US3624700A

US3624700A - Fluid isolator

Info

Publication number: US3624700A
Application number: US879490A
Authority: US
Inventors: Donald K Schaeve; Edward H Ashby
Original assignee: Barber Colman Co
Current assignee: Barber Colman Co
Priority date: 1969-11-24
Filing date: 1969-11-24
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30

Abstract

A fluid isolator for use between a high-pressure fluid line and a low-pressure fluid line for actuating one of a plurality of operators from a common source of pressure fluid. Through first and second free-floating pistons mounted in first and second cylinders, power is transferred from a primary fluid circuit to a secondary fluid circuit to actuate the operator. A valving arrangement comprising a spool-type control valve actuated by a spool-type pilot valve is operable to direct high-pressure fluid alternately to the cylinders to drive the pistons through power strokes. The pilot spool is physically attached to the first piston so that the movement of the piston shifts the pilot spool to cause the control spool to shift. To accommodate changes in the volume of the fluid, herein hydraulic fluid, in the secondary circuit, the second cylinder is larger in volume than the first cylinder. In one embodiment, the pilot valve is formed concentric with the control valve, and the pilot spool slides within a central passage in the control spool.

Description

United States Patent flonald K. Schaeve;

3,100,965 8/1963 Blackburn....................

[72] Inventors Edward Ashby both Rockhrd' Primary Examiner-Martin P. Schwadron [2]] Appl. No. 879,490 A E A M Z 22 Filed Nov. 24, 1969 f s'f p g s 8 J V & 0 Patented Nov. 30, 1971 norneyo e, u ar ey lg, oit sann [73] Assignee Barber-Coleman Company Rockfordv ABSTRACT: A fluid isolator for use between a high-pressure fluid line and a low-pressure fluid line for actuating one of a plurality of operators from a common source of pressure fluid. [54] FLUID ISOLATOR Through first and second free-floating pistons mounted in first 14 Claims, 6 Drawing Figs.

. and second cylinders, power IS transferred from a primary [52] U.S. fluid circuit to a secondary fluid circuit to actuate the opera- 60/51, 91/46] .Fl5b 15/18,

tor. A valving arrangement comprising a spool-type control [5 l] lnt. valve actuated by a spool-type pilot valve is operable to direct high-pressure fluid alternately to the cylinders to drive the pistons through power strokes. The pilot spool is physically attached to the first piston so that the movement of the piston shifts the pilot spool to cause the control spool to shift. To accommodate changes in the volume of the fluid, herein hydraulic fluid, in the secondary circuit, the second cylinder is larger in volume than the first cylinder. in one embodiment, the pilot valve is formed concentric with the control valve, and the pilot spool slides within a central passage in the control spool.

8&3 33 m xx 1 4 new mm 7 77 63 33 F 1 11 mm m s I WM m .1 m9 W mm m1... M mm m n. mm W" m5 ME 36 u Tl fl In nA m m mT mh o m e m RwHR n n 4] N56 U ww ll il 92 o l m M F n3 1 1 1 0 6 U U 23 FLUID ISOLATOR BACKGROUND OF THE INVENTION This invention relates to a fluid isolator for use between a high-pressure fluid line and a low-pressure line for actuating one of a plurality of operators from a common source of pressure fluid. To isolate the operator from the high-pressure line,

' two separate fluid circuits are used with the primary circuit being connected between the high-pressure line and the lowpressure line and the secondary circuit, which is normally filled with hydraulic fluid, being connected to the operator to form a closed circuit. Two cylinders with free-floating pistons join the circuits together for transmission of power from the primary circuit to the secondary without the transmission of fluid between the circuits. In the primary circuit, a valving arrangement with a valve member which moves between two positions is operable to direct pressure fluid first to one cylinder and then the other to drive the pistons through power strokes to cause a flow of hydraulic fluid in the secondary circuit. With this arrangement, the high-pressure fluid line is isolated from the operator so that, if a leak occurs in the secondary circuit, fluid does not escape from the high-pressure line and the latter is still able to service the other operators.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a valving arrangement which provides positive shifting of the valve member between the positions to provide quiet, smooth, positive, functioning of the isolator during normal operation and which, upon leak occurring in the secondary circuit stops the valve member in one of the positions and holds it there thus providing a quiescent state of the valve arrangement to prevent nonuseful expenditure of energy and damage to the parts of the isolator and to eliminate noise caused by moving parts.

It is another object to provide such a valving arrangement which is capable of using either hydraulic or pneumatic pres sure fluid in the primary circuit.

