US2165966A - Hydraulic motor - Google Patents

Description

July 11, 1939- F. B. HALL El AL HYDRAULIC MOTOR Filed May 26, 1957 3 Sheets$heet 1 W MM W au m AG m Mm M M@ Cmfiw m me 3J7 July 11, 1939.

F. B. HALL El AL HYDRAULIC MOTOR Filed May 26, 1937 3 Sheets-Sheet 2 W 2 M .J M M EU, m z mm u 7 i w m D \wk J k w m x w mfg u F :TTMW

July 11, 1939. F. B. HALL ET AL 5 HYDRAULIC MOTOR Filed May 26, 1957 5 Sheets-Sheet s Fby. 9.

FEED 15. /7'ALL. FE/wKu/v G. Tee/w HAEOLO WALTON.

Patented July 11, 1939 UNITED STATES PATENT OFFICE HYDRAULIC MOTOR Application May 26, 1937, Serial No. 144,906

11 Claims.

This invention relates to hydraulic motors, and more particularly to an improved valve mechanism for motors of the reciprocable type adapted to actuate the fuel feeding rams of furnace stokers.

One construction which has been utilized extcnsively heretofore comprises a cylinder and piston forming a power mechanism, a main valve actuated by hydraulic pressure to control the movements of the piston, and a pilot valve actuated mechanically'by the piston to control the movements of the main valve. The mechanism required for actuation of the pilot valve adds considerably to the cost of the apparatus, and furthermore makes it necessary to place this valve close to the piston, whereas a remote location for the valve is often desirable. If an obstruction should prevent the piston from moving sufficiently to actuate the pilot valve, as occasionally happens with furnace stokers, the piston will stall and no further movement will occur until the condition has been noticed by the person in charge and the diflicultyremedied.

In the operation of furnace stokers it is desirable to impart a comparatively rapid movement to the ram and to vary the rate of fuel feed by maintaining the ram stationary for predetermined controllable periods between strokes. It is also desirable, when the stoker motor is actuated by fluid supplied under pressure by a pump, to by-passthis fluid at a comparatively low pressure during these idle periods and thereby reduce the power requiredto drive the pump. These facts have been recognized heretofore, but the mechanisms which have been proposed for the purpose have been complicated, expensive, and not thoroughly dependable in operation.

It is accordingly one object of the invention to provide a comparatively simple and dependable valve mechanism for a hydraulic motor which is.

actuated solely by fluid pressure, and which can be located at a distance from the motor if desired.

It is a further object of the invention to provide a comparatively simple and dependable valve mechanism for a hydraulic motor which will an; tomatically reverse the motor whenever the latter becomes stalled, whether its stroke has been completed or not. i

It is a. further object'of the invention to provide a simple, inexpensive and reliable valve mechanism for a hydraulic motor which is adapted for operation by fluid supplied by a pump and arranged to by-pass the fluid at a comparatively low pressure during idle periods.

It is a further object of the invention to provide a valve, mechanism for a hydraulic motor including a main valve, and to construct this valve in such a way as to by-pass the operating fluid at a comparatively low pressure during idle periods.

It is a. further object of the invention to provide a valve mechanism for a hydraulic motor which is so constructed and. arranged as to avoid undue throttling of the operating fluid.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one em- 16 bodiment of the invention, and in which like reference numerals indicate .like parts,

Fig. 1 is an elevation of a hydraulic motor arranged to operate a furnace, certain parts being shown in vertical longitudinal section for clear- 21) ness of illustration;

Fig. 2 is a plan view of the valve mechanism of the motor;

Fig. 3 is an enlarged vertical longitudinal section through the valve mechanism, the section being taken on the line 33 of Fig. 2;

Fig. 4 is a section on the line 4-4 of Fig. 3;

Fig. 5 is a section on the line 5-5 of Fig. 3;

. Fig. 6 is a section on the line 6-6 of Fig. 3;

Fig. 7 is a fragmentary view showing a portion of Fig. 3, with certain parts in different positions; and

Figs. 8 and 9 are views similar to Fig. 3, but showing the parts in different positions.

