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Backwash process of sand filters requests specific surface velocity to reach the recommended filter bed height expansion, however the expansion of the filter bed height is very influenced by their characteristics. This work had as aim to evaluate the effect of different sand particle size, static filter bed layer and expansion of the filter bed height on a prototype of sand filter during backwash process. The tests were accomplished using a sand filter prototype that had structural similarity and shape as commercial equipments (24 cm of height and 12.7 cm of diameter). The treatments consisted from combinations of five separate sand particle sizes (0.15; 0.34; 0.51; 0.72 and 0.92 mm of medium diameter), five static filter bed layer (5; 7; 9; 11 and 13 cm) and different expansion of the filter bed height, with three replications. In general, the sand filter prototype was effective in characterizing with accuracy the backwash process, being possible using to obtain superficial velocity to reach specific filter bed height expansion using different sand particle sizes and static filter bed layer. [ABSTRACT FROM AUTHOR]