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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: 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.

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