Damping: Damping refers to the process of reducing vibration by physically contacting a vibrating component.

Darcy-Weisbach equation: The Darcy-Weisbach equation is used to calculate the frictional head loss in pipes for fluid flow. The friction factor (f) must be determined, and it can be calculated using the Colebrook, Swamee-Jain equations, or by referring to the Moody diagram.

DCI: DCI stands for Disassembly, Cleaning, and Inspection, which is the initial step in any maintenance, repair, or upgrade process.

Dead ending: Dead ending is a procedure that isolates the stuffing box, where no flushing lines or recirculation lines are connected.

Dead head: Dead head is a hazardous condition that occurs when a pump is operating but no discharge is present due to a blocked line or a mistakenly closed valve. The pump continues to run until a safety shutoff pressure is reached, which may lead to overheating and damage if recirculation within the pump occurs.

Decanting: Decanting is the gradual transfer of fluid from one container to another.

Deflection: Deflection refers to the radial movement of a shaft located along the axial direction.

Density: Density is the mass per unit volume of a material and is often expressed in grams per milliliter (g/mL) or grams per cubic centimeter.

Design duty point: The design duty point is the specific operating point on a pump’s efficiency graph that has been optimized during the design process. A process fluid’s capacity at a given head or pressure is given by this number. Ideally, this point should align with the pump’s best efficiency point.

De-staging: In multi-stage pumps that have multiple impellers, de-staging refers to the process of removing one or more impellers to decrease the overall head.

D-frame adapter: A D-frame adapter is a device used to align the shaft of the pump with the shaft of the motor. D-frames are utilized when the system is manufactured in metric dimensions, while C-frames are used for standard dimensions.

D-Gun process: The D-Gun process is an alternative method to the plasma process for depositing metal. It is typically employed to apply a layer of hard metal over a softer metal surface.

Dial indicator: A dial indicator is a measuring instrument used to assess the axial alignment of a shaft. Any displacement in the alignment will cause the dial indicator to deflect.

Diaphragm pump: Also known as a positive displacement pump or an air-operated diaphragm pump, a diaphragm pump utilizes a diaphragm to pump fluids. Diaphragm pumps with double diaphragms offer smooth operation and are particularly effective for pumping viscous, toxic, chemically aggressive, or abrasive liquids.

Differential Pressure: The differential pressure refers to the variance between the pressure at the inlet and outlet of the pump within a system. It indicates the pressure difference across the pump.

Diffuser: The diffuser is a component located within the discharge region of a pump. It is designed to reduce turbulence in the discharged liquid by facilitating a gradual decrease in velocity. Typically, a diffuser consists of a set of vanes that are an integral part of the pump.

Dilatant: Dilatant refers to the behavior of a liquid that exhibits non-Newtonian characteristics, whereby its viscosity increases as the applied shear strain increases. For instance, a mixture of cornstarch and water demonstrates dilatant behavior.

Dilatant liquid: A dilatant liquid is a type of fluid whose viscosity increases with an increase in shear rate, such as during agitation. It displays non-Newtonian behavior, wherein the viscosity rises as the shear strain applied increases. A classic example of a dilatant liquid is a mixture of cornstarch and water.

DIN standard: DIN standard refers to a standard published by the “Deutsches Institut für Normung” or German Institute for Standardization. It is a set of guidelines and specifications established to ensure uniformity and quality in various industries and products.

Disaster bushing: A disaster bushing is used in API glands to provide support to the shaft in the event of a bearing failure or to prevent product from escaping to the atmosphere following a seal failure. This bushing is designed with a close clearance, typically around 0.025 inches or 0.5 mm, which directs most of the leakage through a drain connection in the seal gland to an appropriate container.

Discharge head: The discharge head refers to the pressure at the outlet or discharge of a pump. It indicates the pressure level of the fluid as it exits the pump.

Discharge recirculation: Discharge recirculation occurs when flow reversal or recirculation happens at the discharge tips of the impeller vanes. It involves connecting a line from the pump’s discharge side to the stuffing box. To increase the stuffing box pressure, it is recommended to use a close-fitting bushing at the end of the stuffing box. This setup is commonly employed when pumping a fluid that is close to its vapor point.

