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Glossary of pump terms: O

OD: Outside diameter.

OEM: The company that makes the product, not the company that distributes it. Acronym that stands for Original Equipment Manufacturer.

Oil analysis: A preventative maintenance procedure in which a lubricant’s properties are analysed in a laboratory to check for particles, water and wear debris.

Oil life: The working life of a lubricant. Oil will maintain its useful properties for about 30 years at 30 °C, if not contaminated.

Oil mist: A system where oil is atomised with air and subsequently sent into the pump bearings.

Oil whirl: This can occur in bearings that are lubricated hydrodynamically. It’s an instability caused by a sudden disturbing force to the shaft being supported by the bearing and causes an eccentricity to occur by an increased amount of oil on one side of the shaft compared to the other.

Open free flow: When the discharge pipe or hose is fully open at the end with no restrictions.

Open impeller: An impeller with vanes attached to the hub with no front or back shrouds; the impeller may have small web in-between vanes for structural support.

Operating length: The length of a seal when it is in operation, i.e. while it is under compression.

Operating point: The point on the pump performance curve at which a pump operates. It corresponds to the flow rate and total head sustained by the pump.

Operating region: Refers to the range in pump performance curve in which the pump operates.

Optical flat: A very flat (usually ¼, 1/10^th or 1/20^th of a wavelength variation across its surface) piece of glass used in combination with light to measure the flatness of test pieces.

O-ring groove: The machined slot on a piece of metal or elastomer where an o-ring is inserted. Forces the O-ring to stay in a set position.

OSHA: Occupational and Safety Health Act. Governmental regulations that impact the workplace. Designed to keep workers safe.

Outboard: A reference to the position of something with respect to the pump coupling. Outboard is further away from the pump coupling, while inboard is nearer.

Over hung impeller: An impeller on a shaft that is supported on one side only.

Overhung pump: A pump whose impeller shaft is supported by bearings on one side only. Also known as a cantilevered pump.

Overrunning clutch: A clutch that engages in only one direction. Also known as a “freewheel”. Most bicycles have overrunning clutches on their rear wheels.

Oxidizer: A chemical that reacts with carbon to form an aggressive compound. Will attack most metallic components inside a pump, including seal faces, etc.

Ozone: A variant of oxygen (O₂) with three oxygen atoms (O₃) instead of two. This makes it highly reactive. Is formed by electric sparking (e.g. by electric motor brushes).

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