Hydraulic fluid

Hydraulic fluid is the working medium that transmits force in compact hydraulic power units and connected tools-from the drive to the cylinder or the hydraulic demolition shear. In applications such as concrete demolition and deconstruction, rock excavation, or building gutting, it largely determines how precisely and reliably tools like concrete demolition shears or rock wedge splitters and concrete splitters operate. Its properties influence response behavior, speed, efficiency, and component service life as well as safety and environmental compatibility on the construction site. Proper selection and condition management of the fluid underpin consistent performance, reduced downtime, and compliance with safety concepts.

Definition: What is meant by hydraulic fluid?

Hydraulic fluid is a specially formulated pressure fluid for energy transfer in hydraulic systems. It simultaneously serves as a lubricant, corrosion protection medium, and heat transfer medium. Depending on requirements, mineral oil-based hydraulic oils, synthetic fluids, and water-containing, fire-resistant media are used. Characteristic parameters include viscosity (e.g., ISO VG 32/46/68), viscosity index, additive package (anti-wear, oxidation stability, foam suppression), air release properties, demulsifying behavior, and material compatibility with seals and hydraulic hose lines.

• Energy transfer: pressure build-up and force transmission to cylinders and shears.
• Wear protection: formation of protective films and damping of load peaks.
• Heat and corrosion management: removal of heat and protection of metallic surfaces.

In practice, commonly used families include HLP and HVLP grades for mobile hydraulics, fire-resistant HFC and HFDU media where ignition risks exist, and readily biodegradable esters for nature-adjacent work areas.

Composition, base oils, and additives in hydraulic fluids

Modern hydraulic fluids consist of a base oil and a precisely matched additive package. Mineral oil bases (mostly Group I-III) are widespread; synthetic esters or polyalphaolefins are used where extended temperature range and service life are required. Fire-resistant media (e.g., HFC water-glycol, HFDU synthetics) are used where fire protection is paramount, such as in tunnels or when cutting and separating. Additives provide anti-wear protection (e.g., AW/EP), oxidation stability, corrosion protection, foam suppression, good air release, and clean valve behavior. The goal is stable, clean, and well-controllable hydraulic behavior across the entire operating range.

• Shear stability: maintains viscosity under high load and over service life.
• Filterability: avoids premature filter blockage and maintains cleanliness.
• Hydrolytic stability: resists water-induced breakdown and sludge formation.
• Ashless vs. zinc-containing packages: selected to balance wear protection with material and environmental requirements.

Hydraulic fluid interacting with power packs, cylinders, and shears

In Darda GmbH hydraulic power packs, the fluid is pressurized by the pump and delivered to the connected tools. Hydraulic rock and concrete splitters and concrete demolition shears convert oil pressure into linear or shearing forces. The hydraulic fluid must balance two opposites: sufficiently low viscosity for good cold-start behavior and low pressure losses-and, at the same time, sufficient viscosity when warm to ensure lubrication and damping. Consistent, clean fluid quality is crucial so that valves close precisely, cylinders run without play, and fine control edges do not erode.

Unwanted air ingress and water contamination impair compressibility, promote micro-dieseling, and can cause jerky motion or cavitation noise. Correct viscosity, rapid air release, and effective dehydration help maintain quiet, predictable operation of cylinders and control valves.

Viscosity, temperature window, and controllability

The choice of viscosity grade (e.g., ISO VG 32, 46, or 68) depends on ambient temperature, power pack design, and the tool. A high viscosity index (HVLP grades) improves controllability over a wide temperature range-important under changing conditions on the construction site, in underground mining and tunnel construction, or during special demolition operations. In cold environments, a low pour point supports startup; in warm situations, a sufficiently high flash point and stable additives are essential. Excessive viscosity causes pressure losses, slow actuators, and heating; too low viscosity can lead to leakage, increased wear, and unstable valve behavior.

• Rule of thumb: design so that operating viscosity at working temperature is typically in the range of approx. 16-40 mm²/s for mobile components.
• Selection logic: choose ISO VG and viscosity index so that the median ambient conditions land in the target operating viscosity range.
• Cold starts: ensure adequate pumpability at the lowest expected temperature and limit high-speed operation until oil warms up.

Practical relevance

For concrete demolition shears, which often work in building gutting or precise deconstruction, viscosity directly affects sensitive control and clean cuts. Rock and concrete splitters benefit from a fluid that does not aerate or foam excessively under load, allowing splitting wedges to advance in a controlled manner and the rock to form defined cracks. Stable viscosity over the full shift supports repeatable jaw speed and force buildup.

Cleanliness, filtration, and service life

Particles and water are the main enemies of the hydraulic system. Suitable filtration (suction, pressure, and return filters with appropriate staging) keeps cleanliness in a range that minimizes valve wear and protects seals. In the dusty environments of concrete demolition or natural stone extraction, good air and tank ventilation are important. Water content should be monitored and kept low, otherwise cavitation, micro-dieseling, and rust formation increase. Clear oil condition management extends maintenance intervals for hydraulic power packs and keeps tools such as combination shears, multi cutters, or steel shears reliably within their operating window.

Cleanliness targets are typically set according to the sensitivity of valves and pumps. Fine proportional valves require cleaner oil than simple directional valves, and high-pressure circuits generally need tighter control of particulate and water content.

Cleanliness notes

• Use clean coupling points and caps for couplings.
• Change between fluid types only after thorough flushing and material compatibility checks.
• Check filter condition regularly and replace in good time.
• Store sealed containers upright, off the ground, and protect from dust ingress.
• Where feasible, use desiccant breathers to limit moisture ingress through tank ventilation.

