US2958509A

US2958509A - Power balancer

Info

Publication number: US2958509A
Application number: US338012A
Authority: US
Inventors: Walter G Mitchell
Original assignee: Thor Power Tool Co
Current assignee: Thor Power Tool Co
Priority date: 1953-02-20
Filing date: 1953-02-20
Publication date: 1960-11-01
Anticipated expiration: 1977-11-01

Description

NOV. 1, 1960 w M|THELL 2,958,509

POWER BALANCER Filed Feb. 20, 1953 2 Sheets-Sheet 1 INVENTOR.

ZZ/czZfef-G/V BY bmw'a 7 N United States PatentO POWER BALANCER Walter G. Mitchell, Aurora, 111., assignor to Thor Power Tool Company, a corporation of Delaware Filed Feb. 20, 1953, Ser. No. 338,012

12 Claims. (Cl. 254-168) This invention relates to improvements in balancers and more particularly to a novel power driven spring balancer adapted for us as a transfer or material handling device.

Power hoists are commonly used for transferring and handling heavy objects or work pieces during manufacturing operations and the like. The advantage of the power hoist is that it can extend its hook down to the load under power and it can likewise lift the load to any given elevation within its range without appreciable eifort on the part of the operator. However, in many instances it is found that the power hoist has definite disadvantages. For example, with the usual power hoist it is inconvenient and difficult to lift a work piece to an exact location such as would be involved, for example, in placing a crank shaft between centers in a machine.

-With such a device it is difficult to stop the hoist accurately in the required aligned position of the work piece and frequently the centers on the machine are broken or damaged due to accidental contact with the crank shaft when trying to obtain the exact aligned position. These di'fiiculties can be alleviated to some extent by using a high reduction gear mechanism in the hoist so as to provide a slow operating speed. However, from a production point of view a hoist with a slow operating speed is objectionable for obvious reasons.

The spring balancer is a well known device for supporting tools and the like from overhead supports. A balancer of this character generally comprises a drum or reel with a cable windable on the drum and a coil spring connected to the drum for winding the cable on the drum in order to raise the tool or other load attached to the cable. The tension of the spring is adjustable so that the tool or load may be counterbalanced and suspended at the desired elevation. Thus, the operator of the tool can raise, lower, and otherwise handle the tool without supporting its full weight. With a spring balancer of this type it is possible to locate the load with some degree of accuracy.

However, one of the difficulties with the spring balancer arises from the fact that if the spring is adjusted to counterbalance a given load at a given elevation, the operator in order to attach the balancer cable to the load must pull the cable down to the load or the floor which requires a substantial effort on the part of the operator. For example, if the device is adjusted to counterbalance a 100 lb. load, it will require substantially a 100 lb. pull on the part of the operator to move the cable hook downwardly in order to attach the same to the load. As a result of this inherent defect, the use of spring balancers has been confined largely to supporting relatively light weight tools which remain attached to the balancer and which are not hooked or unhooked from the balancer except at infrequent intervals. Consequently, the inherent limitations of the spring balancer have kept it from being employed to any large extent as a transfer or material handling device.

Another objection often associated with the use of a 2,958,509 Patented Nov. 1, 1960 spring balancer is that an extremely strong coil spring is necessary for retraction of the cable and in some instances the extended cable may be retracted with whiplike speed upon release of the load, the resultant backlash creating a serious hazard for the operator.

Accordingly, a primary object of my invention is to provide an improved balancer capable of use as a transfer and material handling device and not subject to the aforementioned disadvantages of the power hoist or the conventional spring balancer as heretofore known.

Another object of the invention is to provide a novel combination of a power device and a spring balancer whereby the cable of the balancer can be withdrawn from the reel and engaged with a load and the load positioned thereafter at a precise elevation without substantial effort on the part of the operator.

A further object of the invention is to provide a novel balancer which is power actuated in one direction of operation and spring actuated in the opposite direction.

An additional object of the invention is to provide a novel spring balancer having power means for extending the balancer cable and also having means for preventing dangerous backlash during retraction of the cable.

Still another object of the invention is to provide a novel spring balancer having pneumatic power means and novel control means for regulating the extension and retraction of the balancer cable.

Another object of the invention is to provide a novel combination of a balancer cable and a manually operable control means such that the control means can be readily and conveniently manipulated by the operator during Withdrawal of the cable and attachment thereof to a load.

A still further object of the invention is to provide novel control means for a power actuated spring balancer.

