3.4.12 Impeller pump
Impeller pump with flexible vanes
An impeller pump is a vane pump where the eccentrically located rotor with vanes are replaced with a flexible rubber impeller concentrically located in the pump housing. The pumping action is created by an eccentric cam located between suction and delivery ports, see figure 3.412a.
In both types of pumps the liquid is drawn into the pump by an increasing volume between the vanes on the suction side, transported to the discharge side whilst trapped between the vanes and forced out by a decreasing volume.
Figure 3.412a Operating principles for flexible vane pump.
In a flexible vane pump, the rotor (flexible impeller), made of a synthetic elastomer, creates a seal between suction and discharge side. The pumps are therefore dry self priming with a vertical suction lift of 4-5 m, i.e. do not require to be filled with liquid to start up. With liquid in the pump it is capable of a vacuum of up to 500 —600 mm Hg.
As the impeller depends on the liquid pumped for lubrication, it is generally recommended that the pump should not operate without liquid for more than 30 seconds. This is more than sufficient time for self priming. Due to the flexibility of the vanes, the pumps are basically low pressure normally with pressures up to 200-250 kPa according to size and up to 300-400 kPa for certain high pressure models.
Flow capacities range from 0.1 to 30 m³/h. The single impeller, multi-vane principle, provides largely pulsation-free flow and enables the pump to handle products susceptible to damage.
Chemical resistance information, compiled by manufacturers of flexible vane pumps, provides a guide to the compatibility of various elastomers with liquids commonly used in industry. Broadly speaking the temperature range of some of these rotor materials is as follows:
- Neoprene min. +4°C max. +80°C
- Nitrile min. +4°C max. +90°C
- Viton (FKM/FPM) min. +7°C max. +110°C
However, as with any type of pump when pumping high temperature liquids (say over 40-50°C), great care must be taken to observe suction limitations.