There are two types of hydraulic pumps used in hydraulic drive systems; they hydrostatic and hydrodynamic. The difference is that the hydrostatic pump is a positive displacement pump while the pump is usually fixed hydrodynamic variable displacement pump.
Displacement refers only to the flow through the pump rotation. Fixed displacement pump is when the transfer can not be adjusted, while the variable displacement pump allows the transfer to be adjusted because it has a more complicated construction. You will get to know more about industrial hydraulic pump through https://www.athydraulics.com.au/product-category/hydraulic-pumps/.
A simpler and more economical than the type of hydraulic pump is a gear pump, which has external teeth and fixed displacement type. Displacement gear pump or volume will be between 1 and 200 cubic centimeters.
Some of this can be noisy compared to other types, but the newer, more modern get much quieter and higher quality than older ones. This pump forces the liquid around the teeth for pressing the outlet side with the meshing teeth together.
Some hydraulic can be fixed or adjustable displacement are simple, such as rotary vane pumps. They are more efficient than gear pumps, but can be used for mid pressures up to 180 bar as well. A simple adjustable pump can be achieved by changing the body's center propeller. Pumps are a kind of constant pressure. That means that the movement is either increased or decreased until equilibrium is reached.