A pressure accumulator includes a housing having a housing cavity, a piston axially displaceable in the housing cavity between a first final position and a second final position and having a pressure surface which together with a wall of the housing cavity delimits at least partially a reservoir connectable to an ICE consumer in a fluid-conveying manner, an energy store cooperating with the piston, the piston being displaceable against the force of the energy store from the first final position into the second final position in that the reservoir is acted on by pressure using a pressure medium, and a locking device for locking the piston in the second final position. A locking tube is connected to the piston and supported within the housing in an axially shiftable manner, and lockable at an end of the housing facing away from the reservoir with the aid of a locking pin.