Abstract: In a preferred embodiment of hydraulic actuator wherein a piston rod is longitudinally positionable via a tail end of a cylinder, tail-end static and dynamic seal members are of plastic, of relatively elongate trapezoidal section, and a single metal spring axially preloads the two seal members in compression, via the series-related respective ends of the seal members. Engagement with the ends of each seal member are frusto-conical, to substantially match the sloped ends of the trapezoidal section, and the slope directions of these seal-member engagements are (in the case of the dynamic seal) such as to locally impart radially inwardly directed force, to drive outer ends of the seal into circumferentially uniform engagement with the piston rod of the actuator; in the case of the static seal the slope directions of seal-member engagements are such as to impart radially outwardly directed force, to drive outer ends of the static seal into similar engagement with the bore of the cylinder.

Abstract: A three-part seal to be fixed in a gland formed on the first of two mating cylindrical structures in a hydraulic apparatus. A continuous Teflon nondeformable bearing ring is provided in the gland. The bearing ring has a first cylindrical surface for contact with the second cylindrical structure, a second cylindrical surface opposite the first surface and a conical rearward facing end surface. A continuous Teflon nondeformable backup seal ring is provided in the gland for mating with the rearward facing conical end surface of the bearing ring against its forward facing conical end surface. A continuous compressible resilient ring is provided on the side of the bearing ring opposite the second cylindrical structure for contacting the bearing ring and the backup seal ring.

Abstract: A polarity control valve enables the undiscriminating interconnection of a pressure line and a return line to two available ports to provide fluid pressure at an output line and a return connection through a return port. This feature of interconnecting either the pressure line or the return line to any of the two available ports is achieved by a pressure positionable spool mounted in a ported sleeve. The spool is positionable between one of two positions depending upon which port is connected to the pressure line. By controlling the distribution of lands on the spool the position thereof always establishes a fluid path from the pressure line to an output port connected to a fluid pressure responsive component. Fluid returning from the component is likewise directed by means of the positionable spool to the return line.

Abstract: A three-part seal to be fixed in a gland formed on the first of two mating cylindrical structures in a hydraulic apparatus. A continuous Teflon nondeformable bearing ring is provided in the gland. The bearing ring has a first cylindrical surface for contact with the second cylindrical structure, a second cylindrical surface opposite the first surface and a conical rearward facing end surface. A continuous Teflon nondeformable backup seal ring is provided in the gland for mating with the rearward facing conical end surface of the bearing ring against its forward facing conical end surface. A continuous compressible resilient ring is provided on the side of the bearing ring opposite the second cylindrical structure for contacting the bearing ring and the backup seal ring.