1.Pump Basics: Displacement vs. Pressure
Hydraulic pumps are designed to move fluid by creating flow. Their primary function is to deliver a certain volume of fluid per unit of time (flow rate). However, the pump itself does not create pressure directly—pressure arises from resistance to flow in the system (e.g., actuators, valves, or orifices).
2. The Role of Pump Design
Most hydraulic pumps are positive displacement pumps. They theoretically deliver a fixed flow per revolution, but in reality, internal leakage (slippage) occurs. As pressure increases:
Fluid is forced back through internal clearances.
Effective output flow decreases, even if pump speed is constant.
This is often described as volumetric efficiency loss.
3.Power Considerations
Hydraulic power is determined by:
Power = Pressure × Flow
For a fixed input power (e.g., from an electric motor or engine), if pressure increases, flow must decrease to keep power within limits. Many systems include pressure-compensated pumps that automatically reduce flow when a set pressure is reached to protect components and manage energy use.
4. System Resistance & Flow Control
When system resistance rises (e.g., a cylinder meets a heavy load or a valve closes partially):
Pressure increases due to the restriction.
Flow may drop if the pump cannot maintain its output against the higher backpressure.
In pressure-compensated pumps, the flow reduction is intentional and controlled.