CONTROLS

Pump control in the broadest sense gives the pump user (1) the flow rate, pressure or liquid level desired, (2) protection for the pump and system against damage from the pumped liquid, and (3) administrative freedom in decisions on operations and maintenance.

Control System Types Pump control systems range in complexity from single hand-operated valves to highly advanced, automatic flow control or pump speed control systems. Pump type and drive type are factors in control system choice. For centrifugal pumps, either change of speed or change of valve setting can control the desired variable. For positive displacement pumps, whether reciprocating, rotary, screw, or other type, control is by change in speed, change in setting of bypass valve, or change in displacement. The last-mentioned method is found in metering and hydraulic drive pumps. Although this chapter considers only control systems having valves as final control elements, the sensing elements discussed also serve in pump speed control systems.

Pump control systems divide readily into two types: on-off and modulating. The on-off system provides only two conditions: a given flow (or pressure) value or a zero value. A valve is therefore either open or closed, and a pump driver is running or not. The modulating system, on the other hand, adjusts valve setting or speed to the needs of the moment. Either type of system can be automatic or manual.

System Essentials All control systems have

1. A sensing or measuring element

2. A means of...