Radial: Arranged like radii. Arranged along the radius of a circle, in this case, the circle refers to the circular shaft.
Radial bearing: Most bearings are meant to support radial loads. Whether they can support axial loads depends on the type of bearing.
Radial flow pump: A centrifugal pump designed so that the pump has medium head and medium flow, or high head and low flow.
Radial split pump: A pump that has its case split along a line that is perpendicular to the centerline of the shaft.
Radial vane pump: Also known as partial emission pump. A pump designed to handle corrosive chemicals at high head, with low flow rates. Developed in WWII to pump fuel into German Ram jet engines.
Rated operating point: The point on the pump efficiency curve at which the pump vendor guarantees the pump’s performance.
Reaction bonded: A method of manufacturing silicon carbide by a reaction between porous carbon (graphite) and molten silicon.
Recessed impeller pump: Sometimes known as vortex pump. A pump design which reduces contact between the impeller and the process fluid by recessing the impeller. Ideal for slurries containing solids or fibres.
Recirculation: Refers to the fact that at both high and low flow (as compared to the BEP on efficiency graph), the process fluid will tend to recirculate at the suction and discharge.
Relative density: Ratio of a liquids density to that of water measured at 4°C. Also known as specific gravity.
Renkin scale: A temperature scale with the same size units as farenheit, but starting at 0° defined as absolute 0.
Repeller: An additional impeller used to lower the stuffing box pressure.
Residual unbalance: The amount of unbalance (in terms of mass) remaining after a rotor, or shaft, has been balanced on a balancing machine. Expressed as ounce inches. This will cause the rotor to vibrate during operation. The magnitude depends on the amount of unbalance and the rotor speed.
Reynolds number: A dimensionless number that relates the ratio of inertial forces (velocity) to viscous forces.
Rheopectic: A fluid whose vicosity increases with time.
Rigid rotor: A rotor that operates at less than or equal to 70% of its first critical speed. Does not vibrate.
Rigid shaft: A pump shaft that operates below its critical speed..
RMS: Root mean square. A statistical measure of the magnitude of variation in some quantity.
Rockwell "C": A scale used to measure hardness of materials.
Rotating seal: In mechanical seals, if the moveable portion of a seal rotates with the shaft, then the seal is said to be a rotating seal.
Rotor: The compilation of all the rotating elements in a pump. Includes the shaft, the impeller, wear rings, bearings, etc.
Run out: If the rotating shaft doesn’t rotate exactly on its centerline, then the run out is a measure of the deviation from true rotation. Expressed as twice this distance.
Runner: Historical term for the impeller, rarely used.