Abstract: A scraper blade assembly utilizes an over-center spring to bias the scraper blade assembly both into engagement and out of engagement with a conveyor, such as a moving belt, on a device for separating solids from liquids. The over-center spring extends between a fixed attachment point on the device and a pivoting attachment point on a handle secured to the scraper blade assembly. The invention is particularly applicable to belt filter presses and gravity belt sludge thickeners. An over-center spring may be secured to both ends of the scraper blade assembly to minimize torsional deformation of the scraper blade by the material being separated from the moving belt.