As shown particularly in Fig. 1, the power mechanism of our hydraulic motor comprises a cylinder it! having a piston H reciprocable there? in and arranged to be actuated in opposite directions by hydraulic fluid. A piston rod l2 extends rearwardly from the piston and this rod is connected to a ram H which is arranged to reciprocate in a ram casing IS. A hopper I6 is mounted on the ram casing above the ram. The hopper delivers fuel by gravity to the ram, and the latter forces the fuel rearwardly through an opening I! in a furnace wall l8.

In order to actuate the piston ll, two conduits or pipes 20, 20' are provided which are connected respectively with the front and rear ends of the cylinder l0, and means is provided to supply fluid under pressure through one of these pipes while allowing fluid to escape from the other pipe and vice versa. For this purpose we prefer to utilize a reversing valve mechanism comprising a hollow casing 2| shaped, as shown particularly in Fig. 3, to provide two control chambers 22, 22' to which the pipes 28, 26' are respectively connected. The casing 2| is also shaped to provide an inlet chamber 23 and an exhaust chamber 24. A suitable operating fluid, such as oil, is supplied under pressure through a pipe 26 to the inlet chamber 23 by means of a pump 21 (Fig. 1), this pump having a suction pipe 28 through which the oil is withdrawn from a tank 29. An exhaust pipe 38 serves to return oil from the exhaust chamber 24 to the oil tank.- The pump 21 is preferably of the positive displacement type driven at a constant speed by a suitable electric motor (not shown), and in order to prevent the delivered oil pressure from exceeding a predetermined value we preferably provide a pipe 3| which connects the pipe 26 with the oil tank, and we provide this pipe 3| with a suitable pressure relief valve 32.

Means is provided to connect the control chambers 22, 22 alternately with the inlet chamber 23 and with the exhaust chamber 24, and for this purpose we preferably utilize a main reversing valve 34 arranged to be actuated in opposite directions by hydraulic pressure. This valve 34 is shaped as a hollow piston slidable within a cylinder or sleeve 35, this sleeve being preferably formed separately from the casing 2| and inserted therein. The ends of the sleeve35 are closed by means of heads 36, 36' secured to the opposite ends of the casing 2|. The sleeve 35 is provided with a port 31 opening into the inlet chamber 23, a port 38 opening into the exhaust chamber 24, and ports 39, 39' located on opposite sides of the port 38 and opening respectively into the control chambers 22, 22'. The valve 34 is provided with ports 40, 4|, and 4|, all of which extend through the cylindrical wall of the valve into its hollow interior. Port 48 is elongated and remains in communication with the sleeve port 31 at allpositions of the valve. Port 4| registers with sleeve port 39 when the valve is at the limit of its travel to the right, as shown in Fig. 3, and port 4| registers with sleeve port 39' when the valve is at the limit of its travel to the left, as shown in Fig. 9. In the outer surface of the -valve 34 there is provided an elongated pocket or recess 42 which remains in communication with the sleeve port 38 at all positions of the valve. This recess 42 connects the sleeve port 38 with the port 39' when the valve is in the position shown in Fig. 3, and with the port 39 when the valve is in the position shown in Fig. 9. R- tation of the valve 34 about its axis is prevented by a screw 43 (Figs. and 6) mounted in the casing 2| and provided with a projecting portion which extends through the sleeve and into a slot or groove 44 in the outer surface of the valve.

The valve 34 is moved back and forth in the sleeve 35 by the application of hydraulic pressure directly to the ends of the valve. As shown in Fig. 3, the casing 2| is shaped to provide two chambers 46 and 41 which communicate with the interior of the sleeve 35 at its opposite ends by means of two passages 48 and 49 respectively, these passages being formed in part in the heads 36, 36'. The casing 2| is also shaped to provide a chamber 58 between the chamber 41 and the exhaust chamber 24. Means is provided whereby fluid may flow at a controlled rate from the chamber 58 to the chamber 41, and for this purpose a pipe 52 leads from the chamber 58 to a manually adjustable .valve 53 (Fig. 2), and a pipe 54 leads from this valve 53 to the chamber 41. This valve 53 can be placed. in any convenient location, and need not be adjacent to the valve casing 2i.

