This medium speed 4 stroke trunk piston installation used engine driven upper cylinder lubrication pumps which distributed the oil to the liners through small bore pipes running through the crankcase to the individual liners. The oil then passed via a simple non return arrangement, consisting of a spring loaded ball, through longitudinal drillings in the liner up to the lubrication points. The oil for the cylinder LO pumps was of the same grade as the crankcase oil, but was supplied from a cylinder LO tank topped up from the main LO storage tank daily.
The main engine lubricating oil was circulated through the main LO coolers and then through a set of Boll & Kirsch backflushing filters. These filters were backflushed to clean them when the differential pressure across them reached a predetermined level. The drain tank to which they backflushed was periodically purified back to the main engine sumps.
The Chief Engineer decided that he would save the company money by not using new LO in the cylinder LO tank, but would use the oil from the B & K filter backflushing drain tank. (his maths doesn't add up - if you don't purify the oil from the drain tanks back to the sumps, you will have to add new oil to the sumps - oil you would have used as cylinder oil)
Anyway, against the advice of the 2nd engineer, he issued his standing order: The cylinder oil tank was to be topped up from the B & K lub oil drain tank. "It's only going to get burnt, laddie, why use new oil?"
Within 48 hours the first piston seized. All together 5 liners and pistons were changed.
Was the oil not suitable? Had it lost all its lubrication properties? No! The reason was a lot simpler than that. The sludge and particles in the oil jammed up the non return valves on the bottom of the cylinder liners, cutting off the supply of oil to the upper cylinder lubricators.