Hydraulic valves are central components in every hydraulic system. They control pressure, flow rate, and flow direction of the medium and thereby determine whether tools operate safely, sensitively, and with high performance. In Darda GmbH applications – from concrete demolition and special demolition through building gutting and cutting to rock breakout and tunnel construction as well as natural stone extraction – valve technology influences the precision and reliability of tools such as concrete demolition shears, stone and concrete splitting devices, rock splitter cylinders, combination shears, Multi Cutters, steel shears, tank cutters, and the associated hydraulic power packs. This article explains the fundamentals, selection, and practice around the hydraulic valve – objective, in-depth, and application-oriented.
Definition: What is meant by hydraulic valve
A hydraulic valve is a mechanical control and regulating device that influences the pressure and/or the flow rate as well as the flow direction of the fluid in a hydraulic circuit. It can switch (on/off, redirect), regulate (set steplessly), or safeguard (limit, hold, block return). Typical valve types are directional control valves, pressure valves, flow control valves, check and load-holding valves, as well as proportional and cartridge valves. Hydraulic valves operate as spool or poppet valves and are actuated manually, electrically, hydraulically (pilot-operated), or mechanically. They are installed as stand-alone valves, in subplate mounting, or in compact manifolds – for example in the hydraulic power packs of Darda GmbH or directly in tools such as concrete demolition shears and rock splitter cylinders.
Design and operating principle
Hydraulic valves generally consist of a body with connection ports (pressure P, tank T, work ports A/B), a movable closing element (spool or poppet), sealing systems, springs for return, and an actuator (lever, solenoid coil, hydraulic pilot stage). When switching or regulating, the actuator moves the closing element, thereby opening, throttling, or closing cross-sections. In this way, the flow is directed or the pressure is influenced. Leak-oil ports route internal leakage in a controlled manner to keep the function stable. The interplay of valve characteristic (linear, progressive), throttle position, and spring forces determines the response dynamics and thus how sensitively, for example, a concrete demolition shear opens or how constant the pressure is maintained in a rock splitter cylinder.
Valve types and their tasks
Different valve types are used depending on the task. The selection is based on the work process, safety requirements, and the desired fine control.
- Directional control valves (2/2, 3/2, 4/2, 4/3): Route the flow to the work ports. In concrete demolition shears they control opening/closing and holding of the jaws. Center positions (open, blocked, diverted) influence standstill behavior and heat generation.
- Pressure relief valves: Protect the circuit against overpressure. They are typically integrated in the hydraulic power pack and limit system pressure when dealing with high-strength concrete or tough natural stone.
- Pressure reducing valves and sequence valves: Create subcircuits with a defined lower pressure, e.g., for function sequences in combination shears or Multi Cutters.
- Check valves and load-holding valves: Prevent backflow and hold loads safely in position. In stone and concrete splitters they secure the splitting pressure; in tank cutters they stabilize tool position.
- Flow control and throttle valves: Set the speed. Sensitive metering is important for low-vibration work in special demolition and building gutting.
- Proportional valves (also pre- or pilot-operated): Allow stepless control of pressure and flow rate. They increase precision and repeatability, e.g., in steel shears for controlled cutting.
- Cartridge valves (Cartridge): Space-saving built-in valves in compact manifolds. Common in mobile power packs and tools with limited installation space.
Hydraulic valves in products and applications of Darda GmbH
Concrete demolition shears: precise control with limited installation space
Concrete demolition shears require directional control valves for directional control, load-holding valves for position safety, and pressure relief valves for protection against load spikes. For delicate separation of components in building gutting, flow control valves are used. Proportional technology improves ramp-up, reduces pressure spikes, and minimizes vibration.
Stone and concrete splitters as well as rock splitter cylinders
When splitting, the pressure must remain stable. Check and load-holding valves maintain the level, while throttles define the pressure build-up rate. Directional control valves govern the cycle: approach of the splitting wedges, pressure build-up, holding, pressure relief. In natural stone extraction, this enables a reproducible splitting line.
Combination shears, Multi Cutters, steel shears, and tank cutters
Depending on the area of use, these tools require a combination of robust poppet valves (for tight holding) and sensitive proportional valves (for metered cutting). This applies equally to steel shears and Multi Cutters. Anti-cavitation valves can cushion return flows and protect components when the tool cut suddenly breaks through.
Hydraulic power packs as the system core
Darda GmbH hydraulic power packs (hydraulic power units) combine pressure generation, filtration, and valve control. Pressure relief valves, pilot stages, flow regulation, and valve blocks ensure reproducible sequences – especially with changing tools and hose lengths in special operations.
Design and selection criteria
The right valve choice determines safety, energy efficiency, and service life. The following criteria are relevant in practice:
- Working pressure and flow rate: Must match the tool and power pack. Plan safety margins without creating excessive throttling losses.
- Switching logic and center position: Open center reduces pressure spikes; closed center holds positions. Select according to tool dynamics.
- Leakage behavior: Poppet valves for tight holding (e.g., splitting pressure), spool valves for low pressure losses with frequent actuation.
