Recirculating pump hydraulics describes hydraulic systems in which the pump’s delivery flow circulates at low pressure in idle and is only converted into work when a valve is actuated. This principle is widespread in compact hydraulic power packs and, in many applications, forms the basis for the reliable use of portable tools, such as concrete demolition shears or hydraulic rock and concrete splitters from Darda GmbH, in fields like concrete demolition and deconstruction, gutting works and cutting, rock breakout and tunnel construction, natural stone extraction, as well as special operations.
Definition: What is meant by recirculating pump hydraulics
Recirculating pump hydraulics refers to a constant-flow system with an open center (recirculating control). In the neutral state, the directional valves are interconnected so that the oil delivered by a fixed-displacement pump is returned to the tank almost without pressure. Only when a function is actuated does the recirculation path close, pressure builds up, and the flow is directed into the working circuit. The system is characterized by simple design, high robustness, and predictable switching behavior. It thus differs from constant-pressure and load-sensing systems, which follow different control strategies.
Operating principle and design of recirculating pump hydraulics
The pump (typically a fixed-displacement unit, often implemented as a gear pump) supplies a continuous flow. Through an open-center directional valve, the oil returns to the tank with a low pressure differential in neutral. When actuated, the recirculation channel is partially or completely closed; the flow is directed to the actuator, and the pressure rises to the level required for the work. A pressure relief valve protects the circuit against overpressure. Check valves, throttles, or flow dividers can be added to control movements or supply multiple actuators. In tools such as concrete demolition shears or stone and concrete splitters, the valve function is sometimes integrated in the power pack and sometimes in the tool, resulting in short response times and reproducible work cycles.
Components at a glance
Pump and drive
Fixed-displacement pumps deliver a defined volume per revolution. In mobile hydraulic power packs, such as compact power units, they are usually driven electrically or by combustion engines. Key selection criteria include flow rate, maximum system pressure, efficiency, noise, and thermal behavior in recirculating idle operation.
Directional valve and control
Open-center directional valves form the heart of recirculating control. They allow low-pressure return flow in idle and connect the actuator when actuated. Depending on the tool, additional functions such as load-holding or lowering brake valves can be integrated to hold loads safely or enable precise motion.
Overpressure protection and return system
A correctly sized pressure relief valve protects the system without converting unnecessary energy into heat. The return line should be designed for favorable flow to minimize losses and oil foaming. Efficient filtration in the suction and/or return lines maintains the cleanliness class, increasing the service life of pumps, valves, and cylinders.
Hydraulic design for concrete demolition shears and stone and concrete splitters
Flow rate and working speed
The working speed of a tool depends directly on the flow rate. In concrete demolition shears, it influences opening and closing of the jaws as well as cycle times. In stone and concrete splitters, it determines the speed of the spreading cylinder up to the point where splitting pressure is reached. Oversizing can cause unnecessary heating, while undersizing extends cycles and reduces productivity.
Pressure level and force requirement
The required force results from pressure times effective piston area. Cutting and splitting processes require high pressures to sever or fracture brittle materials. Typical designs operate in the range of several hundred bar. Adequate safety margins are important so the system can withstand load spikes when a concrete demolition shear bites in or when the splitting wedge is set.
Hoses, couplings, and pressure losses
Line cross-sections, couplings, and hose lengths have a noticeable influence on pressure drop and heating. Short, large-diameter lines with flow-optimized couplings reduce losses. Clean couplings and dust-protected parking positions contribute to system cleanliness and prevent malfunctions in valves and seals.
Applications and typical workflows
In concrete demolition and special demolition, recirculating pump hydraulics enables fast, finely metered opening and closing of concrete demolition shears. In gutting works and cutting, it supports repetitive cycles with stable repeatability. In rock breakout and tunnel construction, stone and concrete splitters benefit from the direct pressure buildup when transitioning from low-pressure recirculation to the working circuit. In natural stone extraction, the robust recirculating control allows long shifts with consistent performance. In special operations—for example with limited energy supply—the simple design of recirculating pump hydraulics is an advantage for integration into compact hydraulic power packs from Darda GmbH.
Thermal management, oil, and filtration
Viscosity and temperature window
The oil viscosity must remain within the recommended range across the entire operating envelope. Oil that is too thin degrades lubrication and increases leakage losses; oil that is too viscous reduces volumetric efficiency and prolongs start-up phases.
Cooling strategies in recirculating operation
Although little pressure heat is generated in idle, flow-induced heat is still present. Heat is dissipated via tank surface, lines, or integrated coolers. Operation adapted to ambient conditions—such as breaks, shutting down at standstill, or variable-speed drives—limits oil temperature.
Filtration and cleanliness classes
Fine filtration in the return line and suitable suction protection prevent particle ingress. Especially with frequent tool coupling, as is common with concrete demolition shears and stone and concrete splitters, a consistent cleanliness strategy pays off.
Control variants and energy efficiency
Even with the recirculating principle, efficiency potential can be leveraged: pressure-compensated flow control valves for uniform speeds, location-appropriate motor power, variable-speed drives to reduce idle load, or priority valves for defined function sequences. The goal is to build pressure only when work is actually performed and otherwise run in recirculation with favorable flow.
Occupational safety and normative guidance
Hydraulics operate at high pressure. Lines, couplings, and valves must be inspected regularly; damaged components must be replaced immediately. When working with concrete demolition shears and stone and concrete splitters, crushing and splinter hazards must be considered. Personal protective equipment, safe placement of the hydraulic power pack, depressurizing before coupling, and compliance with applicable state-of-the-art rules are fundamental measures. Notes on inspection intervals, documentation, and commissioning should generally be observed without assessing the individual case.
Maintenance, servicing, and troubleshooting
Inspection priorities
Oil level and condition, filter loading, tightness, hose condition, coupling cleanliness, pump noises, and temperature development are key checkpoints. Before events such as prolonged downtimes or transports, a renewed visual and functional inspection is recommended.
Typical symptoms and possible causes
- Slow movement: insufficient flow, clogged filters, throttle points, oil too viscous.
- Excessive heating: high recirculation losses, tank too small, contaminated cooler surfaces, valve slightly open continuously.
- Pressure drop under load: leaking lines, internal leakage at cylinders/valves, pressure relief set too low.
- Pulsations and noise: air ingress, pump cavitation, unfavorable suction conditions.
- Jerky movements: contaminated valves, missing pressure compensation, fluctuating viscosity due to temperature.
Comparison with constant-pressure and load-sensing systems
Compared to constant-pressure systems, recirculating pump hydraulics avoids high pressure-holding losses in idle. In comparison with load-sensing systems, the design is simpler and particularly service-friendly in compact power packs. For applications with single functions, repeatable cycles, and short line runs—as with concrete demolition shears or stone and concrete splitters—it is a proven choice. For complex multiple functions or parallel movements, pressure- or consumer-oriented control can offer advantages.
Planning and integration into mobile hydraulic power packs
For integration into hydraulic power packs from Darda GmbH, it is advisable to clearly assign flow rate and pressure to the respective tools used. If several tools are operated sequentially, changeover or selector valves with clearly defined neutral positions are useful. For simultaneous functions, sufficient flow reserves and suitable priority or flow-dividing elements should be planned. Transport, setup, and hose routing should be chosen so that the recirculation line remains short and low-pressure, and the power pack receives sufficient fresh air for cooling.