Abstract: A support assembly supporting a spray boom assembly from a liquid supply assembly. Spaced support arms have opposite ends pivotably mounted on frames of the liquid supply assembly and the boom assembly to afford movement of the spray boom assembly between raised and lowered positions by a changeable length assembly such as a hydraulic piston, and shocks or bouncing action transmitted from the liquid supply assembly are damped by an assembly comprising an elongate shaft, an elongate tube around the shaft, resiliently elastic shock absorbing strips disposed between the shaft and the tube that with surfaces of the shaft and tube are shaped to restrict rotation of the tube around the shaft without resilient compression of the shock absorbing strips. Either the shaft or tube is fixed to the frame or the support arms, the other has an activating arm fixed to and projecting from it, which activating arm is pivotably attached to one end of the changeable length means.