Other objects and advantages of the invention will become apparent from the subsequent detailed description taken in conjunction with the accompanying drawings wherein:

Fig. 1 is an end elevational view of a device comprising one specific embodiment of my invention;

Fig. 2 is a side elevational view of the device as seen substantially along the line 22 of Fig. 1;

Fig. 3 is a transverse sectional view taken along the line 3-3 of Fig. 1;

Fig. 4 is a cross-sectional view taken substantially on the line 4--4 of Fig. 1;

Fig. 5 is a fragmentary sectional view taken along the line 55 of Fig. 3;

Fig. 6 is a fragmentary cross-sectional view taken along the line 66 of Fig. 5; and

Fig. 7 is a fragmentary sectional view taken along the line 7-7 of Fig. 5.

Referring first to Figs. 1, 2 and 4, the device consists broadly of a spring balancer section A, a pneumatic power section B, and a manual control section C. The spring balancer A includes a drum or reel, indicated generally at 11 (Fig. 4), which is mounted for rotation on a shaft 12 journaled in a housing or casing designated generally at 13. The casing 13 comprises a main or body section 14 fitted around the drum 11 and a removable cover section 16 detachably secured to the body section 14 by a plurality of cap screws 17.

The drum 11 comprises a hollow dish-like member 18 having a tapered peripheral portion 19 and provided at its exterior with a spiral groove 21 adapted to receive a cable 22. The cable 22 has its inner end (not shown) secured to the larger end of the drum in the terminal convolution of the spiral groove 21. The outer end of the cable 22 extends downwardly from the drum casing and is equipped with a hook 23 (Fig. 1) or equivalent means whereby a tool or other load may be removably attached to the cable.

A coil spring 24 (Fig. 4) is provided in the interior of the drum for urging the drum in a direction to wind the cable 22 thereon. The other end (not shown) of the spring 24 is anchored to the drum in any suitable manner, and the inner end of the spring 24 is anchored to an axial sleeve 26 which is keyed to the shaft 12 for rotation therewith. A cover plate 27 is secured over the open end of the drum section 18 by means of a plurality of cap screws 28 whereby to enclose the spring 24.

It will be understood that the drum 11 is rotatable with respect to the shaft 12 and the anchor sleeve 26, a pair of suitable

anti-friction bearings

29 and 31 being mounted in the cover plate 27 and the drum section 18, respectively, for rotatably supporting the drum. The end portions of the shaft 12 are journaled in the

casing sections

14 and 16, as at 32 and 33, respectively. It will also be understood that the shaft 12 is normally held against rotation, in this instance by means of a worm gear assembly which also provides an adjustment for the tension of the spring 24. Thus, a worm gear 34 is secured to one end of the shaft 12, and a worm pinion 36 is journaled in the casing section 14 in operative engagement with the worm gear 34. One end (not shown) of the worm pinion 36 is accessible from the exterior of the drum casing to permit turning of the shaft 12 in order to Wind up the spring 24 and thereby adjust its tension.

The balancer casing 14 is also equipped with a book 37 (Fig. 1) or equivalent means for suspending the device from an overhead support. A spring retainer or keeper ring 3% is also provided around the periphery of the coil spring 24 for preventing inadvertent unwinding or displacement of the spring, particularly when removed from the casing, the keeper ring 38 being secured in place by means of a pin 39 extending through the ring 38 (Fig. 4) into the drum section 1-8 and the cover plate 27.

As thus far described, the spring balancer section A of my device will be understood to operate in the manner well known in the spring balancer art. In other words, the coil spring 24 when tensioned urges the drum 11 in a direction to wind up the cable 22 on the drum, and the cable may be unwound or extended from the drum by rotation of the latter in the opposite direction against the action of the spring. By means of the worm gear mechanism 3436, the spring 24 may be regulated to any predetermined tension for counterbalancing a given load at a given elevation. However, my invention differs greatly from the conventional spring balancers in the manner of effecting rotation of the drum for unwinding the cable. As hereinbefore mentioned, with a conventional spring balancer the operator must exert a downward pull on the cable with substantially as much effort required as would be necessary to lift the load without the aid of a spring balancer since the pull of the operator must be great enough to overcome the predetermined tension of the balancer spring. However, in the present invention although the cable drum is rotated by spring action in the usual manner for winding or retracting the cable, I employ a power device, and particularly a pneumatically actuated power device, for eifecting reverse rotation of the drum in order to unwind or extend the cable.

