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: 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 (~400 nm wavelength) to red (~640 nm 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.