A hydraulic line connects hydraulic power units with tools and cylinders. It transmits pressure energy in the form of fluids, usually hydraulic oil, safely and with minimal loss. In applications such as concrete demolition, rock excavation, tunnel construction, building gutting and cutting, the hydraulic line ensures that tools like concrete demolition shears, rock and concrete splitters, combination shears, multi cutters, steel shears or tank cutters operate reliably. Its quality, sizing, and maintenance determine performance, precision, and occupational safety.
Definition: What is meant by a hydraulic line
A hydraulic line refers to the entire conduit path for conveying hydraulic fluids in a pressure system, consisting of hose assemblies or rigid pipework together with fittings, threaded connections and couplings. A hydraulic line must withstand pressure, pulsation, temperature and environmental influences while providing the flow rate required for the function of cylinders, motors and valves. Typical versions are high-pressure hose assemblies for moving sections and pipes for fixed runs.
Design and operating principle of the hydraulic line
Hydraulic lines channel the pressure energy generated by a power unit into a directed oil flow. This actuates tools, closes jaws, moves blades, or builds splitting forces. Lines must accommodate the required operating pressure, pressure spikes and pulsations, deliver with low pressure drop, and withstand mechanical stresses such as vibration, abrasion and bending as a critical hydraulic connection.
Construction of hose assemblies
Hydraulic hose assemblies typically comprise an oil-resistant inner tube, one or more reinforcement layers (steel wire braid or spiral), and an outer cover for protection against abrasion, ozone and weathering. Fittings are crimped on the ends. Key parameters include nominal size, permissible operating pressure, bend radius, temperature range, and media compatibility.
Pipes and formed tubes
Pipes are used where fixed installation, low expansion, and high durability are required. Bent formed tubes and clamps minimize vibration and optimize installation paths. Transitions between pipe and hose decouple movement at the tool.
Hydraulic lines in a system with hydraulic power packs and attachments
Hydraulic power packs supply system pressure and connect via lines to attachments such as concrete demolition shears, rock and concrete splitters, rock splitting cylinders, combination shears, multi cutters, steel shears, and tank cutters. The selection and routing of the lines vary according to the tool’s function, force demand, and freedom of movement.
Single-acting and double-acting
In single-acting systems a pressure line is used to generate force; return occurs via a spring or dead weight, with return flow to the tank. Double-acting systems require two pressure lines for extend and retract strokes. Some drives additionally use a low-pressure leak-oil line.
Pressure, return, and leak-oil lines
Pressure lines are designed for the highest pressure. Return lines carry the flow back at lower pressure but must be matched to temperature and pulsation. Leak-oil lines are designed for low pressure and prevent housing pressure build-up.
Selection and sizing: pressure, flow, and environment
The correct sizing of a hydraulic line is based on system pressure, flow rate, temperature, dynamics, and operating environment. The goal is safe operation with low heat build-up and minimized pressure drop while maintaining good flexibility at the tool.
- Loading: maximum operating pressure, pressure spikes, pulsation
- Hydraulic medium and temperature: compatibility and resistance
- Flow rate: adequate cross-section to avoid flow losses
- Environment: abrasion, impacts, UV/ozone, moisture, dirt, sparks
- Movement: bend radii, kink protection, torsion, vibration decoupling
- Installation: length, transitions, coupling types, service accessibility
Cross-section and pressure drop
Nominal size determines flow velocity. Cross-sections that are too small create high pressure drops and heat, reduce tool speed, and stress the medium. Adequately sized lines improve efficiency, reduce pulsation, and support precision during demolition and splitting.
Routing, bend radii, and protection in harsh duty
In concrete demolition, rock excavation, and tunnel construction, dust, edges, impacts, and vibration act on the lines. Proper routing extends service life and prevents failures in operation.
- Observe bend radius: never tighter than the permissible minimum bend radius
- Avoid kinking and torsional load: route lines in the direction of movement
- Use clamps and supports: dampen vibration, avoid chafing points
- Provide sufficient length for movement: avoid tensile loading
- Avoid contact with hot, sharp-edged, or rotating parts
Protective measures
Protective spirals, textile sleeves, or heat protection can deflect abrasion and sparks. In areas with impact, additional mechanical shielding is proven. Hose bundles group multiple lines, simplify routing, and reduce the risk of individual damage.
