These elements, cooperating with the floor selector panel 20, energize valve controls 86 which are used to actuate the up and down valve means.

To insure precise floor-leveling, a level sensor 90 actuates levelers 88, which act as tine operators on the valve controls 86 when the elevator cab approaches the desired iloor. In particular, the level sensor 90 includes a pair of iron-core inductors 92a and 92b carried by the elevator cab and positioned about four feet apart along a vertical line on the outside of the cab. Centered about the center level of each floor and secured to the building or elevator shaft is a ferromagnetic strip 92e. This strip is vertically disposed and in close adjacency to the ironcore inductors 92(a-b). The cooperation of these elements in leveling the elevator cab will be hereinafter described in conjunction with the overall operation of the control means 22. l

As an example of the electrical-control means 22 controlling an up motion, an operator pushes the button 20-3 to move the elevator cab to the third floor, it being assumed that the elevator cab is at the second floor (the condition shown in Fig. 3). The depression of the button Ztl-3 energizes the relay 84-3 by completing a path through the normally closed contacts 82-3-b and 84-3b; holding contacts 84-3a, receiving current via the contacts 82-3a, keep the relay 84-3 in this energized condition after the release of the push button. The energization of the relay 84-3 closes a circuit from the line 23 through the now closed contacts 84-3c, through the normally closed contacts 82-4c, to the line 94 to energize the up relay 87.

When the up relay 87 is energized, a signal is fed via the line 27 to the up valve means 26, and the hydraulic ram 12 drives the elevator cab upward. At the same time, the normally closed contacts 87-b are opened to prevent any possible energization of the relay 85 which controls downward elevator-cab motion. As the elevator cab moves, the synchro motor 18 receives signals from the synchro generator 14 to drive the cam-operated switches 80. When the floor of the elevator cab is within approximately a foot and a half of the third floor, the cam operated switch 80-3 closes, causing the energization of relay 82-357and the normally closed sets of contacts v is cut off when inductor 92h moves past the lower end of,

energize the relay 82-1.

of this relay open. When the contacts 82-3a open, the holding circuit (S4-3a) for the relay 84-3 is broken, and the relay drops out. Dropping out relay 84-3 terminates current flow to the relay 87 via the line 94.

However, just prior to the operation of the cam-operated switch Sil-3, the level sensor 90 starts operating; in particular, the iron-core inductor 92a comes in operative proximity with the third-floor ferromagnetic strip 92c-3, and the impedance of this element is greatly increased. The increase in impedance causes the dropping out of relay 96, whose coil is connected in series with the ironcore inductor 92a. Dropping out the relay 96 causes its normally closed contacts 96a to couple power to the relay 37. Thus, when the cam-operated switch -3 closes, to fle-energize, in particular, the relay 84-3, the up leveler relay 96 assumes the role of supplying current to the up relay 87, and the elevator cab continues to move upward. This upward movement proceeds until the iron-core inductor 92a moves just past the top end of the ferromagnetic strip 926-3. At this time, the impedance of the iron-core inductor 92a decreases, and the up leveler relay 96 is again energized. Its normally closed contacts 96a open, and all power is removedfrom the up relay 87. The elevator cab thus stops at the third floor.

If, for any reason, there is an overshoot in the leveling operation, the iron-core inductor 9217 becomes operatively close to the ferromagnetic strip 92c-3 and its impedance rises. The increase in impedance causes the down leveler relay 98 to drop out, and current is fed to the down relay S5 which then supplies power via the line 25 to the down valve means 24 to start a downward movement of the elevator cab. Down control the ferromagnetic strip 92c-3, at which time the cab is leveled at the third oor.

As an example of downward motion control, it will again be assumed that the elevator cab is at the second floor (the condition illustrated in Fig. 3) and that the operator wishes to go to the rst floor. In this case, the operator momentarily depresses the push button 20-1, which passes a current through` the normally closed contacts 82-1b to the normally closed contacts 84-1b, energizing the relay 84-1. With the relay 84-1 energized, its holding contacts 84-1a receive current via the normally closed contacts 82-1a of the level relay 824, so that relay 84-1 remains energized. The energization of the drive control relay 84-1 establishes a current path from the line 23, via the now-closed contacts 84-1c, the normally closed contacts 82-1c, and the line 99 to the down relay 85. rent is fed via the line 25 to the down valve means 24,

-thus starting downward elevator cab motion. At the same time, the normally closed contacts h are opened and the up relay 85 is disabled to provide an interlock; up relay 87 cannot be energized while the down relay 85 is energized.

