US954401A - Fluid-actuated balanced hoist. - Google Patents

Description

G. F. STEEDMAN.

FLUID ACTUATED BALANCED HOIST.

APPLIGATION FILED MAR. 1, 1909.

954,401 Patented Apr. 5, 1910.

I 2 SHEETS-SHEET l. in @l/ l Nm?? sneed-pressure a1 which the a citizen of the' suchias will enab to 'which it appertains to make and u Same.

UNITED STATES PATENT QFFICE.

GEORGE F.' STEEDMAN, OF BT. LOUIS, MISSOURI.

FLUID-Activeren BALANGED noIsT.

Specification of Letters Patent. Application ledMarch 1, 1909.

Y To all whom 'it may' concern:

Be it known that I, Y

-United States, residing at a certain Fluid-Ao, of which the followl d exact description,

le .others skilled. in the artA have invented oists,

Patented Apr. 5, 1910.

Serial No. 480,660.

GEORGE F. STnnDMAN,

se the Figure 1 isavertical sectional view of a huid-actuated balanced hoist invention Fig. 2

view of the controlling valve for same; Fig. 3

taken on approximately th 2, the valveV being shown'in embodying my is a detail vertical sectlonal is a vertical and the casing sectional view e line 3-3 of\Fig. elevation and in its neutral osition; Fig. 4 is a view similar to Fig. 3 s ering' position owing the namely cu ies when the load is 5 1s a view similar to valve in its f hoisting position valve Yin its the position it oceing lowered; Fig.` Fig. 3 showing the namely), .the

eine

position'it-oocupies when the load is a VVconra-sedi; Fi trolling va i that shown in Fi a construction in are employed for dinm and balancing med ."6 isa ve of slightly detail -view of g. 2 an which lowdifferent form from d Fig. 7 illustrates tviseparate valves controlling the motive melllm.

`This V invention relates to fluid-actuated hoists,l f and is thatY type' in stantly'iadmitted an impr r hosts; namely,

ovement u on bal- 'mists of air pressure 1s conto one side 'of' theepiston and is admitted to and exhausted fromthe opposite 'side of the `piston by means of an operatng" valve.

vIn

the ordinary balanced pressure air hoists the compressed air that constitutes the motive force of constantly connected to of I the cylinder constitutes the der '-to rsuse the inwardly.

balancing force is admitted to the opposite end` to cause p The balanced-pressure ai the Vhoist is directly and the stuffing-box and compressed end a1r',-.whi c i of the hoist, of the cylinpiston to move outwardly the piston to merg; r hoist...

-. is much'snore .positive in its movementthan the si leacting the stu )acted .t9 P

move mwardly,and pressure permit said piston 4rod to move of the `cylinder being the.b oV posite eind stent y connectedT boxA Vend of ressure tol cause the to the atmosphere.-V

lain air hoist inwhich the cylinder issublpiston rod to 1s exhaustedto' outwardly,

GOD-

single-actin controls eit er the inflow or egress of compressed air from only one side of the piston, the other side of the piston bein under no pressure. When the load is raise part way by admitting pressureunder the piston and the operating valve is then central or neutral position, the inward or .upward acting force of the compressed air balances the outward or downward acting force on the piston `and the piston will remain in this position so long as these two forces remain equal. As soon as the equilibrium of these forcesis destroyed, however, the piston will move until the equality of the opposing forces acting on it is again attained. As the upper end of the cylinder is in constant communication with the atmosphere there is no restraining force on the upper side of theV piston.

