A concrete pump with a pivoting valve and hopper assembly is provided with a novel wear plate and wear ring. The wear plate is mounted on the frame of the pump and remains mounted on the frame as the valve and hopper assembly pivots between open and closed positions. When the valve and hopper assembly is open, the wear plate is accessible for examination and replacement. The hopper is provided with an opening through which the wear plate extends when the valve and hopper assembly is closed. A seal on the hopper around the opening sealingly engages the frame. A wear ring on the valve engages the wear plate when the valve and hopper assembly is closed. A cam plate on each side of the frame is engageable with the valve and hopper assembly as the assembly pivots to a closed position to ensure alignment between the valve and hopper assembly and the frame.