A dosing pump, which is a positive displacement pump, is designed to inject a chemical or another substance into a flow of water, gas or steam. Dosing pumps, which are typically small, provide an extremely precise flow rate for maximum control. They are the central part of an integrated dosing system designed for automatic dispersion of chemicals. This dosing definition applies to a wide range of applications and industries, from waste water treatment to food processing
In addition to water treatment and food industries, dosing pumps, also known as chemical metering pumps, are used in industrial plants, agriculture, manufacturing facilities, medical laboratories and mining operations. A chemical feed pump might be used to add a caustic chemical or an acid to a water storage tank to neutralize the pH. It can also be used as a chlorine pump to kill bacteria. A chemical dosing pump is designed to operate in challenging situations, such as high temperature and high pressure environments.
A dosing pump draws a measured amount of liquid into its chamber and injects the chemical into a tank or pipe that contains the fluid that is being dosed. It's powered by an electric motor or an air actuator and has a controller that turns the pump on and off and manages the flow rate. Some models include more sophisticated control systems.
The main components of a dosing pump include:
These four dosing pump types are designed for different pressures, chemicals and applications. They vary by pumping action and mechanism.
Diaphragm (constant injection) pumps use a diaphragm, piston and valves on both the inlet and outlet to fill and empty its chamber. Drawing in the piston fills the chamber, and a specific amount of chemical is injected at a preset speed, usually a percentage of the maximum flow rate. Certain pump models are capable of variable dosing rates.
Diaphragm (pulse injection) pumps also uses the diaphragm mechanism, but instead of a constant flow rate, a solenoid coil takes in the chemical and injects it in pulses. The flow rate is the length of time between pulses. It is less accurate than the constant injection pump but is simple in design and inexpensive.
Lobe pumps let a certain volume of fluid through meshing gear impellors. It is not as accurate as a diaphragm pump and it is only suitable for high viscosity fluids that will self-lubricate to minimize wear. They're not made for low flow rates, as it is difficult to ensure accuracy.
Peristaltic pumps are highly accurate for dosing. A flexible bent tube lets the fluid pass, and the flow is controlled by a roller that moves by way of a mechanical arm on the outside. This pushes product in the tube into the dosing tube and main fluid stream.