The power section B comprises in this instance rotary pneumatic motor 41 of a conventional type, for example, a pneumatic motor of the type having an eccentric rotor with radially siidable vanes. Inasmuch as the details of the pneumatic motor construction form no part of the present invention, a further description of the motor 41 is not necessary. The motor 41 is disposed adjacent the upper portion of the balancer casing 13 and is mounted thereon by means of a transmission or gear housing 42 secured at its opposite ends to the balancer casing and to the motor casing. For operatively connecting the motor 41 to the drum 11, the drum cover plate 27 has gear teeth, indicated at 43 (Fig. 4) formed integrally around its periphery, and suitable gear connections are provided between the gear teeth 43 and the motor 41. In this instance, the gear connections include a pinion 44 carried on the end of the motor drive shaft and a connecting shaft 46 journaled in a pair of suitable bearings 47 and 48 which are mounted in the gear casing 42. The shaft 46 extends into the balancer casing 13 through an opening in the upper portion thereof, and gear teeth 49 are formed integrally with one end of the shaft 46 for meshing with the pinion 44. A pinion 51 formed integrally at the other end of the shaft 46 meshes with the gear teeth 43 on the drum. It will be understood that the motor 41 and the gear connections are so arranged that when the motor is pneumatically operated in the usual manner, the drum 11 will be rotated against the action of the spring 24 in a direction to unwind the cable 22 from the drum. It will, therefore, be seen that regardless of the tension of the spring 24 and even at a high degree of spring tension, the cable can be unwound from the drum simply by setting the motor 41 in operation and without any substantial effort on the part of the operator.

When the cable is being unwound from the drum in order to secure the hook 23 to a load, it will be apparent that the operator must grasp the end of the cable and the hook 23 in order to carry out the necessary fastening. However during this time it is also necessary for the operator to control the operation of the pneumatic motor 41 so that the cable may be withdrawn to the required extent. Consequently, an important feature of my invention is the provision of a novel control means having its operating portion carried adjacent the outer end of the cable so that the operator may conveniently carry out the required simultaneous manipulation of the motor control and the fastening of the cable to the load. The control section C for accomplishing this objective will now be described in detail.

The control device comprises a valve structure having an upper valve portion 52 and an elongated handle portion 53 (Figs. 1 and 2) depending integrally from the valve portion 52. The valve portion 52 is offset laterally with respect to the handle portion 53, and the latter is provided with an axial bore 54 (Fig. 5) through which the outer end portion of the cable 22 extends whereby the control device is carried on the cable. The control structure is retained in position adjacent the outer end of the cable 22 by means of a pair of retainers in the form of U-bolts 56 clamped to the cable 22 above and below the control structure. Shock absorbing elements are disposed intermediate the retainer clamps 56 and the opposite ends of the control structure, the shock absorbing elements in this case being shown as a pair of balls 57 of rubber or other resilient material threaded on the cable 22.

Referring now particularly to Figs. 5, 6 and 7, the valve portion 52 of the control means comprises a valve body 58 having a transverse central bore 5h which is provided with a sleeve or liner 61 having a pair of diametrically

opposed ports

62 and 63 and another port 64 disposed adjacent the port 63. A plug 66 is threaded into the valve body 58 adjacent one end of the bore 59 for closing the same. A plunger type valve member, indicated generally at 67, is shiftably disposed within the sleeve 61 and is formed with a pair of longitudinally spaced

enlarged portions

68 and 69 with a reduced spool portion 71 therebetween. An axial recess '72 is provided in the end of the enlarged valve portion 69, and a helical compression spring 73 has one end received within the recess 72 and its opposite end abutting the plug 66 for normally urging the valve member 67 into closed posi tion relative to the

ports

62 and 63, as shown in Figs. 6 and 7.

For shifting the valve member 67 to open position, an operating element or projection '74 extends outwardly from the opposite end of the valve member through the adjacent end of the sleeve 61. An operating lever 75 is pivoted to the valve body, as by a pivot pin 76 (Fig. 5 extending through an integral upright ear or lug 77, and the lever 75 operatively engages the outer end of for introducing air to the motor.

the projection 74. A manually operable extension 78 depends from the lever 75 adjacent the handle portion 53 for convenient manipulation by the operator. It will readily be understood, from Fig. 5 in particular, that when the extension 78 is moved toward the handle 53, the valve member 67 will be depressed inwardly against the action of the spring 73. The valve member 67 is retained within the valve body 58 by means of a transverse pin 79 mounted in the outer end of the sleeve 61 and extending through an elongated slot 81 in the projection 74. Pivotal movement of the lever 75 is limited by means of a pin 82 extending from the ear 77 into an arcuate slot 83 provided in one of a pair of side flanges 84 on the lever 75.

