Experimental Investigations on Carbon Segmented Seals With Smooth and Pocketed Pads

The present paper introduces experimental results for radial segmented seals operating at high rotating speed. These seals are made of three or more interlocking, carbon-graphite segments, in permanent contact with the rotor while also accommodating its dynamic displacements. Currently, many efforts are made to model these behaviors and for obtaining accurate leakage flowrate and friction torque predictions. A novel test rig fitted with a casing for measuring leakage and friction torque produced by two carbon segmented seals was developed. The tested seals were composed of three segments. Two types of segmented seals were tested: two seals with flat pads and one seal with pocketed pads. The seals were installed two by two in a casing and were simultaneously tested in a back to back arrangement. The process fluid was air, with a maximum inlet pressure of 0.3 MPa, while it was set to ambient at the outlet. The rotor diameter was 100 mm with a maximum rotating speed of 24,000 rpm. The main measurements were the inlet mass flowrate and friction torque produced by the two seals. Results show that the seal with pocketed pads produced higher leakage rates but lower friction torque compared to the smooth pads. This suggests that the seal with pocketed pads operated with segments completely lifted from the rotor surface. Mass flow rates measurements during run-up/coast-down tests revealed a hysteresis effect, which could be the consequence of segment tilt. The experimental results could also be useful to validate theoretical models.