In the s ingleacting hoist the motion of thepiston is under relatively. poor, control for when the .valve is acting it controls but a single force and the load is supported by a single force; Consequently, any change lin the load or the pressure that supports the 'load causes a relatively lar e and quick motion of the piston and the oad.. In the balarmed-pressure air hoist the constant pressurev or motive `force on the-stulng-box side of the piston is resisted by avariable pressure or balancin force on the op `osite side of the piston so t at the load is he d between tworesisting or balancingpressures. The constant pressure of the reservoir jonthe 'enter or vleave the cylinder through a In crate-sized pi and no motion of the lpiston can ordinari y be made except by t e inward or outward flow of this pressure air,

'valve controls the rapidity ci admission or veach opposing and balancing the other so that the motion ofthe balanced-pressure air hostlismuch more positive and under better .lonirol than the motion of the single-acting `In my prior patent No. 840,876, dated January 8, 1907, -jI Vhave shown meansefor more positivelyre lating the motion, of air hoists consisting o speed-regulating devices that are. independent of the operating valve, and the .object of my present mventlo'n is to rstill fur-ther perfect the control pressure airhoists. I accomplish `this by brought to its' stuing-box end of the cylinder can ogg' and on the opposite side othe piston the of balancfal-4 air hoists the operatingfvalve v exhaust. -Two forces are constantly present,

' y governin controlling the ingress and e ress of the compressed air that constitutes the motive force, and also controlling the admission and ex' haust of the compressed air from the variable pressure side of the piston, gaining thereb great steadiness 'of motion and goo contro and controlling the motive force as wel as the resisting force or ba`1 ancin force.

In i e balanced-pressure air hoists heretofore in use the constant pressure end of the cylindei` is in direct communication with the compressed air supply and any variation in the pressure of the air su ply extends to the constant pressure end o the cylinder irre-4 s ective of the operating valve so that if tiie load is suspended intermediate the two limits of movement 'of the piston and the operating valveis in its central or neutral position any change in the ressure of the compressed air supply will c ange the force acting o'n the lower side of the piston and dest-ro the equilibrium of -the hoist forces and t e piston will move until the forces i are again equalized. This' movement of the piston when the operating valve is in its neutral position, due to variationsof the air supply pressure, is an objectionable feature of the Balanced-pressure hoists heretofore in use, and a further object of my invention is to .provide a balanced-pressure air hoist which is so constructed that changes of pressure in the'l compressed air suppy will Other objects and 'desirablel featuresof my invention will be liereinafter"pointed out.

Referring to the drawings which illustrate the preferred form of my invention, 1 designates aj cylinder having a iston 2 reciprocatingly mounted therein, t e rod 3 of said piston projecting ,through the lower end of the cylinder and being adapted to have a Pipes 4. and lead load 'connected thereto.4 into the upper and lower ends, respectively, of the cylinder 1, and said pi es are connect` ed to a valve casing 6 in whic an oscillati valve A is arranged, the valve seat of sai casing being providedwith ports 4 and 5 with which the pi 'es 4 and 5 communicate. A ipe 7 that lea sifrom` asupply offiuid un er pressure, preferably com ressed air, communicates with the seat of the Vcasin -6, an an "exhaust pipe 8 leads from an ex aust port 8' in said casing, as shown in Fig. 2, t e vided with acheck valve 14. `The va ve .A has a .chamber or duct '9 that establishes communication between the exhaust pipe 8- designed that a blank plortion thereof covers c the port 4, with whi `the pipe 4 communicat'es, when the valve is in its neutral position, as shown in Fig. 3, said valve also being provided with a blank wing 10 that closes the ort 5 when it is in its neutral position. he valve A never closes the port 70 7 with which the supply pi e 7 communicates so that the interior of tiie valve casin is always in direct communication with the supply of compressed air. ,y

An operating lever 11 is connected to the 75 stem o the valve A for turning it, and when said valve is in its neutral position, as shown in Figs. 1 and 3, the pi es that vlead to the upper and lower ends o the cylinder will be cut off from the su ply of com- 30 pressed air and the piston wi Abe locked or eld at rest, the lever 11 assuming an approximately horizontal position at such times. When the lever l1 is shifted in anticlockwise direction `,from its neutral .posig5 tion, shown in'Fig. 3 the iston `will move toward the upper end of t e cylinder, and when saidA lever is shifted in the opposite direction the iston will move toward the lower end oftlie cylinder. `When the valve A is in its lowering osition, as shownr in F' 4, the, port 7 fliiom` the supply pipe and the ports 4al and 5* from the pipes that,