The valve body 58 is also provided with suitable internal passages for admitting air to and discharging air from the valve structure. Thus, I provide a vertical bore 86 (Fig. 7) constituting an air inlet which merges with a horizontal bore 87 in alignment with the port 62. For convenience of manufacture, a lateral bore 88 (Fig. 6) also intersects the

bores

86 and 87 but in normal use of the device this passage is closed by means of a threaded plug 89. An air outlet from the valve structure is provided by means of a horizontal passage 91 in alignment with the port 63 and a communicating vertical bore 92.

For a purpose hereinafter described, the valve body 58 is also formed with a relatively small bleed or vent passage 93 (Fig. 6) communicating through the port 64 with the spring chamber and opening into the atmosphere exteriorly of the valve structure. Flow communication between the

ports

63 and 64 is established through the recess 72 and a radial slot 94 extending through the valve portion 69 into the recess 72. An adjusting element in the form of a set screw 95 extends transversely into the passage 93 for adjusting the size of the bleed or vent opening.

As shown in Figs. 1 and 2, air or other operating fluid is admitted from a suitable supply source through a conduit including a length of flexible hose 96 to the inlet passage 86 of the valve structure. A similar length of flexible hose 97 extends bewteen the suction side of the motor 41 and the outlet passage 92 of the valve structure It will be understood that the

hose sections

96 and 97 are sufliciently long to accommodate full extension or unwinding of the cable from the drum. As best seen in Fig. 6, when the valve member 67 is in its outermost position under the influence "of the spring 73, the enlarged valve portion 69 is interposed between the inlet port 62 and the outlet port 63 so as to prevent the passage of air through the valve means to the motor. However, when the valve member 67 is depressed into its innermost position by manipulation of the lever 75, the

ports

62 and 63 will be placed in flow communication around the spool portion 71 of the valve so that air can pass through the valve structure into the motor for operating the latter and thereby unwinding the cable. In this open position of the valve member 67, the radial slot 94 of the enlarged valve portion 69 is out of communication with the port 63 so that air cannot enter the bleed passage 93 during normal operation of the motor.

The handle portion 53 of the control device provides a convenient grasping means by which the operator can manipulate the end of the cable into the desired position for attachment to a load. At the same time, the operator while grasping the handle 53 can manipulate the lever extension 78 by means of his thumb so as to obtain accurate control over the operation of the pneumatic motor 41 and the resultant unwinding of the cable. Inasmuch as the air control for the motor operation is disposed immediately adjacent the end of the cable which the operator must manipulate to attach the same to a load, it will be apparent that the device is extremely convenient and simple in its operation.

Another highly important advantage of my invention resides in the provision for avoiding excessively rapid retraction of the cable and the hazard attendant upon undesirable backlash. Because of the fact that the drum 11 is directly connected to the motor 41 by the geared connections hereinbefore described, it will be evident that when the air supply to the motor is cut off by release of the valve operating lever 75, the subsequent reverse rotation of the drum 11 under the influence of the tensioned spring 24 will also cause reverse operation of the pneumatic motor 41. Consequently, during such reverse operation the motor 41 functions as a compressor drawing air in from its exhaust ports and discharging the same through the hose 97 into the valve means 52. At this time the valve member 67 is in closed position relative to the main air inlet and

outlet ports

62 and 63, as seen in Figs. 5 and 6. However, in order to permit venting of the compressed air from the hose 97 during reverse operation of the motor 41, the radially extending slot 94 of the valve portion 69 provides flow communication between the

ports

63 and 64, as hereinbefore described. Thus, as seen in Fig. 6, compressed air may freely pass in reverse fashion through the

air outlet passages

92 and 91, the port 63, the slot 94, and the recess 72 into the interior of the sleeve 61 and thence through the port 64 and the bleed passage 93 into the atmosphere. By regulating the adjustment of the set screw 95, the rate of venting of compressed air from the motor 41 can be readily controlled so that the reverse rotation of the drum 11 during retraction or winding of the cable can be regulated for any desired safe speed and without danger of hazardous backlash of the cable when the load is detached.

