First - post this in the "fluid power engineering" section. Bud will see it and he is the Zen master of all things hydraulic.
Back to you question - "what happen if the sloshing height is bigger that the freeboard?" Happens all the time in off-road equipment. If you have a choice put the long axis of the reservoir perpendicular to the axis of travel to minimize problems. There are two issues to watch out for:
1. Make sure that the pump inlet is not uncovered. Usually not a big deal unless you have a shallow oil level.
2. Position of the breather and dipstick ports are very important. The dipstick will be OK if it has an O-ring seal (which it should anyway for cleanliness reasons).
The breather can be a very tricky problem. I have worked on many different types of machines where aggressive driving can have oil dripping out of the breather.
-- First line of defense is to put the breather port as close as possible to the center of the roof. If that is not possible seriously consider an internal pipe.
-- Next make sure that any plumbing for the breather will drain back to tank. Low spots create a P-trap which will "pump" oil out. The pumping action is provided by both the oil during sloshing and air during cylinder retraction. (note that even on 2-way cylinders the rod displaces oil, which goes back into tank, which forces air out.) I calculated an exiting air speed >40mph on one machine during the worst case cylinder retraction. Put your hand out the window at 40mph to get an idea of how much oil it can push!
-- In the same vein you can make the breather line larger. This decreases the air speed.
-- You can try a breather with built in low pressure check valves. Note that this will only work if you can guarantee that you will not be displacing air out while the sloshing is occurring.
-- You can try an expansion chamber, but I've had bad luck with the simple/cheap designs. I did design a very effective one on my last project though. It was a somewhat complicated rotomolded job, but it solved the problem and only cost $1.50 (for 10k units/yr).
Let me know if you have a more specific question. ISZ
