Pressure flushing is a widely used method for efficiently transporting drill cuttings out of the borehole and reliably binding dust when drilling rock and concrete. In the context of concrete demolition, special demolition, rock demolition and tunnel construction as well as natural stone extraction, it plays a central role—especially when boreholes have to be created for the use of rock and concrete splitters or rock wedge splitters. In practice, a well-planned pressure flushing acts like a quality anchor: it stabilizes the process, improves borehole quality, and reliably prepares downstream steps with a concrete pulverizer, Multi Cutters and other tools.
Definition: What is meant by pressure flushing
Pressure flushing refers to the removal of drill cuttings from the borehole using a flushing medium introduced under pressure. Water, compressed air, or an air-water mixture are typically used as flushing media. The medium is introduced into the borehole through the drilling tool, picks up the drill cuttings, and transports them along the annular space to the surface. Depending on the material, drill diameter and depth, this is done as an open flushing (discharge at the borehole opening) or in a partially closed flushing circuit with collection and separation of solids. Pressure flushing thus differs from dry drilling with dust extraction and from pure wet drilling without a targeted flushing flow, as it relies on defined pressure and flow-rate conditions to ensure removal, cooling and stabilization.
Use of pressure flushing in drilling for rock and concrete splitters
Rock and concrete splitters as well as rock wedge splitters require precise boreholes, often in series with consistent depth and geometry. Consistent pressure flushing ensures that the borehole is free of drill cuttings, slurry residues and loose aggregates. This makes it easier to insert wedges or cylinders, the contact surfaces are loaded more evenly, and the resulting split pattern becomes more predictable. In reinforced concrete, a clean borehole bottom simplifies alignment of subsequent measures, such as precisely preparing cutting edges for a concrete pulverizer or Multi Cutters. In rock excavation and tunnel construction, pressure flushing also supports borehole stability, reduces friction heat on the tool and minimizes dust exposure in enclosed spaces—an essential advantage for special operations with high requirements for occupational safety and emission control.
How it works and flushing media
Water pressure flushing
Water effectively binds fine dust, cools the tool and efficiently transports drill cuttings away. The flushing pressure must be selected so that the return flow starts reliably without scouring the substrate or causing edge spalling. In concrete, the aggregate structure is not dissolved; nevertheless, fine slurry can form that should be removed and separated in an orderly manner. Advantage: very good dust suppression and tool cooling. Consideration: orderly water and slurry management to avoid contamination.
Air or air-water flushing
Compressed-air flushing or mixed flushing (air with a small water content) is useful when water can only be used to a limited extent, for example during building gutting in existing buildings or in sensitive areas. Air flushing keeps the borehole dry, while small amounts of water bind fine dust. Advantage: lower moisture loads, clean view of the borehole opening. Consideration: effective dust extraction and safety measures against airborne particles.
Benefits, limits and impact on process quality
- Quality improvement: Clean boreholes improve the placement and effectiveness of splitters and rock wedge splitters.
- Occupational safety: Reduced dust exposure, better visibility, lower tool temperatures.
- Process reliability: Stable removal of drill cuttings, fewer blockages, uniform drilling progress.
- Compatibility: Supports follow-up processes such as applying a concrete pulverizer, Multi Cutters and steel shear to deliberately weakened components.
- Limits: Treatment of flushing water required; excessive flushing pressure risks spalling at the borehole mouth, while too little pressure risks clogging.
- Material dependency: Heterogeneous concrete with reinforcement or schistose rock require sensitive parameter selection.
Effects on borehole quality and splitting result
Pressure flushing influences runout, surface cleanliness and dimensional accuracy of the borehole. A uniform flushing flow prevents drill cuttings from sticking and reduces scoring. For rock and concrete splitters, this means easier insertion, a defined bearing of the splitting system, and a more uniform stress distribution in the component. In concrete demolition, a clean drilling pattern can reduce the power demand of downstream tools such as a concrete pulverizer, because predetermined breaking lines form more precisely. In rock excavation and natural stone extraction, a stable borehole wall favors the alignment of hole rows, which is essential for controlled fracture surfaces.
