1. Working principle: This type of stern shaft sealing rubber ring is used to generate force on the working surface by the pressure of liquid (sea water or lubricating oil) to compress the rubber ring lip on the shaft sleeve surface to achieve the purpose of sealing. There are four oil seals in this unit, and and NO.2 are working towards the propeller to seal the water; The No. 3 channel and No. 3S channel work towards the main engine to seal oil. When the new installation is just put into use, No. 1 channel plays a water sealing role, and No. 2 channel is in standby state. When No. 1 channel is damaged, the sea water enters between No. 1 channel and No. 2 channel, and No. 2 channel plays a water sealing role. No. 3 channel plays an oil sealing role, and No. 3S channel is a spare oil seal. When No. 3 channel is damaged, it can be put into use by changing the oil pressure at the front and back of No. 3S channel. There is a spring on the working surface of the rubber ring, which is used to ensure that the rubber ring lip can be compressed on the surface of the shaft sleeve under normal conditions, especially when the contact position between the shaft sleeve and the rubber ring lip is worn, to ensure that there is always a pressure difference on both sides of the rubber ring.

2. Based on the sealing principle of the sealing device, to achieve the sealing effect, a prerequisite is that there must be sufficient pressure difference on both sides of the rubber ring, and the liquid pressure on the working face must be greater than the pressure on the back.

3. Setting and function of stern shaft lubricating oil tank:

1) The oil chamber between No. 1 and No. 2 sealing rings shall be filled with lubricating oil during installation in the dock. Since the sea water is sealed by sealing ring when it is just put into use, it cannot reach the chamber between and No.2. If the chamber is not filled with lubricating oil, No.2 sealing ring will be burned due to dry friction.

2) For the oil chamber between NO2 and NO3, a lubricating oil tank (called stern seal lubricating oil tank) is set separately in the engine room, and the oil tank has an open air vent in the engine room. The function of lubricating oil in this chamber is to lubricate No. 2 and No. 3 sealing rings. The functions of setting up separate stern seal lubricating oil tank and open air vent are as follows: A. When the water seals of channel and channel NO.2 are damaged, the leaked seawater can be discharged into the engine room through the air vent of the oil tank, and will not leak into the stern tube to endanger the lubrication of the stern bearing; B. When the NO.3 oil seal is damaged, the lubricating oil of the stern tube is higher than the stern seal lubricating oil tank because the stern tube lubricating oil circulating oil tank (or the stern bearing gravity oil tank) is set, and the lubricating oil of the stern bearing will leak into the stern seal oil tank and overflow from the air vent, reminding the engineer to enable the standby NO.3S seal ring of the oil seal; C. When the No. 3 and No. 3S oil seals are damaged, the lubricating oil leaked from the lubricating oil circulating oil tank of the stern tube can overflow from the vent of the stern seal oil tank and will not enter the sea through the No. 1 and No. 2 water seals.

3) Stern tube lubricating oil circulating tank (stern bearing gravity oil tank), the lubricating oil of this system is used to lubricate the stern bearing and is an important lubricating system of the ship. The lubrication and wear condition of the stern shaft can be judged by testing the metal content of the lubricating oil in the system. Emulsion is not allowed in daily management. The oil shall be tested on time and unqualified oil shall be replaced in time. The oil must be sampled at the drain valve of the tailshaft barrel. During sampling, the oil in the pipeline shall be drained to ensure that the oil sample can represent the lubricating oil in the tailshaft barrel.

4) The front sealing lubricating oil tank of the stern shaft, the front sealing device of the stern shaft tube, has two rubber sealing rings. The one close to the propeller is in working condition when it is just installed, and the one close to the engine room is the spare oil seal. Therefore, it is necessary to set this oil tank in the chamber between the two oil seals, and inject lubricating oil to lubricate the spare oil seals, so as to avoid burning out due to dry friction. When the rear oil seal is damaged, the lubricating oil in the stern tube circulating oil tank will leak to this oil tank. If lubricating oil overflows from the air vent of the oil tank, it can be confirmed that the oil seal close to the propeller has been damaged. The air vent of the oil tank can be closed to put the spare oil seal close to the engine room into use.