A further object of the invention is to provide a valving arrangement which is operable, when a leak occurs, to direct high-pressure fluid to both cylinders to drive both pistons to the ends of their cylinders adjacent the secondary circuit and to connect the valving arrangement to one piston so that the valve member is fixed in its final position by the final position of the one piston. More specifically, the valving arrangement comprises a spool-type control valve with the spool being the valve element and a spool-type pilot valve to actuate the shifting of the control spool, and the pilot spool is physically con- 7 nected to the one piston so that the spool is physically connected to the one piston so that the pilot spool moves with the one piston and shifting of the control spool is responsive to the position of the one piston.

It is an object in one embodiment of the invention to reduce the overall size of the valving arrangement and to eliminate conduits extending between the two valves by forming the pilot valve as a spool slidably telescoped with the spool of the control valve.

The invention also resides in providing cylinders of different volume so that the larger cylinder can serve as a reservoir for the hydraulic fluid in the secondary circuit to accommodate volume change in the hydraulic fluid in the secondary circuit while the piston in the larger cylinder moves through a stroke equivalent to the stroke of the piston in the smaller cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial schematic view of a hydraulic system and shows an enlarged schematic view of an isolator embodying the novel features of the present invention.

FIG. 2 is a fragmentary schematic view of the control and pilot valve and shows both cylinders and pistons.

FIG. 3 is a fragmentary perspective view of a second embodiment of the valving arrangement.

FIG. 4 is a cross-sectional view of the valving arrangement of FIG. 3.

FIG. 5 is a view similar. to FIG. 4 and shows parts in a moved position.

FIG. 6 is a view similar to FIG. 4 and shows parts in another moved position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the drawings for purposes of illustration the invention is embodied in a fluid isolator 10 (FIG. I which connects a high-pressure fluid line 11 and a low-pressure fluid line 12 to a load or operator 13 for actuating the operator. A plurality of operators are connected to the high and low pressure lines through individual isolators which isolate the operator from the pressure lines so that, if a leak should occur in the fluid circuit of the operator, the isolator will prevent the loss of pressure in the high-pressure line thus enabling the highpressure line to continue to service the other operators.

Herein, the isolator 10 comprises a primary fluid circuit I4 which is connected to the high and low-pressure fluid lines 11 and 12 and a secondary fluid circuit 15 which is connected to the operator l3 and is filled with a hydraulic fluid such as oil. In this instance, the high pressure is approximately 3,000 p.s.i., and the low pressure is approximately p.s.i. The two circuits are connected together so that power but not fluid from the primary circuit is transferred to the secondary circuit to actuate the operator. For this purpose, first and second cylinders 17 and 18 each communicate at one end, the primary end, with the primary circuit and at the other end, the secondary end, with the secondary circuit. To prevent the interchange of fluid through the cylinders and to transmit power between the circuits, first and second free-floating pistons 19 and 20 are slidably mounted in the cylinders, one piston per cylinder.

To drive the pistons 19 and 20 alternately through power strokes, a valving arrangement 21 (FIG. 2) in the primary circuit l4 directs pressure fluid from the high-pressure line 11 alternately into the primary ends of the cylinders 17 and 18. These alternating power strokes cause an alternating flow of oil in the secondary circuit 15, and this flow is transformed into a unidirectional flow to pass through and actuate the operator 13. As shown in FIGS. 1 and 3, four

check valves

22, 23, 24 and 25 are arranged in the secondary circuit to transform the alternating flow to unidirectional flow. When the first piston 19 is positioned to begin its power stroke, the second piston 20 is positioned to begin its return stroke (FIG. 1). High-pressure fluid is directed to the primary and of the first cylinder 17 to drive the first piston through its power stoke thus causing a positive flow of oil from the first cylinder and into the secondary circuit. This flow is directed through the check valve 24 to the intake line 27 of the operator. Flow into the operator causes low-pressure exhaust flow out of the operator through a low-pressure line 28, and this flow is directed through the check valve 22 to the secondary end of the second cylinder 18 thus pushing the second piston 20 through its return stroke. When the first piston reaches the end of its power stroke, the valving arrangement 21 is operable to direct the high-pressure fluid to the primary end of the second cylinder to drive the second piston through its power stroke to force oil from the second cylinder and through the check valve 23 and into the intake line 27, the exhaust flow from the operator passing through the check valve 25 to move the first piston through its return stroke. Thus the alternating flow from the cylinders is transformed into unidirectional flow through the intake line and to the operator. With this arrangement, the secondary circuit is a closed circuit isolated from the primary circuit.

In the valving arrangement 21, a valve member 30 (FIG. 2) is shifted between a first position and second position to direct the pressure fluid first to one cylinder and then the other. The shifting of the valve member is arranged so that the pistons 19 and 20 move through equivalent power strokes.

