Abstract: The invention concerns a hydraulic machine with a set of teeth, having a toothed ring with an inner toothing and a gear wheel with an outer toothing, the gear wheel rotating and orbiting in the toothed ring, the inner toothing and the outer toothing touching each other in contact areas, thus separating pressure chambers, and with a valve arrangement controlling a connection between a connection arrangement having a high pressure connection and a low pressure connection, and the pressure chambers. It is endeavoured to achieve a stable operation, particularly with low speeds. For this purpose, each contact area is provided with an opening, which, at the time when a pressure chamber reaches an extreme value of its volume, produces a short-circuiting with the neighbouring pressure chamber.

Abstract: Motorised head pulley comprising a rotating drum, which is driven by a permanently mounted hydraulic motor situated in the pulley. Between the motor and the pulley, a reduction gear is inserted. The motor and the reduction gear comprise moving parts, which are designed for operation in contact with a water-based, lubricant-free pressure fluid. The motorised head pulley can by this be used without having to pay attention to the risk of pollution from the hydraulic medium. The motorised head pulley is especially appropriate to drive conveyors in food processing production.