Glossary

RADIAL

In the direction perpendicular to a shaft axis.

RADIAL EXPANSION

The ability for a packing material to spread out in the radial direction of a stuffing box when it is compressed.

RADIAL LIP SEAL

A type of seal which features a flexible sealing member referred to as a lip. The lip is usually of an elastomeric material. It exerts radial sealing pressure on a mating shaft in order to retain fluids and/or exclude foreign matter.

RADIAL LOAD

The total force (load) acting on the seal lip which tends to maintain contact of the lip on the shaft. It is the sum of the forces developed from seal interference and the garter spring.

RADIAL WALL VARIATION

The difference between the minimum and maximum radial wall dimensions when measured around 360I of the seal lip.

RECIPROCATING

Motion of a shaft back and forth in the direction of its axis.

RECIPROCATING MOTION

An oscillating, back and forth motion as it normally pertains to a piston rod or valve stem.

RECIPROCATING PUMP

A type of pump that relies on the reciprocating motion of a plunger, or series of plungers, to generate pressure and cause flow.

RECOVERY

The degree to which a product returns to its normal dimensions or shape after being distorted.

RECOVERY (GASKETING)

The increase in thickness of a gasket after a load is removed.

REGULAR BRAID

A type of braided construction which yields a soft, flexible packing material having a square cross-section. Also referred to as "Square Braid".

REMOTE HANDLING

Handling without direct individual contact, usually done with robotic arms.

RESILIENCE

The ratio of energy given up by the elastomer upon releasing it from a definite deformation to the energy required to produce the deformation. Unless the deforming is momentary, the result obtained will be complicated by the partially plastic nature of the elastomer.

RESILIENT

Able to recover rapidly, i.e. elastic.

RETAINING RINGS

Segmented metal rings installed directly against the back of the expansion joint flange and bolted through to the metal flange of the pipe.

RIB

A long, narrow projection which is normally triangular in cross-section and which is molded into the outside lip surface of a helix seal. It is oriented at an angle to the shaft axis. One end of the rib forms part of the seal-lip contact surface.

RISING STEM VALVE

A valve in which the movement of the stem is simply reciprocating, with no rotation.

RISING/ROTATING STEM VALVE

A valve in which the movement of the stem is both reciprocating and rotating at the same time, usually following a helical path.

RMA

Abbreviation for the Rubber Manufacturers Association.

RMS

Abbreviation for Root Mean Square, used in describing surface finishes of a material. Common units are Micro inches (u inch) or Micrometers (u m).

RMS (SEE FINISH)

Root Mean Square, or average deviation from a theoretically perfect surface, is used to define surface finish roughness.

ROD

The metal shaft which extends from the piston to outside the cylinder.

ROLL

Sheet rubber and gasketing material of a uniform width rolled up on itself from which gaskets and other products of various shapes may be cut.

ROTARY

The motion of a body turning on an axis.

ROTARY SERVICE

A dynamic type of sealing application in which one member remains stationary while the other moves past it in a rotating mode. This type of service generally involves a continuous motion between members and higher surface speeds than those encountered in reciprocating applications. The generally higher degree of frictional heating combined with the fact it is concentrated in one area, sometimes lead to heat-related seal problems.

ROTATION (FLANGE)

The warping, bowing or bending of a flange that can occur from too much bolt load.

ROUGH TRIM

A trimmed surface with irregularities on the outside and inside lip surfaces in the immediate vicinity of the contact line.

ROUGHNESS

Irregularities in shaft surface texture which result from the production process. (See SAE J448a [June, 1963].)

ROUND BRAID

A braiding method that yields a hollow tube of yarn. See also "Braid Over Braid" and "Braid Over Core".

RPM

An abbreviation for "Revolutions Per Minute", a measurement of the rotary speed of a rotating shaft.

RUBBER

A material that is capable of recovering from large deformations quickly and forcibly and can be or already is, modified to a state in which it is essentially insoluble (but can swell) in boiling solvent such as benzene, methyl ethyl keytone, and ethanoltoluene azeotrope.

RUN OUT

A measurement of how far a shaft moves in the radial direction.