Main characteristic parameters and assembly procedures of mechanical seals

The mechanical seal consists of a static ring, a moving ring, a compensation buffer mechanism, an auxiliary sealing ring and a transmission mechanism. The end faces of the static ring and the moving ring are perpendicular to the axis of the pump and fit together to form a rotating sealing surface. The static ring and the gland, the moving ring and the shaft are all sealed with the auxiliary sealing ring, and the compensation buffer mechanism is used to push the sealing ring to move along the axial direction of the pump, keep the end faces of the moving ring and the static ring in contact, and prevent the wear of the end face of the sealing ring Make compensation.

01 Main characteristic parameters of mechanical seal
1. Shaft diameter: The shaft diameter range of the pump mechanical seal is generally 6~200mm, and the special one can reach 400mm. The shaft diameter of the pump is usually determined according to the strength requirements, and it is rounded or adjusted with a shaft sleeve to meet the standard shaft of the mechanical seal. path.

2. Speed: generally the same as the pump speed, the general centrifugal pump speed is ≤3000r/min; the high-speed centrifugal pump is ≤8000r/min; the special pump is ≤4000r/min.

3. The average peripheral speed of the sealing surface: refers to the peripheral speed of the average diameter of the sealing surface. The average linear velocity of the sealing surface has a great influence on the heating and wear of the sealing surface (that is, the friction pair). The peripheral speed of the general mechanical seal is ≤30m/s; the peripheral speed of the spring static mechanical seal is ≤100m/s; the special one can reach ≤150m/s.

4. End face specific pressure: End face specific pressure pc is the contact pressure (MPa) on the sealing surface. The end face specific pressure of the end face seal should be controlled within a reasonable range, if it is too small, the sealing performance will be reduced, and if it is too large, it will aggravate the heating and wear of the sealing surface. Reasonable end face specific pressure value of pump mechanical seal; built-in mechanical seal, generally take pc=0.3~0.6MPa; externally installed mechanical seal, take pc=0.15~0.4MPa. When the lubricity is good, the specific pressure of the end surface can be appropriately increased. For liquids with high viscosity, the specific pressure of the end surface should be increased, and pc=0.5~0.7MPa is preferable; for liquids that are volatile and poor in lubricity, a smaller end surface should be selected. Specific pressure, preferably pc=0.3~0.45MPa.



02 Assembly procedure of mechanical seal
The structure of the mechanical seal is different, and the assembly method is also different. However, almost all mechanical seals are carried out in two steps of pre-assembly and final assembly.

1. Pre-assembly: It is to assemble the parts into transmission components and stationary components. Install the moving ring sealing ring into the inner hole of the moving ring to form the moving ring assembly. Install the spring and the push ring successively on the spring seat, screw the transmission screw into the push ring, adjust the pre-compressed compression of the spring, and form a compensation buffer mechanism. Align the pins to install the moving ring assembly into the compensation buffer mechanism to form the transmission assembly.

Install the static ring sealing ring on the static ring, put it into the sealing chamber of the static ring, and evenly tighten the gland to form a static assembly.

2. Final assembly: Put the transmission components and static components into the shaft and seal cavity to complete the assembly of the mechanical seal. Use a depth vernier caliper to measure the distance from the end face of the moving ring seal to the end face of the seal chamber and the distance from the end face of the static ring seal to the end face of the end cover. The actual compression of the mechanical seal is the specific pressure. In actual work, the specific pressure can be adjusted appropriately.

Excessive compression of the mechanical seal spring affects the life of the mechanical seal, otherwise the mechanical seal is prone to leakage.