Work and environmental protection in pressure flushing
Dust and aerosol management
Dust suppression is a key argument for water or mixed flushing. Nevertheless, aerosols can form. Suitable separators, shields at the borehole opening and personal safety equipment must therefore be planned. With pure air flushing, scour formation at the outlet should be avoided using spacers or catchment devices.
Water and slurry treatment
Flushing water with drill cuttings should be sedimented or filtered. Drains must be secured against discharge into sensitive areas. An orderly separation of solids facilitates disposal. Legal requirements are site-dependent and should be checked in advance; binding statements are not possible without a case-by-case review.
Noise and vibrations
Compressed air increases noise emission at the borehole opening, so noise control must be observed. Compared to impact-intensive methods, pressure flushing supports smooth drilling progress and can reduce vibrations, which is advantageous in special demolition and in tunnel construction.
Practical guide: planning and execution
- Material analysis: assess strength, aggregate structure, reinforcement content or layering in the rock.
- Method selection: choose water, air or mixed flushing to suit the location and emission targets.
- Set up the flushing circuit: size the pump or compressor, secure flushing hoses, set up separation.
- Fine-tune parameters: select flushing pressure and flow rate so that drill cuttings discharge continuously and the drill bit is sufficiently cooled.
- Monitor and document: observe the appearance, color and consistency of the return; adjust parameters as needed.
- Post-processing: check the borehole for residual slurry, if necessary briefly flush again; clean the work area.
- Prepare the follow-up process: insert rock and concrete splitters or align for a concrete pulverizer/Multi Cutters along the planned separation line.
Parameters and influencing factors
The optimal pressure flushing results from the interaction of drill diameter, drilling depth, tool geometry, flushing pressure, flow rate and medium. Temperature, aggregate content in the concrete, or jointing in the rock also have an effect. Manufacturer specifications of the equipment used and material-specific experience values should be considered; fixed reference values do not replace project-specific adjustment.
- Drill diameter and depth influence the required flow rate for reliable removal of drill cuttings.
- Flushing pressure must be sufficient to stabilize the return flow without causing edge spalling.
- Water quality (solids content) and filter stages determine tool wear.
- With air flushing, particle velocity at the outlet must be limited to reduce dust turbulence.
Common disturbances and remedies
- Blockage of the annular space: briefly increase pressure, lift the tool, and restart flushing with a higher flow rate.
- Spalling at the borehole edge: reduce flushing pressure, apply contact pressure more uniformly, mitigate the outlet with a deflector surface.
- Insufficient dust suppression: switch to mixed flushing or increase the water content; optimize separators.
- Slurry residues at the borehole bottom: flush again and promptly insert the splitting system to avoid deposits.
Relation to tools and application areas
In contexts such as concrete demolition – deconstruction and special demolition, pressure flushing enables precise rows of boreholes for rock and concrete splitters; components can thus be deliberately weakened before a concrete pulverizer, Multi Cutters or steel shear are applied in a targeted manner. During building gutting and cutting, it creates clean, defined starting points for Multi Cutters and facilitates precise separation work in confined environments. In rock excavation and tunnel construction, stable, low-dust drilling processes are a basic prerequisite for safely setting rock wedge splitters, especially in areas with limited ventilation. In natural stone extraction, uniform flushing improves the reproducibility of fracture lines. For special operations—such as in facilities highly sensitive to moisture—air or mixed flushing provides a practical option as long as dust and noise control are consistently implemented.
Quality assurance in conjunction with products from Darda GmbH
The performance of rock and concrete splitters, rock wedge splitters and complementary tools from Darda GmbH is maximized when the boreholes are dimensionally accurate, clean and free of drill cuttings. Appropriate pressure flushing makes a decisive contribution to this without unnecessarily stressing the material. The result is that splitting forces are applied more precisely, cutting edges for a concrete pulverizer are more clearly defined, and follow-up work becomes more predictable. This makes the entire workflow in concrete demolition, tunnel construction and natural stone extraction structured, safe and efficient.