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 Glossary of pump terms: C

C frame adapter: Alignment of the pump shaft with the driver shaft is critical for efficient pumping. The C frame adapter is one method to help accomplish this.

Calculation software: Calculating fluid mechanics solutions manually, to determine pump ratings and sizes as well as piping run lengths, diameters and flow rates can be a tedious process with many points where errors can be introduced. There are several software packages that can resolve complicated systems with many components, and perform all the necessary calculations, allowing the end user to focus on choosing the appropriate pump according to the calculated parameters.

Canned pump: A pump in which the armature, and shaft of the motor are in a can, used for pumping clean lubricating fluids.

Cantilevered pump: Centrifugal pumps often used in sump pump applications where it’s not desirable to have the bearings/motor under water. The impeller is at the end of a shaft which is cantilevered from the bearing housing assembly. Also known as an overhung pump.

Capacity: The amount of liquid pumped per unit time. Measured in gallons / min, cubic meters per sec, etc.

Carbide: A series of compounds formed when carbon combines with an element. Very hard and often used in seals and as cutting tools for metals. For example, Silicon Carbide.

Carbon bushing: A bushing made of carbon. Often used as a thermal barrier in high temperature application. Can also be used as a disaster bushing and to support a deflecting shaft in many mechanical seal applications.

Carbon / graphite: An element commonly used as in mechanical seals as part of the face, as carbon is chemically inert when it comes into contact with most other fluids.

Carbonising: Production of carbons at seals. Can interfere with proper movement of the seal and cause leakage.

Carcinogen: Any chemical that has the propensity to cause cancer.

Cartridge seal: An assembly containing the seal, gland sleeve and the rotating seal faces. Because it is self contained in can be installed without any measurement. Used in API seals.

Case: The part of the pump that is the volute chamber, encloses the impeller(s). The case can be split radially or axially.

Case crowning: In a horizontal split centrifugal pump this is a method of transferring a higher amount of the bolt load towards the case bore to better seal the case gasket and prevent washout. It’s recommended when working above 2150 psi.

Case retiring thickness: As cases wear, the wall thickness diminishes due to erosion or corrosion. The thickness of the case at which it will be retired is known as the case retiring thickness.

Catalyst: A chemical that is added to a reaction to speed the reaction up. It is not consumed by the reaction.

Cavitate: Formation of cavities (bubbles) in fluid flow applications in areas of low pressure, causing a collapse in the high pressure area of the pump and loss of capacity, excessive noise and possibly damage.

Centre line design: A pump design where the pump is attached to feet that are attached to the sides of the volute instead of the bottom. Commonly used in high temperature pumping applications.

Centipoise: A unit of dynamic viscosity. Equivalent to 1 mPa second.

Centistoke: A unit of kinematic viscosity. Also sometimes referred to as diffusivity of momentum. The kinematic viscosity in centistokes is equal to the dynamic viscosity in cP divided by the liquid density.

Centrifugal force: This is the apparent force that causes a rotating body to move away from the centre of rotation. Not to be confused with centripetal force. Caused by inertia of the rotating body as it’s path is continuously redirected.

Centrifugal pump: A pump that transports fluids by conversion of rotational kinetic energy into hydrodynamic energy of fluid flow. Typically fluid enters the pump near to the rotating axis, and is accelerated by an impeller, flowing radially outward to a volute chamber where it exits the pump.

Centrifugal separator: Uses centripetal force to separate solids from liquids.

Ceramic: In general, ceramics are inorganic, nonmetallic solids. They may be crystalline or amorphous. They are produced by heating followed by subsequent cooling.

Change of state: When a substance changes from one state to another. For example, solid to liquid, liquid to gas, or solid to gas.

Check valve: A mechanical device that allows flow of a liquid in one direction only. A one-way valve that prevents fluid from flowing backwards in a pump.

Chemraz®: An elastomer used to produce seals with high chemical resistance, retaining efficient elastic qualities. Registered trademark by Greene Tweed.

Chloride stress corrosion: Stress corrosion refers to the growth of cracks in a corrosive environment. Certain stainless steels and aluminium alloys are subject to stress corrosion in the presence of chloride.

