1. IN COMBINATION WITH A KNEELER PIVOTALLY MOUNTED FOR SWINGING MOVEMENT BETWEEN TWO END PORTIONS, CONTROL MEANS OPERABLE FOR DAMPING THE MOVEMENT OF THE KNEELER TOWARD EACH END POSITION, THE SAID MEANS COMPRISING A FIXED ARM EXTENDING WITHIN THE ANGLE OF SWINGING MOVEMENT, AND A SPRING MOUNTED BETWEEN A PIVOTAL MOUNTING ON THE KNEELER AND A PIVOTAL MOUNTING ON SAID FIXED ARM WHEREBY THE SPRING IS PLACED UNDER PRESSURE BY THE KNEELER DURING THE FIRST PART OF THE KNEELER MOVEMENT AND THE SPRING PRESSURE IS RELEASED BEYOND THE DEAD CENTER POSITION FOR DRIVING THE KNEELER DURING THE SECOND PART OF THE MOVEMENT AT A CONTROLLED RATE.