Fire protection and fire-resistant pressure fluids

Where ignition sources, hot surfaces, or flying sparks are present-e.g., when working with a Tank Cutter or during cutting work in tunnel construction-fire-resistant fluids can be beneficial. Water-glycol (HFC) offers inherent flame retardancy; synthetic fire-resistant fluids (HFDU) combine good fire protection with a broader temperature window. When switching, seal compatibility, miscibility, and approval of the components used must be considered. Selection should be based on safety concepts, the operating environment, and the technical specifications of the equipment used.

Operational notes

• HFC media typically have lower lubricity and a narrower temperature window than HFDU; adjust maintenance intervals and filtration accordingly.
• Verify compatibility of seals, paints, and coatings; replace incompatible materials during the conversion process.
• Avoid mixing with mineral oils; flush thoroughly and monitor early-life samples after switching.

Ecological aspects and handling

In sensitive areas-such as natural stone extraction, in the field, or near bodies of water-readily biodegradable hydraulic fluids (e.g., ester-based) are an option. They can reduce risk in the event of leaks. Depending on the region, regulations on water protection and the classification of water-hazardous substances may apply. The disposal of used hydraulic fluids should follow appropriate disposal routes. Manufacturer information and local requirements must be observed; statements here are generally of a general nature and do not replace individual assessment.

• For biodegradable esters, ensure hydrolytic stability is adequate for expected humidity and temperature profiles.
• Implement spill prevention and containment measures and maintain appropriate absorbents on site.

Material compatibility and seals

Hydraulic fluids must be compatible with seals, hoses, and coatings. NBR seals are widespread; for higher temperatures or synthetic media, FKM/FPM may be considered. Incompatibilities manifest as swelling, shrinkage, or hardening of elastomers and lead to leakage or sticking valves. When changing the medium-for example, from mineral oil-based to fire-resistant or biodegradable-a careful compatibility review is advisable.

After a medium change, deposits can be released and transported to sensitive valves. Close monitoring of filters and early oil sampling during the first operating hours after conversion helps prevent secondary damage.

Oil condition monitoring and maintenance

Regular condition checks extend the service life of power packs, cylinders, and shears. Typical test parameters are viscosity, acid number, additive reserve, particle count, water content, and foaming tendency. Simple sampling at defined intervals enables trend monitoring and predictive maintenance, supported by hydraulic oil analysis.

Practical procedure

1. Document a baseline sample in new condition.
2. Take samples under operating conditions at defined intervals.
3. Evaluate results, check filter condition, derive causes (e.g., dust, moisture, thermal load).
4. Targeted actions: filter, remove water, oil change with flushing.
5. Document corrective actions and verify effectiveness after a defined operating period.

Selection criteria for different areas of use

The optimal hydraulic fluid depends on temperature, fire protection requirements, environmental regulations, and the tool category. In concrete demolition and special deconstruction, clean, thermally stable HLP/HVLP grades are common; in building gutting with concrete demolition shears, fine controllability is the focus; in rock excavation/tunnel construction, fire protection and moisture resistance play a major role; for special demolition assignments, an extended temperature window may be required. Mixing different fluid families without explicit release is to be avoided.

Guidelines

• Cold environments: low pour point, high VI grade (HVLP), potentially lower ISO VG.
• Warm environments/high continuous load: oxidation-stable fluids with adequate flash point and shear stability.
• Tunnel construction/hot work (e.g., near tank cutting): fire-resistant media (HFC/HFDU) after suitability checks.
• Nature-adjacent areas: readily biodegradable fluids; observe compatibility and switching procedure.
• Intermittent vs. continuous duty: prefer higher VI and robust anti-wear packages for frequent cycling and variable loads.

Typical failure patterns and countermeasures

Foaming oil, sluggish actuators, jerky motion, or unusual noises indicate air or water content, incorrect viscosity, or contaminated valves. If the splitting or cutting performance of rock and concrete splitters or concrete demolition shears declines, check cleanliness, viscosity, and temperature control. A systematic approach-visual inspection, temperature measurement, filter check, oil sample-helps narrow down causes and prevent damage.

• Milkiness points to water ingress; dewater and investigate sources such as breathers and couplings.
• Stick-slip or drifting cylinders suggest viscosity mismatch or varnish deposits; correct grade and consider cleaning measures.
• Rapid filter clogging may indicate incompatible fluids or aging by-products; review filter rating and fluid condition.

Storage, transfer, and handling

Hydraulic fluids should be stored in clean, closed containers, dry, cool, and protected from UV light. When transferring, clean funnels, fine strainers, or filling filters are useful. Containers should be clearly labeled to avoid mixing. After connecting tools, short venting cycles at low speed are recommended until smooth operation is achieved.

• Apply first-in-first-out principles and observe indicated shelf life.
• Avoid temperature cycling that promotes condensation inside containers.

Standards and designations

Common designations are ISO VG viscosity grades and grades according to DIN (e.g., HLP, HVLP). Fire-resistant fluids are commonly known as HFC or HFDU. For practical use, information on flash point, pour point, viscosity index, air release, and demulsifying behavior is also important. These parameters facilitate coordination with hydraulic power packs and tools such as combination shears, multi cutters, steel shears, or concrete demolition shears.

Relevant frameworks include widely used specifications for mineral oil-based hydraulic oils and recognized standards for fire-resistant media, supporting clear identification and comparison of product families such as HLP, HVLP, HFC, HFDU, and biodegradable HEES types.