With liquid-filled pressure gauges, white foam can occasionally form inside the case. This is the well-known phenomenon of an electrochemical reaction between aluminium components (e.g. pointers, dial) and the case filling (mainly with glycerine-water mixtures). For technical reasons, this medium is mainly used for lower pressures up to and including 4 bar. However, the foamy bubbles that are produced are only of an optical nature and have no effect on the correct functioning of the pressure gauge. The foaming is therefore not a reason for complaint. If you are still dissatisfied with the visual appearance of the instrument, WIKA can offer you possible alternatives (e.g. silicone-oil case filling).