The piston valve V-KV-11-5-3 operates “positively”, meaning it is opened by hydraulic pressure and immediately closes again by spring force as soon as this hydraulic pressure drops. The switching pressure for releasing the spray water is preferably taken from the Schreitzylinder, but can also be connected to other switching functions, e.g., on the slide cap. The piston valve V-KV-11-3 operates “bi-stably”, meaning it remains open by impulse switching and sprays until a closing impulse (HD2) ends the spraying process.