In the 80's & 90's I worked in engineering developing the Hydro mechanical Transmission used in the US Armies Bradley Fighting vehicle System.
The heart of the Transmission consisted of two 21 cubic inch ball piston pumps.
The transmission held 15 gallons of 15w40 oil.
We purchased oil in 55 gallon drums and recycled the used test oil for reuse after running it thru a filter cart with 30 micron filters.
Being in charge of spare parts, oil & filters I thought I would install filters with a smaller micron rating.
I installed 1/2 or 1 micron filters in both the new and used filter carts, this resulted in the used oil looking as clean as the new oil but would plug after filtering 55 gallons of recycle oil. I settled on 15 micron filters for the recycle oil system.
The surprise for me was the fact that the 1 micron filters for the new oil would also plug after filtering approx 3 barrels (165 gallons) of new oil.
Inspection of the empty new oil drums found contamination settled out on the bottom.
My thoughts (not facts) on oil delivery;
Quart, gallon and 5 gallon pails are cleaner (less contaminates) than 55 gallon drums, and a 55 gallon drum is cleaner than bulk tank truck delivered oil.
Also to consider with tanker truck delivery is the possibility of your oil being contaminated with residue from the previous tanker load and also the introduction of contaminates during each transfer of oil.
They claim to flush when changing loads but how thorough can they really be?
