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Glossary of pump terms: E

Eccentric: In contrast to concentric, where circular parts have the same centre, eccentric parts do not have the same centre.

Eccentricity (shaft): The amount that a circular shaft varies from its outer diameter as it rotates with reference to its true centre.

Eddy current: Electrical currents induced within conductive materials by a change in the magnetic field. These eddies have inductance, inducing magnetic fields in the conductive material.

Effective diameter: When referring to metal bellows construction, it is the diameter where the pressure penetrates between the metal plates. This is then used to help determine the hydraulic diameter of the seal face.

Efficiency: The measured power out of a piece of equipment divided by the power produced by the piece of equipment. Always between 0 and 1.

Elasticity: A physical material property in which materials return to their original shape after being deformed.

Elastic range: In material science, when a material is stressed and returns to its original shape, it is said to be in the elastic range of stress.

Elastomer: Derived from the terms “elastic polymer”, is a substance with viscoelasticity. This term is often used interchangeably with rubber. Simply, it is a substance that when released from a stress, returns to its original shape.

Electrical run-out: This results from non-uniform electrical properties of a shaft material. In contrast to mechanical run-out, which eccentricity of the shaft, electrical run-out is non-uniformities within the shaft.

Electrolysis: A chemical reaction caused by ions in liquid carrying an electric current.

End-suction pump: End suction pumps are the most common type of centrifugal pump. End suction pumps have a horizontal shaft with an overhung impeller. The flow goes in the end of the casing, and discharges from the top.

Endurance limit: In material testing, this is the point at which a metal will fatigue without applying any additional stress.

End-user: The ultimate person who is using the equipment. There may be many middlemen in between the manufacturer and end-user, including distributors, third party integrators, etc.

Entrance suction loss: The loss of suction between the inlet of a pump and the impeller.

EPA: Environmental Protection Agency. Governmental agency with a mission to protect human health and the environment.

EPR: Ethylene Propylene Rubber. An elastomer that is a copolymer of ethylene and propylene. Commonly used to seal water based and petroleum based products.

Equivalent length: A way to calculate the friction of fittings, like bends, tees, returns, and valves, in straight run equivalents. Measured in length.

Erosion: Wear and tear caused by the action of the liquid on the materials of the system. If the process fluid has solid particles, the wear will be higher.

External gear pump: A pump that uses gears to displace the process fluid. The gear or gears are housed in a casing with low clearance. One edge of the gear faces the inlet while the other faces the outlet. When the gear turns, liquid is trapped in the space between the teeth and is thereby moved from the inlet to the outlet.

Expeller: A type of gland seal that reduces the bypass pressure from the pump into the gland or rotary sealing area of the pump. Used in applications pumping slurries. Achieved through a combination of centrifugal force and component tolerances.

Extrusion: Displacement of an O-ring into a gap due to the fluid pressure.

Eye of the impeller: The centre of the impeller, where the process fluid begins its journey outwards to the outlet or discharge.

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