Speed valve

A speed valve plays a central role in hydraulics when movements of cylinders and motors must be precise, reproducible, and energy-efficient. In tools and attachments for deconstruction and rock processing—such as concrete demolition shears or stone and concrete splitters—it decisively determines the feed and closing speed. In combination with hydraulic power packs and the control blocks commonly used in the field, a suitable speed valve enables short cycle times, controlled load movements, and a sensitive approach to the material, without intending to be promotional.

Definition: What is meant by a speed valve

A speed valve is a hydraulic valve that specifically influences the flow rate to an actuator and thus controls its speed. Depending on the design, this may be a throttle valve, a pressure-compensated flow regulator, a throttle check valve, a proportional flow valve, or a rapid-traverse (regeneration) valve. Unlike directional control valves, which primarily switch the direction of the oil flow, speed valves regulate the quantity of oil flow and thus the motion dynamics. In tools such as concrete demolition shears or stone and concrete splitters, this cleanly separates the rapid approach phase from the actual work feed at higher force.

Operating principle and hydraulic fundamentals

The speed of a hydraulic cylinder results from the relationship v = Q/A. The decisive factors are therefore the supplied flow rate Q and the effective piston area A. A speed valve influences Q and thus directly the motion. Throttling solutions create a defined pressure drop that limits the flow rate. Pressure-compensated variants keep the flow rate largely constant even with fluctuating system pressure. In regeneration or rapid-traverse circuits, the return flow from the rod side is routed to the piston side. As a result, flow rates are added, the speed increases significantly, while the available force decreases in this phase. In practice, once a certain pressure level is reached, switching from rapid traverse to power mode takes place to perform the actual splitting or crushing process with maximum force.

Types and designs of speed valves

Depending on the task, load case, and power unit, the design and control characteristics differ:

• Throttle valve: Simple, robust flow limitation via adjustable orifice. Cost-effective, but dependent on load and viscosity.
• Throttle check valve: Throttle in one direction, free flow in the reverse direction. Ideal for controlled lowering or closing movements, fast reset.
• Pressure-compensated flow control valve: Pressure-compensated, keeps the flow rate largely constant. Suitable for uniform feeds.
• Proportional flow valve: Electrically actuated, for sensitive, reproducible speed profiles.
• Regeneration or rapid-traverse valve: Switches a regeneration circuit for fast rapid travel. Switching to power mode occurs in conjunction with pressure signals.
• Lowering brake and load-holding function (in combination): Limit lowering speed with suspended loads and prevent uncontrolled movements.

Distinction from other valve functions

Speed valves often work together with directional control valves, pressure relief valves, flow dividers, or load-holding valves. Directional valves select the path, pressure valves safeguard the system, and flow dividers split flow rates. Speed regulation, however, remains the task of flow control or the regeneration logic.

Application in concrete demolition shears and stone and concrete splitters

With concrete demolition shears, a fast rapid traverse to approach the component is useful, followed by a finely controllable work feed to initiate cracks in a controlled manner and steer the fracture path. A pressure-compensated speed valve or a proportional solution ensures smooth, jerk-free movements even with changing counterforces. For stone and concrete splitters, a defined feed speed of the splitting cylinder enables reproducible widening of the split joint with minimal collateral damage. In combination with suitable hydraulic power packs, the ratio between rapid-traverse time and working time can be optimized.

• Fast approach with regeneration circuit, switching to power mode from a defined pressure level.
• Constant feed speed despite varying material density and reinforcement content.
• Delicate metering of the closing movement to minimize unwanted spalling.
• Lower heat generation due to proper sizing and short, targeted strokes.

Speed valves also support the balance between swift cycles and controlled force application in combination shears, multi cutters, steel shears, tank cutters, and stone splitting cylinders—in particular when alternating between empty closing and force-intensive cutting or splitting.

Design, sizing, and selection criteria

Correct sizing is guided by the hydraulic framework and the application requirements. Important influencing factors are flow rate, operating pressure, cylinder area ratio, oil viscosity, and thermal boundary conditions.

