Experimental investigation on large clearance shaft seal for gas-liquid mixtures

In order to find a solution for the oil leakage problem of a large clearance shaft seal on a marine diesel engine, a series of improvement measures were proposed based on the mechanisms of centrifugal separation, reverse pumping, oil groove and staggered labyrinth. A shaft seal test system that can simulate the gas-liquid environment was built, and verification tests were conducted. Test results showed that the oil leakage didn’t decrease after adding radial or inclined ribs on the oil slinger but increased significantly instead. Adding an oil groove on the oil baffle also didn’t reduce any oil leakage. Fortunately, the addition of the staggered labyrinth effectively reduced the oil leakage. By combining with CFD simulation, the test results were explained, and the sealing functions of different structural features were studied. For structural design work of the non-contact shaft seal, the following design suggestions were proposed. First, the centrifugal effect on the liquid medium can be enhanced by adding ribs on the oil slinger, but the obstruction of oil return should be avoided at the same time. Second, the rotational speed should be fully considered when using the reverse pumping effect. Third, the oil guide groove should be adapted to the airflow and rotation state at its location. Finally, the staggered labyrinth has a stronger throttling effect compared with the straight-through labyrinth, which can reduce the outward transportation of oil by airflow.