Hydraulic pumps convert mechanical energy into hydraulic energy. When the hydraulic pump is running, it performs two functions. Its mechanical action creates a vacuum at the inlet of the pump, allowing pressure to push the liquid from the reservoir into the pump's inlet line.
Secondly, its mechanical action delivers this liquid to the outlet of the pump and presses it into the hydraulic system. The pump produces liquid movement or flow: it does not generate pressure. It generates pressure to produce the required flow rate, which is a function of the resistance of fluid flow in the system.
For example, for a pump that is not connected to the system (load), the fluid pressure at the pump outlet is . In addition, for pumps delivered into the system, the pressure will rise to the level required to overcome load resistance.
Classification of pumps
Many pumps can be classified as positive or non-positive. Most of the pumps used in hydraulic systems are positive displacement pumps. Continuous flow from positive displacement pumps.
However, since it does not provide a secure inner seal to prevent slippage, its output varies significantly with pressure. Centrifugal and propeller pumps are examples of non-positive displacement pumps.
If the output port of a non-positive displacement pump is blocked, the pressure will rise and the output will decrease to to. Although the pumping elements will continue to move, the flow will stop due to pump slippage.
In positive displacement pumps, slip is negligible compared to the volumetric output flow of the pump. If the output port is clogged, the pressure will increase to the point where the pump's pump element or its housing will fail (which is possible if the drive shaft is not broken), or the prime mover of the pump will stall.
