The hydraulic knee control for a prosthetic leg has a cylinder and piston assembly. In addition, within the cylinder is disposed a free floating plug so that the space between the free plug and the head end is filled with air or a compressible fluid, and the spaces between the free plug and the crank end is filled with a liquid or hydraulic fluid. The piston is disposed within this liquid and has sealing means which prevents the liquid from bypassing therearound. Disposed outside of the cylinder are two bypass passageways wherein one end of each passageway communicates with the cylinder in the region between the piston and crank end and the other end of each passageway communicates with the cylinder in the region between the piston and the floating plug. One of the passageways has a one-way adjustable valve which allows the liquid to move only from the head end to the crank end in a controlled manner, and the other passageway has a one-way adjustable valve which allows the liquid to move only from the crank end to the head end in a controlled manner.

A sealing device is mounted in the bore of a housing in which a piston is slidably mounted. A fluid tight seal is mounted between a shoulder of the housing and a washer circumscribing the piston. The washer has an outer diameter substantially equal to that of the bore and comprises an outer annular groove in which at least one fixing element is disposed. Each fixing element comprises a tongue-shaped portion penetrating through a corresponding radial bore defined at the bottom of the annular groove. When the piston is inserted through the washer, the fixing elements are moved radially towards the outside of the washer through the tongue-shaped portions and penetrate into a facing annular groove formed in the bore.

A re-chargeable self-contained servo cylinder for the control of force with variable piston positions under load includes an elongated cylinder housing having a tubular body with open receiver end and closed opposite end by a cap which includes a central port provided with integral directional check valve for supply of working fluid under pressure during cylinder charging, a piston and rod assembly slidably received inside the cylinder including a rod end closure with seals slipped over piston rod and secured inside the open receiver end so as to protrude an end portion of the piston rod for attaching to a load carrying platform, an integral flow control valve with control rod inside an elongated central bore of the piston rod for control of working fluid communication between the sides of the piston via a fluid opening provided therein when cylinder becomes pressurized by the working fluid and for maintaining a given piston position inside cylinder fixed when the flow control valve is closed thereby also fixing the length of piston rod protrusion until control rod becomes moved externally to open flow control valve internally for restart of fluid flow between the piston sides with axial piston travel within the stroke limitations provided by the cylinder when piston rod position change is desired.

A valve stem seal for an intake or exhaust valve in an internal combustion engine where the seal allows a metered amount of oil to run down the valve stem for lubrication of the stem in its valve guide. The seal has a cylindrical wall engaging the valve guide boss and an upper inwardly extendng flange provided with twin sealing lobes on the internal surface separated by an annular groove; the lobes and groove providing a pumping action for oil during reciprocation of the valve stem.

An improved fluid section for piston type paint pumps having the piston made from unplated stainless steel and wherein the seal is a multiple lip type formed of ultra-high molecular weight polyethylene and the seal further includes one or more U-shaped internal stainless steel springs.