Q. What intake design considerations are important for submersible vertical turbine pumps?
A. Submersible vertical turbine pumps can be installed in a wet pit or closed bottom can as shown in Figure G.1. Well motor types are recommended for both wet-pit type and closed-bottom can type of below-grade suction intakes in a rotodynamic pump.
Figure G.1. Submersible vertical turbine pump (Courtesy of Hydraulic Institute)A submersible well-type motor normally requires a minimum flow of liquid around the immersed motor to provide adequate motor cooling. For many applications, a shroud is required to ensure proper cooling flow around the motor. Sizing of the cooling shroud for internal flow velocities must be referred to the pump manufacturer. The top of the shroud must include a cover to restrict downward flow of liquid to the pump inlet while allowing for venting air from the shroud. The confined flow pathway provided by the motor cooling shroud is very desirable in developing a uniform flow to the first-stage impeller.
The characteristics of the flow approaching an intake structure are among the most critical considerations for the designer. When determining direction and distribution of flow at the entrance to a pump intake structure, the following must be considered:
- the orientation of the structure relative to the body of supply liquid
- whether the structure is recessed from, flush with or protrudes beyond the boundaries of the body of supply liquid
- strength of currents in the body of supply liquid perpendicular to the direction of approach to the pumps
- the number of pumps required and their anticipated operating combinations
For more information on the design criteria for various pump intakes, refer to ANSI/HI 9.8 Rotodynamic Pumps for Pump Intake Design.
Q. What types of alternating current (AC) single-phase motors are used in centrifugal pumping applications, and what are some typical applications?
A. Many types of single-phase motors are used throughout the commercial and industrial world. Listed below are a few types of single-phase AC motors used in certain pumping applications:
Split-phase: A split-phase motor is a single-phase induction motor equipped with a main winding and an auxiliary starting winding. This type of motor has a switch that deactivates the starting winding as the motor comes up to speed. Split-phase motors are used in spa, jetted tub and aboveground pool pump applications. The motors are usually rated from 1/6 horsepower (hp) through 1.5 hp.
Capacitor-start: A capacitor-start motor is a single-phase induction motor equipped with a main winding and an auxiliary starting winding with a series capacitor. This type of motor has a switch that deactivates the starting winding and capacitor as the motor comes up to speed. They are usually rated from 1/6 to 7.5 hp. Capacitor-start motors are the most common type of single-phase motors found on in-ground pool, irrigation and dewatering pump applications.
Permanent-split capacitor: A permanent-split capacitor motor is a single-phase induction motor equipped with a main and an auxiliary starting winding with a series capacitor. The motor does not have a switch and both the main and starting windings are always energized. The motors are typically rated from 1/2 to 15 hp and are commonly found in dewatering and irrigation applications.
Capacitor-start, capacitor-run: A capacitor-start, capacitor-run motor is a single-phase induction motor equipped with a main and an auxiliary winding with a series run capacitor. Both windings and the run capacitor are permanently energized. In addition, this motor has a second capacitor called a start capacitor that is deactivated by a switch as the motor comes up to speed. This type of motor is also called a two-value capacitor motor. The motors are usually rated between 1.5 and 15 hp and are commonly found in dewatering and irrigation applications.
For more information on centrifugal pumps, refer to ANSI/HI 1.3 Rotodynamic Centrifugal Pumps for Design and Application.