Chopper pump: A pump in which the impeller also acts as a cutting blade. Used with solid containing fluid applications to prevent pump blockage.

Chromecarbide: Produced when stainless steel is welded. Forms in the heat affected zone when chrome combines with carbon.

Chrome oxide: The protective layer (passivated layer) that forms on stainless steel to prevent further oxidation.

Circular casing: A type of casing used in centrifugal pumps when the pump is used for circulation rather than building pressure / head.

Clam shell: Used to set the distance between convolutions during the production of a metal bellows.

Close-coupled: The situation when the pump impeller is mounted directly on the rotating drive shaft. There are no separate bearings.

Close-coupled pump: A pump in which the impeller is mounted on the drive shaft. Close-coupled pumps have the advantage of being compact, but are limited in size.

Closed or open impeller: In a closed impeller, the impeller vanes are contained within a shroud, causing the fluid to always be in contact with the impeller. An open impeller lacks this shroud. Closed impellers are more efficient, but can also clog easier if the process fluid contains solids.

Closed impeller: An impeller whose vanes are completely enclosed by two shrouds, one on the front and one on the back.

Coated Face: When the face of a seal is plated or welded onto the base of the seal, made of a softer material.This design can present problems if the two metals in question have different thermal expansion rates.

Coke: A fuel produced by heating or“cracking” petroleum products. It can interfere with seals of pumps.

Colebrook equation: In fluid mechanics, it’s important to understand the friction caused by interaction of the fluid with the internal surface of the pipe. The Colebrook (a.k.a. Colebrook and White) equation is one equation that can be used to calculate the friction factor of a fluid flowing in a pipe.

Composite: In the context of mechanical seals, it refers to either a non-metallic material or a combination of a non-metallic face inserted into a metallic base material.

Compression set: Rubber seals become “compression set” when they are overheated. Elastomeric material loses its shape and takes on a new shape. Can cause leaks in seals.

Concentric dual seal: A dual seal where one seal is situated concentrically within another seal. Used when radial dimensions are not limiting.

Concentricity: When rotating parts each share the same axis of rotation, they are said to be concentric with each other.

Condensate: The fluid formed after a vapour has condensed. For example, water is a condensate of steam.

Constant level oiler: A means to maintain the correct oil level in a bearing housing. Automatically replenishes oil as it is used.

Convection: Fluid movement caused by local differences in density. Areas of hot fluid (less dense) will naturally rise, while colder fluid (denser) will sink.

Convection tank: A container used to hold the fluid between two mechanical seals. Integrated heater / coolers are used to control the temperature of the barrier fluid.

Convolution : During construction of metal bellows plates, when they are welded together, they form a convolution.

Cooling jacket: An extra casing surrounding the stuffing box to control the temperature of the process fluid within the stuffing box.

Corebox: Metal parts that are cast have an outer“pattern” – the pattern that is found on the outer surface of the casting, and an inner “corebox” – the pattern that is found on the inside of the casting.

Corrosion resistant: Corrosion resistant material must corrode at less than the the following rates: less than 0.002 inches (0.05 mm) per year.

Coupling: A connection between the pump shaft and the motor shaft. Can compensate for axial movement, but not radial misalignment.

Cover: In a radial split pumps, it’s the part of the pump that completes the case.

Critical speed: Objects that are elastic (e.g. O-rings) will have natural resonant frequencies. When a pump / shaft rotates at this frequency, minor imbalances will be magnified. The speed where these natural frequencies occur are called critical speeds.

Cryogenic: Very low temperatures.

Cutwater: DA device that directs the process fluid to the pump discharge pipe.

Cutwater diameter: The cutwater diameter is an important measurement in a centrifugal pump. It is used to determine the appropriate B-gap and limit pressure pulsations and forces to reasonable levels.

CV coefficient: The flow coefficient of a mechanical device that is an indicator of its efficiency at allowing fluid flow. It describes the relationship between the pressure drop across an opening and the flow rate.

Cyclone separator: A device that separates solids from liquids by using centrifugal force.

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