Coolant and emulsions often are polluted with lubricating and hydraulic oils. Since the emulsion itself is already a mixture of oil, water and chemicals, this 'strange' oil or 'tramp' oil can have significant negative effects on the production process which depends on the quality of the emulsion.
The interaction between the tramp oil and the emulsion can have several negative effects on the quality and lifetime of the emulsion. A very common problem is bacteria growth in the coolant, due to the presence of tramp oil, especially in stagnant situations.
In the application where the picture to the left was taken, another problem played a significant role.. The tramp oil cause problems with the automatic changing of tools because they were sticking in the fitting, due to the oil.