Some vessels are equipped with a water lubricated stern tube. When at sea, operating under normal conditions, the water service valve from the ship's saltwater system to the bearing should be __________.
• Water-lubricated stern tube bearings and why they need a flow of seawater • Purpose of shaft packing: sealing vs. cooling and lubrication • What is considered normal leakage at a stern tube or stuffing box under normal operation
• Think about whether a water-lubricated bearing needs a constant supply of seawater while the shaft is turning, or if it can run dry. • Consider why a small amount of leakage past the shaft packing might actually be intentional and beneficial. • Ask yourself what could happen to the bearing and packing if the valve is closed or if there is absolutely no leakage over a long voyage.
• Verify whether a water-lubricated bearing is designed to operate with the cooling water valve open or closed at sea. • Check if some leakage is normally expected and even necessary at shaft packings/stuffing boxes for cooling and lubrication. • Make sure the choice you select is consistent with preventing overheating and excessive wear of both the bearing and packing.
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