• Required speed and stroke length (cycle time, strokes per minute).
• Available flow from the hydraulic power pack and permissible pressure drop across the valve.
• Stability under load fluctuations: need for pressure-compensated or proportional control.
• Return-line pressures, leakage paths, and cavitation tendency at high speeds.
• Oil quality, filtration, sensitivity to contamination.
• Environmental influences: temperature range, dust, humidity, vibrations.

1. Define target speed and calculate flow (Q = v × A).
2. Select valve size based on the required Kv value or flow capacity.
3. Check permissible pressure differential and heat balance; select a larger nominal size if necessary.
4. Provide pressure-compensated or proportional variants for varying loads.
5. Define switching criteria for rapid traverse/power mode (pressure threshold, position signal).
6. Test under real load cases, fine-tune the throttle, and document the settings.

Short calculation example

A cylinder with an 80 mm piston diameter has an effective piston area of around 50 cm². For a feed of 30 mm/s, a flow of about 9 L/min is required on the piston side. If the same axis is to reach 100 mm/s in rapid traverse, approximately 30 L/min is necessary. The speed valve and the lines must provide this flow with an acceptable pressure drop without provoking cavitation in the return line.

Circuit examples and practical solutions

In practice, several standard circuits have proven themselves, which also occur in the application areas of Darda GmbH:

• Rapid-traverse circuit (regeneration): Return flow from the rod side to the piston side, quick approach with reduced force; switching to power mode when a pressure threshold is reached.
• Throttle-check controlled feed: Controlled throttling in the working direction, free return flow when opening the shear or during the return stroke of the splitting cylinder.
• Lowering and lowering-brake function: With suspended loads or vertical movements, the combination of speed valve and load-holding valve prevents uncontrolled overrun.
• Two-stage operation at the hydraulic power pack: Switching between high flow at low pressure (rapid traverse) and low flow at high pressure (working mode).

Impact on productivity, wear, and safety

Properly sized speed valves shorten cycle times and increase process reliability. Excessive throttling, however, generates heat, can accelerate oil aging, and stress seals. A balanced ratio of flow area, line dimensions, and pressure limitation is therefore essential. From a safety perspective, defined speeds when approaching the workpiece are important to avoid uncontrolled movements—especially in concrete demolition, gutting works, or tunnel construction.

Fault patterns and diagnosis

Typical symptoms of faulty speed control are jerky movements, fluctuating feeds, excessive oil temperatures, or cavitation (whistling noises, foaming return flow). Causes are often contamination, incorrect settings, worn sealing systems, or unsuitable viscosity. Remedies include clean filtration, checking pressure and flow values, calibrating switching points for rapid traverse/power mode, and stepwise adjustment of the throttle.

Maintenance, adjustment, and operation

For stable operation, settings should be documented, locknuts correctly tightened, and adjustment ranges secured against unintended changes. With seasonal temperature differences, adjusting viscosity and fine-tuning may be advisable. Regular functional tests—particularly of the switching logic in regeneration circuits—as well as the condition of filters, seals, and lines contribute to component service life. Any adjustment work should generally follow and observe the respective operating manuals.

Relevance in the application areas

In concrete demolition and special demolition, a speed-controlled feed allows reinforcement to be engaged in a controlled manner and components to be opened in a targeted way. In gutting works and cutting, a smooth closing feed facilitates precise separation without unnecessarily stressing adjacent structures. In rock excavation and tunnel construction, reproducible motion profiles are important to reduce vibrations and maintain the stability of the surroundings. In natural stone extraction, a constant splitting motion supports clean opening of natural joints. In special deployments, defined speeds help absorb unpredictable load changes and guide tools safely.

Terminology in practice

In German-speaking contexts, speed valves are also referred to as flow controllers, throttle check valves, rapid-traverse, or regeneration valves, depending on the function. In technical documentation, the exact circuit symbols are decisive, as identical terms can be interpreted differently in various contexts. For use in concrete demolition shears, stone and concrete splitters, and other tools from Darda GmbH, it is crucial whether constant feed control, rapid-traverse switching, or a combination of both is required.