The present invention contemplates the provision of a novel valving arrangement 21 which results in positive shifting of the valve member 30 between its two operating positions to provide quiet, smooth and positive functioning of the isolator during normal operation and which, when a leak occurs in the secondary circuit stops the valve member in one of the operating positions and holds it there in a quiescent state to prevent nonuseful expenditure of energy and damage to the parts and to eliminate noise of moving parts, Further the arrangement of the novel valving permits the use of either a hydraulic fluid or a compressible gas in the pressure lines 11 ad 13 and in the primary circuit 14, To these ends, the valve member 30 is a part of a control valve 31 and is shifted from one operating position to the other under the control of a pilot valve 32 which is positively actuated by one of the pistons 19 and 20, herein the piston 19. The pilot valve causes the valve member to shift to one operating position at the end of the power stroke of the piston 19 and to the other operating position at the end of the return stroke of the piston. Thus, should a leak occur in the secondary circuit 15, both pistons will come to rest, and preferably will bottom, and the member will be locked in one operating position or be shifted to the other operating position to be locked in that position.

in the embodiment of FIG. 2, the control valve 31 comprises a housing 33 with the control spool 30 being mounted in a chamber 34 in the housing for endwise sliding. Two intake ports 36 and 37 connect the opposite ends of the chamber to a line 38 leading to the high-pressure line 11 for the admission of high-pressure fluid into the chamber. In this instance, oil is used in the lines 11 and 12 and in the primary and secondary circuits l4 and 15. The low-pressure line 12 is connected by a line 39 to a port 40 leading into the center of the chamber, and

ports

41 and 42 connect the chamber with the primary ends of the cylinders 17 and 18 through

lines

43 and 44 so that highpressure oil may be directed to the cylinders and low-pressure oil may flow from the cylinders. From FIG. 2, it will be observed that the control spool comprises a small diameter shaft 45 which is longer than the chamber but shorter than the housing, and the opposite end portions of the shaft are slidably mounted in a pistonlike manner in

secondary chambers

46 and 47 in the end portions of the housing. To direct the flow of high-pressure and low-pressure oil through the chamber 34 and to prevent mixing of the two, tow lands 48 and 49 are formed on the shaft.

The control spool 30 is shifted between the first position shown in FIG. 2, and a second position (not shown) to direct the high-pressure oil first to one cylinder then the other. When the control spool is in the first position the port 37 communicates with the port 41 to direct high pressure oil to the primary end of the first cylinder 17, and the second cylinder 18 is connected to the low-pressure line 34 through ports 40 and 42. To direct the flow are high-pressure oil to the second cylinder, the control spool is shifted downwardly until the lower end (FIG. 2) of the shaft engages the bottom of its secondary chamber 46. This movement slides the lands 48 and 49 in the chamber 34 so that the port 36 communicates with the port 42 in the chamber 34 so that the port 36 communicates with the port 42 to direct the high-pressure oil to the primary end of the second cylinder 18 while connecting the first cylinder with the low-pressure line through ports 40 and 41. It will be observed that in neither position are the intake ports 36 and 37 blocked by the lands thus maintaining generally equal pressure in the opposite end portions of the chamber so that only a small amount of force is needed to shift the control spool.

To shift the control spool 30, the pilot valve 32 is operable to direct high-pressure oil alternately to the

secondary chambers

46 and 47 to cause the end portions of the shaft 45 to act as pistons under pressure. In this instance, the pilot valve comprises a housing 50 and a pilot spool 51 slidably mounted in a chamber 52 formed in the housing. A line 53 extends between ports 54 and 55 in the upper and lower ends of the housing and a port 56 in the lower end of the control housing 33 to connect the chamber 52 with the lower end of the secondary chamber 46, the port 56 being of smaller diameter than the secondary chamber. The upper end of the secondary chamber 47 communicates with the pilot chamber 52 through a port 58 in the pilot housing and a port 59, similar to the port 56, in the upper end of the control housing, the ports 58 and 59 being 5 joined by a line 60. A line 61 connects a port 62 to the highpressure line 38, ad a line 63 connects a port 64 to the lowpressure line 39. As shown in F IG. 2, the pilot spool comprises a long shaft 65 which extends through the bottom of the housing 50, a short land 66 on the upper end of the shaft. and a long land 67 spaced downwardly on the shaft from the short land. To operate the control valve, the pilot spool is slid up and down in the pilot housing to direct the high-pressure oil alternately to one of the ports 56 and 59 while connecting the other to the low-Pressure line. In order that the pilot valve moves with the piston 19 thereby insuring that the spool 30 is held in a predetermined fixed position when a leak occurs in the secondary circuit 15, the lower end of the shaft 65 is rigidly connected to the piston 19 so that the pilot spool slides up and down as the first piston moves through its power and return strokes.

