For instance, take mine for example, and I presume most are similar construction. My 3pt upper lift arms are encased in a hydraulic box which is bolted on top of the hydraulic reservoir. In turn, the reservoir is bolted to the top of the rear end. the top links fastens to the same casting. So to create a sort of down pressure, you would move the upper lift arms all the way up so they can't go any farther. It isn't really down pressure, it's just moving the upper lift arms all the way up so they can't move up anymore, thereby your implement could not move up anymore.
I can actually do this by extending one of my side links all the way down so when my box blade is tilted, the corner of it is pressing into the ground. I cut my gutters that way. I'm very careful, but I figure since only a sharp corner is engaged, like a plow blade or furrower, it is more likely to cut than say the entire rear blade of the box. Nevertheless, I really watch it when I use it that way.
When I extend both side link cylinders down all the way, the box blade is very close to touching the ground but misses by a couple inches. I could make it touch by repositioning the upper lift arms on the splined rod, but I'm reluctant to do it for fear of what I said above. Most of the construction equipment that do have down pressure, they are ten times beefier than our tractors and the connections are designed and mounted especially to accept that stress.
