Glossary D

D frame adapter

  • Used to connect and align the pump and motor (manufactured in metric dimensions). The Imperial version is called a “C” frame adapter.

D-Gun process

  • A metal spray process used to put a hard surface on a softer metal. This is the normal method of applying nickel base tungsten carbide. It is preferred over the popular Plasma Process if you arre manufacturing a mechanical seal face.

D.I.N. standard

  • The German standard for industrial products.


  • The physical touching of a component to arrest vibration.

Dead ending

  • Isolating the stuffing box. No recirculation or flushing lines in or out.


  • Movement or displacement of the shaft in a radial direction.


  • Measured in gm/cmor lb/in 2 A measure of the weight of the fluid. A better term than specific gravity.

Dial indicator

  • A tool used to measure concentricity or displacement of a shaft.


  • A liquid that thickens (increases its viscosity) with agitation.

Disaster bushing

  • Used in A.P.I. glands to support the shaft in the event of a bearing failure, or to prevent product from rushing to atmosphere after a seal failure. The close clearance (0.025 inch or 0.5 mm.) directs most of the leakage through a drain connection in the seal gland to an appropriate container.

Discharge recirculation

  • Connecting a line from the discharge side of the pump to the stuffing box. Should be used with a close fitting bushing in the end of the stuffing box to increase the stuffing box pressure. A common application when pumping a fluid close to its vapor point.

DN factor

  • Do not use precision bearings if the bearing bore (millimeters) x rpm. is 300,000 or greater

Double balanced seal

  • Hydraulically balanced in both directions. A desirable feature, but seldom provided by seal manufacturers.

Double seal

  • An out dated term describing two seals in a pump. The latest terminology is “dual seals”. In the past the term was used to describe a higher pressure barrier fluid between dual seals.

Double suction pump

  • The rotor is suspended between two bearings with the fluid entering on either side of the impeller. Used at higher capacities.

Double volute

  • A centrifugal pump design that incorporates two cut waters to prevent shaft deflection when the pump is operating off of the B.E.P. Lowers the efficiency of the pump and therefore seldom used on smaller size impellers.

Drive lugs

  • These lugs or pins transmit the torque from the set screws to the seal face.

Dry running

  • Running without fluid at the seal face.

Dual Seal

  • Two seals running in various configurations: back to back, tandem, face to face, or concentric.


  • The property of a metal that lets you give it a great deal of mechanical deformation without cracking.

Dynamic elastomer

  • The rubber part that has to move to move or flex to compensate for seal face wear or shaft movement.

Dynamic head (system head)

  • The pump head created by friction in the piping system.