Radial
90 degrees to the centerline of the shaft.
Radial bearing
In an end suction centrifugal pump it is the bearing located
closest to the stuffing box. This bearing handles most of the
radial loads put on the impeller.
Reaction bonded
A method of manufacturing silicone carbide mechanical seal faces.
These materials are sensitive to caustic and some other high pH
liquids.
Renkin scale
Used to measure low temperatures in the Fahrenheit scale. Similar
to Kelvin which is used to measure low temperatures in the Centigrade
system.
Repeller
A second impeller used to lower the stuffing box pressure.
Reverse balance
A common type of hydraulic balance used on outside mounted mechanical
seals.
Rigid shaft
A shaft with a rotating speed lower than its first critical speed.
RMS
Root mean square. A measure of surface finish or smoothness.
Metric uses C.L.A. or centerline average for the same purpose.
Rockwell "C"
The scale most often used to measure hardness of the hard seal
face.
Rotating seal
When the spring loaded or moveable portion of the seal rotates
with the shaft.
Run out
Twice the distance that the center of the shaft is displaced from
the axis of rotation.