Gear pump or piston pump
A displacement-type pump - either a gear pump or a piston pump - can be used to provide the necessary inlet pressure for the flow controller. In a gear pump, a fixed liquid volume in between interlocking teeth of rotating gears is repeatedly displaced to generate a flow, whereas in a piston pump a liquid flow is generated at subsequent strokes of a piston filling and emptying a fixed volume. Overall, small pumps are favourable, as a pump with a small internal volume reduces the fill and refresh time of the system. Whichever pump type has been chosen, always make sure that the wetted pump materials are compatible with the processed liquid. Because the relevant displaced fixed liquid volume in gear pumps is generally smaller than in piston pumps, gear pumps are the preferred choice if a customer wants to have a reasonably stable flow control for low liquid flows. However, gear pumps are limited to a maximum operational pressure of 10 to 15 bars. Piston pumps can handle higher pressures, from several tens to more than 100 bars - which are frequently occurring process conditions in low-flow applications.
More about pumps
The dual-piston pumps we use at Bronkhorst are shifted 180° in phase, resulting in a very stable pressure/flow delivery which is important in the low-flow range.
However, whether or not this is sufficiently accurate depends on the customer’s application process. The required amount of liquid is accurately dosed, but due to the pumping principle it will be dosed as small pulses. When the process volume is sufficiently large, there will be enough mixing capacity to smoothen the pulses. However, if you want an evenly distributed dosing over a short period of seconds, such a piston pump setup is less ideal and a gear pump may still be the preferred choice.