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Glossary of pump terms: B

BA: The width of the impeller in a pump. Commonly measured from the OD of the impeller excluding the width of the impeller walls. This measure is proportional to pump capacity.

Back plate: Used in some centrifugal pumps. The back plate consists of a gland ring facing the bearing side where the mechanical seal or gland packings are arranged in such a way that the pumped fluid cannot leak. The other side of the back plate is situated towards the impeller and becomes one of the wall between the suction casing.

Back pull out pump: A pump design that allows the entire power end of the pump to be removed for maintenance/replacement while the wetend of the pump remains in place.

Back-to-back: In the case of impellers, an arrangement where two impellers are placed back to back on a single shaft sharing the same backplate. This arrangement provides almost double the flow of a single impeller design.

Back to back double seal: A mechanical seal configuration typically used when the process fluid is toxic, flammable, or hazardous. This seal is used to prevent the process fluid or its vapour from leaking into the environment.

Back Vane: Part of the design scheme in impellers used to balance axial thrust on an impeller.

"Bad actor" pump: A pump that fails more frequently than it should based on its MTBF (Mean Time Between Failure).This pump is the type of pump that is ripe for replacement or overhaul.

Balance holes: Another impeller feature that helps to balance axial thrust.

Balance ratio: The standard balance ratio is 70-30 used by most mechanical seal companies. This means that 70% of the seal face area is exposed to the hydraulic closing force, while 30% is not.

Balanced seal: The most effective tool to counter heat generation in the stuffing box. The area of the seal face is reduced (i.e. balanced) to reduce the heat generation between the two faces of the seal.

Ball bearing: A bearing that uses balls to maintain the separation between the bearing faces.

Ball shuttling: A situation where the balls in a ball bearing rotate perpendicular to their rolling axis. This can result in premature failure of the bearing by accelerating the microscopic wear. This can be seen as an appearance of a polished raceway.

Bar: Non-SI unit of pressure. Exactly equal to 100,000 Pa. About equal to the atmospheric pressure at sea level.

Barometric pressure: Another term for atmospheric pressure. Often used in weather reports.

Barrel pump: A pump used to transfer fluid from a barrel.

Barrier fluid / liquid: The fluid used between the two mechanical seals of a double seal. Used to isolate the process fluid from the atmosphere. Also known as buffer fluid.

Base circle: A reference circle in a volute design that is used as a basis calculating the cutwater diameter. In most cases, the base circle diameter corresponds to the maximum impeller diameter.

Base plate: The plate on which the pump and motor are mounted.

Bayonet: The mechanical seal drive lugs wear into the drive slots and prevent the seal faces from moving forward to compensate for wear.

Bearing: A machine element that one part to support (i.e. bear) another. They constrain relative motion between moving parts to only the desired motion (e.g. rotation around an axis).

Bellows: Part of the design in a mechanical seal that prevents the build up of deposits on dynamic gaskets.

Bellows plate: Metal bellows in mechanical seals contain thin stamped plates welded together to form a convolution. Each of these plates is known as a bellows plate.

Belt drive: A series of belts and pulleys that transfer the torque from a drive shaft to the required shaft at the correct speed.

BEP: Best Efficiency Point. The kinetic energy that a pump produces is never converted with 100% efficiency to pressure energy. There are always losses due to friction in the seals/bearings, friction of the pumped fluid over the impeller, etc. The BEP is the volumetric flow rate of the pump for which the pump was designed to convert the most kinetic energy into pressure energy.

Bernoulli's Law: Describes the behavior of fluid under varying conditions of flow and height. Formulated by Daniel Bernoulli in 1738.

B-gap: The radial gap between the impeller vanes and the volute tongue or diffuser vanes. Careful attention to this gap can keep vibrations down.

BHP: Brake horsepower. The measure of an engine’s horsepower before the loss in power caused by any load (gearbox, etc.). Measured by attaching a “Prony brake” to the engine’s shaft.

Bingham plastic: A material that behaves as a rigid body at low stress, but flows as a viscous fluid at high stress.Mayonnaise and toothpaste are common examples of this type of material.

Body bound bolts: A bolt/bolt hole configuration where there is an interference between the bolt and its mating hole.

Bourdon pressure gauge: The Bourdon tube is a sealed tube that changes shape in response to applied pressure, causing an attached indicator to reflect a pressure change. This is the most common pressure sensing gauge in use.

Bowl (vertical turbine pump): In multi-stage vertical turbine pumps, the bowl is the casing of one of the stages.

Brinnell hardness: A scale for measuring hardness of materials. It uses an indenter to penetrate the material using a certain force, and characterizes the indentation made.

Buffer fluid: The fluid used between the two mechanical seals of a double seal (see barrier fluid).

Buna N: Commonly known as Nitrile rubber. It is a synthetic rubber that is a copolymer between acrylonitrile and butadiene.

Bushing: An independent plain bearing that is inserted into a housing to provide a bearing surface. For use in rotary applications.

Bypass line: A design that bypasses a portion of the pump system. This can be from the discharge to the stuffing box, the stuffing box to the pump suction or the pump discharge to any lower pressure point in the system.

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