Varnish in turbine oils

The condition of the oil in lubrication and hydraulic
systems is indicative of the health of the entire system. To ensure
productivity, avoiding malfunctions and reducing operating costs, we need to
monitor the fluid condition and operate a continuous maintenance of operating

Varnish refers to oil ageing products that form
deposits in the fluid system which have a gel/resin-like consistency or
resemble solid varnish. These oil ageing products are readily deposited on cool
surfaces such as the tank, valve housings or coolers. This causes an increase
in bearing temperatures, malfunctions in hydraulic valves and cooling problems.
In most cases, however, the above malfunctions are not correctly attributed to
the real cause. This results in ineffective, and often very expensive, repair

The base oils generally used today for the production
of turbine oils have changed in recent years. They reflect the increased
demands with regard to higher turbine efficiency, higher bearing temperatures
and reduced levels of hazardous substances. Whereas oils used to be produced
exclusively by the distillation of crude oil (ASTM Group I oils), for some
years now further refinement processes have been employed.

But after 3 or 4 years of operation, and due to the
low proportion of polar substances, these oils also have low electrical
conductivity. If this oil flows through the filters in the hydraulic system, an
electrostatic charge can be generated. This can lead to sparking in the system.
In addition to damaging the filter elements, it can cause failures in
measurement and control systems, and deflagrations may occur in return lines or
in the tank.

The Varnish Elimination Unit (VEU) produced by HYDAC
is an efficient solution for cleaning the varnish in the oil.

This system is similar in construction to an offline
filter and works 24h per day, 365 days per year. The service-friendly Varnish
Elimination Units VEU prepare and refurbish damaged mineral oils. The removal of varnish is based on reducing the oil solubility for
varnish with subsequent filtration.


  • Removal
    of solid or gel-type oil ageing products
  • Operating
    reliability of the system is increased because there are fewer deposits in
    hydraulic valves
  • Increase
    in the oil service life
  • Available
    as a complete unit for retrofitting to existing systems, as well as a modular
    system for new systems

For more information, click here

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