1. A ROTARY HYDRAULIC MECHANISM OF THE VANE TYPE COMPRISING A VANED ROTOR ROTATABLE IN A WORKING CHAMBER DEFINED BY AN OVAL CAM RING BETWEEN STATOR END PLATES AFFIXED TO SAID CAM RING, WITH AN ANNULAR MAINFOLD AND HYDRAULIC FLUID PASSAGEWAYS PROVIDED IN EACH OF SAID STATOR END PLATES, AND WITH ONE OF SAID MANIFOLDS CONTAINING HIGH PRESSURE FLUID AND THE OTHER CONTAINING LOW PRESSURE FLUID, AND FURTHER WITH THE HIGH PRESSURE MANIFOLD COMMUNICATING WITH A PORTION OF THE WORKING CHAMBER AND THE LOW PRESSURE MANIFOLD COMMUNICATING WITH THE REMAINING PORTION OF THE WORKING CHAMBER; SUCH LOW PRESSURE STATOR END PLATE COMPRISING INTEGRAL RIM AND HUB PORTIONS, HAVING IN CONJUNCTION THEREWITH AN ANNULAR BALANCING RING ENGAGING SAID HUB PORTION, AND HIGH PRESSURE FLUID DELIVERY MEANS IN COMMUNICATION WITH THE BACK OF SAID ANNULAR BALANCING RING, CAUSING THE BALANCING RING TO EXERT A BALANCING MOMENT ON SAID HUB PORTION AND IN TURN ON SAID STATOR WALL PORTION TO COUNTERACT THE TENDENCY OF THE STATOR WALL PORTION TO BE DEFLECTED BY THE HIGH FLUID PRESSURE IN SAID WORKING CHAMBER.