Hydraulic pumps are used in hydraulic drive systems and can be hydro-static or hydrodynamic. The difference between the two is that hydro-static pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps. fixed displacement pumps implies that the displacement cant be adjusted, or variable displacement pumps, which have a more complicated construction that allows the displacement to be adjusted.
Types of pumps used for mining
Gear pumps have external teeth and a fixed displacement. Such pumps are extremely simple and economical.
The displacement of gear pumps for hydraulics will be between around 1 cm3 and 200 cm3. They have the lowest volumetric efficiency of all three basic pump types. These pumps create pressure through the meshing of the gear teeth, which forces fluid around the gears to pressurise the outlet side. For lubrication, the gear pump uses a minor quantity of oil from the pressurised side of the gears, bleeds this through the hydrodynamic bearings, and vents the same oil either to the low pressure side of the gears, or through a dedicated drain port on the pump housing. Some gear pumps can be quite noisy, compared to other types, but modern gear pumps are highly reliable and much quieter than older models
Rotary vane pumps have fixed and simple adjustable displacement and contain higher inefficiencies than gear pumps, but are also used for mid pressures up to 180 bars in general. Modern units can exceed 300 bars in continuous operation, although vane pumps are not regarded as “high pressure” components. Some types of vane pumps can change the centre of the vane body, so that a simple adjustable pump is obtained. These adjustable vane pumps are in general constant pressure or constant power pumps: the displacement is increased until the required pressure or power is reached and subsequently the displacement or swept volume is decreased until equilibrium is achieved.
Screw pumps have a fixed displacement and consist of two Archimedes’ screws that join and are enclosed within the same chamber. These pumps are used for high flows at a fairly low pressure (max 100 bar). They were used on board ships where a constant pressure hydraulic system extended through the whole ship, particularly to control ball valves but also to help drive the steering gear and other systems. The benefit of the screw pumps is the low sound level of these pumps; however, the efficiency is not high.