Restrictive valve

moments after starting the vac the red ball rises to the top and the machine quits sucking. I turn the machine off, the ball drops, I turn the machine on, the ball rises the machine quits sucking, I turn the machine off the ball falls, I turn the machine on........etc. What am I doing wrong? It works fine and then all of the sudden it starts the same stuff again. I thought it was because the retrieving container was getting too full or the cleaning soln container was not full enough, but it doesn't seem to matter. Please help