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Glossary and index of fluid power principles and components

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OFFSET-LATERAL, PARALLEL
The distance the ends of a hose assembly are displaced in relation to each other as the result of connecting two misaligned terminations in a system or intermittent fixture required in a hose application.

OHM'S LAW
Stated that the current in a circuit is directly proportional to the voltage and indirectly proportional to the resistance. Expressed as a formula: I = E / R.

OPEN CENTER CIRCUIT
One in which pump delivery flows freely through the system and back into the reservoir in neutral.

OPEN CENTER VALVE
One in which all ports are interconnected and open to each other in the center or neutral position.

OPEN CIRCUIT
A circuit in which a complete path for electrical current flow does not exist.

OPEN STEAM CURE
A method of vulcanizing in which steam comes in direct contact with the product being cured.

OPERATIONAL AMPLIFIER (OP AMP)
An integrated circuit amplifier with special characteristics (high gain, high input impedance, low output impedance, differential amplification) that make it especially suitable for electrohydraulic control systems.

OPERATING PRESSURE
The maximum level of pressure at which a component, pipe, tube, hose or other fluid passage will experience during application of maximum expected fluid pressure. See also BURST PRESSURE and PROOF PRESSURE.

O-RING
A seal, made from rubber or other synthetic material in the shape of a circle and of circular or other polygonal cross-section. See GASKET.

OR LOGIC GATE
A seal, made from rubber or other synthetic material in the shape of a circle and of circular or other polygonal cross-section. See GASKET.

ORIFICE
An opening or passageway which can be have tapered edges.

OUTPUT STAGE
A spool or other device that is controlled by a smaller spool or torque motor.

OVERALL LENGTH ( OAL)
The total length of a hose assembly which consists of the free hose length plus the length of the couplings.

OVERLAP
The condition of a spool and body in a servo valve or other spool valve wherein the spool must move a specified amount (the overlap) before exposing two adjacent cavities.

OVERSHOOT
Occurs when the process exceeds the target value as operating conditions change.

OXIDATION
The absorption of oxygen into fluid and the subsequent plating of the oxygen/ fluid mixture onto metal surfaces evidenced by a change in the appearance or feel of the surface or by a change in physical properties.

OZONE CRACKING
The surface cracks, checks, or crazing caused by exposure to the atmosphere containing ozone.