tailieunhanh - Marine Machinery 7 E Part 8

Tham khảo tài liệu 'marine machinery 7 e part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 270 The propeller shaft Joint Face sealing strip Figure Detail of a Crane sea which rotates with the shaft and of the main seal unit which is stationary and clear of the shaft. This mating contact of the seal faces which are hydraulically balanced is sustained by spring pressure and by the method of flexibly mounting the face of the main seal unit. The flexible member consists of a tough but supple reinforced bellows. Thus the main seal unit is able to accommodate the effects of hull deflection and vibration. The bellows member is clear of the shaft and its flexibility therefore cannot be impaired as may happen when a flexible member is mounted on the shaft and hardens seizes or becomes obstructed by a build-up of solids. The mechanical design principles also ensure continued sealing under fluctuating pressure conditions . changing draught. An emergency sealing device can be incorporated into the design. The device when inflated with air or liquid forms a tight temporary seal around the shaft enabling repairs to be made or a replacement seal fitted when the ship is afloat without the shaft being drawn or drydocking being necessary. Lubrication systems The static lubrication system for vessels with moderate changes in draught have header tanks placed 2 3 m above the maximum load waterline. The small differential pressure ensures that water is excluded. The cooling of simple stem The propeller shaft 271 tubes necessitates keeping the aft peak water level at least m above the stern tube. Tankers and other ships with large changes in draught may be fitted with two oil header tanks Figure for either the fully loaded or ballast condition. Hydrodynamic or hydrostatic lubrication The requirement for steaming at a slow economical speed during periods of high fuel prices or for other reasons gives a lower fluid film or hydrodynamic pressure in stem tubes due to the slower speed. The possibility of bearing damage occurring prompted the installation of forced .