- Actuation type: Manual is robust, electric is flexible, pilot-operated for high flow rates with low actuation effort.
- Contamination sensitivity and filtration: Valves with fine gaps require clean oil; design the filtration concept accordingly.
- Thermal behavior: Throttling generates heat. Optimized control circuits minimize power loss in continuous operation.
- Mounting style: Subplate or block mounting for compact manifolds; cartridge valves for high integration density.
- Environment and protection class: Dust, moisture, and temperature fluctuations in demolition require a robust design and suitable sealing systems.
Safety and accountability in operation
Hydraulic valves fulfill safety-related functions: holding loads, limiting overpressure, stopping movements. In demolition and cutting applications, a risk-based consideration of the control circuit is advisable. This includes suitable valve combinations (e.g., load-holding valve plus directional valve), regular function tests, and proper maintenance. Industry standards and guidelines for machine safety should be considered; binding assessments are project-specific and belong in expert hands.
Maintenance, servicing, and troubleshooting
Clean oil and correctly adjusted valves extend the service life of tools and power packs. The following principles help in day-to-day operations:
- Filtration: Choose an appropriate filter fineness; monitor differential pressure; replace filters in time.
- Cleanliness: Clean couplings, keep dust away, use protective caps. Particles cause spool sticking and leaks.
- Oil condition: Check viscosity and aging; water and air in the oil promote cavitation and corrosion.
- Document settings: Record pressure values, throttle positions, and switching times to ensure reproducible results.
- Record the symptom (e.g., slow opening of the concrete demolition shear, rough running).
- Measure hydraulic pressure (compare supply and working pressure).
- Check valve function (switching noises, electrical actuation, pilot pressure).
- Inspect lines and couplings (pressure loss, air ingress, cross-section restrictions).
- Remove and clean the valve, inspect seals, replace if necessary.
- After maintenance, perform a functional test with documented target values.
Typical failure patterns and causes
- Pressure drops under load: Leaky poppet valve, worn seals, or faulty pressure relief valve.
- Shear/jaw moves jerkily: Air in the system, overly aggressive throttling, missing damping, or spool sticking due to particles.
- Overheating of the oil: Continuous throttling losses, unfavorable center position, undersized tank, or insufficient cooling in the power pack.
- Cavitation/howling: Suction issues, return flows without an anti-cavitation path, too little prefill.
- Uncontrolled movement under load: Defective load-holding valve, incorrect installation orientation, or leakage in the pilot stage.
Energy efficiency and fine control in demolition
Efficient hydraulics reduce heat, save fuel, and increase service life. Proportional valves, sensible center positions, and load-pressure-dependent controls help minimize losses. In practice, such concepts have a direct effect: smoother operation during building gutting inside structures, fewer pressure spikes in special demolition, controlled splitting in natural stone extraction. For concrete demolition shears and stone and concrete splitters, this means finely metered ramp-up, reproducible clamping forces, and stable holding functions.
Integration into mobile and stationary systems
In mobile applications, compact manifolds with cartridge valves are common; they save space and reduce hosing. Stationary power packs benefit from modular valve plates: clear functional assignment, good accessibility, rapid maintenance. In both cases, a coordinated pilot stage is crucial for mastering high flow rates precisely – for example with steel shears or Multi Cutters that require different cutting modes. Quick couplers and defined leak-oil returns ensure tool changes in special operations.
Practical examples from typical fields of application
Concrete demolition and special demolition
In selective deconstruction, components must be separated in a controlled manner. A directional valve with a closed center keeps the concrete demolition shear stable; flow control valves dampen movement. Pressure relief provides protection when reinforcement suddenly gives way.
Building gutting and cutting
Sensitive proportional valves enable slow ramp-up of combination shears and Multi Cutters. Anti-cavitation valves prevent pressure dips during unloading – important in enclosed spaces to keep vibration and noise low.
Rock breakout and tunnel construction
Rock splitter cylinders require safe load-holding valves that conserve splitting pressure over the entire cycle time. Check valves prevent backflow; throttles modulate the propagation of the crack front for controlled results in rock demolition and tunnel construction.
Natural stone extraction
Constant pressure retention and repeatable timing are crucial for achieving clean split surfaces. Manifold blocks with cartridge valves combine holding, regulating, and relieving in the tightest space.
Special operations
Under challenging conditions, robust valve technology counts: large temperature range, dust exposure, rapid tool changes. Poppet valves with low leakage and clearly defined switching sequences increase operational safety.
Planning and documentation
A clear functional description of the control circuit – including pressure levels, switching sequences, throttle positions, and test ports – facilitates commissioning and service. Measurement points at P, A, B, and T as well as documented valve settings support diagnostics. For Darda GmbH tools, a combined view of the hydraulic power pack, lines, couplings, and manifold is recommended to ensure consistent design.
Best practices for long service life
- Provide reserved pressure and flow margins without permanent throttling.
- Label valves in the flow direction and observe installation orientations.
- Use soft switching edges or pilot throttles to dampen pressure spikes.
- Regular functional testing of load-holding valves under load.
- Establish oil care as a continuous process (filtration, temperature, aging).