The velocity of the section. 
   Namespace:   Autodesk.Revit.DB.Mechanical  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 18.0.0.0 (18.2.0.0) 
  Since:  2013 
Syntax
Remarks
 In one section, all section members have same velocity. Default unit is Feet per second. For Duct, unit type is UT_HVAC_Velocity. For Pipe, unit type is UT_Piping_Velocity