Operating pressure

Operating pressure is the central control variable in hydraulic systems used in demolition and cutting technology. It determines how much force a concrete crusher generates when closing, how effectively hydraulic rock and concrete splitters initiate cracks, and how quickly tools work under real-world conditions. Across Darda GmbH’s product groups – from hydraulic power packs and concrete crushers to rock and concrete splitters, combination shears, multi cutters, steel shears, tank cutters, and rock splitting cylinders – the correct operating pressure is crucial for controlled results in concrete demolition, strip-out and cutting, rock demolition and tunneling, natural stone extraction, and special applications.

Definition: What is meant by operating pressure?

Operating pressure (also working pressure, system pressure, or hydraulic pressure) is the pressure present in the hydraulic system during normal work. It is generally specified in bar and is generated by the hydraulic pump of the power pack. This pressure acts on the piston area of cylinders and produces force. Operating pressure must be distinguished from the system’s maximum permissible pressure, the set pressure of the pressure relief valve, and the test pressure, which is used for testing with a safety margin. The actual effective pressure at the working point can deviate from the reading at the power pack due to line losses, temperature, viscosity, hose length, and couplings.

• Operating pressure: target working level during typical load cycles.
• Maximum permissible pressure: design limit that must not be exceeded.
• Pressure relief valve set point: protective threshold for overpressure events.
• Test pressure: elevated level used for verification with safety margin under controlled conditions.

Units: bar and MPa are standard in industry practice, with optional indication in psi to aid international comparability.

Classification: Why operating pressure determines tool performance

Operating pressure translates directly into working force: the higher the pressure and the larger the piston area, the higher the resulting splitting, cutting, or crushing force. At the same time, flow rate influences movement speed. For concrete crushers this means: pressure provides the closing force, while volumetric flow defines the closing speed. With rock and concrete splitters, pressure generates the spreading force in the borehole and initiates crack propagation in the material. An optimally set operating pressure enables controlled work, protects components, reduces wear, and increases repeatability – across all the applications mentioned.

• Pressure sets force for cutting, crushing, clamping, and spreading.
• Flow sets speed for jaw closing, cylinder extension, and cycle times.
• Stability matters: pressure consistency under load supports predictable outcomes and dimensional accuracy.

Hydraulic basics: pressure, flow, and force

Hydraulic systems convert pump power into mechanical work. Simplified: Force = Pressure × Piston Area. The speed of a movement depends on the flow rate; it is approximated by volumetric flow divided by piston area. It follows that adjusting operating pressure changes the achievable force, while adjusting flow changes working speed. Both variables must be matched to the tool and the task to cut, split, or clamp reliably. Rearranging for sizing tasks: Pressure = Force ÷ Area and Flow = Speed × Area.

Units and typical working ranges

Operating pressure is measured in bar (1 bar ≈ 0.1 MPa). Depending on design and task, hydraulic tools in demolition and cutting technology may operate – depending on the manufacturer – in ranges from the low to high hundreds of bar. The specifications of the respective tool and the hydraulic power pack are decisive. It is common for the power pack to provide an adjustable working pressure and for an integrated pressure relief valve to safeguard the maximum system pressure.

Operating pressure in the product groups of Darda GmbH

The product groups of Darda GmbH use operating pressure in different ways, always with the aim of controlled, reproducible work steps under real construction site conditions. Compatibility between the hydraulic power unit, hose set, and tool-side hydraulics is essential for reliable pressure transmission and repeatable performance.

Concrete crushers

In concrete crushers, operating pressure is converted into closing force. For demolishing reinforced components, sufficient force is required to crush concrete and expose or cut reinforcing steel (depending on the crusher type). Too low a pressure leads to incomplete separations or extended cycles; too high a pressure can load components uncontrollably or overstress the tool. Correct pressure settings are therefore essential for concrete demolition, strip-out, and cutting tasks. Trending pressure under comparable load cycles helps detect wear before performance drops.