' lead to theupper and lower ends of the cylinder,wil1 `be o en so that .compressed air g5 will be admitte on top of the piston until the downward forces Iare greater than the resisting forces and the piston is thus caused to move downwardly, the compressed air in the lower end of the cylinder` being forced out through the poi't 5i and into the general supply through the port 7'* or into the upper end of theAY cylinder through the ort 4*.

When it is desired to Vraise the load t e valve A is turned' into its hoisting osition, as105 shown in Eig. 5,A so as to brin t e chamber 9 therein into alineiiient with t e port 4 for the pipe that leads to the upper end of theA cylinder and thus permit the air on the upper sideof the cylinder to exhaust through the pipe 4 and the pipe 8, the ressure fluid or motivefforce being admitte to the lower side of the piston through port, and pipe 5 and thus causing the piston to move up- Wal'dly. 115

I f it is desired to sto theipiston at some point intermediate its imits of travel, the

valve A is turned into its neutral position,

as shown in Fig. 3, so vas to simultaneously close the ports 4 and 5*. for the pipes that 120 lead to the upper and lower ends of the cylinder. The air on both sidesof the piston will -thus be trapped or out off from the source of supply so that the piston will come to rest and remain in this position until the load yis changed or the valve A is turned to uncover the ports 4which it closes.

If the load on the iston is diminished the piston will move slrliwly toward the upperv end of the cylinder until the air on the up- 13or rside of the piston has suiiiciently and the air on the lower side of the piston has ex anded enough to again make a balance an thus compensate for the weight of that portion of the load which is removed. For example, if the hoist is be ing used for raisin a, ladle of molten metal ,that is to be pour to form a casting, when the ladle arrives in the position at which it is desired to tilt same, the valve is turned into its neutral ition, as shown in Fig. 3, and when the adle is tilted to discharge some of the metal therein and thus diminish theload on the piston, the piston will move upwardly a vslight distance until the air on the upper side thereof has been compressed suiciently and the air on the lower side has expanded sufficiently to renew a balance or to oilset or compensate for the weight of the .metal that has been poured out of the ladle, the piston comin to rest'and remaining in this position unti the load is again reduced Vor the valve is turned. The load can be raised higher by .turning the valve into its hoisting position, as shown to relieve the balancing pressure or force on the upper side of the piston, and when it is desired to have the piston move downwardly the valve is turned into its lowerino position, as shown in Fig. 4, so as to simultaneously open the ports 4 and 5, thus (permitting the air to flow into the upper en of the cylinder so as to force the piston downwardly against the pressure under it, and also torce the air in the lower end of the cylinder back into the pressure-su ply system or into the up er end of the cy inder.

1he hoist is preferably provided with speed-regulating valves similar to those described in my prior patent No. 840,876, previously referred to, said valves bein mounted in valve casings 12 and 13 arrange( in the ipes 4 and 5, respectively. The casing 12 is rovided with two check valves 12a and 12 t at open in opposite directions, as indicated by the arrow in Fig. 1, and the casing 13 is provided with two check valves 13a and 13b that open in opposite directions, but as said regulating Valvesform no part of my present invention, a detailed description of same is not deemed necessary.

The main advantage of an air hoist of the principle above described is that the motion of the piston is well controlled while the valve is open, and the piston is not affected by external changes when it is intermediate its ends and the controlling valve is closed.

