Answer: Common types of shaft seals include oil seals, labyrinth seals, mechanical seals, etc.
(1) Oil seals. The working principle is as follows: The simplest shaft end seal is the oil seal. In the free state, the inner diameter of the oil seal is smaller than the shaft diameter, that is, there is a certain amount of interference. After the oil seal is sealed on the shaft, the pressure of its blade and the contraction force of the spring's self-tightening spring produce a certain clamping force on the seal shaft, blocking the leakage gap and achieving the purpose of sealing.
Oil seals are divided into frame and frameless, with springs and without springs. The oil seal has a small installation position and a small axial size, making the machine compact, with good sealing performance and long service life. It is easy to disassemble and repair, and the price is cheap, but it cannot withstand high pressure.
(2) Labyrinth seals. Labyrinth seals have teeth and tooth grooves arranged axially in the circumferential direction. These teeth can be on the inner circle of a stationary sealing ring (called a stationary ring) or on the outer circle of a rotating shaft or a sleeve tightly fitted on the rotating shaft (called a rotating type). Each tooth divides the pressure difference between the required sealing point and the leakage point from high to low into a series of pressure units, thereby achieving the purpose of reducing the leakage. The material of the tooth seal can be aluminum, brass or other polymer materials. It is worth mentioning that the advantage of the rotary labyrinth seal is that a softer and more easily abrasive material can be used as the sealing sleeve, so that the radial clearance can be very small, which can greatly reduce the leakage.
(3) Oil-isolated mechanical flat seal. The working principle is as follows: Its structure consists of a carbon ring and a sealing seat. The carbon ring and the sealing seat each have a smooth axial plane attached to each other. This carbon ring can float radially to a limited extent. The pressure of the sealing oil entering the sealing device should be slightly higher than the gas pressure required for sealing. Under the action of the sealing oil pressure, the axial plane of the carbon ring is tightly attached to the smooth sealing plane of the sealing seat to form a seal. Most of the sealing oil will mix with the working gas and flow to the leakage port on one side of the working gas, while a small part will flow to the leakage port on the other side. The leaked sealing oil can be recycled after being collected and separated from the gas. The leakage of the sealing oil mainly depends on the design gap of the seal. This shaft end seal can theoretically be applied to any common pressure seal. Its leakage is smaller than that of carbon ring and tooth seal. Its disadvantage is that it needs a large sealing oil supply and treatment system because it needs to provide sealing oil and post-process the oil.
(4) Applicable occasions. The sealing pressure of oil seal and labyrinth seal should generally be less than 4bar(1bar=105Pa). Mechanical flat seal can be used for any common sealing pressure.
