A pressure vessel (1) for spraying a liquid comprises a piston pump, which is arranged inside the pressure vessel and which can be actuated from the outside by piston strokes for building up high pressure inside the vessel. The piston pump has a pump cylinder (6) which is mounted on the container and which projects into the interior of the container. To simplify the mixing of the constituents of the liquid, the piston pump is rotatably mounted about its longitudinal axis on the container (11), a drive (10) for rotating the pump cylinder (6) is arranged on the outside of the container and the pump cylinder entrains the mixing elements (12) which extend into the liquid as it rotates.