In order to secure the best control of the speed of hoisting or lowering when the valve is open I prefer to use a valve of the Jform shown in Fig. 6, wherein the orts are long and narrow. Said valve is opsiibstantially the same construction as the valve shown in Fig. 2, and comprises a movable part A* that coperates with ports in the casing 26,

been compressed casing, and pipes in Fig. 5, so as said part having a duct Q9. A supply pipe QT communicates with a port 27 in said 2i and 25 lead from ports 24a and 25a in said casing to the upper and lower ends of the cylinder. An exhaust pipe 28 leads from an exhaust port 28 in said casing, and the movable part A of the valve is provided with a blank wing 2O that controls the passage of the motive medium through the port 25B. In a valve of this construction a small opening of the port 24* to admission or exhaust is accompanied by a correspondingly small uncovering of the port 25", so that the ingress or egress of air from the upper part of thc cylinder is oontrolled simultaneously with the flow of air from and to the lower end of the cylinder. A larger opening of the upper port 24. would likewise be accompanied by a large opening of the lower port 25a.

Another great advantage of the hoist above described over the balanced-pressure hoists heretofore in use is that it is much stea dier under variable loads when the valve is closed or in its neutralposition, as shown in Fig. 3. In the balanced-pressure air lioists heretofore in use the constant prcssure'end of the cylinder communicated at all times with the source of air supply that constituted the motive force, and a diminished load would lieaccompanied by an upper movement of the piston until the air above the piston was compressed sufficiently to restore the balance, the air under the piston remaining at constant pressure. lith my improved hoist the movement of the piston under the same conditions would be less because the air is entrapped in both ends of the cylinder and a diminished load would be accompanied by a compression of the air onl the upper side of the pistou and an expansion of the air on the lower side of the piston, thus causing equilibrium to be established with a less movement. of the piston as the moving force decreases as thc piston' moves, and the opposing force increases simultaneously.

In Figs. 1 to 6, inclusive, I have shown a single valve combining the functions of controlling tl'ie exhaust and admission of air to the upper part of the cylinder, and the ingress and egress of the air to the lower art of the cylinder. It` is obvious, however, that these two functions can bc carried out by separate valves l0 and 50, as shown in Fig. 7. In this construction the supply pipe 41 leads to a pipe that communicates with the casings of said valves, and a pipe 4Q leads from the casing of the valve 40 tothe upper end of the cylinder, the casing of the valve 50 being connected with the lower end of the cylinder by means of a pipe 43, and the casing of the valve 4() being provided with an exhaust pipe 44. The valve 4() is provided with a duct 40 that establishes communication between the supply pipe and the pipe 42 that leads to the upper end of the cylinder and also establishes communieation between said pipe 42 and the exhaust pipe LH. The valve 50 is merely provided with a port 50a that. permits the motive medium to pass into or exhaust from the pipe 43 that leads to the lower end of the cylinder, These valves 40 and 50 can be operated by two men or the hands of one man, or the stems of the valves could be connected, as, for example, by a rod 45 fastened io arms in' on the stems so that both valves would move when the operating means 47 was actuated. In such a construction it would be preferable to have the valves so connected to the operating means that both valves would move simultaneously to open or cover proportionately the same area of the ports 4 and 5a shown in Figs. l to 5, but, it' desired, one valve could have a slight lead on the other Without departing from the spirit of my invention. I prefer to use the construction shown in Figs. l to 4, however, on account of its simplicity, and Wherever l have used the term V' means for cutting off the fluid that is admitted to opposite sides of the piston or similar expressions, I mean to include either a construction such as that shown in Figs. 1 to 4 in which a single member is provided with two separate and distinct portions that cooperate 'With independent ports, or a construction such as that shown in Fig. T in' which the valves that control the passage of the fluid into the cylinder are mounted on separate stems.

ln the constructions herein shown the cylinder i is arranged in a vertical position and I have therefore described the piston as moving to the upper and lower ends of the cylinder, but it will, of course, be obvious that the cylinder could be arranged horizontally or in an inclined position without departing from the spirit of my invention.

