It can prevent high-pressure liquid from leaking out of the pump and prevent air from entering the pump. Although the shaft seal in the pump doesn’t occupy a lot of space, whether or not the pump can operate properly is closely related to the shaft seal. If the used shaft seal is not suitable, it not only requires high-frequency maintenance during the operation but also leaks a lot of liquid that is delivered. Besides, fire, explosion and poisoning accidents may occur due to the leakage of the flammable, explosive and toxic liquid. The consequences are unimaginable. Therefore, the shaft seal structure must be selected reasonably to ensure the safe operation of the pump.
1. Due to the unequal atmospheric pressure inside and outside the cylinder, the steam inside the cylinder and the air outside the cylinder will leak out or leak in through the radial clearance between the main shaft and the cylinder, which would cause a lot of consequences, like losing the working quality, worsening the operating environment, heating the shaft neck or making the steam enter the bearing chamber which will lead into the deterioration of the oil quality, besides, the leakage of the air can destroy the vacuum, thus increasing the pumping load. All of these consequences will reduce the efficiency of the unit. For this reason, the steam seal should be installed at both ends of the cylinder, this kind of steam seal is called shaft seal, short for shaft end steam seal. The high-pressure shaft seal is used to prevent the steam from leaking out of the cylinder, and the low-pressure shaft seal is used to prevent the air from leaking into the cylinder.
2. During the operation of the steam turbine, a part of steam will leak from the end of the shaft to the atmosphere, causing the loss of working quality and heat, and also affecting the working environment of the turbo generator. And if the adjustment is appropriate, the leakage of steam will be very large, and the bearing temperature near the shaft seal will increase or the water will mix with the oil in the bearing. For this reason, all kinds of units have been installed with shaft seal heaters to recycle the steam leaks from the shafts seals of the steam turbine.
3. It can prevent the steam inside the cylinder and valve stem from leaking outward so as to avoid polluting the environment of the steam turbine room and the quality of the lubricating oil on the bearing. During the normal operation of the unit, it can prevent the high-temperature steam from flowing through the large shaft of the steam turbine and heating it, resulting in the excessive temperature of the bearing. It can prevent air from leaking into the vacuum part of the cylinder. It can ensure the vacuum effect and vacuum degree of the condenser when the unit starts, and recycle the steam seals and the air that leaks the valve stem to reduce working load and energy loss.
4. In the process of stopping the steam turbine and in the process of the whole thermal shutdown of the condenser which needs to maintain the vacuum, it can prevent the air from leaking into the steam turbine, which will accelerate the internal cooling of the steam turbine and bending the large axis.