As stated in post #4
In more detail; the hydraulic flow and return pipes to the jack are connected together with a valve and away from the supply and return lines, forming a closed-circuit passageway through which fluid can flow when the piston is moved, (by the other jack acting on the control surface). The slight resistance to the flow of this fluid through the closed-circuit passageway when the piston moves, is what provides the damping effect.
I cannot find the diagram of this in the FCOM now - sure it used to be there?