MPC Varnish test (70ml) is a method for determining the tendency of an oil to varnish. Varnish is a build-up of oxidation products in a system and can coat components, block valves and filters and cause reduction in heat loss through oil cooler pathways. Overall, varnish is very difficult to remove without specialist filtration equipment or chemical cleaning/flushing once it forms and so the ideal situation is to avoid varnish build up and prevent it occurring in the first place. Hence the importance of monitoring MPC Varnish potential on a regular basis as part of an annual or biannual health check of the system. After an initial incubation period of up to 3 days, the MPC method involves a filtration with solvent through a 0.45 micron filter patch. The result is read using a colour spectro-photometer sensor to accurately determine the colour and hence level of varnish (i.e. the insoluble oil degradation products) in the sample.
Tested On: Hydraulics, Compressors, Steam turbines and Gas turbines.
Diagnostic significance & Typical Diagnostic limit: Above is an example of the varnish report graph. Serious is considered >40. <15 is considered normal. 15 and 30 are the two choices of caution limit popularly used depending on whether there is a previous varnish problem or based on OEM recommendations.