In order to admit and exhaust fluid alternately from the chambers 46 and 41, thereby reciprocating the main valve 34, we provide a reversing pilot valve 56, which is preferably arranged to reciprocate in a line parallel to the direction of movement of the main valve. This pilot valve 56 comprises two spaced cylindrical portions 51 and 58 which are arranged to slide within a cylindrical sleeve 59 mounted in the casing 2|, the ends of the sleeve communicating with the exhaust chamber 24. This sleeve 59 is provided with five annular groups of ports 6|, 62, 63, 64, and 65. Ports 6| serve as exhaust ports for the chamber 46, and ports 62 serve as inlet ports for this same chamber. Ports 63 serve to deliver fluid from the inlet chamber 23 to the interior of the sleeve 59 between the cylindrical valve portions 51 and 58, regardless of the position of the valve. Ports 64 serve as inlet ports for the chamber 58, and ports 65 serve as exhaust ports for the chamber 41. These various ports are so constructed and arranged that when the pilot valve 56 is at the limit of its movement to the left, as shown in Fig. 3, the valve portion 51 will close ports 6| and open ports 62, while the valve portion 58 will close ports 64 and open ports 65. If on the other hand the pilot valve is at the limit of its movement to the right, as shown in Figs. 8 and 9, the valve portion 61 will open ports 6| and close ports 62, while the valve portion 58 will open ports 64 and close ports 65..

The pilot valve 56 is preferably arranged to be actuated in opposite directions by hydraulic pressure. For this purpose the casing 2| is provided with two cylindrical bores or chambers 61, 61 axially aligned with the pilot valve and at opposite ends thereof, these bores preferably being somewhat larger in diameter than the interior of the sleeve 59. Within the bores 61, 61' there are mounted slidable pistons 68, 68 having inwardly extending stems 69, 69' which engage the opposite ends of the pilot valve. The pistons 68, 68' are preferably made separable from the pilot valve, to facilitate manufacture and assembly. The stems 69, 69' may be connected to the pilot valve by means of pins 10, 18 coaxial with these parts.

Means is provided to apply hydraulic pressure to the pistons 68, 68' alternately and thereby reciprocate the pilot valve. As shown particularly in Fig. 3, the head 36 is shaped to provide a passage 12 connecting the control chamber 22 with the outer end of. the bore 61. A slidable check-valve 13 controls the flow in this passage, this valve being urged toward its seat in a cage 14 in the head 36 by means of a coiled compression spring 15. This spring is light enough to allow the check-valve to open with comparative freedom for the exhaust of fluid which is forced outwardly from the bore 61 by movement of the piston 68 to t e left. In order to open the check-valve when it is desired to force the piston 68 to the right, we provide a fluid-pressure responsive elementzin the form of a piston 11 slidably supported in the head 36 and subjected through the passage 12 to the fluid pressure in the control chamber 22. The piston 11 is urged inwardly against this pressure by means of a comparatively heavy coiled compression spring 18 supported in a hollow spring chamber 19 secured to the head 36'. A passage 88 formed in the head 36 connects the interior of the spring chamber 19 with the exhaust chamber 24 in the casing 2|, so that the outer face of the piston 11 is always subjected to the exhaust pressure. The piston 11 normally rests against the cage 14, and in no way interferes with outward movement of the check-valve 13. The inner portion of the piston 11 closely surrounds the valve 13,

and the latter is provided with an annular flange 8| located outwardly of this inner portion to form a shoulder, the parts being so constructed and arranged thatif the fluid pressure in the control chamber 22 increases sufficiently to force the piston 11 outwardly against the spring 18, the piston will engage the flange 8| and move the valve 13 away from its seat, as shown particularly in Fig. '1. The valve 13 thus functions not only as a check-valve but also as a pressure relief valve. By inserting or removing shims 82 between the outer endof the spring 18 and the spring chamber 19, the force of the spring can be adjusted. This adjustment is preferably such that the fluid pressure required to force the piston 11 outwardly is somewhat in excess of that required to actuate the main piston H under normal operating conditions.

It will be noted that the head 36 is similar to the head 36, and is provided with a passage 12', a check-valve 13, and a cage 14 forming a valve seat. The check-valve is urged inwardly toward its seat by means of a light spring 15'. There is also provided a piston 11' which is urged inwardly toward the valve cage 14 by means of a comparatively heavy spring 18' supported in a spring casing 19, the latter being connected by a passage 80 with the exhaust chamber 24. The checkvalve 13 is provided with a flange 8| for engagement by the piston 11'. Shims 82' may be used to adjust the spring 18'. These various parts may be identical with those previously described in connection with the head 36.