For a summary of the operation of the valves 31 and 32, assume that the first piston 19 is at the primary end of the first cylinder 17 and the second piston 20 is ready to begin its return stroke. As shown in FIG. 2, the high-pressure oil is directed by the pilot valve 32 to the lower end of the secondary chamber 46, and the control spool 30 is in the first position directing the high-pressure oil to the primary end of the first cylinder and connecting the second cylinder 18 to the lowpressure line 39. As the first piston moves through its power stroke, the second piston moves through its return stroke, and the pilot spool slides down in the pilot chamber 52. When the first piston reaches the secondary end of its cylinder, the pilot spool is located so that the high-pressure oil is disconnected from the secondary chamber 46 and is connected to the secondary chamber 47, the high-pressure oil passing through ports 62 and 58 and through the chamber 52 between lands 66 and 67. The resulting pressure of the oil against the upper end of the control shaft 45 forces the control spool to shift and thus to disconnect the high-pressure oil from the first cylinder and to connect the high-pressure oil through ports 36 and 42 to the second cylinder in which the second piston has completed its return stroke. As a result'of the shift in the highpressure oil, the second piston is moved through its power stroke thus moving the first piston through its return stroke. As this occurs, the pilot spool slides upwardly in the chamber 52, and when the first piston nears the end of its return stroke the lower end of the land 67 passes by and uncovers the port 62 to direct the high-pressure oil through the port 55 to the port 56 to push against the lower end of the shaft 45 to shift the control spool 30 into the position shown in FIG. 2 ready to begin another cycle of operation.

If an oil leak should occur in the secondary circuit 15, the pistons 19 and 20 will end up at the secondary ends of the cylinders 17 and 18, and the control spool 30 will be locked into its second position. If the leak occurs during the power stroke of the first piston 17, the latter will continue to the end of its power stroke to pull the pilot spool 51 and shift the control spool to direct high-pressure oil into the second cylinder 18 to drive the second piston 20 through its power stroke. Once the leak occurs,' no low-pressure oil will flow into the secondary end of either cylinder. Thus, neither piston would be returned. With the first piston at the secondary end of the first cylinder and no low pressure oil available to push the piston through a return stroke, the pilot spool will remain in a position to direct high-pressure oil into the secondary chamber 47 thus locking the control spool in its second position. If the leak occurs during the power stroke of the second piston, the latter will be driven to the secondary end of its cylinder. Because no low-pressure oil will be directed into the secondary end of the first cylinder 17, the low-pressure oil from the first circuit, the oil being under approximately l00 p.s.i. will push the first piston to the secondary end of its cylinder thus pulling the pilot spool down to lock the control spool in its second position in the manner described above.

In accordance with another aspect of the invention, the second cylinder 18 is utilized to accommodate the changing volume of the oil in the secondary circuit due to thermal expansion of the fluid and the effect of using an unbalanced operator 13 thereby eliminating the need for a separate reservoir in the secondary circuit. To these ends, the volume of the second cylinder is greater than the volume of the first cylinder and the sliding of the pilot spool 51 is controlled exclusively by the first piston 19 so that, while the first piston normally moves through a stroke which extends from end to end of the first cylinder 17, the second piston in the larger cylinder will normally move through a stroke which is shorter than the full distance from end to end of the second cylinder.

While it is not necessary, both cylinders 17 and 18 have, in this instance, generally equal diameters wi the length of the second cylinder 18 being greater than that of the first cylinder 17 to effect the greater volume of the second cylinder. The piston 20 is free-floating within the second cylinder and thus may move through its power or return stroke anywhere within the length of the second cylinder. When the oil is cooled, its volume decreases, and the second piston moves through its strokes in the secondary end portion of the cylinder. When the oil is heated, its volume increases to fill a portion of the second cylinder, and the second piston moves through its strokes in the primary end portion of the cylinder. The same action of the piston 20 occurs when an unbalanced operator [3 is used. The stroke that the second piston moves through, barring a leak, is always shorter than the length of its cylinder because the shifting of the control spool 30 is exclusively controlled by the first piston 19 through the connection of the shaft 65 of the pilot spool 51 to the first piston, and thus the second piston moves through strokes correlated to the length of the stroke of the first piston.

A modified valving arrangement 21' embodying novel features of the present invention is shown in FIG. 3 through 6 in which parts corresponding to those of the valving arrangement 21 are indicated by the same but primed reference numerals. Like the valving arrangement 21, the valving arrangement 21' includes a control valve housing 33' (FIG. 4), a control spool 30' slidably mounted in a chamber 34' in the housing, and a pilot valve spool 51 with a shaft 65' which is connected to the first piston 19. In accordance with this aspect of the invention, the pilot spool 51' is slidably telescoped with the control spool 30 and is concentric with the control spool and the control valve housing 33'. With this arrangement, all the interconnecting passages are fabricated in the parts themselves to eliminate all the small diameter lines and long passages. Additionally, a separate pilot valve housing is not required.

