Abstract: A variable displacement pump including a first sensor configured to measure a position of the variable displacement pump. The first sensor may be a rotary angle sensor that is mounted to the yoke shaft of the variable displacement pump. A controller is configured to receive position data from the first sensor and control a single or dual stage hydraulic control valve thereby adjusting the output of the first variable displacement pump.

Abstract: A rotary union for supplying a heat exchange fluid to a rotating body includes a pair of hydrodynamic bushing bearings to retain the union housing within the desired alignment with the rotating body, a thrust bearing assembly secured to the rotating body, and a seal assembly positioned forwardly of the pair of bushing bearings. The hydrodynamic bushing bearings are located within the union and are lubricated by the flow of the heat exchange fluid within the union.

Abstract: A propeller device is provided with vent apertures and plugs which fit into the vent apertures to be retained in position during use of the propeller device. The vent plugs are provided with openings therethrough so that fluids can flow from a region within a hub of the propeller device to a region proximate the outer cylindrical surface of the hub. The fluids flowing from the internal portion of the hub flow towards regions of low pressure near the propellers. The plugs can be changed to modify the size of the ventilation aperture without having to change the propeller device itself. One embodiment of the plug is provided with a moveable cover that closes the opening progressively in response to increasing rotational speed of the propeller device.