What Is a Pump Coupler?

A pump coupler is a device used to join the output shaft of a drive motor to the input shaft of a pump mechanism. Although some pump couplings are rigid, one-piece elements, the majority are of a flexible nature. This element of flexibility allows for a degree of misalignment and end play between the pump and motor. This makes installation of the pump easier and creates less wear and tear during operation. There are many types of pump coupler, with flange, bellows, and geared types being among the more common.

Most pumps are driven by separate electric motors or gasoline and diesel engines. Both the power plants and pump units typically feature rotary shaft power output and input arrangements. For the pump to work, the shaft of the drive unit must be connected to the input shaft of the pump. In some applications, this is a relatively straightforward operation and can be achieved with a simple set of rigid flange couplings. In most cases, though, and this is particularly true of heavy industrial pumps, an element of flexibility in the pump coupler is required.

This flexibility is needed to accommodate the small amounts of lateral misalignment and end play, which almost invariably exists in this type of application. Lateral misalignment is generally caused by slight differences in the mounting levels between the pump and motor, while end play, or end movement, as it is also known, is caused by wear on the pump mechanism or surges in fluid flow. Both of these factors require a certain amount of give in the coupling between the pump and motor drives.

Rigid pump coupler sets are typically little more than two flange-equipped sleeves, one of which fits over the motor shaft and one over the pump shaft. Both are generally held firmly in place on the shafts with slotted keys. The two flanges feature matching holes that are used to bolt the two together, thereby transferring the motor drive to the pump. Flexible pump couplers are similar in general design and feature matching units that lock onto both shafts. The main difference between the two types, however, is a flexible element included in each unit.

This is often a toothed rubber insert which slots into corresponding cutouts in the individual pump coupler units. In some cases, a flexible rubber bellows forms the flexible element, while other coupler types include a loosely meshing set of gears between the two coupling units. All serve a common purpose in allowing a degree of lateral and axial deflection between the pump and motor shafts. In this way, undue wear or damage is prevented to both pump and motor units during pumping operations.