Model Testing of Magnetic-Fluid Seals

Abstract

A series of tests on a transparent model of a multistage magnetic seal were run in order to both verify a previously conducted analysis of magnetic-fluid sealing as well as to extend our knowledge on the nature and mechanism of seal operation and seal failure. The model seal consisted of a five-stage sealing arrangement placed within the path of an electromagnet of 1500 turns. A diester-base magnetic fluid with a 250-300-gauss saturation magnetization value was used. The results of the tests can be summarized as follows: 1. Filling and Loading of Stages. These tests yielded information on the manner in which the individual stages in a multistage seal can be filled with magnetic fluid, and how the total load is distributed among them. 2. Seal Capacity. The maximum Δp was determined as a function of the number of stages (1 to 5) and of two field intensities, 600- and 450-ampere-turns. Capacities of over 27.6 kPa (4 psi) per stage were achieved, the highest capacity per stage occuring with four stages. 3. Mechanism of Failure. Breakdown of magnetic sealing was observed to pass through three phases. In the first two forms, the leakage is slow, and should the Δp be lowered, the seal is easily restored. In the blowout phase, the failure is irreversible. 4. Agreement with Theory. Good agreement with analysis was obtained with regard to fluid element configuration and Δp capacity as a function of the relevant physical and magnetic parameters.