The operation of the device may be briefly summarized in the following manner. In its rest position, the cable is normally retracted or wound on the drum and thus the handle portion 53 is in elevated position. When it is desired to utilize the device, the operator reaches up and grasps the handle portion 53 and then manipulates the operating lever 75 by thumb pressure on the extension 7 8 to admit air through the valve structure to the motor whereby the cable is unwound with no effort on the part of the operator and at any desired speed within the operating range of the motor. As the cable is thus Withdrawn, the operator still grasping the handle portion 53 attaches the hook 23 to the load and then releases the valve operating lever 75 whereby to cut off the supply of air to the motor. With the motor thus at rest, the tensioned spring 24 causes the drum to rotate in the opposite direction so as to retract the cable and lift the load to the desired elevation as determined by the predetermined setting of the spring 24. If slight adjustment of the load to a precise elevation is thereafter required, the operator may accomplish this manually with little effort. Retraction of the cable is accomplished at a completely safe speed without the possibility of dangerous backlash by reason of the reverse operation of the motor 41 in response to spring actuated rotation of the drum 11. During reverse operation, the motor 41 acts as a compressor or brake and the discharge of compressed air is controlled by means of the adjustable bleed passage 9395 in the valve structure so that the rate of retraction of the cable is under complete control at all times.

Because of the fact that my invention as dmcribed above completely eliminates the necessity for great effort on the part of an operator in extending the balancer cable, the device is highly useful for transfer and material handling operations which were not heretofore feasible with the conventional spring balance-r. In addition, the device retains all of the advantages of the spring balancer in accuracy and speed of operation. Moreover, by means of the use of a pneumatic motor and the control means described above, my invention obviates one of the most objectionable hazards heretofore associated with spring balancers, namely, the possibility of dangerous backlash during retraction of the cable.

Although the invention has been described above with particular reference to certain specific structural embodiments, it will be understood that various modifications and alternative constructions may be resorted to without departing from the scope of the invention as defined in the appended claims.

I claim:

1. A power balancer comprising a rotatable hollow drum, a cable windable on the drum, spring means inside the drum for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a detachable cover plate secured to the drum at one of its axial ends, said cover plate being formed with gear teeth at its periphery, a motor, and gear connections between the motor and said gear teeth whereby unwinding of the cable from the drum is effected by operation of the motor.

2. A power balancer comprising a housing, a hollow drum rotatably mounted within said housing, a cable windable on the drum, spring means inside said drum for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a detachable cover plate secured to said drum at one of its axial ends, said cover plate being formed with gear teeth at its periphery, a motor mounted adjacent said housing, said housing having an opening adjacent said gear teeth, a gear casing secured to said motor and to said housing around said opening in the latter, and driving connections within said gear casing including a shaft operatively connected at one end to said motor and extending at its other end through said opening into operative engagement with said gear teeth for effecting unwinding of the cable from the drum by operation of the motor.

3. In combination, a cable adapted to have one end thereof secured to a load, operating means for extending and retracting the cable and including a pneumatic motor, manually operable valve structure for controlling the supply of air to said motor, an elongated handle having the cable extending axially therethrough, said handle supporting said valve structure, retainer means secured to the cable at opposite sides of said valve structure and said handle for fastening the valve structure and the handle on the cable, and shock absorbing elements carried on said cable intermediate said retaining means and said valve structure and handle.

4. A power balancer comprising a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a rotary pneumatic motor operatively connected to the drum for unwinding the cable from the drum, means for supplying air to the motor to eifect unwinding of the cable, said motor being operable in reverse direction in the manner of a compressor by the action of said spring means during winding of the cable on the drum, and bleed means for controllably discharging compressed air from said motor during reverse operation thereof whereby said motor acts as a brake during winding of the cable on the drum and excessively rapid retraction of the cable is thereby avoided.

5. A power balancer comprising a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a rotary pneumatic motor operatively connected to the drum for unwinding the cable from the drum, control valve structure having an air inlet, an air outlet, and an air vent, means for supplying air to said inlet, means for supplying air from said outlet to said motor to effect unwinding of the cable, said motor being operable in reverse direction by the action of said spring means during winding of the cable on the drum, a movable valve member in said valve structure operable to permit air flow from said inlet to said outlet, and means in said valve structure providing flow communication between said outlet and said vent and permitting controlled bleeding of air from the motor during reverse operation thereof whereby said motor acts as a compressor during winding of the cable on the drum and excessively rapid retraction of the cable is thereby avoided.

6. A power balancer comprising a rotatable drum, 2. cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a rotary pneumatic motor operatively connected to the drum for unwinding the cable from the drum, control valve structure having an air inlet, an air outlet, and an air bleed passage connectible with said outlet, conduit means communicating with said inlet for supplying air to said valve structure, and conduit means connected between said outlet and said motor for supplying air to the motor to effect unwinding of the cable, said motor being operable in reverse direction by the action of said spring means during winding of the cable on the drum whereby said motor acts as a compressor during said reverse operation and air is controllably discharged through said last-named conduit means and through said bleed passage for avoiding excessively rapid retraction of the cable.

