Circulating pressure is a central concept in hydraulics and determines the pressure present in the system while the oil is circulating and no consumer is actively operating. In applications such as concrete demolition, rock breakout, strip-out, and cutting, it influences responsiveness, energy efficiency, and heating of the hydraulic power units. For tools such as stone and concrete splitters, concrete demolition shears, combi shears, multi cutters, steel shears, tank cutters, as well as stone splitting cylinders driven by hydraulic power packs from Darda GmbH, a correctly set circulating pressure is crucial for reliable, safe, and material-friendly operation.
Definition: What is meant by circulating pressure
Circulating pressure is the hydraulic pressure present in a system’s idle state when the pump is delivering, but the medium flows back to the tank via the valve block or a bypass/pressure relief valve without active load. Circulating pressure—often also referred to as idle pressure, standby pressure, or circulation pressure—results from flow resistances in the return line, internal leakages, valve positions, and the base setting of the pressure relief. It is significantly lower than the load or peak pressure, but it provides the basis for the instantaneous start-up of consumers and largely determines the thermal balance and the energy demand of the system.
Hydraulic background and operation
In circulation mode, the pump conveys oil through the valve block back to the tank. In open systems, circulating pressure is generated by pressure losses in lines, couplings, filters, and valve throttles, as well as by the presetting of the pressure relief valve. In closed systems or with pressure-compensated valve blocks, the pump maintains a low standby pressure via internal control so it can provide flow quickly when an actuator is actuated. The level of circulating pressure depends on the pump (fixed- or variable-displacement), the oil’s viscosity and temperature, the cross-section and length of the lines, and the condition of filter and valve components. Excessively high circulating pressure causes unnecessary bypass flow, which generates heat and stresses components; excessively low circulating pressure can delay responsiveness or, in unfavorable constellations, lead to oscillations in the valve block.
Practical relevance: demolition, splitting, cutting
In concrete demolition and special demolition, circulating pressure determines how quickly concrete demolition shears or combi shears switch from idle to working stroke. In rock breakout and natural stone extraction, it affects the efficiency of stone and concrete splitters and stone splitting cylinders, especially during frequent changes between rapid travel and power stroke. In strip-out and cutting, it influences heating of the hydraulic power pack and thus oil aging and seal service life. A carefully adjusted circulating pressure supports reproducible tool control, limits noise during partial-load operation, and stabilizes cycle times.
Relation to stone and concrete splitters
When splitting concrete or natural stone, tools are often positioned without load and only subjected to load when wedges are set or pressure builds. A moderate circulating pressure enables a fast rapid stroke with low losses, while the system is ready to switch immediately to the power stroke as soon as load occurs. Excessively high circulating pressures lead to unnecessary heating during waiting periods, for example between drillings or when repositioning wedges, and can cause oil temperature to rise during long operations.
Relation to concrete demolition shears
Concrete demolition shears require a direct response when closing and a stable holding function during the separation process. Circulating pressure determines how quickly the system transitions from idle to load operation. Values that are too low can delay the shear’s engagement, while circulating pressures that are too high cause heat buildup at standstill, for example when the shear is frequently positioned without cutting immediately. Load-holding valves and suitable pressure reliefs ensure the shear maintains its position without excessive oil recirculation.
Influencing factors on circulating pressure
- Oil temperature and viscosity: As temperature rises, viscosity drops and flow resistance decreases—circulating pressure can fall while internal leakages increase.
- Line sizing: Small cross-sections, long hose bundles, and many couplings increase pressure loss in circulation.
- Valve technology: Open vs. closed center in the directional valve, pressure-compensated sections, and internal throttles influence standby pressure.
- Pump type and condition: Variable-displacement pumps actively regulate standby pressure; wear increases leakage paths and can change circulating pressure.
- Pressure relief valve: Setting, contamination, or spring fatigue act directly on circulating pressure.
- Filter and return path: Clogged return filters increase backpressure; bypass openings and check valves change the flow path.
