Follow-up pressure is a central term in hydraulics and describes pressure conditions that remain effective after switching off or switching over a drive. In the context of concrete demolition, special demolition, rock excavation and tunnel construction, follow-up pressure influences the behavior of hydraulic tools such as concrete demolition shear and rock and concrete splitters, as well as the associated hydraulic power pack. Properly understood and controlled, it improves operational safety, efficiency, and component friendliness in daily use.
Definition: What is meant by follow-up pressure
Follow-up pressure is the pressure remaining or subsequently arising in lines, valves, and actuators when the drive source runs down, a valve closes, or the flow is delayed by inertia and throttling points. It can be driven by several effects: residual pressure in isolated volumes, inertia of the oil flow (pressure build-up behind restrictions), back pressure in the return line, and thermal expansion of the hydraulic oil. Follow-up pressure must be distinguished from purely static residual pressure (enclosed pressure) and from continuous return back pressure caused by line resistances and filters. In the field, follow-up pressure often appears as a brief “continued pushing” of a cylinder or as delayed pressure decay after releasing the control lever.
Causes and mechanisms in the hydraulic system
In practice, follow-up pressure results from the interaction of hydraulic, mechanical, and thermal factors. Typical causes are:
- Inertia of the oil flow after a valve closes (short pressure spikes, pressure surge)
- Restrictions in lines, valves, quick coupling and return filters
- Check and load-holding valves that trap volumes and thus preserve residual pressure
- Thermal expansion of the oil due to solar radiation or rising system temperature
- Superimposed load forces that continue to act on the actuator after the valve closes
In tools with closing or spreading movements—such as concrete demolition shear or rock wedge splitter and concrete splitter—follow-up pressure can cause the jaws or wedges to briefly push on or delay the return stroke. In return lines, follow-up pressure appears as counter- or return back pressure that impedes discharge and generates heat.
Importance in concrete demolition, special demolition and rock excavation
In the mechanically highly stressed environment of concrete demolition and natural stone extraction, follow-up pressure directly affects process quality and tool service life. Also during gutting works and cutting, special operations in existing structures, or in tunnel construction, it influences motion precision, energy demand, and the thermal balance of the hydraulic power pack.
Concrete demolition shear: controlled holding, opening and closing
When gripping and holding with a concrete demolition shear, load pressure must not run on uncontrollably. Follow-up pressure in the pressure or return circuit can change opening and closing speed, distort holding forces, and stress seals. Load pressure control, suitable load-holding valves, and a low-back-pressure routing on the return side are crucial so that the shear depressurizes in a defined way without pressure spikes migrating into the return line. Excessive build-up of return back pressure also slows the return stroke and raises oil temperature.
Rock and concrete splitters: reproducible spreading
Splitting wedges require rapid pressure build-up for controlled spreading and clean depressurization for resetting. Enclosed residual pressure in lines or couplings complicates connecting and disconnecting and can cause undesired follow-on pushing when restarting. Pressure-relievable couplings and defined relief sequences help keep follow-up pressure under control and execute splitting cycles with repeatable accuracy.
Effects on performance, efficiency, and component protection
Follow-up pressure impacts several dimensions:
- Performance and speed: Increased return back pressure reduces the usable pressure differential at the actuator; movements slow down.
- Thermal balance: Additional throttling losses convert energy into heat; oil temperatures rise, viscosity drops.
- Wear and seals: Pressure spikes stress sealing lips, hoses, and couplings; micro-cavitation can occur.
- Repeatability: Incomplete depressurization disrupts repeatability when gripping, cutting, or spreading.
Overall, controlled, preferably low follow-up pressure increases process reliability and protects the power pack, valves, cylinders, and tools such as concrete demolition shear, combination shears, multi cutters, and steel shear.
Measuring and diagnosing follow-up pressure
For evaluation, measurement points are used on the pressure and return lines, directly at the actuator or at the valve block. Suitable devices are gauges or electronic sensors, optionally with memory to capture short pressure spikes.
- Bring the system to operating temperature; perform a typical work movement.