As will be explained hereinafter, the movement of the main valve 34 to the left is made for the most part at a comparatively slow speed under the control of the adjustable valve 53, and during this movement the piston II is stationary. The pump 21 is of course supplying oil at its full capacity, and in order to handle the surplus oil without increasing the pressure unduly and thus opening the relief valve 32 We preferably provide a by-pass which is controlled by the main valve 34. For this purpose, we have shown the casing 2| shaped to provide a passage 84 (Fig. 6) forming a by-pass which extends from a port 85 in the sleeve 35 to the exhaust chamber 24. A screw 88 is threaded through the casing 2|, and the inner end of the screw extends into the passage 84 to restrict this passage slightly so that sufilcient oil pressure will be maintained for operation of the main valve during the idle periods. The main valve 34 is provided with an elongated port 81 which registers with the sleeve pbrt 85 except when the valve is near the end of its stroke in one direction or the other.

It is desirable to bring the port 81 into register with the port 85 quickly after the pilot valve has been moved to the position shown in Fig. 8, and

also to move the port 4| into register with the port 39' quickly as the main valve 34 approaches the position shown in Fig. 9. For this purpose we provide a port 89 which extends through the sleeve 35 and communicates with the chamber 50, and we provide the main valve 34 with a longitudinal passage 90 which extends from the right hand end of the valve to a lateral port 9|. These ports 89 and 9| are in register when the valve is in its extreme right hand position,.as shown in Fig. 3,

and the port 89 is so located that it will be uncovered by the right hand end of the valve slightly before the valve reaches the extreme left hand position shown in Fig. 9.

The operation of the invention will now be apparent from the above disclosure. With the various parts in the positions shown in Fig. 3, oil will be delivered from the pump 21 through the pipe 28 to the inlet chamber 23, thence through the ports 31 and 40 to the interior of the main valve 34, thence through the ports 4| and 39 to the control chamber 22, and thence through the pipe 20 to the front end of the cylinder I0, forcing the piston II and ram l4 rearwardly and feeding a charge of fuel through the opening l1. At the same time the oil will flow from the rear end of the cylinder l through the pipe 20 to the control chamber 22', thence through the port 39,

recess'42 and port 38 to the exhaust chamber 24, and thence through the pipe 30' to the tank 29. During this part of the cycle the pressure of the oil supplied by the pump will be merely that which is required to force the piston l l rearwardly against the resistance of the ram. When the piston reaches the rear end of the cylinder the oil pressure will immediately increase to the value for which the spring 18 is adjusted, thereby forcing the piston 11 outwardly and opening the check-valve 13 as shown in Fig. '1. Oil will then flow from the control chamber 22 through the passage 12, and past the check-valve 13 into the outer end of the bore 61, thus forcing the piston 68 and the pilot valve 56 to the right hand position shown in Fig. 8. During this movement of the pilot valve, the piston 68, will force oil outwardly from the bore 81, past the checkvalve 13' (which will open readily against the light spring 15'), and through the passage 12 to the control chamber 22, which is in connection with the exhaust as explained above.

With the pilot valve in its right hand position, oil will flow from the inlet chamber 23 through the ports 63 and 69 into the chamber 58 and thence through the ports 89 and 9| and the passage 98 to the right hand end of the sleeve 35, forcing the main valve 34 quickly to the left until ports 89 and 9| are out of register, as shown in Fig. 8. During this movement of the main valve the oil is free to escape from the left end of the sleeve 35 through the passage 48, chamber 48 and ports 6| to the exhaust chamber 24. The main valve continues to move to the left under the influence of oil which is delivered from the chamber 50 through the .pipe 52, manually adjustable valve 53, pipe 54, chamber 41 and passage 49 to the right end of the sleeve 35, and its rate of movement can be controlled by adjusting the valve 53. The piston II will thus remain stationary in its rearmost position during a time interval which may be readily varied as desired. Slightly before the main valve :reaches its extreme left hand position, its right hand end will uncover the port 89, and oil will immediately flow through this port from the chamber 50, forcing the main valve qu ckly to the left and bringing port 4| quickly into register with port 39', as shown in Fig. 9, thus 1 avoiding undue throttling of the oil through partially open ports. 1

During the major portion of the movement of the main valve 34 to the left, whilethe valve is moving comparatively slowly under the control of the manually adjustable valve 53, the port 81 will be in register with the port 85. Under these conditions all of the oil delivered by the pump (except the slight amount utilized to continue the 84 so that a slight oil pressure will be provided for continuation of the valve movement.

