power steering pump problem?

Hi, I've had a problem with squeeling from the belt on my disco 300tdi. Changed the belt but squeeling carried on. Fitted new tensioner but still had same problem....also belt became frayed at one edge. Refitted belt but noticed the steering pump pulley was out of line and the belt was riding over the inner rim of the pulley. After rmoving the belt again I found the steering pump pulley moved in and out by about 1/2". I realined the pulley and refitted the belt and all seems to be fine.
Q...is this normal or is the steering pump knackered?
I've tried to find a diagram of the pump..but with no luck. Any sensible suggestions?
Thanks

Do you mean it in and out on the shaft, if so it ain't right.