- Observe the measurement during switching or stopping; compare pressure profiles in the pressure and return lines.
- Evaluate follow-up and return back pressure separately: How long does pressure remain? How high are the spikes?
- Check filter differential pressure and coupling resistance; consider the temperature situation.
As a practical guideline: Continuous pressure levels on the return side should be low to avoid diminishing the pressure differential at the actuator. Concrete limit values always depend on the specifications of the respective system and the tools from Darda GmbH.
Design and valve technology to limit follow-up pressure
With appropriate design, follow-up pressure can be limited and used purposefully:
- Design the return hydraulically “wide”: generously sized return lines, manifolds, and low-back-pressure return filters
- Select the valve center position appropriately (open to tank or depressurized circulation) for safe relief
- Adjust load-holding and lowering brake valves gently to balance holding safety and depressurizability
- Provide decompression and thermal valves to reduce trapped pressure in a controlled manner
- Use quick coupling with pressure-relief function to allow safe coupling under residual pressure
- Use accumulator and damping elements to smooth short pressure spikes
With hydraulic power units from Darda GmbH, coordinated control hydraulics supports low-pressure recirculation when shutting down so that follow-up pressure is not unnecessarily preserved.
Site operation practice
With a few routines, follow-up pressure can be safely managed in everyday work:
- Depressurize before disconnecting: run the drive at idle, briefly move the controls to both end positions until pressure drops.
- Do not let lines heat up in the sun; thermally induced pressure rise can block couplings.
- Keep return paths clear: avoid kinks and cross-sectional constrictions, regularly check filter condition.
- Carry out tool changes in a structured manner; with concrete demolition shear, open the jaws without pressure; with splitters, relieve the wedges.
- Watch for unusual delays and noises; they indicate restrictions or incorrect valve positions.
These procedures are equally relevant when using combination shears, multi cutters, steel shear, and tank cutters, especially when frequent tool changes and changing operating states occur.
Particularities of hydraulic power pack
The power pack architecture has a major influence on follow-up pressure. With open center positions, oil can recirculate to the tank without pressure after shutdown, while closed center positions trap residual pressure. Return filters with high differential pressure increase counterpressure; a low-back-pressure tank return reduces the tendency to follow-up. Thermal relief valves protect against pressure build-up in idle circuits, for example during prolonged solar heating of the hose sets.
Influence of oil, temperature, and environment
Viscosity and temperature determine how quickly follow-up pressure dissipates. Cold, viscous oil increases throttling losses; warm, low-viscosity oil favors leakage equalization but may damp pressure spikes less effectively. In rock excavation and tunnel construction, line runs are often long; volumes and friction losses increase, as does the importance of low-back-pressure returns. Clean, air-free filling prevents compressible gas pockets that can make follow-up reactions unpredictable.
Practical examples from typical applications
Concrete demolition shear in deconstruction of load-bearing components
After releasing the control lever, the shear does not immediately depressurize because check valves and the load are acting. A brief, controlled pressure equalization via the valve prevents unintended follow-on pushing into the concrete. A low return back pressure improves the return stroke and reduces oil temperatures during continuous operation.
Rock and concrete splitter in natural stone extraction
When relieving before repositioning, enclosed residual pressure in the hose bundle can make reconnecting difficult. Pressure-relievable couplings and a defined relaxation sequence ensure that the system is ready without pushing on and that the splitting wedges work reproducibly.
Planning, commissioning, and maintenance
Even in planning, a holistic view of pressure, control, and return circuits helps. Commissioning protocols should document measurement points, filtration condition, and valve settings. For maintenance: replace filters based on condition, visually inspect couplings, seals, and hoses, and monitor temperature and noise in continuous operation. For tools from Darda GmbH, regular functional testing of cylinder and valve relief behavior is recommended, especially prior to special operations with changing load spectra.
Safety and responsibility
Work on pressurized systems always requires safe depressurization and appropriate personal protective equipment. Depressurization steps must always be performed so that loads are not moved uncontrollably. Legal frameworks and recognized rules of technology must be observed; specific measures must be adapted to the respective machine, tool, and use case.