The measurement technology for this method relies on the IR absorption spectrum of water. As the brake fluid flows through the test pipe enroute to the recipient vehicle brake system in a closed loop, it is exposed to IR light – a measurement wavelength is then compared to a relative wavelength. The difference then gives an indication of the percentage moisture present.


Transmission-Photometers for the determination of moisture in brake fluid

Transmission-Photometers for the determination of moisture in brake fluid

The chemical composition of modern brake fluids are of such a nature that small amounts of moisture of max. 0.2 % do not adversely affect the functionality of the brake fluid. However, these fluids are highly hygroscopic and therefore absorb atmospheric moisture easily – the moisture contaminant then lowers the boiling point of the brake fluid to a point where even during ‘normal’ usage the brake fluid could boil causing vapour pockets to form and these vapour pockets are compressible. Another ‘by-product’ reaction of the presence of moisture in the system is that at the temperatures present in the brake fluid (400 to 500°C) an electrochemical reaction then makes the brake fluid so acidic that further corrosion can eventually cause the brake system to fail. It is therefore imperative to conduct preventative maintenance at various stages in the life cycle of any motor vehicle:

  1. Test the moisture content of the brake fluid when the new motor vehicle brake system is filled for the first time.
  2. Regularly test the brake fluids for moisture contamination – some tests have shown that even a one year old motor vehicle already contained a 2% moisture contamination!
  3. Flush the brake fluid completely every 40 000 km to 50 000 km or every 2 years (Refills should preferably be conducted in such a manner that the new brake fluid is exposed to a minimum to the atmosphere).

Surveying the above list, it is obvious that a large portion of the preventative maintenance calls for testing of the moisture contents of the brake fluid, starting with the initial filling action by the OEM manufacturer. For this application, mobile in-line Pier Electronic photometers offer an edge over traditional laboratory methods as the measurements are available immediately, as the brake fluid is filled into the brake system, do not require samples to be sent to a remote laboratory exposing the fluid to additional contaminants and also do not require the use of additional chemicals for the purpose of titration.