An Acoustic Emission Study on the Starting and Stopping Processes of a Dry Gas Seal for Pumps

The starting process and the stopping process of a double dry gas seal for pumps were investigated by acoustic emission (AE) testing. The characteristic frequency band of contact of the seal faces was distinguished from noises in three different comparative experiments. The root mean square (RMS) of the AE signals after band-pass filtering was determined to effectively reflect the contact condition of the seal faces. Based on the characteristics of the AE RMS, both the starting process and the stopping process could be divided into three periods, and a lift-off rotational speed and a touch-down rotational speed were defined. The lift-off speed varied non-monotonically with the inlet pressure. The lift-off speed was smallest at a certain pressure, which meant that at that speed the seal faces lift-off most easily. The behavior of the touch-down speed was similar to that of the lift-off speed, but was a little smaller than the latter. These results reveal the potential of AE technology for monitoring the contact condition of dry gas seals during the starting and stopping processes and may help in the design and operation of the dry gas seals.