Feedback: The output signal from a feedback element.

Feedback Loop: Any closed circuit consisting of one or more feedback elements which transmit a signal to a summation point.

Filter: A device used to separate and retain insoluble contaminants from a fluid.

Flooded: A condition where the pump inlet is charged by placing the reservoir oil level above the pup inlet port.

Flow Control Valve: The volume, mass, or weight of a fluid passing through any conductor per unit of time.

Force: Any push or pull measured in units of weight. In hydraulics, total force is expressed by the product of pressure ( force per unit area) and the area of the surface on which the pressure acts (F=P * A).

Form Factor: The ratio of the RMS value of a harmonic signal to its average value in one half wave.

Four Quadrant: Refers to a motion system which can operate in all four quadrants i.e. velocity in either direction and torque in either direction. This means that the motor can accelerate, run and decelerate in either direction.

Frequency: The number of times an action occurs in a unit of time.

Friction: A resistance to motion, Friction can be constant with varying speed (Coulomb friction) or proportional to speed (viscous friction).

Full Flow: In a filter, the condition where all the fluid must pass through the filter element or media.