- Additional components: Accumulators, pressure compensators, and load-holding valves shape the pressure profile in circulation.
Measurement, adjustment, and documentation
Circulating pressure is determined with a suitable pressure gauge at a measuring point in the valve block or in the pressure line with consumers unactuated. Meaningful readings are taken with the system at operating temperature and with lines connected in a typical working configuration. Adjustments to pressure relief or control valves should only be performed by qualified personnel and documented in accordance with the documentation from Darda GmbH to ensure reproducibility and safety.
- Depressurize the hydraulic power pack, connect the pressure-rated measuring device, check for leak tightness.
- Bring the system to operating temperature, keep all consumers in neutral position.
- Read the circulating pressure at the measuring point; if necessary, observe fluctuations for several seconds.
- If required, adjust the pressure relief valve step by step and document each step.
- Perform a functional test under typical load and ensure that peak pressures remain within the intended limits.
Typical symptoms and remedies
Circulating pressure too high
- Symptoms: Excessive oil temperature at idle, audible bypass flow, reduced energy reserves in mobile power units.
- Possible causes: Pressure relief valve set too tight, contaminated return filters, restricted couplings, unsuitable viscosity.
- Remedies: Check filter condition, inspect line cross-sections and couplings, clean or replace valves, evaluate oil condition and observe specification.
Circulating pressure too low
- Symptoms: Delayed response when actuating concrete demolition shears or stone and concrete splitters, unstable control behavior in neutral valve position.
- Possible causes: Excessively low viscosity at high temperature, internally leaking pump, internal throttles opened too far.
- Remedies: Keep oil temperature within range, check leakage paths, verify valve presets and correct professionally if necessary.
Energy efficiency, thermal management, and service life
An optimally set circulating pressure reduces throttling losses, protects the oil, and extends the service life of seals, hoses, and valves. This is especially relevant during long operations in rock breakout and tunnel construction as well as in natural stone extraction. Mobile hydraulic power packs additionally benefit from lower heat generation and more efficient idle operation, which increases the available work cycles and keeps maintenance intervals stable.
Safety and general notes
Working on pressurized components entails risks. Adjustments to the hydraulic system should only be carried out by qualified personnel, observing the documentation from Darda GmbH as well as applicable standards and occupational safety requirements. Personal protective equipment, clean couplings, and controlled commissioning are essential. Legal requirements may vary depending on country and use case; these notes are general and do not replace an individual review.
Relation to other hydraulic parameters
Circulating pressure is directly related to flow rate, return pressure, and peak pressure. During the transition from rapid stroke to power stroke—e.g., with concrete demolition shears or combi shears—the pressure differential determines switching-point accuracy. Damping measures in the valve block, appropriate hose sizing, and functioning check valves and load-holding valves prevent pressure spikes and ensure tool integration. A coherent interaction of these parameters delivers reproducible cuts, controlled splitting, and stable holding forces.
Practice-oriented notes for the application areas
Concrete demolition and special demolition
Frequent tool changes and short idle phases require a circulating pressure that enables quick response without excessive bypassing. Clean quick couplers and suitable hose lengths avoid unnecessary pressure losses.
Strip-out and cutting
Indoors, low heat and noise levels are important. A moderate circulating pressure and regular temperature checks on the hydraulic power pack support smooth operation and stable cutting quality with concrete demolition shears, multi cutters, and steel shears.
Rock breakout and tunnel construction
Long hose runs and changing ambient temperatures alter flow resistances. An application-oriented check of circulating pressure under real conditions helps avoid performance losses.
Natural stone extraction
With repeated setting of splitting tools, short, low-loss idle cycles are advantageous. A well-matched circulating pressure supports fast positioning and reduces oil aging in continuous operations.
Special operations
Exceptional boundary conditions, such as special materials or limited accessibility, require adapted pressure settings and documented functional tests before the actual work cycle starts.