The valve is mounted at the bottom of the tank body of tank car and connected with the tank body. The valve is connected with the cylinder through the air passage to drive the piston and start the valve. The maximum charge is over 2000 litres per minute. The valve body is provided with a cut-off groove. When the tank body is subjected to a strong impact, the valve body breaks down and seals, so that the tank and the pipeline are separated, thus ensuring that the tank body is independent and closed to prevent the liquid in the tank from leaking out.