Hydraulics Glossary: O

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A glossary of the key terms you may encounter when working with hydraulic systems. Introducing the letter 'O'…

O-RING
A circular seal made from synthetic material.
OPEN-CENTRE CIRCUIT / SYSTEM
A hydraulic system in which the flow of the pump has a free-flow passageway through the system and back to the reservoir, while in the neutral condition.
OPEN-CENTRE VALVES
One in which all ports are interconnected and open to each other in the centre or neutral position. Open centre hydraulic valves are the same as the tandem centre, except that in the neutral position all lines are connected back to the reservoir. The primary use of this system is to prevent “shock” loading when the valve is placed in neutral. This takes pressure off the hydraulic motor. This system is used in situations where the operating device needs to be moved by hand.
OPEN CIRCUIT
A circuit in which there is no complete path for electrical current flow.
OPERATING PRESSURE
The maximum pressure that a system or component will experience during operation at the maximum expected fluid pressure.
An opening or passageway which can have tapered edges.
The output of a hydraulic pump (gallons per minute, or GPM) is related directly to its operating speed. The pressure of a hydraulic pump is determined by its manufactured capabilities.
A spool or other device that is controlled by a torque motor or smaller spool.
The absorption of oxygen into fluid and the plating of the oxygen/fluid mixture onto metal surfaces.
Substance added in small quantities to petroleum products to increase its oxidation resistance.

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