Load-sensing control is a variable-pump control technology for open hydraulic circuits that maintains constant actuator speed regardless of load variations. The system senses the highest load-induced pressure downstream of a metering orifice and adjusts pump flow to hold a fixed pressure drop across that orifice. This design ensures consistent flow and therefore consistent actuator speed, even as load conditions change – a critical capability in hydraulic excavators, material handlers and other mobile machinery.

How Load-Sensing Control Works

In a typical load-sensing circuit, a variable-displacement pump – usually an axial-piston design – is fitted with a load-sensing controller, and a directional control valve features an integral load-signal gallery. The load-signal gallery connects the A and B ports of each valve section through a series of shuttle valves, ensuring the actuator with the highest load pressure is sensed and fed back to the pump controller via a dedicated signal line.

When an operator moves a valve spool to activate a function, the load-induced pressure downstream of the valve is communicated to the pump controller. The controller responds by adjusting pump displacement so that the pressure upstream of the valve rises by a corresponding amount, maintaining a constant differential. The typical maintained pressure drop – often called delta p – ranges from 10 to 30 bar (145 to 435 psi). This fixed pressure differential across the orifice keeps flow rate constant, and therefore actuator speed constant, independent of load.

Power Savings Compared With Fixed and Pressure-Compensated Systems

Hydraulic systems subject to wide fluctuations in flow and pressure can waste substantial input power if pump output is not matched to instantaneous demand. Fixed-displacement pumps convert excess flow to heat over the relief valve. Pressure-compensated variable pumps regulate flow at maximum system pressure, wasting power through large pressure drops across metering valves when the load-induced pressure is below the set relief pressure.

A load-sensing controlled variable pump largely eliminates these inefficiencies. The power lost to heat is limited to the relatively small, constant pressure drop across the metering orifice, held steady across the entire operating pressure range. In systems where only a portion of available flow is required at less than maximum pressure – a common scenario in earthmoving and construction equipment – the energy savings can be significant.

Pressure-Compensated Flow Sharing for Multiple Functions

Modern load-sensing systems incorporate pressure compensators within the control valve to enable flow sharing during simultaneous operation of multiple functions. When two or more functions are activated at the same time, each drawing different load pressures, the pressure-compensated flow-sharing valve distributes available pump flow proportionally according to each function's demand, while maintaining consistent control response for each actuator.

This capability is particularly valuable in material-handling equipment, where operators routinely combine boom, stick and bucket movements. Without flow sharing, the actuator with the lowest load pressure would consume all available flow, starving the higher-load functions. Pressure compensation equalizes the pressure drop across each metering orifice, ensuring predictable, proportional control regardless of load differences.

System Components and Configuration

The core components of a load-sensing system include the variable-displacement pump with integrated load-sensing controller, the directional control valve with load-signal gallery, and the shuttle-valve network that selects the highest load pressure for feedback. Kawasaki Heavy Industries manufactures dedicated load-sensing components including the K3VLS series axial piston pump – available in displacement from 50 to 150 cm³ and rated to 28 MPa – and the KLSV series load-sensing control valve, which features low pressure loss and supports flows from 240 to 450 litres per minute.

The load-sensing system is widely used in construction, material handling and agricultural machinery. The orifice in a load-sensing circuit is typically a directional control valve with proportional flow characteristics, though a needle valve or even a fixed orifice can be employed depending on the application. The key requirement is that flow across the orifice must vary predictably with the pressure drop across it; maintaining that pressure drop constant ensures flow remains constant.

Operational Benefits in Construction Equipment

Load-sensing control enables load-independent flow control, which results in consistent machine operating speed and superior controllability. Operators experience predictable response from joystick inputs regardless of whether the bucket is empty or loaded, or whether the excavator is working uphill or downhill. This consistency reduces operator fatigue and improves cycle times, particularly in repetitive tasks such as trench digging or truck loading.

The system also contributes to energy savings. By matching pump output to instantaneous hydraulic demand and minimizing pressure drop across control valves, less engine power is converted to waste heat. This efficiency gain translates to lower fuel consumption and reduced cooling-system load, extending operating hours between refuelling and reducing thermal stress on hydraulic components.

Technical Context and Application Scope

Load-sensing control is one of several strategies for managing hydraulic power in mobile machinery. It represents a middle ground between simple fixed-displacement systems with relief-valve control and more complex closed-loop hydraulic circuits or electric-hydraulic hybrids. The technology is mature, field-proven and supported by multiple component suppliers worldwide.

Understanding load-sensing control is essential for maintenance technicians and fleet managers responsible for hydraulic excavators and other mobile equipment. Effective troubleshooting requires knowledge of how the pump controller responds to load signals, how shuttle valves select the highest pressure, and how pressure compensators within the valve enable flow sharing. Misdiagnosed faults in load-sensing circuits often stem from contamination in the signal line, worn shuttle valves or incorrectly set pressure compensators – all of which disrupt the feedback loop that maintains constant differential pressure.