Conveying capacity

Conveying capacity describes the volumetric throughput of a medium per unit of time. In the practice of concrete demolition, building gutting, and rock excavation, this almost always means the hydraulic flow rate that a hydraulic power pack supplies to tools such as concrete pulverizers, hydraulic splitters, hydraulic demolition shears, Multi Cutters, steel shears, or tank cutters. The correct sizing of the conveying capacity determines cycle times, energy demand, thermal stability, and the reliable execution of the required separation, cutting, or splitting tasks in deconstruction, tunnel construction, and natural stone extraction. In technical documentation and on data plates the conveying capacity is frequently also referred to as volume flow, delivery rate, or throughput.

Definition: What is meant by conveying capacity?

Conveying capacity is the volume flow of a fluid, typically specified in l/min or m³/h. In hydraulic systems it is the amount of hydraulic oil that the power pack provides per minute. Conveying capacity must be distinguished from pressure: The operating pressure generates force or torque, while the volume flow determines the speed of a movement (e.g., the closing and opening motion of a concrete pulverizer or the advance of a stone splitting cylinder). Both variables act together and define the hydraulic power. As a rule of thumb: P [kW] ≈ p [bar] × Q [l/min] × 0.0066. Too little conveying capacity leads to long cycle times; too much conveying capacity can cause flow losses, heating, and unnecessary energy use. Typical unit conversion: 1 m³/h = 16.67 l/min.

Hydraulic conveying capacity in the interaction of volume flow, pressure, and power

In hydraulic drives, the volume flow Q determines the motion speed (piston speed or rotational speed). The pressure p provides the force required for this. Hydraulic power results from the product p × Q and becomes usable work only if losses are kept low. For applications such as concrete demolition and special demolition this means: The work progress per unit time depends on whether the provided volume flow enables the required speed and the pressure delivers the necessary force. If Q is doubled at constant pressure, the theoretical speed doubles – provided that suction, return, and valve cross-sections are adequate. This applies in particular to concrete pulverizers and hydraulic splitters, whose use in reinforced concrete and natural stone demands both high forces and reproducible cycle times.

Importance of conveying capacity for concrete pulverizers

For concrete pulverizers, conveying capacity decisively influences the closing and opening times of the attachment. The volume flow through the cylinders or the swing mechanism of the attachment determines how quickly concrete cross-sections are approached, gripped, and fragmented. The available pressure provides the necessary separating force at the cutting edge or the crushing jaws. Too low a conveying capacity prolongs cycle times, reduces daily throughput, and often increases the thermal load on the system (because the power pack runs under load for longer). An excessively high volume flow that does not match the hydraulic valve technology or the hose cross-section can promote pressure losses, flow noise, and unnecessary heating. In addition, insufficient return capacity can cause backpressure or even cavitation during fast opening strokes, which accelerates wear.

Practical aspects for concrete pulverizers

• Select the volume flow to match the cylinder area and the hydraulic valve orifice to achieve smooth movements without jerking.
• In building gutting and cutting with frequent partial-load cycles, fine controllability at moderate volume flows is advantageous.
• In reinforced concrete, repeated load changes are common; a stable conveying capacity supports consistent cycle times.
• Where available, use regeneration circuits for rapid closing at low load to shorten idle strokes.

Conveying capacity for stone and concrete splitters

Stone and concrete splitters as well as stone splitting cylinders require sufficient volume flow to execute the feed and spreading motion quickly. The splitting force is generated by pressure on the wedge or piston areas, while speed comes from the volume flow. Especially for pilot boreholes in rock, for advance in confined areas, or in special demolition, precise, predictable movement is essential so that the split progresses in a controlled manner and the material fractures along the intended line. Balanced conveying capacity also helps avoid stick-slip effects during the critical transition from approach to splitting.

Typical effects in practice

• The initial approach phase with higher stroke volume benefits from higher volume flow to minimize time losses.
• In the actual splitting phase, pressure dominates; the volume flow must hold position and be finely metered.
• With long hose runs in tunnel construction, pressure and flow losses must be taken into account.
• For deep boreholes or long wedges, ensure sufficient return cross-section to prevent heat buildup during retraction.

Designing hydraulic power packs by the conveying capacity

Hydraulic power packs deliver the volume flow for the connected tools. Selecting appropriately sized Hydraulic Power Units helps align capacity with tool demands. For dimensioning: The maximum required conveying capacity determines the power pack size, the control strategy, and the energy demand. For multi-application use (e.g., switching between a concrete pulverizer and a hydraulic demolition shear), the highest requirement is decisive, if necessary with reserve for temperature and altitude. Multi-circuit concepts, variable-displacement pumps, and variable-speed drives enable demand-based supply and reduce idle losses.

Procedure for dimensioning

1. Determine the required operating pressure and volume flow for each tool (e.g., concrete pulverizer, hydraulic splitter, steel shear).
2. Check the sum or peak demand during parallel operation; otherwise consider alternating operation.
3. Include line losses due to hose lengths, quick coupling, hydraulic valves, and filters in the calculation.
4. Define the thermal concept (oil cooling, tank size), since volume flow and throttling losses generate heat.
5. Define the control (e.g., variable-speed drive) to provide only the conveying capacity actually needed.
6. Consider cold-start viscosity, permissible suction conditions, and altitude-related derating for motors and cooling.