Having thus described my invention, what l claim as new and desire to secure by Letters Patent is:

l. A fluid-actuated balanced hoist, provided with a cylinder, a piston arranged in said cylinder, means for creating a uniform pressure in said cylinder on both sides of the piston to cause the piston to move in one di rec-tion and for ret'lucing the pressure on one side of the piston to cause it to move in the opposite direction, and means for cutting oil* the supply of pressure to both ends of the cylinder so as to hold the piston at rest.

A fluid-actuated balanced hoist, provided With a piston that is adapted to move a load, means for creating a uniform pressure on both sides of the piston to cause it to move in one direction, means for reducing the pressure ou one side of the piston to cause it to raise said load, and means for cutting otl1 the supply of fluid to both sides of the piston to hold the piston at rest be tween its two limits of movement.

3. A Huid-actuated balanced hoist, comprising a cylinder, a piston arranged 1n said cylinder and adapted to move a load, means for introducing a fluid under pressure into one end ot said cylinder and simultaneousl connect the other end of the cylinder with7 the atmosphere so that the piston can raise the load, and means for cuttin off the supply of fluid to the cylinder and also closing the cylinder to the atmosphere so that the piston will come to rest intermediate its imits of travel.

4. A fluid-actuated balanced hoist, comprising a cylinder, a piston arranged in said cylinder, a conduit leading into one end of said cylinder and communicating with a sugply of Huid under pressure, a conduit lea mg into the opposite end of said cylinder, a.. va

ve for permitting the fluidto enter the conduit last referred to, means on said valve for permitting the fluid Which it has admitted to the cylinder to exhaust therefrom, and meansl for preventing the fluid which entered the cylinder through the conduit lirst referred to from escaping When said valve closes the conduit which it controls, thereby causing the piston in the cylinder to remain at rest.

5. A fluid-actuated balanced hoist, comprising a cylinder, a piston arranged in Said cylinder and adapted to move a load, means for connecting the opposite ends of Said cylinder with a supply of Huid under pressure to cause the piston to move in one direction, means for permitting the fluid to exhaust from one end of the cylinder without cutting oli1 thc supply of fluid to the other end of the cylinder so as to cause the piston to move in a direction to raise the load, means for cutting oil the exhaust from the cylinder, and means for closing the port to the other end of the cylinder so as to hold the piston at rest at some point intermediate its limits of movement.

A lluid-actuated balanced hoist, comprising a cylinder, a piston arranged in said cylinder and adapted to move a load, a pipe leading from the lower end of said cylinder and communicating with a supply of motive fluid under pressure, a ipe leading to the upper end ot said cylinder, a valve for admitting fluid from said supply into the upper end of the cylinder to cause the piston to descend and for permittin the fluid to eX- haust from the upper end oigthe cylinder to cause the piston to ascend, and means for cutting ofi' the supply of fluid to the lower end of the cylinder when said valve is turned into a position lo close the pipe that leads to the upper end of the cylinder. v

T. A fluidaictuated balanced hoist, comprising a cylinder, a piston arranged in Said cylinder, a pipe leading from the lower end i ducing the pressure of said cylinder and communicating with a supply of tluid under pressure so that the lwer side of the piston will be constantly subjected to pressure, means for ualizing the pressure on the upper side of the piston to causait to move in one direction and reon the upper side of the piston to cause it to move in the opposite direction, the lower side of the piston of fluid.

8. A fluid-actuated balanced hoist, coniprising a cylinder, a piston arranged inside of said cylinder, a valve casing, pipes leading from the opposite ends of said c linder to said valve casing, a supply pipe eading into said casing, and means arranged inside of said casing for permitting the fluid from the source ot supp y to enter the lower end of said cylinder and the fluid in the upper endof the casing to exhaust therefrom, said means also being adapted to permit the fluid from the source of supply to enter both ends of the cylinder simultaneouslypor positively close the pipes leading to both ends of the cylinder.'