When the main valve 34 reaches its extreme left hand position as shown in Fig. 9 the by-pass port 85 will be closed, and the oil from the inlet chamber 23 will flow through the ports 31 and 40 to the interior of the main valve, thence through the ports 4| and 39' to the control chamber 22', and thence through the pipe 20' to the rear end of the cylinder l0, forcing the piston I I and the ram l4 forwardly. The oil is free to escape from the front end of the cylinder Ill through the pipe 20, chamber 22, port 39, recess 42 and port to the exhaust chamber 24. The

pressure of the oil supplied by the pump will be only that required to efiect movement of the piston and ram. As the piston reaches the forward limit of its travel the oil pressure will increase suificiently to force the piston 11' outwardly against the spring 18, opening the check-valve l3 and admitting oil from the passage 12' to the outer end of the bore 61'. This will force the piston 68' and the pilot valve 56 to the left, and the piston 68 will force the oil outwardly from the bore 61 past the check-valve 13 (which will open readily against the light spring 15) and thence through the passage 12 to the control chamber 22, which is in connection with the exhaust as already explained. At the completion of this movement of the pilot valve, oil will flow from the inlet chamber 23 through the ports 63 and 62 to the chamber 46, and thence through the passage 48 to the left end of the sleeve 35, forcing the main valve to the right. During this movement, oil will escape from the right end of the sleeve 35 through the passage 49 to the chamber H and thence through the ports to the exhaust chamber 24. When the main valve reaches the limit of its travel to the right the various parts will be once more in the positions shown in Fig. 3, and the piston It will again be forced to the rear.

If the-ram should become blocked during its movement in either direction, as sometimes happens when a foreign body enters the ram casing with the fuel, the elfect on the valve mechanism will be the same as though the piston it had reached the end of its cylinder. Under these circumstances the oil pressure will increase momentarily, reversing the valve mechanism andthereby reversing the movement of the piston and ram. Frequently that is suflicient to,dis1odge the obstruction so that the next stroke of the ram will be a full stroke. If at any timethe oil pressure should increase unduly, the pump and its motor will be protected by the relief valve 32, which is adjusted to open at a pressure somewhat in excess, of that required to force the pistons TI or TI outwardly.

We have shown the various parts so arrangedthat the controllable pause in the movement of the ram takes place when the ram is at its inward limit of travel. We prefer this arrangement since the ram, while in that position, closes the opening l1 and prevents gases from escaping outwardly through this opening and into the hopper l6. However, if it is considered desirable to provide the pause in the ram movement when the ram is at its outward limit of travel, this can readily be accomplished by connecting the pipes 20 and 20' to the control chambers 22' and 22 respectively.

It will be noted that our improved valve mechanism is actuated solely by fluid pressure, and that only two conduits connect the valve, mechanism with the power mechanism. These mechanisms can be widely separated if desired. Similarlythe pump 2'! can be remote from the valve mechanism. The valve mechanism is comparatively simple and inexpensive to manufacture, and thoroughly reliable in operation.

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

1. A valve mechanism for a hydraulic motor having a reciprocable element adranged to be actuated in opposite directions by hydraulic pressure comprising a main reversing valve arranged to be actuated in opposite directions by hydraulic pressure and to control the supply of flu for actuation of the reciprocable element, a r versing pilot valve arranged to be actuated in opposite directions by hydraulic pressure and to control the supply of fluid for actuation of the main valve, means providing two passages arranged for the admission of fluid for the actuation of the pilot valve in opposite directions, the main valve serving to direct pressure fluid into said passages alternately, and valve means associated with each passage arranged to allow free outward flow therethrough and to prevent inward flow therethrough until the fluid pressure exceeds a predetermined value.