Influencing factors and loss sources in the hydraulic system

The nominal conveying capacity of a power pack is only achieved at the tool if the entire chain from tank to cylinder is designed for favorable flow. Narrow points and throttles reduce the effective volume flow and convert energy into heat. Suction and return lines require particular attention to avoid cavitation or backpressure that can compromise controllability.

Relevant parameters

• Viscosity and oil temperature: Cold increases, heat decreases viscosity; both affect internal losses and sealing performance.
• Hose inner diameter and length: Cross-sections that are too small or great lengths increase pressure drops and reduce effective flow.
• Couplings and valves: Quick coupling and proportional or directional valves cause flow losses; their characteristics must be observed.
• Filter condition: Clogged filters reduce throughput and accelerate oil aging.
• Return line and tank venting: Insufficient return cross-section can cause backpressure and heating.
• Suction line quality: Generous diameters and short runs reduce inlet losses and the risk of cavitation at the pump.
• Recommended oil velocities: As a guide, approx. 2-4 m/s in pressure lines and 1-2 m/s in return lines help keep losses and noise low.

Conveying capacity across application areas

The requirements for conveying capacity vary depending on task and environment. In concrete demolition and special demolition, changing load cases with many cycles dominate, while in rock excavation and tunnel construction long line routes and continuous work steps are typical. In natural stone extraction, reproducible splitting processes are crucial. In special deployments (e.g., contaminated sites or remote-operated applications) conveying capacity is often deliberately limited to minimize heat development and media movement. Duty cycles, ambient temperature, and accessibility on site further influence the optimum setup.

Examples of typical requirements

• Concrete demolition and special demolition: Concrete pulverizers and hydraulic demolition shears require a volume flow that enables fast work cycles without thermally overloading the system.
• Building gutting and cutting: Multi Cutters and tank cutters benefit from precisely controllable conveying capacity for clean cuts in confined areas.
• Rock excavation and tunnel construction: Hydraulic splitters require stable conveying capacity over long distances; pressure and flow measurement are essential.
• Natural stone extraction: Stone splitting cylinders work efficiently when the volume flow supports controlled crack propagation and allows the tool to respond sensitively.

Measurement, monitoring, and documentation

The actual conveying capacity can be checked with suitable measurement technology (flow and pressure sensors) at the power pack or near the tool. Regular monitoring of the key values increases process reliability and prevents performance losses due to gradual changes (filter condition, oil aging, mechanical wear). In critical applications in tunnel construction and special demolition, documented commissioning with a target-actual comparison is recommended. Permanently installed test ports simplify repeatable measurements without opening the circuit.

Practical notes

• Use measuring devices in a suitable measuring circuit with sufficient cross-section.
• Monitor the heat balance: log oil temperature and adjust cooling if necessary.
• Record the tools’ cycle times to detect deviations at an early stage.
• Calibrate sensors at defined intervals and check zero drift before each measurement campaign.

Optimizing conveying capacity in operation

An adapted conveying capacity reduces energy consumption, emissions, and wear. Variable-speed drives and demand-oriented controls help provide only the volume flow that the tool actually needs. This keeps concrete pulverizers, hydraulic splitters, and steel shears efficient and reproducible in operation. Load-sensing concepts or pressure-compensated proportional valves can further stabilize speeds when load changes occur.

Concrete action points

• Match the volume flow to the task (fine metering for delicate cuts, higher throughput for idle strokes).
• Maintain hydraulic power packs regularly, replace filters, and check oil condition.
• Design hose routing for favorable flow, avoid unnecessary quick couplings.
• Verify valve orifice settings and relief valve response to prevent throttling losses.

Fault patterns with unsuitable conveying capacity

If conveying capacity deviates significantly from the requirement, typical symptoms appear: Too low a volume flow leads to sluggish movements, long cycle times, increased oil temperature, and declining daily output. Too high a volume flow can cause unstable starts, throttling losses, flow noise, and heat issues. In extreme cases there is a risk of cavitation in the return and premature wear on seals and hydraulic valves. Additional warning signs include foaming oil, spongy actuator response, and audible crackling that indicates incipient cavitation.

Guide: Determining conveying capacity for the respective tool

For a practical design, a structured approach is recommended: Check the tool data sheet (required pressure and recommended volume flow), match hose and valve sizing to the target volume flow, plan thermal reserve, and verify the resulting cycle times on site. This ensures that concrete pulverizers, hydraulic splitters, hydraulic demolition shears, Multi Cutters, steel shears, and tank cutters operate reliably and efficiently in their respective applications. Conservative margins for extreme ambient conditions and wear states increase robustness over the service life.

Step sequence at a glance

1. Record tool-side requirements (pressure range, volume flow, permissible return pressures).
2. Select a hydraulic power pack with sufficient conveying capacity and suitable hydraulic control.
3. Adapt the line system (inner diameter, length, quick coupling, filters).
4. Design heat management (tank volume, cooling, oil quality).
5. Perform a functional test measuring pressure, flow, temperature, and cycle time.
6. Document baseline values and acceptance criteria for future comparison.

Safety and responsibility

Handling hydraulic systems requires care. Settings for conveying capacity, pressure relief, and valves should only be made by qualified personnel. Operating manual of Darda GmbH and applicable safety regulations must be observed. Specifications for conveying capacity and pressure are always to be understood as technical reference values; suitability in individual cases depends on boundary conditions such as ambient temperature, component geometry, material, and line routing.