US2280291A - Power transmitting system - Google Patents

Description

Aprii 21, 1942. 1.. F. JASVEPH 2,230,291

POWER TRANSMITTING SYSTEM Filed April 10, 1939 W 21 azz/M Patented Apr. 21, 1942 POWER, TRANSMITTING SYSTEM Lawrence F. Jaseph, Memphis, Tenn., assignor to Rotary Lift Company, Memphis, Tenn., a

corporation of Delaware Application April 10, 1939, Serial No. 267,035

7 Claims.

The present invention relates to hydraulic power transmitting systems and has for its primary purpose the provision of such a system wherein an actuated device is accelerated gradually and safeguarded against damage when the operatively connected to a plunger that actuates some part or object that is to be moved. For instance, in direct driven electric hydraulic plunger elevators the electric motor drives a pump, the discharge of which is connected to the plunger.

The pumps utilized in such systems are frequently of the positive displacement type. It has been found that when a commercially obtainable electric motor is started by direct connection to the power lines, the initial ac celeration of the elevator, particularly when lightly loaded, is so great as'to cause noticeable discomfort to passengers. The rapid initial acceleration results from the fact that the motors have relatively high starting torques. It is, of course, possible to decrease the rate of acceleration by starting the motors at reduced speed, but to dothis requires complicated electrical equipmerit having not only a high initial but also a highmaintenance cost.

In certain localities limitations upon the maximum instantaneous current that can be drawn from the power lines are imposed by power companies. This makes it impossible to utilize the ordinary induction motor without the use of expensive accessories. Motors designed for across-the-line starting taking small amounts of current, having reduced starting torque, are obtainabie, as are other motors having low starting torques-such as synchronous motors.

The primary object of the present invention is to provide a hydraulic power transmitting system wherein the actuated device is started gradually' to eliminate the shock of acceleration.

A further object of the present invention is to provide a hydraulic power transmitting system wherein the pressure applied to theactuated device is increased gradually.

A further object of the present invention is to provide a new and improved power transmitting system of the type comprising an electric motor and a pump of the positive displacement type, wherein the motor may be started by direct connection to power lines and the actuated device is accelerated at a desired rate.

A more specific object of the invention is to provide a new and improved power transmitting system of the type comprising an electric motor having a high starting torque and a pump of the positive displacement type wherein the motor may be started by direct connection to power lines and the device accelerated at a desired rate.

Another more specific object of the invention is to provide a new and improved power transmitting system of the type comprising an electric motor having a low starting torque, such as a synchronous motor, and a pump of the positive displacement type wherein the motor may be started by direct connection to the power lines and allowed to come substantially to full speed before it is loaded to a substantial extent,

after which the actuated device is accelerated.

at a desired rate. I

A further object of the present invention is to provide a. unitary valve structure adapted to be connected to the delivery side of a pump so constructed and arranged that the delivery pressure of the latter is built up gradually.

A further object of the present invention is to provide a hydraulic power transmittingsystem comprising a prime mover, a pump, and an actuated device in which the delivery pressure of the pump is made relatively low upon the starting of the prime mover by by-passing substantially the entire output of the pump, and after the prime mover and pump have reached substantially full speed, the pump delivery pressureis gradually increased at a rate to effect acceleration of the actuated device at a desired rate, and as the actuated device reaches full speed the by-passing of the output is entirely terminated.

A further object of the present invention is to provide a unitary valve structure for effecting the above-described operation.

A further object of the present invention is the provision of a new and improved hydraulic power transmitting system comprising a prime mover, a pump, and an actuated device in which the delivery pressure of the pump is made relatively low upon the starting of the prime mover by buy-passing substantially the entire output of the pump, and after the prime mover and pump have reached substantially full speed, the pump delivery pressure is gradually increased to a value sufficient to effect initial movement and acceleration of the actuated device at a desired rate, and as the actuated device reaches full speed the by-passing is terminated entirely, and

wherein the system is provided with a safeguard I provide a unitary valve structure for effecting the above-described operations, that is, a valve that may be termed a start-cushioning and relief valve.

further object of the present invent on is to provide a valve of the type described so constructed and arranged that it is effective to damp pulsations in the pump output resulting from various causes during operation of the pump.

