Mechanical lubricators proved to be a much more reliable setup for mountain railroading. There advantage is from the pressure differential achieved though the terminal check valve in the delivery line.
We used to set the check valve to open between 325 and 350 lbs. This makes for a very positive and reliable flow. When you are bringing an engine off the mountain lite you have to go back and forth between using compression and the driver brakes so as to not over heat either. When using compression you can achieve very high cylinder pressures. Hydrostatic lubricators run more from gravity than pressure as the only differential in pressure comes from the speed of steam flow thru “cylinders” pump or running ear with respect to flow restriction at the turret or throttle. Not much. If you pay attention a hydro static lubricator is mounted as high in the cab as possible. The water displaces the oil as high in the lubricator as possible an as long as your engine is running down hill and has no cylinder pressure higher than the boiler pressure it might work. Hydrostatic lubricators work ok for air pumps. Although a K28 going up a 4% grade would be a bad setup . You generally don’t use much air going up a 4% grade .
Mad Jack