3.4.9 Metering pump

Metering pump

The purpose of a Metering pump is to add a defined volume of liquid to a process. The volume is controlled by adjusting rotational speed, number of reciprocal strokes and stroke length depending on the pump design. Metering pumps are also known as a proportioning pumps.

Certain processes require the metering (dosing) of small quantities of fluid to a larger fluid flow. Figure 3.49a shows examples of this type of process requirement.

3.49a

 

 

The functions which are thus required of metering pumps consist of:

  • Energy increase
  • Feed
  • Regulation and control

The feed function of a metering pump is indirectly determined by the choice of pump construction whose volume is independent of back-pressure, i.e. displacement pumps, usually piston, piston diaphragm, diaphragm or peristaltic type.

The volume flow rate is thus varied by means of varying the stroke length, see figure 3.49b or by varying the speed.

Figure 3.49b Piston type metering pump with variable stroke length. Raising or lowering the “Z”-shaped crankshaft changes the length of the stroke.

Piston type metering pump with variable stroke
Figure 3.49b

When it is required to meter several different fluids to the main flow it may be convenient to combine several pump elements together. For regularly repeated doses the recipe was recorded on punched cards in the past, to enable numerical control by means of electronic circuits. Today, accurate control is made possible by Interfaces integrating the pumps into a fully automated processes with built in microprocessor technology and sophisticated monitoring functions ensuring reliability in operations and minimum of chemical waste.

The construction of metering pumps for moderately aggressive media is illustrated in figure 3.49c.

Metering pump for moderately corrosive media
Figure 3.49c

For higher pressure an intermediate liquid, oil for example, is introduced and acts against a diaphragm, so called diaphragm or piston diaphragm metering pumps. The movement of the diaphragm being limited by supporting walls with slots on each side of the diaphragm.

Metering pump for high pressure or strongly corrosive media (leak-free)
Figure 3.49d

.
Figure 3.49d Metering pump for high pressure or strongly corrosive
media (leak-free)

«
»