A useful option on the Tong Peal box tippers is the hydraulically operated clampe box lid.

Before the box is tipped a lid is lowered to the top of the box.  When tipped there is no spillage of crop. 

When a full lid is fitted then normally a hydraulically opening flow door is fitted.  The box is fully tipped and the flow door opens releasing the crop.

When half a clamp lid is fitted then half of the lid is open.  The tipper lifts in increments which is controlled by crop sensors controlling the hydraulics as the crop leaves the box.