Whereas the price of a pump will be proportional to its size, the price of the controls is independent of the flow being controlled. There is a break-even point, beyond which centrifugal pumps with closed loop control will be more economical, and below which metering pumps will be more cost effective. For more difficult applications, the point shifts upward. High pressure centrifugal pumps, whether high speed or multistage, are expensive, whereas metering pumps can all produce higher pressure even though it is not always required. Because of their relatively small size, metering pumps are more likely to be made of corrosion resistant materials as standard.
Centrifugal pumps are also very limited in the fluid viscosity they can handle.
Another consideration is whether the process calls for remote or automatic control of the flow rate. Controlling the set point of a flow controller or a speed controller from a remote location is a simple matter. Controlling the displacement of a metering pump from a remote location, or automatically following a process signal, requires additional equipment, namely actuators. The closed loop speed control used on rotary metering pumps falls somewhere in between the variable displacement metering pumps and the closed loop flow control used with centrifugal pumps, since it does not use a flowmeter but is easy to control automatically. Conclusion For controlling low flows, metering pumps should always be the first choice.