Another and further object of the present invention is to provide a valve of the type described above wherein the movable valve member is quickly returned to its normal position whenever the pump is rendered inoperative.

In brief, the valve comprises a valve chamber within which is mounted a movable valve member controlling the by-pass of the pumped fluid from the delivery to the suction side of the pump. The movable valve member is normally held in place to close the by-passage with a relatively light pressure so that when the pump is started,

a very slight pressure only is required to open so that the valve is closed gradually, thereby to effect a gradual increase in the delivery pressure of the pump.

When the pressure increases to some value determined by the load in the elevator, the elevator is moved and accelerated at a substantially constant rate. This results from the fact that the pump delivers a substantially constant flow a part of which, when the elevator starts t2: move, flows to the elevator actuating plunger containing chamber, and the remainder of which is bypassed. The valve member thus, to maintain the existing pressure, must close the by-passage a corresponding amount. The elevator attains its full speed during the time interval required for the valve member to cut off entirely the flow of fluid through the by-passage, which is done at a substantially constant pressure to provide a substantially constant acceleration. If this time interval is not sufflcient to accelerate the elevator to full speed at the existing pressure, some pressure increase will occur during the accelerating period-but the increase is considerably less than would be the case if the pressure were limited only by the available torque of the pump-driving motor. Where the loads are relatively constant, the valve can be designed to accelerate the elevator to full speed at a substantially constant rate.

If the actuated device encounters an obstruction so that the resisting load exceeds some pre determined maximum value above the normal operating pressure, then the movable valve member is again moved against the force tending to hold it in closed position, and the output of the pump is by-passed to provide the ordinary relief valve function.

From the above brief description, it may be noted that the present invention is capable of use in systems where the source of fluid is of the constant volumetric flow type-be it a pump driven at constant speed or a reservoir.

Other objects and advantages of the present invention will become apparent from the ensuing 7 5 description, in the course of which reference is had to the accompanying drawing in which:

Fig. 1 is a view, mostly diagrammatic, of a sys- -tem embodying the present invention;

Fig. 2 is an enlarged cross-sectional view through the combined start-cushioning and relief valve of the system illustrated in Fig. 1;

Fig. 3 is a horizontal half section through the valve shown in Fig. 2, the sectional portion of the view being taken along line 3-3 of Fig. 2;

Fig. 4 is a view similar to that shown in Fig. 2 of a modified form of valve; and

Fig. 5 is a partial sectional view illustrating a further modification of the valve.

Referring now to Fig. 1, it may be seen that the system shown therein comprises a prime mover III, a constant volume, positive displacement pump I2, an actuated device I, a combined prime mover and actuated device controller I6, and a combined start-cushioning and relief valve l8, which functions in a manner to be described hereinafter to by-pass all or part of the fluid delivered by the pump to a fluid reservoir 20, or to direct part or all through a check valve 22 to effect movement of the actuated device.

The prime mover is a commercially obtainable electric motor, for instance, a three-phase induction motor of the squirrel cage type as illustrated. It may be also a single-phase repulsioninduction motor or a direct current motor. These motors have substantially constant speeds and relatively high starting torques so that it may be assumed the pump is driven at a substantially constant speed and constitutes a constant volume pump. Instead of the motor being one having following it is assumed the motor is, as stated above, an induction motor of the squirrel cage type.

The motor is supplied with power from the power lines 24 through a switch 26 operated by a solenoid 28 in a manner to be described more fully hereinafter. The motor is connected directly to the power lines when started and is, therefore, effective to produce a starting torque so great that if no means were taken to counteract the effects thereof, the actuated device H would be accelerated too rapidly for certain purposes.

The pump l2, which has been illustrated somewhat diagrammatically, is of the positive displacement type; for instance, it may be a radial pump. It is supplied with fluid from the reservoir 20 through an inlet conduit 30 and a strainer 32. The pumped fluid is preferably oil.

The pump is connected to both the combined start-cushioning and relief and the check valves through a delivery or discharge conduit 34, a fitting 36, and nipples 38 and M, respectively. The valve I8 is connected by a by-passage 4| to the reservoir 20, and the check valve-is connected by a conduit 42 to the actuated device M.

The actuated device is illustrated as an elevator or lift of the type utilized particularly for raising automobiles to render them accessible for lubrication. The actuated device itself is the plunger and it is movable vertically within a cylinder H.

