No disrespect swoop-I'm just not sure we're talking about the same valve. There's a valve in the outlet port ( the velocity fuse ), the other valve in the bottom of the ram itself (inside the cylinder). You are correct that the velocity fuse is to limit downward travel of the carriage in case of a hyd line failure. The valve inside the cylinder is the differential valve- it's purpose is to equalize the pressures of the cyl below & above the lower packing assy ( this valve is only used in differential type cylinders).