The dosing pump belongs to the positive displacement pump family and is typically a diaphragm pump.
Diaphragm pumps are leakage-free because the diaphragm forms a seal between the pumped medium and the surroundings. The diaphragm pump is fitted with two non-return valves – one on the suction side and one on the discharge side of the pump.
The flow of a diaphragm pump is adjusted by either changing the stroke length and/or the rotation speed of the motor. To increase operating range, a frequency converter can be connected to larger diaphragm pumps.
On smaller diaphragm pumps, the diaphragm is activated by a connecting rod, which is attached to an electromagnet. The coil (see illustration) thereby receives the exact number of strokes needed. On larger diaphragm pumps, the diaphragm is typically mounted on the connecting rod, which is activated by a motor-driven camshaft.
On a third type of diaphragm pump, the diaphragm is activated by an eccentrically driven connecting rod and a stepper motor, or asynchronous motor. A stepper motor drive increases the pump’s dynamic area, and its dosing accuracy is improved considerably. With this construction it is no longer necessary to adjust the stroke length because the connecting rod is mounted directly on to the diaphragm. The result is optimized suction conditions and excellent operating features.