Dosing & Metering

Dosing pumps also known as metering, chemical injection, or proportioning pumps are used for the consistent and accurate delivery of fluids into a process. These can range from flavourings into a recipe, chemicals in a wastewater treatment application or liquids in a liquid filling machine. 

A range of technologies are used for dosing which include Peristaltic, Progressing Cavity, and Solenoid Metering Pumps. Air Operated Diaphragm Pumps can also be utilised when used in conjunction with an external plc controller as part of a larger assembly, as well as gear pumps. 

Positive displacement designs of pumps are used in such applications as due to their internal design, they provide a fixed volume displacement proportional to speed, which does not vary with pressure as in Rotary Centrifugal Pumps.

How Dosing Pumps are controlled

Metering pumps can be controlled in a number of ways mainly depending on their internal design:

Peristaltic & Progressing Cavity Metering Pumps 

These provide a fixed volume displacement by RPM, and so the volume dosed in time varies with unit speed.

Solenoid & Diaphragm Metering Pumps

These are controlled via the stroke length and stroke rate.

A motor is connected to the pump head via a worm gear box converting rotational movement to cam movement, whilst also reducing input speed to the pump head.

The movement drives a Piston within the unit to compress a diaphragm within the head expelling fluid via an outlet valve. As the piston withdraws, the diaphragm expands drawing in fluid via an inlet valve. It is the piston length and speed at which it compresses the diaphragm which controls the volume and speed at which the pump doses.

Options include:

• Pulse dosing according to the pulses received by a flowmeter. Pumps can dose according to the number of feedback pulses received and can be either a dose per pulse or every X doses.

• Timer – the chemical is dosed every X mins, hours, typically used in a circulation process

• Level control – once a certain level is reached the pump will begin dosing to reduce the level 

• Volume dosing – according to the volume of liquid

• Feedback via a 4-20ma input where monitoring is place for measurement of PH, Redox (RX), and Chlorine or other chemical in PPM (parts per million)

Examples of metering applications:

Chlorine dosing into swimming pools

Additives into drinking water such as calcium hydroxide, aluminium sulphate, sodium silicofluoride, liquified chlorine

Chemicals into a process for mixtures

Some formulas require precise amounts of chemicals to ensure the finished product has the consistency, and required characteristics for use.

Batching

When decanting bulk fluids from IBC's which are repackaged and resold in reduced volumes e.g. 5L containers

Various models and variations are available depending on the proportioning required. 

There are a range of symbols which can be used in Process and Instrumentation drawings - learn more.

North Ridge Pumps supplies a comprehensive range of pumps for varying industrial applications - view our pumps for dosing and metering here.