The invention relates to a screen changer in a system that processes flowable plastic. The screen changer includes an element, such as a portafilter, that is movable between two positions; two hydraulic pumps that effect position change of the screen changer; and a motor that operates both pumps. One pump provides greater flow volume and the other provides a lower flow volume, but with greater pressure. A non-return valve in the supply line to the hydraulic cylinder controls flow to the cylinder that moves the movable element between positions. The volume pump is used to move the movable element when resistance to movement of the screen is low and the high-pressure pump to move the element when resistance is high. The non-return valve selectively enables or interrupts flow from the pumps to the hydraulic cylinder. The screen changer allows use of a non-pressurized hydraulic fluid reservoir.