The elevator cab starts moving down. When it is approximately two feet from the desired level of the rst ioor, the iron-core inductor 92]; becomes operatively disposed opposite the rst-oor ferromagnetic strip 92c-1. The impedance of the solenoid 9212 greatly increases, causing the de-energization of the relay 98, whose coil is in series with the solenoid of dow-n leveler relay 98. Re-` lay 98 drops out, and its normally closed contacts 98a establish a current path yfrom the line 23 to the solenoid of down relay 85. Thus, the down relay 85, at this time, is being energized via two paths. However, when the oor of the elevator cab is about 18 inches from the desired level, the cam-operated switch ilis closed to ent'upon the level sensor 90 and when the oorof'the ele# Down relay 85 becomes energized, and a cur-V The energization of this relayv vatorcab reaches the level of the first floor, the iron-core inductor 92b is just leaving the bottom edge of the vfirstoor ferromagnetic strip 92c-1, and the leveler relay 98 becomes re-energized. Re-energization of relay 98 causes its normally closed contacts 98a to open, and all power t0 the down relay 85 ceases. The elevator cab thus stops at the desired level of the irst iioor.

Although the electrical control means is shown for servicing a four-floor system, it should be realized that any number of floors can conveniently be serviced by the addition of the required number of push buttons 20 and the associated Hoor-level elements, which include a cam-operated switch 80, a level relay S2, a drive relay 84, and a ferromagnetic strip 92C.

Fig. 4 shows an alternative embodiment of the "down Valve means 24, the up valve means 26 andthe hydraulic control means 28 for operation with a hydraulic cam having a head and tail section. Since there are many similarities between this and the embodiment of Fig. 2 primed reference characters will be employed for corresponding elements.

When the elevator cab is to be moved downward, a signal on the line 2S energizes the normally closed solenoid-operated valve 24a and the normally open solenoid operated valve 24b'. Fluid is bled from the fluid chamber 36 of the main valve 30' and pressure from the fluid source operating through port 44 against cup 39' forces the main-valve stem 40' to the left. The valving element 62' follows this motion until there is a connection between the ports 64 and 66', which permits the flow of iluid from head of the hydraulic ram 12 to the fluid sink. There is also a connection established between the tail of the hydraulic ram 12 and the liuid sink via the ports 46' and 66'. Fluid is drained from both the head and tail sections of the hydraulic ram. At the same time, there is a rightward movement of the stem 48' in the pilot valve 32', resulting in a connection of the port 52' with the port 54. Since the solenoid valve 24b' is at this time closed, this movement has no effect on the valve system;

Athence via the pipe 76 through the ports 54' and 52', the

normally opened solenoid-operated valve 26h' and the pipe 70, and continues until the main and pilot valves reach their rest positions.

When the elevator cab is to be moved upward, a signal on line 27 energizes the solenoid-operated valves 26a' and 26b'. Fluid enters the fluid chamber 38' from the uid source via the now-opened solenoid-operated valve 26a', and the pipe 70. The main-valve stem 40 moves to the right, and when the valve eiement 42 is completely displaced, there is a connection between the ports 44' and 46', directly supplying'the tail of the hydraulic ram 12 from the uid source. The concurrent movement of the valve element 62 establishes a connection between the ports 64' and 66 to permit a discharge of fluid from the head of the hydraulic ram. At the same time, the stern 48' of the pilot-valve 32' is moved to the left, permitting a connection of the ports 52' and 56'. Since the solenoidoperated valve 2Gb is closed at this time, this connection does not affect the valve system.

When the elevator cab reaches the desired floor, the signal on the line 27 terminates, and the solenoid-operated valves 26a' and 2Gb' are de-energized. Fluid leaves the fluid chamber 36" via the pipe 70, the now-opened solenoid-operated valve 26b', the pipe 75, the ports 52' and 56' and drains to the iiuid sink. Fluid in the uid chamber 36' continues to bleed ofI until the connection between the ports 52' and 56' is broken.

There have thus been shown two embodiments of electrifying the hydraulic controls for a hydraulic operated elevator system. The system, as shown, requires very little mechanical skill to operate and is highly reliable and fast operating. In particular, it will be seen that the invention is applicable to existing hydraulic elevator systems with minimum modiiication, so that such existing systems may be fully modernized with modern electric-control systems, including those of the most sophisticated nature, the presently described electrical controls being merely illustrative.

