11/05/2005 · Of course F2 must maintain belt sag within acceptable limit. Now to be more specific, I'm calculating the required weight for automatic tensioning of a conveyor with the following: Q : 140 t/hr (Sand) L : 120 m. H : 8 m. V : 1 m/s. Pmotor : 15 kW. Distance bet. Counter weight and drive drum : 14 m.