2. A valve mechanism for a hydraulic motor having a reciprocable element arranged to be actuated in opposite directions by hydraulic pressure comprising a main reversing valve arranged to be actuated in opposite directions by hydraulic pressure and to control the supply of fluid for actuation of the reciprocable element, a reversing pilot valve arranged to be actuated in opposite directions by hydraulic pressure and to control the supply of fluid for actuation of the main valve, means providing two passages arranged for the admission of fluid inwardly therethrough for the actuation of the pilot valve in opposite directions, the main valve serving to direct pressure fluid into said passages alternately, and a pressure relief valve in each passage arranged to open and allow flow inwardly of the passage when the fluid pressure exceeds a predetermined value, each pressure relief valve being constructed to serve also as a check valve arranged to open freely for outward flow through the corresponding passage.

3. A valve mechanism for interposition between a source of fluid pressure and a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element, means to actuate the reversing valve at predetermined intervals, and means providing a by-pass through which fluidmay escape from said source at a comparatively low pressure, the 'by-Ipass being arranged to be opened by the reversing valve during such intervals.

4. A valve mechanism for a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element, means to actuate the reversing valve in opposite directions, and means providing a by-pass for the fluid arranged to be closed by the reversing valve when the valve is at the limits of its travel and to be opened when the valve is intermediate its travel limits.

5. A valve mechanism for a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element, means to move the reversing valve rapidly in one direction and at a controlled rate in the opposite direction, and means providing a by-pass for the fluid arranged to be closed by the reversing valve when the valve is at the limits of its travel and to be opened when the valve is intermediate its travel limits.

6. A valvemechanism for a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element, means providing a by-pass for the fluid arranged to be closed by the valve when the valve is at the limits of its travel and to be opened when the valve is intermediate its travel limits, and means to move the valve rapidly during the first part of its movement in one direction and then comparatively slowly at a controlled rate, whereby the bypass is opened quickly irrespective or the speed at which the valve is moved thereafter.

7. A valve mechanism for a hydraulic motor having a reciprocable element comprising a mainreversing valve adapted to control the supply 01' fluid for actuation of the reciprocable element and arranged to be actuated in opposite directions by hydraulic pressure, means providing a by-pass for the fluid arranged to be closed by the valve when the valve is at the limits of its travel and to be opened when the valve is intermediate its travel limits, means providing a port through whichfluid may flow to move the valve rapidly during the first part or its movement in one direction, the valve closing the port as it opens the by-pass, and means to supply fluid to the valve at a controlled rate to continue its movement after the port is closed.

8. A valve'mechanism for a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element, means to move the reversing valve rapidly-in one direction, means to move the reversing valve rapidly during the flrst part oi'its return movement in the other direction, then comparatively 1 slowly at a controlled rate during the intermedi- 5 ate part of its return movement, and then rapidb during the flnal part of its return movement, and means providing a by-pass for the fluid arranged to be closed by the reversing valve when the valve is at the limits of its travel and to be opened when the valve is intermediate its travel limits.

9. A valve mechanism for interposition between a source of fluid pressure and a hydraulic motor having a reciprocable, element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element and arranged to be actuated in opposite directions by hydraulic pressure, a pilot valve arranged to control the supply of fluid for actuation of the main valve, and means providing a by-pass through which fluid may escape from said source at a comparatively low pressure when the main valve is intermediate its travel limits, the main valve being arranged to close the bypass when at the limits of its travel.

10. A valve mechanism for interposition between a source of fluid pressure and a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid for actuation of the reciprocable element and arranged to be actuated in opposite directions by hydraulic pressure, a pilot valve arranged to control the supply of fluid for actuation of the main valve, an adjustable valve arranged to regulate the rate of fluid flow and thereby control the speed of movement of the main valve in at least one direction, and means providing a by-pass through which fluid may escape from said source at a comparatively low pressure when the main valve is intermediate its travel limits, the main valve being arranged lto close the by-pass when at the limits oi its traveL' 11. A valve mechanism for a hydraulic motor having a reciprocable element comprising a main reversing valve adapted to control the supply of fluid -for actuation of the reciprocable element and arranged to be actuated in opposite directions by hydraulic pressure, means to supply fluid to the valve at a controlled rate to move the valve in one direction, and means providing a port arranged to be opened by the valve as it approaches its limit'oi travel in said direction, the port being arranged to supply fluid to the valve to complete its movement at a rapid rate and thereby avoid undue throttling of the fluid.

FRANHIIN G. TREAT. map B. HALL. HAROLD I". WALTON.

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