As best shown in FIG. 4, the control valve housing 33' forms the chamber 34 in which the control spool 30' is slidably mounted; and a number of ports connect the chamber with lines leading to the first and second cylinders 17 and 18 and to the high and low-pressure lines 38 and 39. Thus, a line 43' through a port 41' in the lower end portion of the housing connects the chamber with the primary end of the first cylinder 17, and a line 44' through a port 42' in the upper end portion of the housing connects the chamber with the primary end of the second cylinder 18. The low pressure line 39 is connected to the chamber by

lines

70 and 71 which are connected to upper and lower

low pressure ports

72 and 73 in the opposite end portions of the housing. To introduce high-pressure oil into the chamber, the high-pressure line 38 is connected to a port 74.

As shown in progressive steps in FIGS. 4 to 6, the control spool 30 is shifted between a first position (FIG. 4) and a second position (FIG. 6) to direct the high-pressure oil first to one cylinder then the other. The control spool is cylindrical with a body 75 of smaller diameter than the diameter of the chamber 34' and with

lands

76 and 77 at opposite ends of the body to divide the chamber 34' and with

lands

76 and 77 at opposite ends of the body to divide the chamber and block the flow of oil between various ones of the ports. When the control spool is in its first position (FIG. 4), the high-pressure port 74 communicates with the port 41 to direct high pressure oil to the first cylinder 17, the oil passing through the chamber around the body of the spool and between the lands. In this position the upper low-pressure port 72 communicates with the port 42' to connect the second cylinder to the low-pressure line 39. When the control spool is in its second position (FIG. 6), the high-pressure port 74 communicates with the port 42' to direct high-pressure oil to the second cylinder and the lower low-pressure port 73 communicates with the port 41' to connect the first cylinder to the low-pressure line.

As with the first embodiment, the shifting of the control spool 30' is controlled by the shifting of the pilot spool 51 in response to the movement of the first piston 19. In this instance the pilot spool 51 is an elongated cylindrical stem 65 with a single land 79 formed thereon. The stem is connected at its lower end to the upper surface of the first piston 19 and extends upwardly therefrom onto the control housing 33' through a hole 80 in the bottom of the housing. To prevent oil from leaking out the hole, a seal 81 is placed in the bottom of the chamber 34'. As shown in FIGS. 4 through 6, the upper portion of the stem extends through an axial passage 82 in the control spool 30 with the land 79 being positioned within the passage.

Bushings

83 and 84 at the upper and lower ends of the passage seal around the stem to form a chamber of the passage. To allow high-pressure oil into and out of the passage, a port 85 is formed through the wall of the control spool at the vertical center of the spool and, to vent the passage to low pressure, two

slots

86 and 87 are milled into the stem. One slot 86 extends axially from just above land 79 upwardly while the other 87 extends axially downwardly from just below the land. The stem and the control housing are dimensioned such that, when the first piston 19 is positioned to begin its power stroke, the top of the stem is just below the top of the housing (FIG. 4) and, when the first piston completes its power stroke, the top of the stem is just above the bottom of the upper low-pressure port 72 (FIG. 6).

As the first piston 19 moves through its power and return strokes, the sliding of the pilot spool 51' relative to the control spool 30' shifts the bias of the high-pressure oil in the control spool to cause the latter to shift between the first and second positions. In following through a cycle of operation, assume that the first piston 19 is poised to begin its power stroke and the control spool is positioned in its first position (FIG. 4) directing the high-pressure oil to the first cylinder 17. The high-pressure oil also fills the passage 82 below the land 79, the oil having flowed into the passage through the port 85. As the first piston moves through its power stroke, the land 79 moves downwardly in the passage thus forcing the high-pressure oil out of the passage through the port 85, and low-pressure oil flows into the passage above the land, the oil flowing through the slot 86. As shown in FIG. 5, the upper slot 86 is of such a length that, when the land moves past the port 85, the upper end of the upper slot moves past the bushing 83 to break the communication of the passage with the low-pressure fluid. The lower slot 87 is of such a length that, when the land 79 moves downwardly past the port 85, the lower end of the lower slot moves past the bushing 84 to establish communica tion between the portion of passage below the land and the low-pressure through the port 73. Thus when the land moves downwardly past the port 85, the upper portion of the passage fills with high-pressure oil and the oil in the lower portion of the passage becomes low-pressure oil. This occurs as the first piston reaches the end of its power stroke, and the high pressure above the land, in effect pushes against the bearing 83 and forces the control spool to shift, as shown in FIG. 6, to its second position.