Displacement: Displacement refers to the change in position of an object over time, typically measured with respect to its initial position. In the context of dynamic movement, it often refers to the peak-to-peak displacement.

DN factor: The DN factor indicates that precision bearings should not be used when the product of the bearing bore diameter (in millimeters) and the rotational speed in RPM is equal to or greater than 300,000.

Dosing: Dosing is a controlled method of pumping that enables the precise discharge of specific amounts of fluid.

Double balanced seal: A double balanced seal is a type of seal that is hydraulically balanced in both directions. This characteristic is desirable but is rarely provided by manufacturers.

Double row, deep groove, ball bearing: A double row, deep groove ball bearing configuration positions the rows of balls in such a way that the load is transmitted at an outward converging angle, thereby increasing the thrust load capacity.

Double seal: A double seal refers to a pump configuration that utilizes two mechanical seals on the drive shaft. It is designed to prevent the process fluid from leaking, especially when pumping hazardous liquids.

Double suction pump: In a double suction pump, the process fluid is directed to both sides of the impeller within the casing. This configuration provides excellent hydraulic balance, resulting in stability and reduced vibrations.

Double suction impeller: A double suction impeller is an impeller design that features two inlets, allowing the liquid to enter the impeller from both sides. This configuration provides hydraulic balance and stability, but it can be more expensive to implement.

Double volute: A double volute refers to a centrifugal pump that incorporates two cutwaters within its casing. The purpose of the double volute design is to minimize shaft deflection when the pump operates away from its best efficiency point.

Drawdown: Drawdown refers to the reduction in the volume of a liquid within a container as a result of the liquid being pumped out by a pump. It typically denotes the decrease in liquid height along the walls of the container.

Drive collar: In a cartridge seal, the drive collar is the component that connects the seal sleeve to the shaft. It facilitates the transmission of rotation and prevents axial movement of the sleeve.

Drive lugs: Drive lugs are a more robust method of transmitting torque to the seal face compared to setscrews. They provide a secure and reliable means of transferring torque.

Drooping curve: A drooping curve refers to a pump efficiency curve in which the head initially rises at low flow rates and then drops as it approaches the shut-off head point. This type of curve indicates reduced efficiency at low flow conditions.

Dry critical speed: Dry critical speed, as defined by API 610, refers to the natural frequency of a rotor calculated under the assumption that the rotor is supported solely by its bearings, which are considered to have infinite stiffness. In simpler terms, this calculation disregards any damping effects caused by the process fluid. For a comparison, see wet critical speed.

Dry running: Dry running refers to the operation of a pump without any process fluid or a seal without any lubricant. It implies that the equipment is running without the necessary fluid or lubrication.

Dual seal: A dual seal configuration refers to the presence of two seals arranged in one of several possible configurations, such as back-to-back, face-to-face, tandem, or concentric.

Dual mechanical seal: In a dual mechanical seal configuration, two seals are installed within the same chamber in one of several possible positions, including tandem, concentric, face-to-face, or back-to-back arrangement.

Ductility: Ductility refers to the ability of a metal to deform without breaking. It is often characterized by the ease with which the material can be stretched into a wire.

Dynamic elastomer: The dynamic elastomer refers to the elastic components of a seal that are responsible for compensating for seal face wear or shaft movement. Typically made of rubber or other elastic polymers, these components contribute to the sealing action and flexibility of the seal.

Dynamic head (system head): The dynamic head, also known as the system head, represents the component of the total dynamic head in a system that is caused by friction between the process fluid and the pipe walls. It accounts for the energy loss due to fluid interaction with the system.

Dynamic unbalance: Dynamic unbalance occurs when the axis of inertia of a rotor, such as an impeller, is not aligned with its geometric axis. This condition, also referred to as two-plane unbalance, requires correction in two planes. Centrifugal pumps are most commonly affected by dynamic unbalance.

Related Links

• Pump Glossary
• Pump info