The valve spindle (7) is located in the bonnet in two guide bushes (4). The steam-side end of the valve spindle is a relief cone (2) and is mounted on the main cone (1) with an interference fit. The other end of the valve spindle carries the piston disc (8). The valve spindle penetration is effectively sealed by the guide and labyrinth bushes. The steam-side guide bush is also provided with a sealing edge. With the emergency stop valve open, the steam pressure acting in the direction of the hydraulic section forces the valve cone with its specially provided backseat against this edge to from a steam-tight seal. In this way, leakage steam cannot escape via the labyrinth bushes while the emergency stop valve is open, At the same time, this ensures that as long as the valve is open, the valve cone will not rotate.