轮机长

考试试题

[问答题]After the shut-off valve of the starting air receiver has been opened, the air flows at full pressure through the filter to the main start valve “A” (with complicated construction), thereby applying pressure to pipe between the main start valve “A” and the starting air control valve. Providing that maneuvering hand wheel is in the "Stop" position, all other pipes are without pressure. If the wheel is turned towards the “Start” position, a pawl above the starting air control valve is actuated and the valve is opened, allowing air to flow to the main start valve “A”. It opens to allow a direct through-flow of air. All cylinder starting valves are thus exposed to air pressure and, furthermore, air flows to the starting air distributor, which is controlled by the camshaft. The distributor has a series of slide valves arranged radially around the camshaft-one slide valve for each cylinder. These supply pilot air to the cylinder starting valves with pistons in the “Start” position. The rotation of the engine crankshaft commences, after which the cylinder starting valves are opened in the correct sequence. The crankshaft is thus brought to speed of rotation necessary for compression and ignition. When the maneuvering hand wheel is turned, the governor is actuated through a flexible cable setting the fuel pumps. However, a fuel index limiting arrangement is inserted, which keeps the regulating shaft and thus the fuel pumps at zero index during the starting process, ensuring that fuel is not injected into a cylinder during the supply of starting air. When the engine crankshaft has reached the necessary speed, the hand wheel is turned further past the “Start” position with the result that the arm above the starting air control valve is released and the valve is closed and vented. At the same time, the control piston in the main start valve “A” is also vented , thus blocking the supply of air to the cylinder starting vales, the starting air distributor and the fuel index limiter. Gradually, as the handle is turned further towards the maximum position. The governor increases the fuel pump index and the crankshaft rotates more quickly. The governor ensures that the maximum permissible speed is not exceeded. (The following questions are based on the passage above)