There is nothing in the water fill valve that affects the operation of the motor. I don't know how hard you're taping on the valve, or where you're making contact with it. Also, are you leaning on the lid, while you're tapping on the valve?

Usually the first thing we recommend you check when a washer doesn't go into a spin is the lid switch. The next suspected component is the timer. It could be that you only have a loose connection somewhere in the console, and by rapping on a component, you're reestablishing a close enough contact to get it started again.