Elements to be mixed in with pressurised water (HWBF) to give the water lubricity and corrosion protection. They usually make up 2 to 5% of a hydraulic fluid. A distinction is made between three groups:
Emulsions:
Concentrates based on mineral oil containing everything developed for mineral oils in terms of additives. They may segregate out and sometimes decompose and are also susceptible to microbes.
Solutions:
Concentrates based on soluble polyglycols. They are stable and demonstrate relatively good wear behaviour; they are biodegradable.
Microemulsions:
New type of concentrate made from a mixture of mineral oil components and synthetic fluids. Characteristics are still largely unknown.