Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs. For more information, visit www.pumps.org.
Calibrated electric motors are satisfactory for determining the power input to the pump shaft. The electrical input to the motor is observed, and the observations are multiplied by the motor efficiency to determine the power input to the pump shaft. Calibrated laboratory type electric meters and transformers shall be used to measure power input to all motors.
For more information about this topic, see ANSI/HI 6.6 Reciprocating Pump Tests.
Q. What methods are used to cool a motor that drives a rotodynamic pump?
A. Many cooling methods can be used in motor design. When the cooling air is drawn from the surrounding environment, circulated around the internal components and expelled back into the surroundings, the cooling method is an open circuit. This type of cooling is only possible in open-enclosure motors.
Closed-circuit cooling involves an internal coolant in a closed loop that passes heat to another coolant either through the surface of the machine or with a heat exchanger. This type of cooling is by definition associated with totally enclosed machines because the primary coolant remains contained within the motor.
Most motors use shaft-mounted fans to circulate air as the primary coolant. One drawback of this approach is that the velocity at which the cooling air is circulated decreases if the speed of the motor decreases. In some applications, a constant velocity of air is necessary. In these cases, separately powered fans are often employed to deliver a regular velocity of air regardless of the motor’s rotational speed. While air is the most common fluid used as primary and/or secondary coolant in electric motor design, units can be built using others—such as refrigerant, hydrogen, nitrogen, carbon dioxide, water and oil.
VS0-style pumps, with the motor submerged, must have a minimum flow of cooling liquid past the motor during operation to properly dissipate heat. In applications such as open channels with a relatively low velocity of flow around the motor or installations in which the flow will not naturally flow past the motor, a flow sleeve needs to be installed to draw flow around the motor casing and protect the motor internals from overheating. For hot pumped liquid applications, consult the pump manufacturer.
For more information about motor cooling methods, see ANSI/HI 2.3 Rotodynamic Vertical Pumps of Radial, Mixed, and Axial Flow Types for Design and Application.