Out of the troubles on sterntube oil seal devices, the most critical problem is the cracks on the seal ring found in many seal devices. The phenomenon of these cracks can be divided into two categories, i. e. (1) numerous hair cracks on lip face, and (2) circumferential long cracks on bend parts of seal ring. Among the various conceivable causes of these cracks, it is considered that, particularly on large ships, one of the most important factor is the large deformation and stress concentration of the seal rings under the high pressure. At balast condition, the seal rings are subject to the large differential pressure created by the oil head tank and draught, and this pressure generally exceed 0.5 kg/cm2G in case of 50, 000 DWT and larger ships. This paper deals with the results of hydrostatic test conducted on the existing 670 type seal ring, in order to investigate the actual behavior of seal rings under the pressure. The results show that, the mode of deformation of bellow part, when they are kept free of restriction, is considerably different from when they are restricted for axial movement by support ring. And the bellow part is bended sharply at the fastening edge of casing and support rings. The seal lip is pressed down on to the liner and contacts in full width of lip face at the pressure of 1 kg/cm2G. When the back pressure is given, the seal ring leaks at the pressure of 1.1 mAq. High pressure test shows that, mechanical strength of a new seal ring of the existing type is sufficient and it can withstand comparably high pressure without burst.
Ultrasonic-treatment was seemed one of the most favorable treatment methods to be developed in addition to conventional centrifugal equipments for marine diesel fuel oil, so this experimental study was carried to make clear its effects upon physical and chemical properties of some kinds of heavy fuel oil. A special ultrasonic equipment, named K-7, was applied. Viscosity, surface tension, gravity and specific heat of fuel were measured strictly and gaschromatography tests, spot tests, evaporation and combustion tests of single oil droplet, and engine firing tests were carried before and after the treatment in accordance with many expectant conditions on board. The most effective result of the treatment is the fact that large floating sludges in oil are crushed and separated into very small particles by its cavitation effect then oil itself becomes so homogeneous. Evaporation and combustion qualities of single oil droplet become slightly favorable and this affects on engine performance more or less, but other changes for substantial properties of oil as a whole hardly can be expected by the way of the treatment such as we used here.