Seems to be agreement moving the specific big trailer with the specific tractor isn’t advisable. Still the hold capacity v lift capacity question is a pertinent one for a variety of scenarios.
Dealing with a variety of tractors over the years, this is my understanding with the caveats: 1) all tractors may not be identical, 2) this is relevant to open center systems such as those on the UTs, CUTs, and SCUTs most here have, and 3) I’m certainly open to correction by those with more expertise.
There is a relief valve, but it’s one relief valve for the whole system. It’s on the output side of the pump to prevent an over pressure situation damaging the pump. For example trying to lift an immovable object with the 3 point creates a deadhead situation for the pump so the relief valve releases enough pressure to protect the pump from grenading.
However, if the control valve for the cylinder involved in having a load put on it is closed, the fluid stuck between the closed valve and the hydraulic cylinder ram has nowhere to go when the pressure in the line rises and the cylinder doesn’t move as there is no relief valve between the control valve and cylinder. Fluid isn’t compressible so if you put a load on a hydraulic cylinder that is immobilized by a closed control valve, it will hold the load until something breaks. Could blow a seal, blow a hose, or more likely bend or break the axle/loader/whatever the cylinder supports.
So, yes the three point, loader, or any other hydraulic cylinder on an open center tractor will hold a LOT more than it will lift, but it’s a really bad idea to intentionally set up a scenario where it’s holding a load well over its capacity to lift.
