What is Mechanical Seal(I)

Leakage is one of the common faults in mechanical equipment. The causes of leakage are mainly twofold: first, it is caused by mechanical processing. The surface of mechanical products inevitably has defects or shape and size deviations, and clearances will inevitably occur at the joints of mechanical parts; second, there is a pressure difference on both sides of the seal, and the working medium will leak through the clearances.

Reducing or eliminating clearances is the main way to prevent leakage. The function of the seal is to close the clearances between the mating surfaces, isolate or cut off the leakage channel, increase the resistance in the leakage channel, or install small working components in the channel to exert pressure on the leaking substance, offset or completely balance the pressure difference causing the leakage, to prevent leakage.

I. Basic Concepts of Mechanical Seal

A mechanical seal refers to a device that prevents fluid leakage, consisting of at least one pair of end faces perpendicular to the axis of rotation, maintaining conformity and relative sliding under the action of fluid pressure and the elasticity of compensating mechanisms (or magnetic forces). The auxiliary sealing device for compensating rings is called a bellows mechanical seal.

II. Components of Mechanical Seal

A mechanical seal mainly consists of the following four types of components:

  1. Main sealing components: Moving ring and static ring.
  2. Auxiliary sealing components: Sealing ring.
  3. Tightening components: Springs, thrust rings.
  4. Transmission components: Drive seats and keys or fixing screws.

III. Considerations for the Operation of Mechanical Seals

1. Installation Precautions

a. Pay great attention to avoiding installation deviations during installation.

(1) The tightening of the pressure cover should be carried out after aligning the couplings. The bolts should be evenly tightened to prevent the end face of the pressure cover from skewing. Check each point with a feeler gauge, and the error should not exceed 0.05 millimeters.

(2) Check the fit clearance (concentricity) between the pressure cover and the outer diameter of the shaft or shaft sleeve after installation. It should be uniform on all sides, and the tolerance at each point should not exceed 0.01 millimeters.

b. The compression amount of the spring should be in accordance with the regulations, and phenomena of excessive or insufficient compression are not allowed, with an error requirement of 2.00 millimeters. Excessive compression will increase end-face overpressure, causing accelerated wear of the end face. Insufficient compression will result in insufficient overpressure, rendering it unable to seal.

c. After the installation of the moving ring, ensure that it can move flexibly on the shaft, and the moving ring should be able to automatically spring back after being pressed toward the spring.

2. Disassembly Considerations

a. When disassembling the mechanical seal, be careful and strictly prohibit the use of hammers and flat chisels to avoid damage to the sealing elements. A pair of wire hooks can be made to insert into the gap of the transmission seat, pulling the sealing device out. If disassembly is not possible due to scaling, it should be cleaned before disassembly.

b. If mechanical seals are used at both ends of the pump, take care of each other during assembly and disassembly to prevent neglecting one end.

c. For used mechanical seals, if there is loosening of the pressure cover causing the seal to move, the dynamic and static ring components must be replaced, and they should not be re-tightened and continued to be used.

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