Equations for calculating the pressure distribution along the labyrinth gland, the critical condition of the last throttling and the leakage of fluid through the gland are derived taking the state of imperfect throttling into consideration for the straight through type axial flow labyrinth gland. The calculated values from those equations are in good agreement with the experimental values obtained by the equipment with various geometrical dimensions. The flow coefficient of the labyrinth fins and the imperfect throttling factor of the expansion chamber are evaluated from the experimental results. A method of obtaining the most effective number of throttling fin for a given gland length is also presented and compared with the experimental values.
On the stern tube sealing, the abnormal phenomenon that lube oil supplied in the chamber between seal rings leaks outboard actually occurs nowadays, even though its seal rings have no damage. Thereupon, the authors feel keenly that in recent years with the tendency of the larger size and the higher speeds of ships, this phenomenon is an important item to be investigated and have investigated for grasping the working conditions of seals and its surroundings on large oil tanker. As the results of it, the authors found that a large pressure fluctuation is caused in the chamber between seal rings and that this pressure fluctuation is very related to the claracteristics of stern tube sealing. Then, the authors have carried out experiments in our laboratory with a seal testing apparatus under conditions of pressure, vibration, etc. similar to those of an actual ship. And the authors have grasped it from the results that the causes of the pressure fluctuation are the inertia force of oil flow in the circumferential direction in the chamber between the seal rings excited by the lateral vibration of the shaft, that of oil flow in the axial direction in the recess of the stern tube beairng excited by the axial vibration of the shaft, etc. Furthermore, the authors have analyzed theoretically the mechanism of occurrence of the pressure fluctuation and have grasped the characteristics of lip type stern tube sealings in the relationship between shaft vibration, pressure fluctuation and oil leakage and about the necessary pressure for sealing in the chambers enclosed seal rings.
With an increase in the size and power rate of ships, there is a growing tendency toward the possible absence of oil film due to the misalignment of the propeller shaft at the after end of stern tube bearings. The authors have developed two different calculating methods on shaft alignment; one is the optimum shaft alignment which makes the uniform distribution of contact stress in the bearing, and the other is to obtain the thickness of oil film on the stern tube bearings under operating condition. The obtained results are summarized as follows. 1) On the assumption that the supporting point is set up at the after end of the stern tube bearings, the reduction of reaction force at the after end is superior to that of the shaft inclination. 2) If the allowable bending stress of the propeller shaft is large, the reaction force at after end becomes small, and the edge loading is considerably reduced. 3) When the revolution of propeller shaft is high, the oil film is formed enough to protect the bearing metal from damage.When the revolution is low, however, it is difficult to form the oil film, and the metal-to-metal contact will occur. 4) In the case of the ship “A”, the calculated thickness of oil film agrees qualitatively with the measured value, though the quantitative coincidence of the thickness is insufficient.