The combined prime mover and actuated device controller I 6, which is illustrated diagrammatically herein, may be of the general type disclosed in United States Letters Patent No. 2,026,938 to Charles W. Eisererand assigned to the assignee of the present invention, operable manually from a normal neutral position to what may conveniently be termed up" and down" positions. The

controller and its associated hydraulic system are so arranged that in the neutral position the motor is deenergized and the actuated device remains in the position it occupies at the time. In the"up" position the motor is energized and operates to move the device upwardly, and in the "down position the motor is tie-energized and the actuated device moves downwardly under the influence of gravity, ail-in a manner now to be described.

The controller. comprises a pivoted operating handle resiliently biased by suitable means (not shown) into a vertical neutral position in which it is shown and manually movable to the left (as shown in Fig. 1) into an up position and to the right into a down position selectively to energize the motor 10 and to open a check valve 48, respectively. In the neutral position the motor is de-energized and the check valve, which is arranged normally to prevent the flow of fluid from the cylinder to the reservoir through conduit 48, is closed. The actuated device, therefore, remains stationary in whateverposition it occupies because the fluid in the cylinder is confined therein by check valves 22 and 46.

In the down" position the motor is ,de-ener gized and check valve 4 open, the latter in opened by the depression of a valve operating member 58 by an extension 52 of the operating handle. The actuated device, therefore, moves downwardly at a rate dependent upon the opening of the valve under the control of the operator. 1

Thus, when the motor is a three-phase induc-.

tion motor of the squirrel cage type having a relatively high starting torque, the pump is of the positive displacement type, and the output of the latter is connected directly to the actuated device to effect upward movement thereof, the in itial acceleration of the latter would be so great as to cause discomfort to the passengers who may be in the car being lifted unless steps be taken to decrease the rate of acceleration. The combined start-cushioning relief valve l8 of the present invention serves this useful purpose in the system specifically described above.

The start-cushioning relief valve is designed to permit starting of the elevator by connection of the pump motor directly to the power lines. The start-cushioning operation is effected by by-passing the entire output of the pump on the starting of the motor for a time sufficient to allow the pump and motor to come to full speed before the elevator begins to move. The by-passage is then gradually closed, thereby to effect automatically a gradual increase in the delivery pressure of the pump until this is suificient to raise the elevator and to accelerate it at a substantially constant rate, during which period the amount of fluid bypassed is decreased. The by-passage is closed entirely when the elevator attains full speed. If it should happen, because of the nature of the load, that an increase in pressure occurs before the elevator is accelerated to full speed, as by closure of the by-passage before the elevator reaches full speed, the increase isso limited by the valve that the acceleration is much smoother than if it were limited solely by the available torque of the pump motor.

The relief function is the same as that performed by a conventional relief valve, and which is desirable in systems of the type described to safeguard the parts from excessive pressure and the motor from overload, which may occur by an overload being'placed on the elevator; the presence of mechanical obstructions'in the hoistway, or the failure of other safety devices and consequent striking by the elevator of the usual stop provided at the limit of its movement.

The above-discussed functions are accomplished by gradually increasing the pressure tending to maintain the movable valve member in position to close the by-passage until a normal operation pressure obtains, and yet permittin the movable valve member to be opened when the pressure exceeds the predetermined maximum pressure at which the relief function is designed to be effective.

Referring now more particularly to Figs. 2 and 3, it may be seen that the start-cushioning and relief valve comprises a movable valve member 86 of piston-like construction controlling the bypass of fluid from the pump to the reservoir; and specifically, the communication between nipple 38 and the conduit ll. Under normal conditions and when the pump is inoperative, the .valve member 88 is at the lower end of a cylindrical chamber 68, within which it fits closely, in abutting engagement with nipple 38, which thus constitutes a stop for limiting downward travel of the valve member.

The movement of the valve member is controlled in part by a pair of dissimilar helical springs 18 and 12 having interposed therebetween an upper piston-like member ll similar in construction to the valve member 66. These two members have opposed skirt-like portions 15 and 18, respectively, providing bearing surfaces and means for maintaining the members in proper space relationship with respect to the spring 10. The spring 18 is considerably heavier than spring 12 for reasons appearing fully hereinafter, so that the latter is normally substantially fully compressed and the former almost fully relaxed. The upper end of the cylindrical chamber 88 is made slightly larger in diameter than the remainder to define what is called an upper chamber 80. Under certain conditions of operation the upper piston-like member-l4 moves downward and a stop ring 82 is provided to limit this travel to a predetermined amount.

