The metering pump is designed to deliver exact volumes of liquid, e.g. a specific volume of fuel to be pumped from a fuel tank to the burner of an engine-independent heater.

The automotive component industry develops increasingly effective emission control systems for the purpose of protecting the environment against exhaust gas emissions. The metering pump is used in diesel particulate filters as an additive doser or HC doser. The fuel injected directly – or indirectly via an evaporator – upstream of the diesel particulate filter serves to regenerate the particulate filter.

Typical metering pumps (or micro-metering pumps) take the form of reciprocating pumps or diaphragm pumps.

In a reciprocating pump the plunger is connected to an armature which is centrally surrounded by the coil. When no current is applied, all the cavities are filled with the medium to be delivered. When current is applied to the coil, the armature moves the plunger against the force of a spring. The plunger opens a valve and expels the medium from the pump chamber. When this happens the inlet to the pump chamber is closed off and the liquid continues to flow into the armature space.

When the supply of electricity is interrupted, the spring pushes the armature and plunger back. A partial vacuum is created in the pump chamber and the liquid enters the open inlet.

The metering pump handles the functions of all otherwise necessary system components such as a pump, metering valve, stop valve and possibly a pressure sensor – all at once. Combining the benefits of excellent metering accuracy and long service life with a compact and sturdy design, the metering pump is a highly versatile and efficient product.

In a diaphragm pump the diaphragm is moved either directly or indirectly via the solenoid plunger, thus enlarging the pump chamber. The supply of liquid is controlled by check valves at the inlet and outlet. The pump draws in the liquid during one plunger motion and delivers it against system pressure during the return motion.

By selecting an appropriate diaphragm material and hydraulic connections, the pump can be adapted to suit the particular medium.

In addition to diesel and petrol/gasoline, Thomas pumps can handle fuel oil, methanol, ethanol, sea water, additives, acids and alkalis.