Varnish
Varnish turns up in 2 fields: tribology, railroad. Here is what it means to the people in each one.
Varnish in tribology
Thin, sticky, amber-to-brown deposit from degraded oil that coats valves, bearings and coolers.
A film of polar oxidation and thermal breakdown products that drop out of solution when oil cools, especially in turbine, compressor and hydraulic systems running hot on Group II base oils. It forms on cold spots such as coolers, filters, servo valve spools and bearing shells, causing sticking valves, plugged filters and hotter bearings. Varnish potential is tracked with MPC, and the fixes are adsorbent or electrostatic filtration, stronger antioxidants and cooler running.
"Inlet guide vane servo is sticking again, pull the spool and I bet it's coated in varnish."
Varnish in railroad
Freight crew slang for a passenger train, after the glossy varnished finish of wooden coaches.
Freight crews call passenger trains varnish, after the glossy varnished finish of wooden passenger coaches. The word covers intercity and commuter trains alike, and it carries a touch of envy or irritation from crews who run behind them. Passenger trains get preference on the freight railroads that host them, so freight crews hear about the varnish every time they are told to take the siding.
"Get in the clear at Elm and let the varnish by, Amtrak's running thirty late and the DS is getting yelled at."