Emergency shut-off device

An emergency shut-off device that shuts off supply of control oil to a trip-and-throttle valve of a steam turbine and closes the trip-and-throttle valve in an emergency, the emergency shut-off device comprising:

• a cylinder;
• a first piston that slides into the cylinder;
• a spring that applies a biasing force to the first piston;
• a plurality of piston valves disposed on the first piston;
• and
• a plurality of chambers that are formed by the piston valves, wherein
• the control oil is supplied to and drained from the plurality of chambers,
• a sliding surface of each of the piston valves has a spiral groove to leak the control oil in a corresponding one of the chambers to another one of the chambers that is adjacent to the corresponding chamber in an axis direction,
• the plurality of piston valves includes:
• a first piston valve disposed on a first end side of the first piston in the axis direction;
• a second piston valve disposed on a second end side of the first piston in the axis direction;
• and
• a third piston valve between the first piston valve and the second piston valve,
• a length of the third piston valve in the axis direction is shorter than a length of the first piston valve and a length of the second piston valve in the axis direction,
• the spiral groove is formed on the sliding surface of each of the piston valves, and the spiral groove has an arc cross section when cut along a cutting surface intersecting an extending direction of the spiral groove,
• a pitch of the spiral groove is 3 mm,
• a depth of the spiral groove is greater than 0.6 mm and less than or equal to 1.0 mm, and
• the emergency shut-off device further comprises:
• a second piston;
• and
• a cam that is in contact with the first piston and the second piston, wherein
• in response to the first piston moving from a normal position during normal operation to an emergency position, the cam rotates and interlocks the first piston with the second piston by moving the second piston from a normal position during the normal operation to an emergency position.