A rack system including a support having multiple longitudinally spaced slots for connecting at least one generally Z-shaped shelf, or any suitable shape. To prevent hydraulic fluid, which escapes at the piston pump arrangement during operation, from passing into the interior of the electric motor, a collecting region is provided, which is connected to a storage chamber in order to receive hydraulic fluid therein. Behind the valve disc 11d, an oil chamber 11e communicates with the inside of the liner 7 which becomes a high-pressure chamber H at the time impact torque is generated, so that the operating fluid channel 11b may be narrowed in proportion to the increase of the operating fluid. A needle tip adjoining the valve sealing face dips into the blind hole when the valve needle bears against the body seat, the needle tip being curved in a concave fashion directly adjacent to the valve sealing face. Techniques for analyzing contention using the lists, including deadlock analysis, are described.