setting up dozers for Greenland or the artic. each one was equipped with 2 filters with valves to shut off the oil to each filter. a valve was on the oil pan also. a filter could be shut off and the filter changed this way while the other filter was in service, also the valve on the pan was opened and five gal was drained out while five gal was poured in. the interesting part was the dozer was always running. it was loaded on the plane running and had been setting running for years- even with oil changes performed while running.