The Fluid Pivot® Tilting Pad Journal Bearing consists of freely-floating pads restrained only by anti-rotation stops. In operation, each pad develops a hydrodynamic oil film to support the shaft. The pad is then supported on a self-generated hydrostatic oil film. This film is created by tapping off a small portion of the pad’s hydrodynamic oil flow to pressurize a recess on the back of each pad.

The pads are free to respond to the action of the oil films acting on them. The formation of a hydrostatic film on the back of each pad allows it to lift and pitch, and tilt axially in response to misalignment, with force and moment equilibrium attained for any particular operating condition. This pad action is predicted using Pioneer’s proprietary computer programs and has been verified by test stand data. (Conventional, off-the-shelf predictive analysis codes are not sufficient due, among other things, to the two different types of oil films.)

The monitoring of the hydrostatic recess pressures is also revealing. In a three-pad bearing, for example, recess pressures for all pads are nearly equal at light loading. The pressures increase sharply as speed is increased, due to the viscous pumping action of each pad’s hydrodynamic wedge. At heavier loads, the loaded pad(s) recess pressure(s) increases considerably, as expected. The behavior of the pad recess pressures confirms the Fluid Pivot® bearing has a good stabilizing effect on a rotor, particularly at high speeds and light loads.

The hydrodynamic pressure tap in each pad has been shown, both analytically and experimentally, to have a negligible influence on bearing load capacity. A series of tests in which the taps were intentionally plugged, one by one, shows the bearing still functioned, even with all pads rendered inactive, the bearing having become, in effect, a fixed-lobe bearing. The possibility of any hole plugging proves in service to be remote.

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