Rock and concrete splitters

Rock and concrete splitters generate high spreading force via wedges or splitting cylinders. Operating pressure defines the peak load in the borehole and influences the initiation of crack propagation. In rock demolition, tunneling, and natural stone extraction, reproducible splitting pressure is important to achieve planned separation planes. Gradually increasing the pressure and monitoring the gauge support safe crack guidance and reduce unwanted secondary fractures. Borehole diameter, spacing, and clean wedge guidance further improve pressure utilization.

Other tools: combination shears, multi cutters, steel shears, tank cutters, rock splitting cylinders

Combination shears and multi cutters combine cutting, crushing, and gripping. Operating pressure determines what material thickness can be separated safely and how quickly the jaws operate. Steel shears and tank cutters require stable pressure to cut metallic structures in a controlled way, often under continuous load. Rock splitting cylinders provide high forces over a compact area; here, the tight coupling of pressure, piston area, and edge distances to the component is particularly important to protect the material.

Operating pressure in the application areas

Depending on the field of application, different requirements arise for operating pressure, pressure stability, and system monitoring.

Concrete demolition and specialized deconstruction

For selective deconstruction, a sufficient but not excessive operating pressure is important to avoid unnecessarily loading remaining load-bearing structures. Concrete crushers benefit from pressure-stable power packs that do not exhibit pressure dips under changing loads. Sequenced pressure ramps can improve control around sensitive interfaces and embedded components.

Strip-out and cutting

In interior work and precise separation tasks, sensitive pressure throttling is helpful. Uniform closing forces contribute to clean cut edges, especially in combination with matched flow for controlled movement speeds. Low-noise operation often benefits from moderate pressure settings paired with optimized flow.

Rock demolition and tunneling

Rock and concrete splitters as well as rock splitting cylinders work with deliberately built splitting pressure. Stable operating pressure supports predictable crack propagation. Longer hose lines in tunneling require attention to pressure losses so that the required force arrives at the tool. Where lines are routed over long distances, minimizing quick-coupling transitions helps reduce throttling and heating.

Natural stone extraction

For extraction along natural joints, a reproducible operating pressure is essential. It makes it possible to standardize splitting sequences and preserve material quality. Consistent hole preparation and surface cleanliness enhance the effectiveness of applied pressure.

Special applications

For atypical materials or complex structural details, it is advisable to approach the required working pressure step by step with close monitoring at the pressure gauge. This allows early detection of material reactions and limits tool stress. Pre-tests on representative sections reduce the risk of overloading.

Matching the hydraulic power pack, lines, and tool

Hydraulic Power Units provide pressure and flow. For effective pressure transmission to the tool, hose cross-sections, lengths, and couplings are crucial. A hose cross-section that is too small or unfavorable couplings cause pressure losses and heating. Clean, fully engaged quick couplers are a prerequisite for pressure-tight connections.

• Prefer adequately sized pressure and return lines to limit pressure drop at peak load.
• Keep hose runs short and with gentle radii to reduce dynamic losses and heat build-up.
• Use compatible, clean quick couplers to avoid throttling and contamination ingress.
• Verify that tool-side valve blocks and test ports are rated for the intended operating pressure.

Pressure relief valve and overload protection

The pressure relief valve protects the system from overpressure. It must match the tool and be correctly set. A setting that is too high can unnecessarily load components and the tool; a setting that is too low reduces working performance. Regular functional checks are important. In demanding tasks, secondary protective elements such as load holding or counterbalance valves may be used to stabilize movements and protect components.

Setting, testing, and documenting operating pressure

Reliable control of operating pressure is performed via suitable pressure gauges, ideally close to the tool or via test ports. Tests must be carried out in compliance with generally accepted safety rules and the manufacturer’s instructions.

1. Depressurize and secure the hydraulic power pack.
2. Connect the test port or pressure gauge professionally; fully lock the couplings.
3. Start the power pack, bring the system to operating temperature, check for leaks.
4. Measure operating pressure under typical load and compare with the target value.
5. If necessary, set the pressure relief valve according to the manufacturer’s specification.
6. Document measured values (date, temperature, hose length, tool, power pack).

