The hydraulic pump converts mechanical energy into hydraulic energy. When the hydraulic pump is running, it performs two functions. Its mechanical action creates a vacuum at the pump inlet, which pushes the liquid from the reservoir into the pump inlet line.
Secondly, its mechanical action carries the liquid to the outlet of the pump and presses it into the hydraulic system. A pump produces movement or flow of liquid: it does not produce pressure. It produces the pressure that produces the required flow, which is a function of the flow resistance of the fluid in the system.
For example, for a pump not connected to the system (load), the fluid pressure at the pump outlet is. In addition, for pumps delivered to the system, the pressure will rise to the level required to overcome the load resistance.
Classification of pumps
Many pumps can be classified as positive displacement or non positive displacement. Most of the pumps used in the hydraulic system are positive displacement pumps. Continuous flow produced by a positive displacement pump.
However, since it does not provide a secure inner seal against slippage, its output varies significantly with pressure. Centrifugal and propeller pumps are examples of non positive displacement pumps.
If the output port of the non positive displacement pump is blocked, the pressure will rise and the output will decrease to. Although the pumping element will continue to move, the flow will stop due to pump slippage.
In the positive displacement pump, compared with the volume output flow of the pump, the slip can be ignored. If the output port is blocked, the pressure will increase to the extent that the pump element or its housing of the pump will fail (possibly if the drive shaft is not broken), or the prime mover of the pump will stall.