Whenever the movable valve member is moved this region by a plurality of circumferentially spaced webs 86, 88, 88' and 80 (see Figs. 2 and 3).

The fluid pressure generated by the pump and acting to force the movable valve member 66 upwardly is transmitted to the upper chamber 88 with a predetermined time delay through a passage 82 having interposed therein an adjustably mounted needle valve 94. The lower end of passage 82, which is formed in an external boss 86 integral with the valve i8, is in constant communication with the region below the valve mempreferably drilled in the manner indicated in Fig.

2., is closed by a threaded plug I84.

The needle valve 84 is threaded into the external boss 96 and securely held in adjusted position by a lock nut I06. Leakage from the valve is prevented by a cap I08 surrounding .the valve.

Before proceeding with a description of the details of the modified form ofthe valve illustrated in Fig. 4, it is deemed advisable to describe the operation of the system and the valve described above. The valve, because of its location in the system, is ordinarily filled completely with liq- V uid, but is not under pressure except for that due to the static head of liquid above the valve.

As a result, the helical springs 10 and 12 are equally stressed and because of the relatively greater strength of the spring 10, the lighter spring 12 is almost fully compressed and the heavier spring I0 almost fully relaxed.

In operation, the motor I6 is energized whenever the elevator is conditioned for upward movement by operation of controller l6 to the left to its up" position. When the controller is so operated, switch 26 is closed to connect the motor directly to the power lines 24, the pump immediately generates pressure, which is transmitted to the underside of the movable valve member 66. Assuming now that the load connected to the pump; i. .e., the load connected to the actuated device l4, requires a considerable pressure to operate it, then, before this pressure is produced the movable valve member 66 is urged upwardly against the springs in and 12 until the port 84 is uncovered. Opening of the port 84 results in the by-passing of the entire output of the pump 12 to the reservoir through a bypassage including the nipple 38, valve l8, and conduit M. The pressure drop across the valve at this time is determined by the strength of spring 10 and the travel of the movable valve member 66 before the latter uncovers port 84. This pressure may well be termed a predetermined minimum value. The pressure drop across the valve determines the pressure produced in the pump discharge line 42, and in the system being described it is assumed to be less than that necessary to raise the unloaded elevator. The elevator, therefore, does not move.

'lhepressure acting against the underside of valve member 66 is admitted to the upper chamber 80 gradually through a restricted orifice, the area of which is determined by the setting of the needle valve 94. Consequently, the increased compression of spring 18, due to the movement of valve member 66,-is completely balanced so that the spring cannot move the upper pistonlike member 14 upwardly. The force exerted by the lighter spring I2, which was originally resisted by the movable valve member 66 (through spring 10, resting against the nipple 38), however, is not balanced at this time, and it is effective to urge the piston-like member. 14 together with the spring 12 and the movable valve member 66 downwardly. This movement continues as fast as fluid flows into the upper chamber through the needle valve. The motion of the piston-like member 14 is relatively slow because of the fact that flow of fluid to the upper chamber is restricted by the needle valve and it continues only until spring 18 is sufliciently compressed to support the pressure exerted by spring 12 as well as the hydraulic load upon it.

The downward movement of the valve member 66 effects gradual closure of the by-pass conduit to effect, in turn, an increase in the pressure at the pump outlet. The increased pressure is transmitted to the upper chamber 88 and the top of the piston-like member 14, again to unbalance the system and to cause the upper piston to move downward. The main spring 10 is further compressed and the valve member 66 moves down slightly to increase the pressure acting on its underside.

It may be well to mention that the above-described operation is actually continuous and does not occur in steps as described above. As a matter of fact, the piston-like member 14 moves downward gradually as soon as the pump has operated to mov the valve member 66 upwardly.

