TO-30 Hydraulic Control Valve

What is the purpose of the long rod, and square piece on the end of the new Hydraulic Control Valve I just bought for my TO-30?  May 10, 2016.

The square piece, mand rod are part of the oscillator. The square piece fits in a cam on the pump crankshaft that reciprocates. This causes the valve to rotate back and forth to keep the valve from sticking. The valve occasionally sticks on earlier models so the oscillator was added to the TO-30, and late production TEA-20 models. As I recall, the replacement valves are notched to accept the oscillator. You should be able to remove the snap ring in the valve, install the oscillator from your old valve, and reinstall the snap ring.