Seals are unobtrusive yet central components of high-pressure hydraulics in demolition and extraction technology. They keep hydraulic oil where pressure work is performed, protect moving parts from dirt and moisture, and ensure reproducible force transmission. In applications such as concrete demolition shears and hydraulic rock and concrete splitters, the quality of the sealing determines function, service life, and safety—from hydraulic power units and cylinders and valve blocks to hoses and fittings.
Definition: What is meant by a seal
A seal is a component or system that prevents the unwanted escape or ingress of fluids, gases, or particles. In hydraulics this includes dynamic seals (for example on rods and pistons) and static seals (for example between housing parts). The goal is a controlled sealing effect under defined movements, pressures, and temperatures—with the lowest possible friction and minimal wear.
Design and function of seals in hydraulics
Hydraulic sealing systems often consist of matched elements: primary and secondary seals for the pressure side, wipers against dirt ingress, guide rings to take transverse loads, and back-up rings to prevent gap extrusion. In the cylinders of rock splitters, concrete demolition shears, or combination shears these components work together to convert pressure into linear or shearing force.
Seal types at a glance
- O-rings and X-rings for static and moderately dynamic sealing
- Rod seals (lip, U-, and compact rings) for reciprocating motions
- Piston seals (single- and double-acting) for pressure separation in the cylinder
- Wipers (single/double) against dust, mud, and splash water
- Guide rings for guidance and to prevent metal-to-metal contact
- Flat gaskets and molded seals on housings, covers, and valve blocks
- Rotary seals at oscillating or rotating interfaces
Materials and resistance
Common materials are NBR/HNBR for mineral hydraulic oils, FKM for elevated temperatures and chemically demanding media, PTFE for low friction and high sliding speeds, and PU for robust, wear-resistant lip seals. Fabric-reinforced composite materials are used for guide and back-up rings. Selection depends on medium, temperature, pressure, speed, and environmental conditions on the construction site.
Seals in products of Darda GmbH
In the hydraulic systems of Darda GmbH, seals assume different functions along the force chain depending on the product family—from the power pack through lines to the tool head.
- Hydraulic splitters: Cylinder seals must safely handle high pressure spikes and alternating loads with shock-like stresses; wipers protect against abrasive particles from rock and concrete.
- Concrete demolition shears: Rod and piston seals ensure sensitive, precise jaw movement; low friction supports controlled closing and opening during deconstruction.
- Hydraulic power packs: Static seals on pumps, valve blocks, and fittings prevent leakage; media- and temperature-resistant materials are crucial.
- Combination shears, multi cutters, steel shears, Tank Cutter: Dynamic seals on actuators and slewing points operate under varying load spectra; good wipers minimize dirt ingress.
- Splitter cylinders: Seal systems reliably separate the pressure and return sides and keep the splitting force stable, even with varying split strokes.
Influence of application areas on sealing
The operating environment decisively shapes the design and material selection of the seals.
- Concrete demolition and special deconstruction: Cement dust and rebar abrasion demand effective wipers and robust guides; cyclic pressure changes foster gap extrusion, which is limited by back-up rings.
- Strip-out and cutting: Frequent load changes and precise movements require low-friction seals with good stick-slip behavior for finely metered force transmission.
- Rock breakout and tunnel construction: Moisture, slurries, and temperature fluctuations promote corrosion and media changes; water-resistant materials and double wipers are advantageous.
- Natural stone extraction: High abrasiveness due to rock flour requires wear-resistant wipers and adapted surface roughness on rods and guides.
- Special operations: Extreme temperatures, special media, or long standstill periods require adapted materials and preservation measures.
Design: groove geometry, tolerances, and surfaces
Seal performance depends on correctly dimensioned grooves, suitable installation squeezes, and controlled clearance gaps. Rod and cylinder bore surfaces must exhibit seal-matched roughness and bearing ratios to limit wear, micro-leakage, and stick-slip. Back-up rings reduce gap extrusion at high pressures.
Friction, tightness, and energy efficiency
There is a trade-off between tightness and friction. Excessive interference increases sealing but also raises friction and temperature. Friction-optimized materials (for example PTFE compounds) and tuned spring or lip geometries help balance efficiency and tightness.
Managing pressure spikes
Rapid pressure rises can damage sealing lips and cause oil film collapse. Low-surge valving, adequate support of the seal, and avoidance of sharp edges in transitions improve safety.
Assembly and installation practice
Careful assembly is crucial for seal service life—especially on cylinders of concrete demolition shears and hydraulic splitters.
- Break and deburr edges; provide lead-in chamfers.
- Ensure a clean, particle-free environment; clean components.
- Use compatible assembly and lubricating agents; avoid media mixing.
- Use installation tools; avoid twisting and damage.
- Check installation position; verify correct seating of back-up and guide rings.
- Vent the system gently; monitor the first pressure cycles.
Maintenance, inspection, and replacement
Coordinated maintenance routines prevent consequential damage and unplanned downtime.
- Visual inspection: Detect oil film, dirt deposits, damaged wipers.
- Functional check: Smooth, jerk-free movements, constant holding forces, no drift.
- Observe pressure and temperature behavior; note unusual heating.
- Replace seals in good time based on operating hours, cycles, or condition indicators.
- Store spare parts cleanly and protect them from UV/ozone.
Hydraulic fluid, filtration, and cleanliness
Compatibility between seal material and hydraulic fluid is fundamental. Particles and water content act as wear accelerators; effective filtration and regular oil maintenance are therefore essential.
- Select media with an eye on temperature window and chemical resistance.
- Design fine filtration to suit the application and flow rate.
- Perform regular oil condition analyses to detect aging and ingress early.
- Establish clean assembly and filling processes.
Typical damage patterns and causes
- Extrusion cracks: Excessive clearances or missing back-up rings at high pressures.
- Lip abrasion: Mismatched roughness, dirt ingress, incorrect lubrication regime.
- Thermal damage: Excessive friction, inadequate heat dissipation.
- Chemical swelling or embrittlement: Media incompatibility, additive effects.
- Ozone and UV cracking: Improper storage, weathering effects.
- Twisted O-rings: Incorrect assembly, unsuitable groove geometry.
Diagnostic notes
Seal damage patterns allow conclusions about the root cause. A systematic analysis of installation situation, operating parameters, and oil condition supports the selection of longer-lasting sealing concepts.
Storage and handling of seals
Unused seals should be stored cool, dry, protected from light, and without stress. Avoid contact with plasticizers, solvents, or ozone-laden air. Original markings ensure traceability and material identification.
Safety and environmental aspects
Hydraulic leaks impair occupational safety and the environment. Targeted sealing, regular inspections, and immediate remediation of leaks reduce risks. Follow the guidance in the operating manual and maintenance documentation; in case of doubt, qualified specialists should be consulted.
Practical relevance: concrete demolition and rock breakout
During deconstruction of reinforced concrete, a concrete demolition shear must grip repeatedly and close in a controlled manner. Low-friction rod seals and intact guide rings stabilize the motion, while wipers keep cement dust away. In natural stone extraction, fine abrasive particles act on splitter cylinders; double wipers, suitable materials, and clean assembly increase service life.
Quality requirements and standards references
Recognized standards and guideline sets exist for O-rings, groove geometries, and surfaces. In practice, a combination of suitable tolerances, appropriate materials, and documented testing processes proves effective. For Darda GmbH the following applies: Only the sum of seal design, manufacturing quality, and care in use ensures the lasting performance of hydraulic splitters, concrete demolition shears, and other hydraulic tools.