Glossary of Pump Terms: M
Magnetic drive:
A type of seal less pump that is most often limited to pumping clean lubricating liquids. Similar in concept to a canned pump.
Magnetic seal:
Uses magnetic materials rather than springs to keep the lapped seal faces together. Limited to non-corrosive fluids because of the magnets.
Magnetite:
Iron oxide ( Fe3O4). Protective coating that forms on iron pipe to prevent further rapid corrosion. Usually black or maroon in color. Can be very destructive to mechanical seal components until the oxide stabilizes. We often find these iron pipes in new hot water systems
Mating ring:
Another name for the hard face in a mechanical seal. It can be either rotating or stationary.
Mechanical seal:
A positive sealing device used to seal all fluids (liquids and gases). The primary seal is a set of lapped seal faces that are installed perpendicular to the shaft.
Metal bellows:
Used in mechanical seal designs to eliminate the need for a dynamic elastomer.
Metal fatigue:
A breakage of the metal caused by the bending and flexing of a metal part beyond its endurance limit.
Minimum flow:
A condition that can cause excessive heat inside the pump volute. A temperature rise of 10?C (18?F) across the operating pump is considered excessive. Normally caused by throttling a pump discharge valve.
Moment of inertia:
Referring to rotation about an axis. In the pump business it refers to a formula that describes the shape of the shaft. A solid shaft would have a different moment of inertia than a hollow shaft.
Glossary of Pump Terms: N
Negative pressure:
Less than atmospheric pressure.
N.P.S.H.A:
The net positive suction head available to prevent cavitation of the pump. It is defined as atmospheric pressure gage pressure static pressure -vapor pressure – friction loss in the suction piping.
N.P.S.H.R.:
Net positive suction head required to stop a pump from cavitating. The pump manufacturer gives this number to you. Since testing with cold fresh water generated the number, it can be lowered in some cases if you are pumping hot water or some hydrocarbons.
Newton:
A metric unit of force. Kilogram x gravity.
Newtonian fluid:
A fluid that does not change viscosity as it is agitated.
Non lubricant:
The fluid that will not maintain a film thickness of at least one micron at its operating temperature and load. A concern with mechanical sealing.
Glossary of Pump Terms: O
O.D.:
Outside diameter.
Operating length:
Measured after the seal has been compressed the proper amount. The measurement is usually made from the face of the stuffing box.
O-ring groove:
The space into which an O-ring is inserted. Dynamic O-ring grooves use a different dimension than static O-ring grooves.
Over hung impeller:
Not supported with bearings on either side of the impeller.
Oxidizer:
Combines with carbon to form carbon monoxide or carbon dioxide. The oxidizers attack all forms of carbon including the seal face and any black O-rings in the system.
Ozone:
Created by oxygen atoms combining with oxygen molecules in a high-energy atmosphere. Will prematurely age Buna rubber. Ozone forms in the shop as a result of the sparking of electric motor brushes.