Understanding Delta p in Load Sensing Systems
🔧 Basic Principle of a Load Sensing System
A Load Sensing (LS) system is a hydraulic control concept where the pump adjusts flow and pressure on demand – depending on the current load requirements at the control valve or actuator.
⚙️ How It Works in Detail
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Pressure Feedback from the Actuator:
The LS system forwards the pressure demand of the active control valve (e.g., an electronically controlled proportional valve) back to the pump – using a dedicated LS line. -
Differential Pressure Control at the Variable Displacement Pump:
The variable displacement pump (e.g. HAWE V60N) maintains a constant differential pressure (Δp) between the LS signal and the pump outlet pressure. Typical Δp value: 18–22 bar.
→ This ensures the valve always has enough pressure to precisely control the flow rate. -
Demand-Based Power Adjustment:
The pump only delivers as much oil as the actuator currently needs. If no valve is actuated, the LS signal drops – the pump goes into standby mode (zero flow).
✅ Application Benefits
- Energy-efficient operation – lower fuel consumption and reduced heat generation
- Precise control through load-dependent pressure regulation
- Multi-circuit capability – multiple simultaneous movements possible
- Lower noise emissions since the pump doesn’t constantly run at full load
📘 Practical Example with HIAB Crane
On a HIAB HiPro crane, the electric proportional valve (e.g., during lifting) sends the required pressure back to the HAWE V60N via the LS line.
The pump then automatically increases the pressure by, for example, 20 bar and delivers exactly the flow needed to move the cylinder.
If no joystick is moved, the LS pressure drops → the pump enters standby → no flow → fuel savings.