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.

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.

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.