When someone realizes that in their design a rotary viscous damper is required many questions arise.  The designer must ask themselves what are the most important features. If a requirement of the damper is the dropping time from start to end position and no slamming is important, then those parameters must be told to Mechanical Motion Technologies Engineers.  We must be told all requirements such as degree of rotation, environmental factors, physical orientation, material compatibility and torque @ RPM.  Correlating torque and RPM is the main focus of our engineering. To achieve a slow close application we design for an over-damped physical situation. So if you are not sure of all the variables, you just need to describe the motion desired and we will engineer the damper to meet the criteria.  We custom engineer & manufacture damping, rotary viscous dampers and friction hinges.