The shifting of the control spool 30' to its second position causes the high-pressure oil to be directed to the second cylinder 18 and causes the first cylinder 17 to be connected to the low pressure port 73. The operation of the pilot spool 51' to shift the control spool from the second position back to the first position is similar to that for shifting the control spool from the first position to the second. As the first piston 19 moves through its return stroke, the stem 65' moves upwardly,

and the land 79 forces the high-pressure oil out of the upper portion of the passage 82 through the port 85 with the lower portion of the passage filing with low-pressure oil through the lower slot 87. As the land passes the port 85, the lower end of the lower slot passes into the bushing 84 thus disconnecting the lower portion of the passage from the low-pressure port 73, and the upper end portion of the upper slot 86 passe through the bushing 83 to connect the upper portion of the passage with the low-pressure port 72. The land passes the port 85 as the first piston reaches the end of its return stroke. When this occurs, the lower portion of the passage is filled with high-pressure oil which flows in through the port 85, and the resulting pressure against the bearing 84 causes the control spool to shift back to its first position thus completing a full cycle of operation. if a leak should occur in the secondary circuit 15, both pistons would end up at the bottoms of their respective cylinders, as described above in connection with the first embodiment of the valving arrangement, and the control spool 30 would be locked into its second position.

From the above, it will be observed that the provision of the pilot spool 51, 51' which is controlled by the movement of only the first piston 19 to control the shifting of the control spool 30, 30 is a particularly advantageous arrangement. With this arrangement, should a leak occur in the secondary circuit 15, the control spool will be locked into its second position to prevent waste of energy and possible damage to the valving arrangement caused by indiscriminately moving parts, Also, the isolator 10 is operable whether the first circuit 14 is filled with hydraulic fluid or a gas. Another advantageous arrangement is the formation of the second cylinder 18 larger than the first cylinder 17 to act as a reservoir to accommodate changes in the volume of the hydraulic fluid in the second circuit. To conserve space and eliminate many parts, the valving arrangement 21' of the second embodiment comprises a pilot spool 5l-which is concentric with and slides through the control spool 30.

We claim as our invention:

1. in a fluid isolator adapted to be connected between a high-pressure fluid line and a low-pressure line for operating one of a plurality of fluid loads from a common source of highpressure fluid, the combination of, a primary fluid circuit adapted to be connected between the high-pressure line and the low-pressure line, a secondary fluid circuit adapted to be connected to the one load, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for operation of the one load, said means comprising a first cylinder, 51 first free-floating piston in said second cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directing high-pressure fluid from the high-pressure line to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause an alternating flow of high-pressure fluid in said secondary circuit, means in said secondary circuit for transforming said alternating flow to a unidirectional flow through the load while directing the lowpressure fluid from the load alternately to the second ends of the cylinders to return one piston toward the first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve connected in said primary circuit for directing pressure fluid to said first end of either of said cylinders while directing low-pressure fluid from the first end of the other said cylinder to the low-pressure line, a pilot valve connected to said control valve and operable to actuate said control valve to change the flow of high-pressure fluid and low-pressure fluid from one cylinder to the other to cause the alternating power strokes of said pistons, and means connecting said pilot valve and first piston for operating said pilot valve in response to movement of said first piston between the ends of said first cylinder whereby if a fluid leak occurs in said secondary circuit, the valves will come to rest in fixed positions to allow the pressure source to continue to be used to actuate the remaining loads.

2. The fluid isolator of claim I in which said means connected to said pilot valve is a rigid connection between the pilot valve and said first piston.

3. The fluid isolator of claim 1 in which secondary circuit is filled with a liquid.

4. The fluid isolator of claim 3 in which said second cylinder has a larger volume than said first cylinder so that said second cylinder serves as a resevoir to accommodate volume changes in the liquid in said secondary circuit while still allowing said second piston to move through strokes equivalent to the strokes of said first piston.