While the invention has been described in detail, for the preferred forms shown, it will be understood that modifications may be made without departing from the scope of the invention as defined in the claims which follow.

What is claimed is:

1. In a hydraulic elevator system wherein the elevator cab is driven to different oors by a hydraulic ram, apparatus for controlling the operation of the hydraulic ram comprising a plurality of floor selectors for generating electrical control functions indicating the selected oors, indicating means for generating electrical control functions indicating the level of the elevator cab, a control means responsive to said door selectors and said level indicating means, said control means generating a first electrical signal when the selected oor is above the indicated level and a second electrical signal when the selected Hoor is below the indicated level, a down valve means energizable by the first electrical signals, an up valve means energizable by the second electrical signals, a hydraulic control means responsive to said up valve means and said down valve means for controlling the hydraulic ram in driving the elevator cab, and means responsive to dse-energizing said up and down valve means for stopping said cab.

2. In a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the quantity of liquid in the hydraulic ram comprising a plurality of level selectors for generating electrical signals indicating selected levels, level-indicating means for generating an electrical signal indicative of the instantaneous cab level, a control means responsive to said level-indicating means and to said level selectors for generating electrical signals, electrical signal operated valving means operated by said control means, a source of pressure iiuid, a sink for receiving fluid, and a pressure operated valving means selectively coupling and decoupling the hydraulic ram with respect to said source and with respect to said sink, said signal operated valving means controlling the pressure exerted on said pressure operated valving means, the sense of connection from said control means to said electrical signal operated valving means being such that upon de-energizing said signal-operated valving means, said ram is decoupled from said source and from said sink.

3. The apparatus of claim 2 wherein a change in pressure on said pressure operated valving means in a first direction couples the hydraulic ram to said sink and a change in pressure in a second direction couples the hydraulic ram to said source.

4. The apparatus of claim 2 wherein said pressure operated valving means includes a luid chamber and valve elements responsive to said fluid chamber for coupling the hydraulic ram to said source or said sink, and said signal operated valving means selectively coupling said source and said sink to said pressure chamber.

5. The apparatus of claim 4 wherein said signal operated valving means includes a iirst valve for coupling said source to said fluid chamber and a second valve for coupling said sink to said fluid chamber.

6. The apparatus of claim 5 wherein said first valve is activated when the selected level is lower than the indicated level and said second valve is activated when the selected level is higher than the indicated level.

7. In a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the quantity of fluid in the hydraulic ram comprising a plurality of iioor selectors for generatingelectrical control function'sindicating selected floors, level indicating means for generating control functions indicating the level of the elevator cab, an electrical control means responsive to said fioor selectors and said level indicating means, said electrical control means generating a first control signal when the selected floor is above the indicated level and generating a second electrical signal when the selected floor is below the indicated level, a first electrically operated valve activated by the first control signal, a second electrically operated valve activated by the second control signal, a source of fiuid under pressure, said source being coupled to one of said electrically operated valves, a sink for receiving fluid, said sink being coupled to the other of said electrically operated valves, and pressure sensitive hydraulic control means including valve means having a first positional relationship determining ascent of said cab, a second positional relationship determining descent of said cab, and a third positional relationship determining arrest of cab movement, and hydraulic means responsive to operations of said rst and second electrically operated valves to determine the first, second, and third positional relationships of said valve'means.

8. The apparatus of claim 7 wherein said pressure sensitive hydraulic control means includes a fluid chamber coupled to said first and second electrically operated valves, a piston operatively disposed at one end of said uid chamber and a valve coupled to said piston, said valve selectively coupling the hydraulic ram to said source and said sink.

9. In a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the operation of the hydraulic ram comprising a plurality of floor selectors for selecting different elevator cab levels, level indicating means for indicating the level of the elevator cab, said floor selectors and said level indicating means generating electrical control functions, an electrical control means for receiving the electrical control functions, said electrical control means including first and second signal generators for generating a first electrical signal when the selected floor is higher than the inidcated level and generating a second control signal when the selected oor is lower than the indicated level, a source of fluid under pressure, a sink for .receiving fluid, first and second solenoid operated valves responsive to said first signal generator, said first solenoid operated valve being coupled to said source, said second solenoid operated valve being coupled to said sink, third and fourth solenoid operating valves responsive to said second signal generator, said third solenoid operated valve being coupled to said source, said fourth solenoid operated valve being coupled to said sink, a main hydraulic valve, said main hydraulic valve having a fluid chamber coupled to said first and said fourth solenoid operated valves, a main piston disposed at one end of said liuid chamber, a main valving means for selectively coupling the hydraulic ram to said source and said sink, a main mechanical member for linking said main piston to said main valving means, and a pilot valve responsive to said main mechanical member, said pilot valve being coupled to said second and third solenoid-operated valves and said fluid chamber, said pilot valve having pilot valving means responsive to said main mechanical member to selectively couple said fluid chamber to said second and third receiving solenoid-operated valves, said yfirst and second solenoid-operated valves being activated when a signal from said first signal generator to increase the fluid in said uid chamber, the increase in fluid causing a displacement of said main valving means and said pilot valving means form a rest position, said first and second solenoid operated valves being deactivated when the indicated level is the same as the selected floor to permit said pilot valving means to couple said fluid chamber to said sink.

