A hydraulic connection is the central interface between the hydraulic power pack (see Darda hydraulic power units), the hydraulic hose line, and the tool. In concrete demolition, building gutting, rock excavation and tunnel construction as well as in natural stone extraction, the right connection determines performance, reliability, and safety. Especially with tools such as concrete demolition shear or rock and concrete splitters, a correctly sized and cleanly coupled connection ensures that pressure, flow rate, and return flow are optimally matched.
Definition: What is meant by a hydraulic connection
A hydraulic connection is the technical link through which hydraulic fluid under pressure is exchanged between components. This includes connections on the power pack, on valve blocks, on hose lines, and on the tool itself. The term covers both quick couplings (for recurring coupling and uncoupling) as well as fittings and threaded ports including sealing system, seal carrier, and mechanical locking. The aim is a leak-tight, pressure-resistant, and flow-optimized connection that reliably transmits the required pressure rating and the necessary flow rate.
Types of hydraulic connections and typical interfaces
In mobile hydraulics, two basic forms dominate: detachable quick couplings and permanently mounted fittings. Depending on the application area and the tool, geometry, sealing concept, and handling differ.
Quick couplings
Quick couplings allow fast coupling and uncoupling without tools. The following designs are used, among others:
- Flat-face couplings (Flat-Face): low-drip during coupling, easy to clean, good for dusty environments in deconstruction and rock excavation.
- Push-to-connect couplings with valve bodies: widespread, robust, with good flow; depending on the design, only limited residual-pressure tolerant.
- Screw-to-connect couplings: high pressure ratings, suitable with residual pressure in lines; proven on heavy tools such as concrete demolition shear.
Fittings and ports
For fixed line connections, ports and fittings are used, e.g., metric 24° cone (with cutting ring), O-ring face seals (ORFS), 37° flare fittings, or cylindrical threaded ports with O-ring seat. In Europe, metric and G threads are common. The selection is based on pressure rating, sealing principle, installation space, and maintenance requirements.
The hydraulic connection in concrete demolition, rock excavation and tunnel construction
With mobile tools from Darda GmbH such as concrete demolition shear or rock and concrete splitters, the hydraulic connection forms the link to the hydraulic power pack. On the construction site, long hose lines are often laid, for example in special deployment scenarios (see Special Application) or in tunnel construction. This increases the demands on tightness, residual-pressure tolerance, and low pressure losses. Flat-face couplings facilitate clean work in dusty environments, screw-to-connect couplings help with safe coupling under difficult conditions.
Routing: pressure, return, and leakage-oil line
A functionally reliable line set typically consists of a pressure line (P), return (T), and, for some tools, a leakage-oil or relief line (L). Concrete demolition shear usually operate double-acting (cylinder pressurized on both sides); returns must accept the flow rate with low back pressure. With rock and concrete splitters, depending on the design, a pressurized advance and a relieved retraction are common. The correct assignment of the couplings — often through color coding or marking on the power-pack and tool side — prevents misconnection.
Pressure ratings, flow rate and nominal diameters
The dimensioning of the hydraulic connection is based on the interplay of operating pressure, flow rate, and line length. Key points:
- Pressure rating: The connection must safely carry the maximum system peaks. Safety margins should be planned.
- Flow rate: It determines the flow capacity of the coupling. Too small nominal diameters cause throttling losses, heating, and sluggish tool movements.
- Nominal diameter (DN): With increasing hose length and dynamic loading, larger DN are advantageous to minimize pressure drops — for example on long runs in tunnel construction.
- Bend radius: Minimum bend radii of the hoses and the required installation space at the tool head must be observed so that connections are not loaded in bending.
Cleanliness, tightness, and safety during coupling
Cleanliness is crucial: dust, drill slurry, and chips attack seals. Before coupling, end faces and sealing zones are wiped, protective caps are removed immediately before mating. When uncoupling, the connection is depressurized; residual pressure is relieved in a controlled manner. Personal protective equipment is mandatory. Connections must never be released under load. The instructions in the Darda GmbH documents for the respective tool and power pack are authoritative and must be observed.
Selection criteria for quick couplings in deconstruction
- Compatibility with the pressure rating and flow rate of the hydraulic power pack
- Contamination level of the environment (flat-face advantage for dusty work)
- Residual-pressure tolerance and everyday coupling comfort
- Flow quality (low pressure loss, suitable DN)
- Sealing system and low-drip performance to protect the environment
- Mechanical robustness against impacts and lateral forces
Flat-face coupling or valve coupling
Flat-face couplings reduce oil loss during coupling and make cleaning of the mating faces easier. Valve couplings score with widespread availability and good flow. The decision depends on environmental conditions and maintenance concept.
Screw-to-connect couplings with residual pressure
If lines heat up or the tool side drifts, a screwable coupling with an appropriate sealing concept helps. It can be coupled under moderate residual pressure and separates reliably without damaging seals.
Identification and documentation
Color codings, embossing, and arrows for flow direction reduce misconnections. Hose lines are marked with year of manufacture, pressure rating, and DN. The Darda GmbH documentation specifies the required connection sizes, types, and tightening torques; these should be filed in the site workshop record.
Typical failure patterns and remedies
- Slow tool movement: DN too small, contaminated couplings, or kinking hoses; check lines and couplings, adjust DN.
- Overheating: high throttling losses due to constricted passages; choose flow-optimized couplings and short hose runs.
- Drip leaks: damaged O-rings or contaminated mating faces; replace seals, clean coupling faces.
- Shock loads in the line: missing pressure relief or improper uncoupling; systematically depressurize, use screw-to-connect couplings if necessary.
- P/T misconnection: leads to malfunctions or pressure build-up; use identification, check flow direction before commissioning.
Practical guide: connecting a tool to a hydraulic power pack
- Check the Darda GmbH tool documentation: required pressure rating, flow rate, number of lines (P/T/L).
- Switch the system off and depressurize, relieve residual pressure in a controlled manner.
- Remove protective caps only immediately before coupling; clean sealing faces.
- Couple the return first, then connect the pressure line; connect the leakage-oil line (if present).
- Ensure kink-free routing with sufficient bend radius, avoid chafe points.
- Trial run: observe tightness, temperature behavior, and tool function; retighten only with the specified torque.
- For uncoupling in reverse order: disconnect the pressure side first, then the return; fit protective caps.
Particularities for concrete demolition shear and rock and concrete splitters
Concrete demolition shear usually require a double-acting connection with a good return so that retraction occurs without back pressure. Screw-to-connect couplings are robust against impacts and residual pressure, flat-face couplings facilitate clean work during dust-intensive demolition activities. Rock and concrete splitters can, depending on the design, operate with a pressurized advance line and a relieved return; the power pack must regulate the pressure build-up precisely, while the connections safely absorb pressure spikes. In both cases: correct DN, clean coupling operations, and clear identification are crucial for repeatable results.
Maintenance and inspection of connections
Regular visual inspection for cracks, deformation, and leaks, replacement of aged O-rings, checking of locking elements, and scheduled hose replacement according to specifications are essential measures. After work in heavily contaminated environments, cleaning the couplings and fitting protective caps is recommended. Check the filter condition in the hydraulic power pack and, in case of irregularities (increased differential pressure, dark oil), flush the lines. This keeps the hydraulic connections durable, safe, and high-performing — in concrete demolition, specialized deconstruction, and rock.