5) Setting and purpose of high and low oil tanks. When the or NO.2 water seal in working condition is in light/heavy load, the liquid force on the working face changes. For ships with large draft and large change of light and heavy load draft, the pressure on the working face of the water seal during heavy load exceeds the pressure difference between the two sides required for the normal operation of the seal ring, so a high-level oil tank is set. When the ship is under heavy load, the pressure difference between the two sides of the seal ring is reduced by providing a counter pressure on the back, so as to extend the working life of the seal rubber ring and the stainless steel sleeve. The engineer shall pay special attention that the draft marked by the seal device manufacturer does not refer to the draft of the ship's draft, but refers to the height of the ship's draft from the centerline of the stern shaft. A set of stern shaft sealing device of the same model is used on different ships, and the height of the stern shaft centerline of these ship types from the hull datum line is different. The equipment manufacturer can only mark the adjustment according to the height of draft from the centerline of the stern shaft to ensure that the liquid pressure of the working face is greater than that of the non working face. In my personal experience, for Panamax ships with small draught difference, it is not necessary to switch between light and heavy oil tanks under normal conditions. In order to maintain the pressure difference between the two sides of the seal ring and ensure the sealing effect of the seal ring, the manufacturer only marked a draft height from the centerline of the stern shaft. However, in case of heavy wind and waves, the draft of the ship's tail varies by several meters, which may cause the pressure at the back of the seal ring to be greater than the pressure at the working face. Lift up the lip of the seal ring, so that the seal ring is in a collusive state. Therefore, for ships with light and heavy loads such as Panamax, the Chief Engineer shall judge according to the height of the ship's draft from the centerline of the stern shaft when adjusting the heavy load oil tank, to ensure that the minimum ship's draft can still reach the height from the centerline of the stern shaft required in the instructions in case of heavy wind and waves, otherwise the low level oil tank is preferred. For some Panamax ships whose stern sealing oil emulsification appears soon after the stern shaft sealing device has just been replaced, most of them are caused by improper conversion of high and low oil tanks.

4. In the daily management process, if the water seal has been damaged and there is a large amount of water leakage, the stern seal lubricating oil tank must not be switched to the high-level oil tank, because the low-level oil tank can ensure that the leaked seawater can be released from the overflow port of the oil tank to avoid entering the stern tube circulating oil tank. The stern tube lubricating oil is responsible for lubricating and cooling the stern bearing, and the emulsification of the lubricating oil will cause serious consequences. If the oil in the stern tube is emulsified and the fluidity has become poor, the ship shall be stopped immediately for oil change.

5. Management and startup of NO.3S spare oil seal: When the stern shaft seal ring was just put into use, NO.3S oil seal was the spare oil seal. The standby and use of this oil seal is controlled by the inlet and outlet valves of the lubricating oil in the chamber between No. 3 and No. 3S oil seals. When No. 3 working No. 3S is in standby, the inlet valve and outlet valve are opened. The oil pressure on No. 3 working face is the oil level pressure of the stern tube circulating oil tank, and the pressure on the reverse side is the oil level pressure of the stern seal lubricating oil tank at the lower position of the oil tank. The pressure difference on both sides of the seal ring makes No. 3 in a sealed working state. The pressure on both sides of NO.3S seal ring is the same as the oil level pressure of the circulating oil tank of the stern tube. The pressure difference between the two sides is zero, and the oil seal does not enter the working state. When the NO.3 oil seal is damaged and leaks, close the inlet and outlet valves. The pressure on the NO.3S working face is the oil level pressure of the circulating oil tank of the stern tube. The pressure on the reverse side is equal to the pressure of the NO.2 and NO.3 chambers because of the NO.3 leakage. Establish a pressure difference on both sides of the seal ring so that NO.3 can be put into sealing work.