They meter the oil flow created by the main piston area, not the flow created by shaft area displacement. This translates to low internal pressure during the compression stroke. Even though damping force builds rapidly, the low internal pressure prevents high friction from the shaft seal. The temperature stability is maintained by using a flow restriction design in the bleed valves that create a turbulent flow at very low piston velocities. Materials with different thermal expansion rates are used to compensate for the viscosity change of the oil caused by changes in temperature.
Optimum settings are easy to find.
The hlins shim system with the ring-shim preload device offers infinite combinations of shim stacks, giving you the possibility to create just about any damping curve your mind can imagine, only limited by the laws of physics. All this with just one piston design. The reservoir has a traditional adjustable needle bleed valve in parallel with it's own shim stack which works only during the compression cycle. The whole system is pressurised by nitrogen gas behind a floating piston to insure separation of the gas and oil. As an option there is an additional compression control adjuster available, providing a total of 4 external adjusters.