' 10. The apparaus of claim 9 wherein said third and fourth solenoid operated valves are activated when a signal is generated by said second signal generator to de-- crease the fluid in said tiuid chamber, the decrease in iluid causing an'opposite displacement of said main valving means and said pilot valving means, said third and fourth solenoid operated valves being deactivated when the indicated level is equal to the selected oor to permit said pilot valving means to couple saidV uid chamber to said source.

11. In a hydraulic elevator system wherein the elevator cab is driven to diiierent levels by a hydraulic ram, apparatus for controlling the quantity of fluid in the hydraulic ram comprising a plurality of oor selectors for generating electrical control functions indicating selected floors, level indicating means for generating control functions indicating the level of the elevator cab, an electrical control means responsive to said floor selectors and said level indicating means, hydraulic control valve means for said ram, a hydraulic pressure source and a sink, solenoidoperated valve means for selectively connecting said control-valve means to said source and to said sink, said electrical control means being operatively connected to said solenoid-operated valve means, said valve means establishing a locked-flow condition for hydraulic fluid fiowing into and out of said ram when said solenoidoperated valve means is de-energized.

12. In a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the quantity of uid in the hydraulic ram comprising a plurality of oor selectors for generating electricalcontrol functions indicating selected floors, level indicating means for generating control functions indicating the level of the elevator cab, an electrical control means responsive to said fioor selectors and said level indicating means, hydraulic control valve means for said ram, a hydraulic pressure source and a sink, solenoidoperated valve means for selectively connecting said control-valve means to said source and to said sink; said electrical control means having a first condition determining excitation of said solenoid-operated valve means to establish a fluid flow from said source to said ram, a second condition determining excitation of said solenoidoperated valve means to establish a fluid flow from said ram to said sink, and a third condition determining a deenergized condition of said solenoid-operated valve means; and means operative upon de-energizing said solenoidoperated valve means for stopping iiuid ow to and from said ram.

13. ln a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the quantity of fluid in the hydraulic ram comprising a plurality of floor selectors for generating electrical control functions indicating selected floors, level indicating means for generating control functions indicating the level of the elevator cab, an electrical control means responsive to said ioor selectors and said level indicating means, hydraulic control valve means for said ram, a hydraulic pressure source and a sink, solenoidoperated valve means for selectively connecting said control-valve means to said source and to said sink; said solenoid-operated valve means havin-g a first energized condition determining hydraulic connections of said control-valve means to drive said cab upwardly, said solenoid-operated valve means having a second energized condition determining hydraulic connections of said control-valve means to drive said cab downwardly, said solenoid-operated valve means having a third and de-energized condition determining hydraulic connections to said control-valve means to stop said cab; and electrical control connections to said solenoid-operated valve means from-v said electrical control means.

14. In a hydraulic elevator system wherein the elevator cab is driven to different levels by a hydraulic ram, apparatus for controlling the quantity of uid in the hydraulic ,ram comprising a plurality of floor selectors for generating electrical control functions indicating selected floors, level indicating means for generating control functions indicating the level of the elevator cab, an electrical control means responsive to said oor selectors and said level indicating means, hydraulic control valve means for said ram, a hydraulic pressure source and a sink, solenoid-operated valve means for selectively connecting said control-valve means to said source and to said sink; said control-valve means including a main valve having a movable valve member for which ow to and from said ram is stopped when said valve member is in a central position, said ram being connected to ascend when said member is positioned to one side of said central position and being connected to descend when said 15. The elevator system of claim 14, wherein said hydraulic means is eective to center said main-valve member for the de-energized condition of said solenoidoper.

ated valve means.

References Cited in the file of this patent UNITED STATES PATENTS Dunn July 24, 1917 Furlow June 4, 1918

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