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Glossary of Pump Terms: M


  • Mach number: Relates the speed of a moving body in a fluid to that of sound. As this is a ratio, it’s a dimensionless number.
  • Magnetic drive: A sealless pump that uses a motor coupled to the pump by magnetic means rather than a direct mechanical connection.
  • Magnetic pickup: A sensor that transduces a varying magnetic field into an AC signal. Used to determine the speed of rotating metallic objects by detecting variations in the magnetic field as the object rotates.
  • Magnetic seal: Seals that use magnetic force rather than springs to provide sealing pressure.
  • Magnetite: Iron oxide ( Fe3O4). A coating that forms in iron pipes. Protects the pipes, but can be very destructive to seals and their components.
  • Mating ring: A.k.a. the hard face of a mechanical seal.
  • Mean Diameter: The average diameter.
  • Mechanical seal: A device that joins fluid-mechanical systems together by preventing leakage between the systems.
  • Mercury (Hg): An element that is both a metal and a liquid at room temperature.
  • Metal bellows: Some mechanical seals use these in place of elastomers.
  • Metal fatigue: Progressive structural damage that occurs through repeated loading of a metal part. .
  • Micro Organisms: Biologically active organisms used in a variety of biochemical processes. Can cause corrosion if not controlled.
  • Minimum continuous stable flow (MCSF): The lowest flow at which a pump can operate within the specifications (noise, vibration, etc.) set forth by a user.
  • Minimum flow: See “low flow”. A condition which causes excessive heat to build up inside the pump casing.
  • Minimum NPSHA: The minimum net positive suction head available. This quantity should be larger than the NPSHR or the NPSH required.
  • Miscible: Refers to the ability of one liquid to mix with another. Water and oil are not miscible, but water and ethanol are.
  • Mixed flow pump: A pump that uses both centrifugal force and lift produced by the impeller to move a fluid.
  • Modulus of elasticity: Also known as Young’s modulus. A physical property of a material that is a measure of stiffness of an elastic material.
  • Moment of inertia: A property of rotating objects that describes their resistance to change in angular momentum.
  • Momentum thrust: As the process fluid enters the pump and is acted on by the impeller it changes direction and therefore the impeller imparts a momentum thrust upon the fluid.
  • Monochromatic light: Light exists as wavelengths of colours from purple (~400nm wavelength) to red (~640nm wavelength). White light is a mixture of all wavelengths, whereas monochromatic light is light of a single wavelength.
  • Motor frame: NEMA (National Electrical Manufacturers Association) publishes standards for sizes of electrical motors. The Motor frame is a quantity that comes in the published sizes.
  • Multistage pump: Any pump with more than one impeller. Typically pumps with two impellers are referred to as two stage pumps.