Couplings, fittings and sealing systems
Hydraulic fittings connect lines with power packs, valves and tools. Common sealing systems are sealing cones with O-ring, cutting-ring fittings, or flat-face connections. The choice depends on pressure rating, installation effort, and leak-tightness.
- Fittings with O-ring: easy to install, good sealing under pulsation
- Cutting-ring/clamp fittings: proven for pipework
- Flat-face connections: robust for frequent disconnecting and coupling
Quick couplings in demolition
Quick couplings enable fast tool changes. Drip-free, flat-face systems reduce air ingress and oil loss. Couplings should be protected from dirt, cleaned regularly, and operated depressurized.
Installation, commissioning, and technical cleanliness
Cleanliness is a central quality factor in hydraulic systems. Particles shorten the service life of valves, pumps, and cylinders and cause malfunctions.
- Prepare lines: protect ends, remove caps only immediately before installation
- Check cut faces and fittings: burr-free, clean, correctly crimped
- Tighten fittings moderately: follow manufacturer specifications, do not damage sealing faces
- Fill and bleed the system: ramp up slowly, check for tightness and temperature
- Retighten and perform visual inspection: monitor the first operating hours with particular attention
Maintenance, inspection, and replacement intervals
Regular inspections increase operational safety. Visual checks detect aging, abrasion, and leaks in good time. Replacement intervals depend on loading, environment, and internal policies.
- Outer cover: cracks, blisters, spalling, chafing
- Fittings: corrosion, loosening, leakage at sealing edges
- Bending: kinks, permanent deformation
- Temperature: discoloration, hardening, odor development
- Marking: legibility for traceability and documentation
Typical failure modes and causes
Failure analysis helps to avoid repeat issues and improve sizing.
- Early hose failure: bend radius too tight, torsion, insufficient protection
- Leakage at fittings: contaminated sealing faces, incorrect tightening torque
- Return-line overheating: cross-section too small, high continuous load
- Vibration cracks in pipes: missing supports, resonance, overly rigid clamping
- Performance drop: pressure loss due to long runs or restrictions
Use cases: concrete demolition, rock excavation and tunnel construction
In practice, the hydraulic line connects the hydraulic power pack from Darda GmbH with attachments. Dust, debris and changing weather demand robust yet flexible routing. Proper sizing and protective measures contribute significantly to availability.
Concrete demolition shears: line requirements
Concrete demolition shears work with cyclic force application and pulsating loads. Double-acting lines with sufficient cross-section ensure opening and closing speed. Protection against edge abrasion and strain-free routing along the boom are decisive.
Rock and concrete splitters: specifics
Splitting creates short-term high pressures typical for rock and concrete splitters. Lines must absorb pressure spikes while enabling precise metering. A stably routed hose bundle, clean couplings, and sufficient length reserves for the motion sequence are especially important here.
Safety and handling high pressure
Hydraulic systems operate at high pressures. Proper handling increases safety for users and surroundings. Before any work on the system, it should always be depressurized. Damaged lines must be taken out of service immediately and replaced professionally.
- Wear personal protective equipment and never check leaks with your hand
- Release pressure before coupling and uncoupling
- Fix leaks at the source; do not mask them by retightening without inspection
- Protect lines from welding sparks, sharp edges, and pinch points
- Use only suitable, mutually compatible fittings and sealing systems
Sustainability, disposal, and documentation
A durable hydraulic line reduces downtime, oil loss, and material consumption. Proper disposal of old lines and clean work on the system protect the environment. Clear identification supports maintenance and quality assurance.
Marking and traceability
Markings with nominal size, pressure rating, manufacturing date, and serial numbers make it easier to keep track of inventory, replacement cycles, and compatibility. Documented installation and test records improve traceability.
Material cycle and avoiding oil loss
Drip-free coupling and clean work keep oil in the system. Cleanliness extends the service life of valves and cylinders and reduces wear. End-of-life materials should be collected segregated by type and disposed of according to applicable regulations.