The operator keeps one hand on the start button to operate the electric motor. This is known as a dead man system. As soon as the operator removes hand from start button the motor and machine stops. The other hand selects 1 off 2 levers to invert and return the machine and clamp and unclamp the tables. This method is very popular not only because of cost saving, but with trained operators they gain experience with what pressure they require to place upon the load they are inverting. As you are opening and closing the valve mechanically it gives the operator much improved feel and control of the machine.