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Glossary of Pump Terms: R

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.


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.


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.

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