Operating pressure oil filter hydro gear 52114?

The filter is on the suction side of the pump if you look at the hydraulic schematic, and the sump (case) of the 2800,3100 and 3400 series units is vented through the plastic expansion tanks. Thus the pressure on the filter is atmospheric (or a slightly less).

To put it simply, the pump draws oil through the filter rather then pushes it so there is no pressure in the filter.