Glossary

DEFORMATION

A stress induced change of form or shape.

DENSITY

The ratio of the mass of a body to its volume, expressed as Lb/Ft3 or gm/cc. It is common for die-formed graphite foil rings to be produced to a specific density.

DESIGN PRESSURE/VACUUM

The pressure or vacuum condition that exists during system start-up and/or shut-down operations. During this cyclic phase in the system, both pressure and vacuum conditions may occur.

DESIGN TEMPERATURE

The maximum or most severe temperature expected during normal operation caused by equipment failure. (See Excursion Temp.)

DIAPHRAGM SHEET

PTFE or sheet rubber (generally fabric-reinforced) from which flat diaphragms are cut.

DIE CUT

Shaped articles cut with a die from a sheet of material.

DIE FORMING

A manufacturing process in which braid or graphite foil is compressed in a mold to form a ring.

DIELECTRIC STRENGTH

The measure of a product’s ability to resist passage of a disruptive discharge produced by an electric stress described in volts/mil (1 mil = 0.001").

DIN

Abbreviation for Deutsches Institut für Normung. English translation is German Industry Standard – it is the European equivalent to ASTM.

DISCHARGE PRESSURE

The fluid pressure measured on the discharge (or outlet) side of the pump where the fluid exits the volute.

DISHED DIAPHRAGM

A molded diaphragm in which the entire center is depressed below the plane of the rim.

DRILL PATTERN

The systematic location of bolt holes on the mating and expansion joint flange through which the expansion joint will be attached.

DRUM CURE

A method of vulcanizing rubber in which the product is wrapped around a drum and cured in hot air or steam, usually with a separator or wrapping jacket.

DUCT ID

The inside dimension of the ductwork measured from the duct walls prior to any form of coating.

DUCTILITY

The ability to be drawn. Example: The stretching of metal wire to a smaller cross-section.

DUROMETER HARDNESS

An arbitrary numerical value measuring the resistance to indentation (without puncturing) of the indentor into the surface or rubber.

DYNAMIC RUNOUT

Twice the distance the center of the shaft is displaced from the center of rotation and expressed in TIR. That runout to which the seal lip is subjected due to the outside diameter of the shaft not rotating in a true circle. Synonym: Shaft Runout.

DYNAMIC SEAL

A seal required to prevent leakage past parts which are in relative motion. The opposite of static seal.