,9. In a {luid-actuated hoist of the balanced type, a cylinder, 'a piston arranged in said cylinder, pipes leading to the opposite ends of said cylinder for introducing opposing forces into said cylinder so as to cause the iston to descend, a valve casing communicating with said pipes, a supply pipe communicating with said casing, and means arranged in said casing for closing the pi es that lead to the opposite ends of the cylint er.

10. In a fluid-actuated hoist of the hal-- anced type, a cylinder, a piston arranged in 'said cylinder, pipes leading to the opposite ends of said cylinder for introducing opposing orces into said cylinder so as to cause the piston to descend, a valve casing communicating with said pipes, a supplyr pipe communicating with said casing, and a yvalve in said casing which closes the pipes that lead to the-opposite ends of said cylinder when it is moved into a certain position, said valve having a chamber or duct that establishes communication between the atmosphere and the pipe that leads to the upper end of the cylinder when said valve is in a different position.

11. In a fluid-actuated hoist of the balanced type, a cylinder,^a piston arranged in said cylinder, pipes leading to the opposite ends of said cylinder ing forces into said cylinder so as to cause the iston to descend, a valve casing communicating with said pipes, and a valve in said casing for opening and closing the pipes that lead to the opposite ends of said cylinder, said valve having means for establish ing communication between the upper end of the cylinder and the atmosphere when it is in a certain position.

from the supply and means for positively cutting oil for introducing oppos-` 12. ln a {luid-actuated hoist of the balanced type, a hoisting cylinder having a piston arranged therein, means for introi ducing a motive medium into the lower end of the cylinder to exert upward pressure on the piston and a balancing medium into the upper end of the cylinder to exert downn' ard pressure on the piston, and means for controlling or regulatin the ingress an egress of the motive medium into the lower end of the cylinder.

13. lna fluid-actuated hoist ot the halanced type, an operating cylinder provided with a piston and having its lower end communicating with a motive medium which exerts upward pressure on the piston. means for admitting and exhausting a balancing medium to and from the upper end of the cylinder to canse the piston to descend and ascend, and means Jfor controlling both the ingress and the egress of the motive medium to and from the lower end of the cylinder.

14. In a fluid-actuated hoist of the balanced type, an operating cylinder provided with a piston that is adapted to move a load, a supply of motive fluid under pressure which is adapted to flow into and out of the lower end of the cylinder, means for regulating or controlling both the inflow and outflow oi said motive medium to and from the lower end of the cylinder. and means for admitting Huid into the upper end of the cylinder and exhausting it therefrom to cause the piston to descend and ascend.

15. A fluid-actuated balanced hoist, comprising an operating cylinder that is rovidcd with a piston, a supply of motive diiid under pressure that con'nnunicates with the lower end of said cylinder, means for cuttino' oil' the lower end of said cylinder Jfrom sait supply ot iluid. and means for admitting and exhausting a l'luid of equal pressure to and from the upper cnd of the cylinder.

16. fluid-actuated balanced hoist. comprising an operating cylinder provided with a. piston. a supply of luid under pressure, conduits that establish communication between said s'upply and the opposite ends of said cylinder, devices that govern and control the iow of the fluid through said conduits, and means for actuating said devices simultaneously to cut oil both ends of the cylinder fromwthe source of supply.

17. A Huid-actuated balanced hoist, comprising an operating cylinder provided with a piston, a supply of liuid under pressure, conduits that establish communication between said supply and the opposite ends ofr said cylinder, and means for controlling the ingress and egress of the fluid to and from the opposite ends of said cylinder and simultaneously varying the size of the luid passagevvays in said conduits.

