Empty Flow provides a starting point for a particle system consisting of a single global event containing a Render operator. This lets you build a system completely from scratch, without having first to delete the default operators provided by the Standard Flow system.
To use Empty Flow, drag it from the depot to the event display. In Particle View, this creates a global event containing a single Render operator. If the Global default display option is active in the Particle View 
Options menu, the global event will also contain a Display operator. Adding an Empty Flow also creates a Particle Flow Source icon in the viewports, at the world origin (0,0,0).
Note: If an orthographic viewport is active when you add an Empty Flow to the system, 3ds Max orients the new source icon parallel to the plane of the active viewport, with the default emission direction pointing forward. For example, if the Front viewport is active, the icon is oriented parallel to the XZ plane in the world coordinate system, with the default emission direction along the positive Y axis. If a Camera or Perspective viewport is active, Particle Flow uses the default orientation: parallel to the XY plane, pointing in the negative Z direction.