As the pressure acting on the underside of valve member 66 and that delivered to the actuated device through the control device [6 increases, the pressure finally reaches a value, which is herein termed an intermediate value because it is greater than the previously mentioned minimum value and less than the maximum working pressure at which the relief function is to be performed, which is sufficient to raise the elevator, and consequently a part of the fluid delivered by the pump enters the cylinder 44 wherein the actuated device is mounted. Since the pump delivers a constant volumetric flow, the flow through the relief valve is diminished by the amount entering the cylinder 44, and consequently the valve member 66 closes the port 84 a corresponding amount to maintain the existing pressure. It may be readily seen that a certain excess of pressure over that required to balance the elevator load must exist and that this excess is used to overcome frictional losses and to accelerate the load. If this excess is limited, for instance, by a controlled by-pass, as in the instant case, the acceleration of the elevator is also limited. The elevator, therefore, attains its full speed during the time interval required for the piston-like members 66 and i4 and spring 10 to move downward and cut off the by-pass flow through the port 84 at constant pressure. If this time is not sufficient to accelerate the elevator at the excess pressure existing, some pressure increase will occur during the accelerating interval, but in any case this increase will be limited so as to produce a much smoother start than if the pressure were limited only by the available torque of the pump motor. The valve thus acts to cushion the starting of the elevator or other actuated device.

When the elevator has attained full speed, the valve member 66 will have closed port 84, thereby entirely cutting off the flow of fluid to the reservoir through the by-pass conduit. The two piston-like members 66 and 14, however, continue to move downward under the influence of spring 12 at a rate determined by the setting of the needle valve 94 and come to rest either when the valve member 66 strikes the nipple 38 or when the upper piston-like member 14 strikes the stop ring 82; the former if the line pressure is low and the latter if the line pressure is high.

to the reservoir 20. .If the piston-like member "I4 is not already in contact with the stop ring 82. it gradually moves down to that position as a result of the transmission of the increased pressure to the upper side thereof through the needle valve. The spring 10 is so proportioned that the compressive force necessary to maintain it in position to open the by-pass conduit when the piston-like member I4 is in contact with the ring 82 is equal to the maximum working pressure for which the system is designed.

'When the pump motor I0 is lie-energized by operating the controller to its neutral or down" scribed modification, whenthe valve member I28 positions, the pump becomes inoperative, and the pressure decreases substantially to zero. The spring I0, being fully compressed, urges the movable valve member 88 and the piston-like member I4 in opposite directions so that the valve member strikes the nipple 38 and the piston-like member I4 rises as fast as oil can escape from the upper chamber 80 to the region below the valve member 88 past the needle valve. The light spring I2 is again compressed until its resistance equals that of spring I0. I

Downward movement of the elevator is effected in part by a pair of dissimilar springs I42 and simply by operating the controller into its down" position to, open the check valve 48. The weight of the elevator forces fluid from the cylinder into the reservoir through conduit 48, at'a rate dependent upon the opening of the valve. The elevator is held stationary when the controller .is in its neutral position as the fluid in the cylinder 44 is then confined by check valves 22 and 48. 3 i

The pump motor I0 may be of the type having a low starting torque and theelevator still started in the desirable manner described above, and, as a matter of fact, a further advantage realized. This further advantage is the starting and acceleration to full speed of the motor before an appreciable load is placed upon it,as may be noted from the following description. When it is desired to raise the elevator, the controller I8 is operated into its raise position. The motor is energized, but when the pressure reaches the aforesaid minimum value, which may be much less than the pressure necessary to actuate the elevator,-the output of the pump is by-passed, thereby rendering it possible for the motor to come to full speed before it is loaded. Once at full speed the operation of the system with a synchronous motor is the same as the abovedescribed operation with an induction motor.

The modified form of combined start-cushioning and relief valve shown in Fig. 4 provides the added function of damping pulsations occurring in the pump for pressures in the working range from any cause, in addition to providing the functions described above. The embodiment also discloses another form of construction that may be used in place of the substantially integral form described above.

The valve, again indicated by the reference characters I8, is connected to the discharge of the pump through the nipple 38 and to the reservoir through the conduit 4I. It comprises a body of two parts I20 and I22 threaded together. The lower portion I20 is provided with a cylindrical bore I24 slidably receiving the close fitting movable valve portion I28 adapted, when in its lowermost position; to seat upon a shoulder I28 formed integrally with the body portion I20. The body portion I20 is also provided with a substantially annular port I30 opening into an annular channel I32 opening, in turn, to the conduit M. It may be seen that, just as in the previously deis moved upward a predetermined distance, the nipple 38 is connected to the conduit 4I so that more or less of the output of the pump is bypassed to the reservoir.