Measurement placement and accuracy

• Position gauges as close to the tool as practical to capture real working pressure.
• Use calibrated instruments with sufficient range and resolution for the expected values.
• Record ambient and oil temperature, as viscosity changes influence readings.

Factors influencing effective operating pressure

• Line losses: Long or too narrow hoses increase pressure drop.
• Temperature and viscosity: Cold oil is viscous (higher losses, slower movement), hot oil is thin (leakage portion increases).
• Seal condition: Worn seals reduce holding and working pressure in cylinders.
• Couplings: Partially opened or worn quick couplers throttle flow and cause heating.
• Air ingress: Air in the system increases compressibility and degrades pressure transmission.
• Back pressure: Elevated return line pressure reduces effective differential pressure on the cylinder.

Operation in cold and hot conditions

At low temperatures, gentle warm-up of the system is recommended before applying nominal loads. At high temperatures, ensure sufficient cooling, clean return flow, and proper oil condition. Overheating accelerates seal aging and degrades pressure stability. Selecting a hydraulic oil viscosity suitable for the climate and duty cycle supports consistent pressure behavior over the full operating window.

Operating pressure, force, and component protection

Operating pressure must be selected so that the required working force is safely achieved without unnecessarily loading adjacent components. With concrete crushers, a stepped pressure build-up can help expose reinforcement and separate it in a controlled manner. For rock and concrete splitters, gradually increasing splitting pressure supports crack guidance along planned lines. In sensitive areas of specialized deconstruction, a conservative pressure approach with close monitoring is advisable.

Practical calculation: from operating pressure to working force

Simplified estimate: Force [kN] ≈ (Pressure [bar] × Piston Area [cm²]) ÷ 100. This approximation helps assess the order of magnitude. Exact values depend on efficiencies, friction, return pressures, and the specific kinematics. Unit consistency is critical when transferring values between bar, MPa, and psi.

Example concrete crusher (simplified)

With an effective piston area of 20 cm² and an operating pressure of 300 bar, the approximate closing force is about 60 kN (roughly 3 kN per cm²). In reality, friction, jaw geometry, and lever arms influence the effective force on the material.

Example rock splitting cylinder (simplified)

With 50 cm² piston area and 500 bar operating pressure, the calculated value is about 250 kN. However, what is decisive is how this force is introduced into the borehole and the rock via wedges or plates.

Typical fault patterns and remedies for pressure issues

• Tool stops under load: Possible pressure drop or too low valve setting; check the pressure relief valve and inspect lines for constrictions.
• Slow movement despite sufficient pressure: Flow is limited; check hose cross-section, couplings, and filters.
• Excessive heating: Throttling losses in couplings/hoses; check leakage oil and filter condition, adjust line routing.
• Pressure fluctuates: Air in the system or pump drawing in air; check tightness and oil level, perform bleeding.
• Ragged cuts/breaks: Pressure or kinematics not suitable; match pressure and flow to the task, check tool condition of blades/wedges.
• Gauge indicates normal but performance is weak: Suspect internal leakage or bypass in cylinders/valves; verify with isolation tests.

Maintenance, oil quality, and service life

Clean hydraulic oil suitable for the temperature range supports stable pressure conditions and reduces wear. Regular filter changes, inspection of quick couplers, and visual checks for chafing on hoses contribute to consistent operating pressure and longer tool service life. For concrete crushers, intact cutting and crushing surfaces improve efficiency, as the required force is not lost to friction. For rock and concrete splitters, cleanly guided wedges and well-maintained splitting faces ensure uniform pressure distribution. Periodic calibration of gauges and scheduled oil condition checks further enhance pressure reliability over time.

Legal and organizational notes (general)

Setting and testing operating pressure should always be carried out in accordance with generally accepted engineering practice, observing the manufacturer’s specifications and applicable occupational safety requirements. Documenting set values, maintenance, and tests facilitates quality assurance on the construction site. These notes are general in nature and do not replace individual instruction. Regional and project-specific requirements may impose additional obligations.