5. in a fluid isolator adapted to be connected between a high-pressure fluid line and low-pressure fluid line for actuating one of a plurality of fluid operators from a common source of high-pressure fluid, the combination of, a primary fluid cir cuit adapted to be connected between the high-pressure line and the low-pressure line, a secondary fluid circuit adapted to be connected to the one operator, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for actuation of the one operator, said means comprising a first cylinder, a first free-floating piston in said cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directing high-pressure fluid to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause in said secondary circuit a flow of pressure fluid operable to activate the one operator while returning one piston toward the first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve connected in said primary circuit and movable between first and second positions, said control valve being operable in said first position to direct high-pressure fluid to said first end of said first cylinder and connect said second cylinder to said low-pressure line and operable in said second position to direct high-pressure fluid to said first end of said second cylinder while connecting said first cylinder to said low-pressure line, a pilot valve connected to said control valve and operable, when moved in one direction, to shift said control valve to said first position, and when moved in the opposite direction to shift the control valve to said second position and thereby to cause the alternating power strokes of said piston and means connecting said pilot valve and said first piston to cause the pilot valve to move back and forth with said first piston whereby, if a fluid leak occurs in said secondary circuit, both pistons will move to said second ends of their cylinders and said control valve will come to rest in one of said positions to allow the pressure source to continue to be used to actuate the remaining operators.

6. The fluid isolator of claim 5 in which the secondary circuit is filled with a liquid pressure fluid.

7. The fluid isolator of claim 6 in which said second cylinder has a larger volume than said first cylinder to accommodate the liquid filling said secondary circuit as said liquid expands or contracts while still allowing said second piston to move through strokes equivalent to the strokes of said first piston.

8. The fluid isolator of claim 6 in which the pressure fluid passing through the primary circuit is a liquid.

9. The fluid isolator of claim 5 in which said control valve comprises a housing and a control spool movable within said housing between said first and second positions, said pilot valve comprises a second housing and a pilot spool movable within said second housing in said directions, and conduits extending between said pilot valve and said control valve to convey high-pressure fluid from said pilot valve to said control valve.

10. The fluid isolator of claim 9 in which said means connecting said pilot valve and said first piston comprises a shaft connected at one end to one end of said pilot spool and connected at its other end to said first piston so that movement of said first piston moves said pilot spool.

11. The fluid isolator of claim in which said control valve comprises a housing and a control spool slidable within said housing between said positions and said pilot valve is formed concentric with said control valve and comprises a pilot spool slidably telescoped with said control spool whereby movement of said pilot spool in said directions causes said control spool to slide between said positions.

12. The fluid isolator of claim 11 in which said control spool has a passage formed therethrough and said pilot spool is slidably telescoped within said control spool.

13. The fluid isolator of claim 11 in which said means connecting said pilot valve and said first piston comprises a shaft connected at one end to said first piston and at its other end to said pilot spool.

14. In a hydraulic isolator connected between a high-pressure hydraulic fluid line and a low-pressure hydraulic fluid line for actuating one of a plurality of fluid operators from a common source of high-pressure hydraulic fluid, the combination of, a primary hydraulic circuit connected between the highpressure line and the low-pressure line, a secondary hydraulic circuit connected to the one operator and filled with hydraulic fluid, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for actuation of the one operator, said means comprising a first cylinder, at first free-floating piston in said cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directly high-pressure fluid to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause an alternating flow of high-pressure fluid in said secondary circuit, means in said secondary circuit for transforming said alternating flow to a unidirectional flow through the operator while directing the low-pressure hydraulic fluid from the operator alternately to the second ends of the cylinders to push one piston toward said first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve having a housing and a control spool with a passage therethrough, said spool being slidable in said housing between first and second positions, said control valve being operable when said spool is in said first position to direct highpressure fluid from the high-pressure line to said first end of said first cylinder and to connect said first end of said second cylinder to the low-pressure line and operable when said spool is in said second position to direct high-pressure fluid to said first end of said second cylinder while connecting said first end of said first cylinder to the low-pressure line, a pilot valve comprising a pilot spool slidably mounted within said passage of said control spool, said pilot valve being operable, when said pilot spool is moved in one direction, to shift said control spool to said first position and, when said pilot spool is moved in the opposite direction, to shift the control spool to said second position thereby to cause the alternating power strokes of said piston, and a shaft extending between and connected to said pilot spool and said first piston to cause the pilot spool to move back and forth with the strokes of said first piston whereby, if a hydraulic fluid leak occurs in said secondary circuit, each piston will move to said second end of its cylinder and said control spool will be locked in one of said positions to allow the pressure source to continue to be used to actuate the remaining operators.