The upper body portion I22 is provided with a cylindrical bore I34 adapted to receive a pistonlike member I38 similar to-but larger in diameter than the movable valve member I26. The upward movement of the piston-like member I38 is limited by a shoulder I38 formed integrally with the body member, and the downward movement is limited by a shoulder I40 formedin the lower body member I20.

The movable parts of the valve are controlled I44. The former corresponds in purpose and function for the most part to the spring I0 of the previous modification, while the spring I44 serves only to restore the valve parts to their initial position when the pump no longer gencrates any pressure and need only be strong enough to raise the weight of the piston-like member I38 and overcome any friction opposing its motion.

The nipple 38 is connected to the upper body I member I22 at a point above the top of the piston-like member I38 by a passage including a small diameter tube I48 attached to a T-fitting I50 provided with an adjustably mounted needle valve I52.

attached to a fitting I54 opening through a small passage I58 into an internal annular groove I58 provided in the lower body member I20 for the same purpose as a similar groove in the previously described modification. The latter opens into the region below the valve through a small passage I80. The upper end of tube I48 is connected to the upper body member through the fitting I50, which has a passage I82 opening directly into the body member. The needle valve is sealed against leakage by a packing nut I84 provided with suitable packing.

The spring I42 is so proportioned that a pressure not exceeding the minimum working pressure, the so-called predetermined minimum pressure, will compress it enough to permit the valve member I28 to rise and uncover the port I30. The pressure acting on the movable valve member also acts upon the upper piston-like member I 38 and because its cross-sectional area is greater than that of the lower piston, it moves downward and moves with it the spring I42 and valve member I28 at a rate determined by the rate of ingress of fiuid through the needle valve I52, until it strikes the shoulder I40. This travel is so proportioned that a pressure exceeding the maximum hydraulic working pressure by a desired margin, the so-called predetermined maximum pressure, is required to move the valve member I28 to open the port I30 to provide the reliei'function described above.

In order to effect the damping of pulsations in the delivery line, it is essential that the mova- The lower end of the tube I48 is 4 ble valve member I26 not be in contact with the shoulder I26 when subject to pressures within the working range, i. e., the intermediate pressures. This is accomplished for a wide range of working pressures by making the travel of the m ivable member I26 necessary to open the port I36 greater than the total length of travel of the piston-like member I36. When so constructed, the-valve may, when the system is not in operation, have its piston-like member I36 raised out of contact with spring I42, but on the application of pressure they will come into contact. The

pulsations are damped by the movement of the valve member against the spring and fluid above it.

The eifectiveness of this form as a damping means thus depends upon the weights of the spring I42 and the movable valve member I26, and also upon the length of the by-passage 6| leading from. the valve to the reservoir. The lighter the spring and valve member and the shorter the by-passage, the greater the effectiveness.

The operation of the last-described modification is substantially the same as that of the one first described. It differs therefrom, in function, only in that it provides the added function of damping pressure pulsations when the pressures are in the working range-i. e., when the pressures are intermediate the predetermined minimum and maximum values.

In some installations it may be desirable to restore the valve parts to their initial positions without the delay necessarily present in the above-described modifications because of the presence of the needle valve. If this is the case, a one-way by-pass around the needle valve may be provided, substantially as shown in Fig. 5.

Referring now to this figure, it may be seen that the valve I6 shown therein corresponds to the first-described valve, identical parts being indicated by identical reference characters. The by-pass around the valve from passage 92 to the portion of the valve chamber above the pistonlike member 16 is indicated by reference character I1II. This passage has a cross-section area greater than the orifice defined by the needle valve 94 and its associated passage I02, so that the rate of flow through the former is the greater. The flow is made uni-directional by a check valve comprising a ball I12 and a spring I14 serving to bias the ball in a direction to close the passage I16. The ball and spring are inserted and maintained in place by a plug I16 removably mounted in the boss 66.

