For decades, if you drove a standard forward-plate compactor into a blind utility trench and reached the end, you had to physically drag a 100 kg [approx. 220 lbs] piece of dead iron backward by hand to make your next pass. It was a fast track to a blown-out lower back. The invention of the reversible vibratory plate compactor completely revolutionized how we approach confined space compaction, and the mechanical logic behind it is brilliant.
Unlike a forward plate, which has a single spinning eccentric weight that naturally pulls the machine forward, a reversible plate utilizes two synchronized eccentric weights inside the exciter housing. When I operate a heavy diesel reversible plate, I have a hydraulic control lever mounted on the handle. When I push the lever forward, the hydraulic fluid alters the phase angle of the two spinning weights so their combined force is directed downwards and forwards. The machine marches ahead.
The magic happens when I pull that lever backward. The hydraulics instantly shift the phase relationship of the weights. Without the engine slowing down or the gears grinding, the combined centrifugal force shifts to direct energy downwards and backwards. The 350 kg [approx. 770 lbs] machine stops on a dime and seamlessly begins walking backward. If I leave the lever dead in the center, the machine hovers in place, directing 100% of its massive compaction energy straight down into one stubborn spot. This "spot compaction" capability is invaluable when you are trying to lock in a heavy catch basin or a manhole ring. It gives the operator surgical control over massive kinetic energy.
