Power Steering Problem

I picked up a used power steering box and pump for my 65 Valiant . I installed it and I finally got to the point where I was ready to start the engine for the first time. The car has all wheels off the ground and when the engine started the steering did a sharp right turn all on its own. It also made a banging noise. I turned the wheel back and when I let go it did the same thing again. I then disconnected the belt to the pump and continued working on adjusting the engine. I just wondered before I pull everything apart has anyone had this happen or does anyone have any suggestions as to where to start looking.