In operation, when fluid is flowing into the upper end of the valve chamber to depress the piston-like member 14, the ball I12 maintains the passage I16 closed so that the fluid has to flow past the needle valve. When the pressure in the delivery line decreases, as when the pump motor is de-energized, the valve parts are quickly restored to their initial positions by the rapid escape of fluid from the upper part of the valve chamber past the check valve.

While the above illustrative embodiments of the invention have included a pump'and motor as the source of fluid under pressure, it should be noted that it is possible to use other sources and retain advantages accruing from the use of the valves. For instance, the source may well be of any type providing a substantially constant volumetric flow-and certain of the advantages tion is applicable to systems other than hydraulically actuated elevators.

What I claim as new and desire to secure by United States Letters Patent is:

l. A combined start-cushioning and relief valve for use with sources of fluid under pressure, including in combination, a valve chamber, a passage therefrom to said source and to the point of application of the pressure, a by-passage from said chamber capableof by-passing substantially the entire flow of fluid from said source to said chamber, a valve member movable a substantial distance in said chamber from a by-passage closing to opening position, spring means biasing said valve into its by-passage closing position and permitting movement thereof to open said by-passage when said member is initially subjected to a minimum pressure, a piston-like member movable in said chamber to compress and move said spring means and valve member, means including a restricted passage leading from said first-mentioned passage to said chamber at a point on the side of the piston-like member opposite the spring for gradually applying pressures corresponding to those obtaining in said first-mentioned passage to said piston-like member, said last-mentioned means moving the piston-like member together with said valve member and spring in a direction to close said by-passage, whereby the by-passage is gradually closed and the pressure obtaining in said first passage is gradually increased from said minimum to an intermediate value, means for limiting movement of thepiston-like member to an extent such that the spring may be compressed further by said valve member, whereby when the pressure in said first-mentioned passage exceeds a maximum value the valve member is moved against the spring to open said bypassage.

2. A combined start-cushioning and relief valve for use with sources of fluid under pressure, including in combination, a valve chamber, a passage therefrom to said source and to the point of application of the pressure, a by-passage from said chamber capable of by-passing substantially the entire flow of fluid from said source to said chamber, movable valve and piston-like members in said chamber, said valve member being piston-like in construction and having a cross-section area slightly less than that of the piston-like member, a relatively heavy spring located between said members for biasing said valve member in a direction to close said bypassage, means limiting movement of said members in opposite directions, a relatively light spring acting upon said piston-like member in the same direction as the first-mentioned spring to return said piston-like member to its limit position, said first-mentioned spring permitting substantial movement of said valve member to open said by-passage when said valve member is initially subjected to a minimum pressure, means including a restricted passage providing communication from the first-mentioned passage to the side of the piston-like member opposite the springs for gradually applying pressures corresponding to those obtaining in said first-mentioned passage to said piston-like member, thereby rendering said piston-like member capable of compressing and moving the springs and valve of the invention are retained when the source is of the variable flow type. Likewise, the invenmember in by-passage closing direction, whereby the pressure obtaining in said first-mentioned passage is gradually increased from said minimum to an intermediate value, and means for ber, whereby said valve member is movable to.

open the by-passage when the fluid pressure reaches a predetermined maximum value.

.3. A hydraulic lift power system, including in combination, a positive displacement pump having an outlet, a conduit from the pump outlet, a

by-pass from the pump outlet capable oi accommodating substantially the entire output oi the pump, a valve interposed between the pump outmember to a position to close communication between the outlet and by-pass when the pump is inoperative. a relatively light spring acting upon let and the by-pass, spring means biasing the valve to a position to close communication between the outlet and by-pass when the pump is inoperative, the force exerted upon said valve by said spring means being overcome by pressure upon the valve when the pump is placed in op-. eration and the valve is moved to a position to aii'ord communication between the outlet and by-pass when the pressure rises to a predetermined value, whereby the pump is enabled to attain substantially full speed at said pressure, and means including arestricted connection from the pump outlet for gradually increasing the force .acting on. said valve through said 'spring means to move the valve in by-pass closing direction, whereby the b'yvpass is gradually closed and the pump pressure is gradually in creased to a higher value.

