to remove corrosion scale and debris from the back of the screen plate and its slots the outer surface 58 of the screen plate can be cleaned with the same cleaning spray when the screen plate is in a closed position 70 after impinging on the surfaces 58 59 of the screen plate the cleaning spray and removed corrosion scale and debris may flow out of the tray such as into and through the filtrate conduits 36 to the repulper 19 when the screen plate 60 is in the closed position 70 the side edge of the plate opposite to the hinge 62 is seated on a ledge in the opposite tray sidewall 48 or a stop piece 72 attached to the lower portion of the opposite sidewall a bracket 74 may be attached to the sidewall 48 and immediately above the edge of the plate to secure the plate in the closed position 70 the screen plate in the closed position 70 may also be supported by one or more ribs 76 extending upward from the bottom 42 of the tray and to the bottom surface 59 of the screen plate the ribs are attached to the bottom of the tray to support.