Seal, cup - A sealing device with a radial base integral with an axial cylindrical projection at its outer diameter.

Seal, dynamic - A sealing device used between parts that have relative motion.

Seal, elastomer - A material having rubber-like properties; i.e., having the capacity for large deformation and rapid and substantially complete recovery on release from the deforming force.

Seal, rod (shaft) - A sealing device which seals the periphery of a piston rod.

Seal, static (gasket) - A sealing device used between parts that have no relative motion.

Sensor - A device which detects and transmits changes in external conditions.

Separator - A device whose primary function is to isolate contaminants by physical properties other than size. (Separators remove gas from liquid medium or remove liquid from gaseous medium).

Sequence Circuit - A circuit which established the order in which two or more phases of a circuit occur.

Servovalve - A valve which modulates output as a function of an input command.

Servovalve, electrohydraulic - A servovalve which is capable of continuously controlling hydraulic output as a function of an electrical input.

Servovalve, electrohydraulic, flow control - An electrohydraulic servovalve whose primary function is control of output flow.

Servovalve hysteresis - The difference in the servovalve input currents required to produce the same output during a single cycle of valve input current when cycled at a rate below that at which dynamic effects are important.

Servovalve null leakage - Total internal leakage from the valve in the null position.

Servovalve, pressure control - A hydraulic servovalve whose primary function is the control of output pressure.

Shrinkage - Decreased volume of seal, usually caused by extraction of soluble constituents by fluids followed by air drying.

Silencer - A device for reducing gas flow noise. Noise is decreased by tuned resonant control of gas expansion.

Snubber - see gage damper.

Solenoid, digital - Electrically energized device which generates on-off signals.

Solenoid, proportional - An electrical device that reacts proportionally to strength of electrical signal.

Sorption - The term used to denote the combination of absorption and adsorption processes in the same substance.

Specific gravity, liquid - The ratio of the weight of a given volume of liquid to the weight of an equal volume of water.

Squeeze - Cross section diametral compression of O-ring between surface of the groove bottom and surface of other mating metal part in the gland assembly.

Stage - A hydraulic amplifier used in a servovalve. Servovalves may be single stage, two stage, three stage, etc.

Standard - A document, or an object for physical comparison, for defining product characteristics, products, or processes; prepared by a consensus of a properly constituted group of those substantially affected and having the qualifications to prepare the standard for voluntary use.

Stokes - The standard unit kinematic viscosity in the cgs (centimeter gram second) system. It is expressed in square centimeters per second; 1 centistokes equals 0.01 stokes.

Strainer - see filter, strainer.

Surface tension - The surface force of a liquid in contact with a fluid by which it tends to assume a spherical form and to present the least possible surface. It is expressed in pounds per foot or dynes per centimeter.

Surge - A transient rise of pressure or flow.

Swell - Increased volume of specimen caused by immersion in a fluid (usually a liquid).

Switch, float - An electric switch which is responsive to liquid level.

Switch, flow - An electric switch operated by fluid flow.

Switch, pressure differential - An electric switch operated by a difference in pressure.

Switch, pressure - An electric switch operated by fluid pressure.

Synthetic fluid, silicate ester - A fluid compound of organic silicates. It may contain additives.

Synthetic fluid - Fluid other than mineral on which has been artificially compounded for use in a fluid power system.