4. A hydraulic lift power system, including in combination, a positive displacement pump having an outlet, a conduit from the pump outlet, a by-pass from the pump outlet capable 01' acoommodating substantially the entire output of v the pump, avalve interposed between the pumpv outlet and the by-pass, movable spring means biasing the valve to a position to close communication between the outlet and by-pass when the pump is inoperative, the force exerted upon said valve by said spring means being overcome by pressure upon the valve whenthe pump is placed in operation and the valve is moved to a position to afford communication between the outlet and by-pass when the pressure rises to a predeterdirection to a point where the spring means is capable of being compressed in a reverse direction, whereby said valve is movable from a bypass closing position to a by-pass opening position when the outlet pressure exceeds a maxi mum pressure.

5. A hydraulic lift power system, including in combination, a positive displacement pump having an outlet, a conduit from the pump outlet, a

by-pass from the pump outlet capable of accom-' modating substantially the entire output of the pump, a valve interposed between the pump outlet and the by-pass, said valve comprising a valve chamber, movable valve and piston-like menibers in said chamber, said valve member being piston-like in construction and having a crosssection area substantially equal to that of the,

piston-like member, a relatively heavy spring located between said members for biasing the valve said piston-like member in opposition to 1 the flrst-mentioned spring, the force, exerted upon said valve member by said first-mentioned spring being overcome by pressure upon'the valve memher when the pump is placed in operation and the'valve member is moved to a position to aflord communication between the outlet and by-pass when the pressure rises to a predetermined value, whereby the pump -is-enabled to attain substantially full speed at said pressure, means including a restricted connection from the pump out-- letto the-side oi the piston-like member at which the second spring is located for gradually; increasing the force acting on said valve member through said first spring to move the latter, the piston-like member and the valve member in bypass closingdirection, whereby the by-pass is gradually closed and the pump pressure is gradually increased to a higher value, and means limiting movement of the piston-like member and first spring in said direction to a point where the spring is capable oi! being compressed in a reverse direction by the-valve member, whereby said valve member is movable from a by-pass closing position to a by-pass opening position when the outlet pressure exceeds a maximum pressure.

6. A hydraulic lift power system, including in I combination, a positive displacement pump hava and having a cross-section area slightly less than that of the piston-like member, a relatively heavy spring located between said members for biasing said valve member -to a position to close communication between the outlet and by-pass when the pump is inoperative, means limiting movement of said members in opposite directions, a relatively light spring acting upon said reverse direction by the valve member, whereby piston-like member in the same direction as the first-mentioned spring to return said member to its limit position, the force exerted upon said valve member by said first spring being overcome by pressure upon the valve member when the pump is, placed in operation and the valve member is moved to a-position to afford communication between the outlet and by-pass when the pressure rises to a predetermined value, whereby the pump isenabled to attain substantially full speed at said pressure, means includlimiting movement of the piston-like member and first spring in said direction to a point where the spring is capable of being compressed in a said valve member is movable from a by-pass closing position to a by-pass opening position I 7. A hydraulic lift power system, including in combination, a positive displacement pump having an outlet, a conduit from the pump outlet, a

by-pass from the pump outlet capable of accommodating substantially the entire output oi the pump, a valve interposed between the pump outlet and the by-pass. a piston-likemember and a movable spring located therebetween and the valve for biasing the valve to a position to close communication between the outlet and by-pass when the pump is inoperative, means limiting movement oi the valve'in by-pass closing direction', the force exerted'upon said valve by said spring being overcome by pressure upon the valve when the pump is placed in operation and the valve is moved a substantial distance to a position to afford communication between the outlet and by-pass when the pressurerises to a predetermined value. whereby the pump is enabled to attain substantially full speed at said pressure. means including a restricted connection from the pump outlet to the side of the pistonlike member opposite the spring for gradually increasing the force acting onsaid valve through said spring and piston-like member to move the spring, piston-like member, and the valve in bypass closlng direction, whereby the by-pass is gradually closed and the pump pressure is gradually increased to a higher value, and means lim iting movement of the piston-like member and valve in said direction to a point where the spring is capable of being compressed in a reverse direction and the valve is movable in bypass opening direction a substantial distance without opening said by-pass. whereby said valve is movable from a by-pass closing position to a by-pass opening position when the outlet pressure exceeds a maximum pressure and is movable to absorb pressure pulsations at pressures less than said maximum pressure.

LAWRENCE F. JASEPH.

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