18. A fluid-actuated balanced hoist, comprising an operating cylinder provided With a piston, a supply of fluid under pressure, conduits that establish communication between said supply and the opposite ends of said cylinder, means for varying the size of the fluid passageway in one of said conduits to permit the Huid to be admitted to and exhausted from one end and means for simultaneously varying the size of the fluid passageway in the other conduit so as to produce a Huid passageway of approximately the same area as that of the conduit first referred, to. t

19. A Huid-actuated balanced hoist, comprising an operating cylinder provided with a piston, a supply of fluid under pressure, an operatin valve for admitting and exhausting the tuid to and from the balancing end of said cylinder and for admitting and exhausting the Huid to and from the motive end of said cylinder, said valve comprising a` movable part provided with two controlling portions, and a` seat for said movable part provided with two approximately elongated ports of substantially the same area, with which said controlling portions coperate.

20. In a balanced pressure air hoist, a cylinder, a piston operating therein and provided with a` piston rod, a source of compressed air, a pipe leading from one end of the cylinder to the source of compressed air, a stop valve arranged to stop the flow of air through said pipe at Will, a second pipe leading from the other end of said cylinder to the source of compressed air, and a valve for permitting compressed air to pass through said second pipe into the cylinder, or escape from the cylinder to the atmosphere, said valve also being adapted to stop the fiow of air through said second pipe in either direction at will. Y

2L In a balanced pressure air hoist, a cylinder, a, piston operating therein and provided with a piston rod, a source of compressed air, a pipe leading from one end of the cylinder to the source of compressed air, a stop valve arranged to stop the flow ot' air through saidpipe, a second pipe leading from the other end of said cylinder to the source of compressed air, and a valve arranged to permit compressed air to pass through said second pipe into the cylinder, or to permit compressed air in said cylinder to escape to the atmosphere, or to stop the tlow of air through said second pipe at will, said two valves being operated by a means common t0 the two, so as to cause them to move simultaneously.

2. In a balanced pressure air hoist, a cylinder, a. piston operating therein and provided witli a piston rod, a source of compressed air, a pipe leading from one end of the cylinder to thesource of compressed air, a stop valve arranged to stop the flow of of the cylinder, l

l air through said pi e, a second pipe leading from the other en of said cylinder to the source of compressed air, and a valve arranged to permit compressed air to escape from said second pipe into the atmosphere, or to stop the flow of air through said second pipe at will, said two valves being operated simultaneously by a means common to the two and so arranged that in the central position both valves close the pipes they conneet with, and when moved, open their respective pi )es in unison.

23. In a balanced pressure air hoist, a cylinder, a piston therein provided with a piston rod, a source of compressed air, a valve casing connected to the source of compressed air, a port in the valve casing leading to one end of the cylinder, another port in the valve casing leading to the other end of the cylinder, and a valve operating in said casing and adapted to open or close one port to the compressed air supply and to open the other port to the compressed air supply, or to close it to the compressed air supply and open it to the atmosphere, the valve and ports being so arranged that when the valve is in central position both ports are closed, and when said valve is moved both ports open in unison.

24. ln a balanced pressure air hoist, a cylinder, a piston therein provided with a piston rod, a source ot' compressed air, and means for simultaneously regulating the flow of the motive `pressure to and from the cylinder and the balancing pressure of the hoist.

25. ln a balanced pressure air hoist, a cylinder, a piston therein provided with a piston rod, a source oi compressedair, and means for regulating the flow of the motive pressure and the balancing pressure of the hoist simultaneously, said means also being adapted to enti-ap the air pressure existing in both ends of the hoist simultaneously.

26. A balanced ressure air hoist provided with lneans or simultaneously regulating the tiow of the motive pressure and the balancine' pressure into and out` of the operating cy inder. y

27. A balanced prcssure'ir hoist provided with a combined valve that is arranged to regulate the How of the motive pressure and the balancingr pressure simultaneously, and a check valve in the compressed air supply pipe arranged adjacent to the valve body to prevent compressed air from leaving the cylinder of the hoist through the compressed air supply pi e.

In testimony whereof I hereunto at x my signature in the presence ot' two witnesses, 125 this 25th day ot' February 1909.

GEORGE F. STEEDMA N.

Tituesses llannnnx l'l. los'r, GEO, E. Herrmann.

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