7. The device of claim 6 further characterized in that said bleed passage is provided with an adjusting element for controlling the venting of air therefrom.

8. A power balancer comprising a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a rotary pneumatic motor operatively connected to the drum for unwinding the cable from the drum, means for supplying air to the motor to effect unwinding of the cable, said motor being operable in reverse direction by the action of said spring means during winding of the cable on the drum, and control valve means for controlling the flow of air to the motor and for regulating the discharge of air from the motor during the reverse operation thereof, said valve means comprising a valve body having an inlet and an outlet, a movable valve member interposed between said inlet and said outlet, and means in said valve body defining a bleed passage connectible with said outlet for controllably venting air from said motor through said bleed passage to the atmosphere during reverse operation of the motor and when said valve member is in closed position relative to said inlet and said outlet, said motor thereby acting as a compressor during winding of the cable on the drum for avoiding excessively rapid retraction of the cable.

9. In combination, a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a pneumatic motor operatively connected to the drum for unwinding the cable from the drum, and manually operable control valve means for controlling the flow of air to the pneumatic motor and for regulating the discharge of air from the motor during reverse operation thereof, said valve means comprising a valve body with an inlet and an outlet, a movable valve member interposed between said inlet and said outlet, said valve body also having a separate bleed passage communicating with the atmosphere for venting air from said outlet to the atmosphere when said valve member is in closed position relative to said inlet and said outlet, and adjustable means in said bleed passage for controlling the venting of air therefrom.

10. In combination, a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a pneumatic motor operatively connected to the drum for unwinding the cable from the drum, and manually operable control valve means for controlling the flow of air to the pneumatic motor and for regulating the discharge of air from the motor during reverse operation thereof, said valve means comprising a valve body having an inlet and an outlet, a movable valve member interposed between said inlet and said outlet, spring means normally urging said valve member into closed position relative to said inlet and said outlet, and manually operable means for shifting said valve member to open position, said valve body also having a bleed passage communicating with the atmosphere, and said bleed passage being adapted to be sealed by said valve member when the latter is in open position to permit air flow between said inlet and said outlet and said bleed passage also being adapted to be placed in flow communication with said outlet through said valve member when the latter is in closed position for preventing the flow of air from said inlet to said outlet.

11. In combination, a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a pneumatic motor operatively connected to the drum for unwinding the cable from the drum, and manually operable control valve means for controlling the flow of air to the pneumatic motor and for regulating the discharge of air from the motor during reverse operation thereof, said valve means comprising a valve body with a central bore and having inlet and outlet passages communicating with said bore, a shiftable valve member in said bore movable between open and closed positions relative to said inlet and outlet passages, said valve body also having a bleed passage communicating between said bore and the atmosphere and said valve member having an axial recess at one end thereof, and a spring member received Within said recess and coacting with said valve member for normally urging the latter into closed position for preventing the how of air from said inlet passage to said outlet passage, and said valve member also having a radial opening extending into said recess whereby to provide flow communication from said outlet passage through said opening, said recess, and said bore to said bleed passage when the valve member is in closed position.

12. A power balancer comprising a rotatable drum, a cable windable on the drum, spring means for winding the cable on the drum, said spring means having one end anchored and its other end connected to said drum for rotation therewith, a pneumatic motor operatively connected to the drum for unwinding the cable from the drum, control valve structure for controlling the supply of air to said motor, an elongated handle supporting said valve structure, said handle being disposed at the outer end of said cable with the cable extending axially therethrough, a movable valve operating member connected to said valve structure and adapted to be manipulated by the hand of an operator while grasping said handle, means for supplying air to said valve structure, and means for supplying air from the valve structure to said motor.

References Cited in the file of this patent UNITED STATES PATENTS 966,601 Rosenfelt et al. Aug. 9, 1910 2,072,582 Douglass Mar. 2, 1937 2,094,182 Nash Sept. 28, 1937 2,254,935 Darling Sept. 2, 1941 2,457,930 Smith Ian. 4, 1949 2,574,131 Steinbrecher Nov. 6, 1951 2,600,887 Lannen June 17, 1952 2,680,004 Herker June 1, 1954 FOREIGN PATENTS 297,273 Great Britain Sept. 20, 1928 717,181 Germany Feb. 9, 1942