Complex sentence: The valve then shuts and the piston is pushed at a slower speed back in the tool, the valve reopens the piston pounds again and the tools moves forward this process is continually repeated until the bore has run the intended distance.
Split into simpler sentences: The valve then shuts and the piston is pushed at a slower speed back in the tool, the valve reopens the piston pounds again and the tools moves forward. This process is continually repeated until the bore has run the intended distance.