Brief Introduction of Mechanical Seal Structure and Leakage Path Analysis1

Introduction to Mechanical Seal Structure and Analysis of Leakage Path Mechanical seal is a combined mechanism composed of a series of simple design elements. The sealing function is completed by two main sealing rings with flat surfaces to prevent leakage. One of the seal rings is connected with the shaft to rotate, and the other seal ring is fixed on the housing. To seal the centrifugal pump shaft, a static seal ring is installed on the seal chamber gland. During the rotation of the pump shaft, the sealing surface of the sealing ring mounted on the shaft rubs against the sealing surface of the opposite static ring. These two seal contact surfaces act like bearings and are subject to wear. Any form of system leakage must pass through this seal interface. The force acting in the axial direction keeps the seal rings in frictional contact at all times. The source can be mechanical or hydraulic, in many designs, the sum of the two. This stable contact prevents or minimizes leakage from between the friction surfaces. The end face clearance between the static ring (Seat) and the moving ring (Seal Face) is the main sealing surface, which determines the key to the friction, wear and sealing performance of Jieyi mechanical seal, and also determines the service life of the mechanical seal. As shown in the picture above, the seal face is free to move axially by the spring to keep it in contact with the seat. Axial mobility allows automatic compensation for wear, eccentricity and thermal displacement of the shaft. The O-ring acts as an auxiliary seal, which can play a role in radial sealing and buffering, so that the entire seal does not have rigid contact in the radial direction. At rest, the abrasive end faces of the moving and stationary rings are in mechanical contact, but when the shaft rotates, complex friction occurs between the end faces and the fluid being sealed. Mechanical seal structure The commonly used mechanical seal structure is shown in the figure above. It is composed of static ring (static ring) 1, rotating ring (moving ring) 2, elastic element 3, spring seat 4, set screw 5, rotating ring auxiliary sealing ring 6 and stationary ring auxiliary sealing ring 8 and other components. 7 is secured to the gland 9 to prevent the stationary ring from rotating. Rotating rings and stationary rings are often also referred to as compensating rings or non-compensating rings depending on whether they have axial compensating capabilities.u200bu200b

There are four channels A, B, C, and D in the above picture for the possible ways of fluid leakage in the mechanical seal. The leakage channels C and D are the seals between the static ring and the gland, and between the gland and the shell, both of which are static seals. The B channel is the seal between the rotating ring and the shaft. When the end face is rubbed and worn, it can only follow the compensation ring for a small amount of movement in the axial direction, and it is actually still a relatively static seal. Therefore, these leakage channels are relatively easy to block. The most commonly used static sealing elements are rubber O-rings or polytetrafluoroethylene V-rings, while rotating rings or static rings as compensation rings are used as auxiliary seals, and sometimes rubber, polytetrafluoroethylene or metal bellows that have the function of elastic elements are used Structure. The A channel is a dynamic seal in which the end faces of the rotating ring and the stationary ring are attached to each other and slide relative to each other. It is the main seal in the mechanical seal device, and it is also the key to determining the performance and life of the mechanical seal. Therefore, the processing requirements for the sealing end face are very high. At the same time, in order to maintain the necessary lubricating liquid film between the sealing end faces, the pressure per unit area on the cavity end face must be strictly controlled. If the pressure is too large, it is difficult to form a stable lubricating liquid film, which will accelerate the end face. wear; the pressure is too small, the leakage increases. Therefore, in order to obtain good sealing performance and sufficient life, when designing and installing mechanical seals, it is necessary to ensure that the pressure value per unit area of u200bu200bthe end face is in the most appropriate range.u200bu200b

Compared with soft packing seals, mechanical seals have the following advantages: ①Reliable sealing In long-term operation, the sealing state is very stable and the leakage is very small. According to rough statistics, the leakage is generally only 1% of that of the soft packing seal. /100; ② Long service life in oil and water media can generally reach 1 to 2 years or more, and in chemical media it can usually reach more than half a year; ③ Friction power consumption is small The friction power of the mechanical seal is only soft 10% to 50% of the packing seal; ④ The shaft or bushing is basically free from wear and tear; ⑤ The end face can be automatically compensated for wear after a long maintenance period. In general, no frequent maintenance is required; ⑥ Good vibration resistance is suitable for rotating The vibration and deflection of the shaft and the deflection of the shaft are not sensitive to the deflection of the seal cavity; ⑦ Wide application range The mechanical seal can be used for low temperature, high temperature, vacuum, high pressure, different speeds, as well as various corrosive media and abrasive-containing media, etc. seal. However, its shortcomings are: 1. The structure is more complicated, and the requirements for manufacturing and processing are high; 2. It is troublesome to install and replace, and requires workers to have a certain level of installation technology; 3. When an accidental accident occurs, it is difficult to handle; 4. One-time investment is high.