Radial flow pump - pump in which the head is developed principally by action of centrifugal force; the liquid enters the impeller axially at the hub and flows radially to the periphery.
Radial split pump - a pump whose casing split, or whose principal joint, is perpendicular to the shaft centerline. The complete casing assembly is usually referred to as the case and cover. It is also known as vertically split pump but the use of this term should be avoided because it can be confused for a vertical pump. A radially split case pump can be either a horizontal or a vertical pump.
Rated operating point - the point at which the pump performance is guaranteed by the pump vendor subject to the performance tolerance of the applicable standard or user specification. The pump may, or may not, actually operate at the rated condition. The point at which the pump operates most of the time is called the normal operating point.
Relative density - Ratio of a liquid density to water density at 39.2 degrees Fahrenheit (4 degrees Centigrade). Also known as specific gravity.
Residual unbalance - the amount of mass unbalance remaining in a rotor after balancing the rotor on a balancing machine - it is commonly expressed in ounce-inches. Residual unbalance causes a rotor to vibrate due to centrifugal force when in operation. The magnitude of vibration increases proportionately by the square of the increase in rotor speed. Thus, the rotor speed is taken into account when calculating the amount of acceptable residual unbalance from the equation, U = K x W / N
U - residual unbalance, per plane, in ounce-inches K - constant ranging from 4 to 8 depending on balance quality W -rotor static weight, in pounds N - rotor speed, in revolutions per minute (RPM)
Use K=4 for balance equal to ISO 1940-1 grade G1, and K=8 for ISO Grade G2.5. (Read more)
Rigid rotor - a rotor that does not operate about 70% of its critical speed and maintains its balance at any speed below 70% of its critical speed.
Rigid shaft - see rigid rotor
Rotor - the assembly of all the rotating elements of a pump such as the shaft, the impeller, wear rings, shaft sleeves, bearings, etc., including the pump half coupling hub.