* i l t i

Claims

1. In a fluid isolator adapted to be connected between a highpressure fluid line and a low-pressure line for operating one of a plurality of fluid loads from a common source of high-pressure fluid, the combination of, a primary fluid circuit adapted to be connected between the high-pressure line and the low-pressure line, a secondary fluid circuit adapted to be connected to the one load, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for operation of the one load, said means comprising a first cylinder, a first free-floating piston in said cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directing high-pressure fluid from the high-pressure line to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause an alternating flow of high-pressure fluid in said secondary circuit, means in said secondary circuit for transforming said alternating flow to a unidirectional flow through the load while directing the low-pressure fluid from the load alternately to the second ends of the cylinders to return one piston toward the first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve connected in said primary circuit for directing pressure fluid to said first end of either of said cylinders while directing lowpressure fluid from the first end of the other said cylinder to the low-pressure line, a pilot valve connected to said control valve and operable to actuate said control valve to change the flow of high-pressure fluid and low-pressure fluid from one cylinder to the other to cause the alternating power strokes of said pistons, and means connecting said pilot valve and first piston for operating said pilot valve in response to movement of said first piston between the ends of said first cylinder whereby if a fluid leak occurs in said secondary circuit, the valves will come to rest in fixed positions to allow the pressure source to continue to be used to actuate the remaining loads.

2. The fluid isolator of claim 1 in which said means connected to said pilot valve is a rigid connection between the pilot valve and said first piston.

5. In a fluid isolator adapted to be connected between a high-pressure fluid line and a low-pressure fluid line for actuating one of a plurality of fluid operators from a common source of high-pressure fluid, the combination of, a primary fluid circuit adapted to be connected between the high-pressure line and the low-pressure line, a secondary fluid circuit adapted to be connected to the one operator, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for actuation of the one operator, said means comprising a first cylinder, a first free-floating piston in said cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directing high-pressure fluid to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause in said secondary circuit a flow of pressure fluid operable to activate the one operator while returning one piston toward the first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve connected in said primary circuit and movable between first and second positions, said control valve being operable in said first position to direct high-pressure fluid to said first end of said first cylinder and connect said second cylinder to said low-pressure line and operable in said second position to direct high-pressure fluid to said first end of said second cylinder while connecting said first cylinder to said low-pressure line, a pilot valve connected to said control valve and operable, when moved in one direction, to shift said control valve to said first position, and when moved in the opposite direction, to shift the control valve to said second position and thereby to cause the alternating power strokes of said pistons, and means connecting said pilot valve and said first piston to cause the pilot valve to move back and forth with said first piston whereby, if a fluid leak occurs in said secondary circuit, both pistons will move to said second ends of their cylinders and said control valve will come to rest in one of said positions to allow the pressure source to continue to be used to actuate the remaining operators.

11. The fluid isolator of claim 5 in which said control valve comprises a housing and a control spool slidable within said housing between said positions and said pilot valve is formed concentric with said control valve and comprises a pilot spool slidably telescoped with said control spool whereby movement of said pilot spool in said directions causes said control spool to slide between said positions.

14. In a hydraulic isolator connected between a high-pressure hydraulic fluid line and a low-pressure hydraulic fluid line for actuating one of a plurality of fluid operators from a common source of high-pressure hydraulic fluid, the combination of, a primary hydraulic circuit connected between the high-pressure line and the low-pressure line, a secondary hydraulic circuit connected to the one operator and filled with hydraulic fluid, means connected between said circuits for transmitting power from said primary circuit to said secondary circuit for actuation of the one operator, said means comprising a first cylinder, a first free-floating piston in said cylinder, a second cylinder, a second free-floating piston in said second cylinder, a first end of each cylinder communicating with said primary circuit and the second end of each cylinder communicating with said secondary circuit, control means in said primary circuit for alternately directing high-pressure fluid to said first ends of said cylinders to drive said pistons through power strokes toward said second ends to cause an alternating flow of high-pressure fluid in said secondary circuit, means in said secondary circuit for transforming said alternating flow to a unidirectional flow through the operator while directing the low-pressure hydraulic fluid from the operator alternately to the second ends of the cylinders to push one piston toward said first end of its cylinder as the other piston moves through its power stroke, said control means comprising a control valve having a housing and a control spool with a passage therethrough, said spool being slidable in said housing between first and second positions, said control valve being operable when said spool is in said first position to direct high-pressure fluid from the high-pressure line to said first end of said first cylinder and to connect said first end of said second cylinder to the low-pressure line and operable when said spool is in said second position to direct high-pressure fluid to said first end of said second cylinder while connecting said first end of said first cylinder to the low-pressure line, a pilot valve comprising a pilot spool slidably mounted within said passage of said control spool, said pilot valve being operable, when said pilot spool is moved in one direction, to shift said control spool to said first position and, when said pilot spool is moved in the opposite direction, to shift the control spool to said second position thereby to cause the alternating power strokes of said pistons, and a shaft extending between and connected to said pilot spool and said first piston to cause the pilot spool to move back and forth with the strokes of said first piston whereby, if a hydraulIc fluid leak occurs in said secondary circuit, each piston will move to said second end of its cylinder and said control spool will be locked in one of said positions to allow the pressure source to continue to be used to actuate the remaining operators.