Pump reliability starts with a firm – and flat – foundation
The reliability of a centrifugal pump begins when the pump is initially mounted to its baseplate. Baseplate flatness can be a determining factor in ease of installation, alignment and reducing future meantime between failures. A typical fabricated steel baseplate for an ANSI or standard industrial pump will be flat to within 0.005 inches per foot.
A flat surface allows the installer to more effectively level the baseplate prior to grouting, and then align the motor to the pump by shimming under the motor feet. When attempting to align the pump and motor shaft to within 0.002 inches total indicated run-out, it is easier to start out on a level playing field rather than have unequal shim stacks under each foot of the motor. A soft foot is where one or more feet are not in contact with the mounting pad when the unit is unbolted. Correct this by shimming, not by tightening the bolt, which could distort the motor frame.
Flatness versus level
Flatness is a measurement. During the manufacturing process, baseplate flatness is measured by attaching a dial indicator to the machine head, unclamping the baseplate so it is in its free state and then measuring various points on the milled surface. Flatness is also a manufacturing tolerance of the machined surface. Flatness measurement and acceptance is done at the manufacturing point.
Level is a state or condition of being. In the field, the installer uses a precision level and wedges (or leveling screws) to bring the flat surface of the baseplate pads to a level condition in both directions. The baseplate should not be twisted or bent.
There are machine limitations such as the tolerance capability of the milling machine. As the milling tool travels the length of the baseplate, it can achieve only certain flatness. Different baseplate designs possess varying abilities to withstand deflection during the machining operation. Similarly, fabricated baseplates may have internal stresses that, as they relieve, may cause the baseplate to distort from the shape during machining. All baseplates have some amount of flex and must be properly leveled prior to grouting. Proper leveling is critical to avoid future issues with alignment, and consequently to optimize pump life.
|George Ceelen is a senior product specialist for ANSI process pumps at|