challenger wrote:As we know, replacing the seal on the hydraulic pump is a reoccurring issue. Let me raise an issue here regarding this matter and get comments from members. I believe that a contributing factor to seal failure may be the closed nature of the hydraulic system. I realize the system was built this way. However, if the internal pressure in the closed system is a contributing factor to early seal failure and forcing hydraulic oil into the crankcase, is there any inherent reason why the system has to be closed and not vented?
No. The seal is exposed to pressure from the output side of the pump. Even at idle, it is subject to a minimum pressure of probably 75 pounds or so. It goes higher when the system operates. Addition of a pound or even five from the reservoir is inconsequential.
The system is sealed to keep contamination out. That is probably why they still work after this many years, in most cases with no routine maintenance. That said, they are not always operated as a closed system. When an implement (e.g. a loader) is added that requires an additional reservoir, the added reservoir is generally vented.