Boiling point: The boiling point must not be reached, even during a hot summer day with high use of the breaks. Otherwise vapor bubbles will appear, which will be compressible and reduce the braking efficiency. The changing boiling point of aging brake-liquid is the major reason to regularly exchange this liquid.
The freezing point must be low enough to avoid freezing even on the coldest winter days.
The viscosity must be adequate in summer and winter to enable a high braking efficiency.
In production, the hydraulic system is pre-evacuated by a vacuum pump. During the charging stage, care must be taken so that fluid droplets do enter the vacuum line and subsequently into the vacuum pump as most DOT liquids are harsh; they can degrade a vacuum pump’s oil and seals.
Leybold has developed special TRIVAC B two-stage rotary-vane DOT pumps (with perfect accessories available) that use adapted sealing materials and even use DOT fluid as pump oil. These special versions covered range of 16 to 40 m3/hr pumping speed, and are proven components of most automotive production lines around the world.