What to Consider When Maintaining Mechanical Seals?

Mechanical seals are one of the sophisticated and complex mechanical components used in various facilities including pumps, feedback mechanical seal decompression tanks, turbo compressors, submersible motors, etc. The sealing function and service life depend on many factors such as selection, precision of the machinery, correct installation and use.

Mechanical seals parts rely on the pressure of the sealing medium to produce appropriate compression force on the contact surface (end face) of the rotating and stationary rings, allowing these two end faces to be tightly combined, maintaining an extremely thin liquid film between the end faces to achieve the sealing purpose. This liquid film has liquid dynamic pressure and static pressure, playing a role in smoothness and balance.

Cleaning and Inspection of Mechanical Seals

• Check whether there are scratches, cracks or other defects on the surface of the dynamic ring, which can cause serious leakage of the mechanical seal. If possible, use public tools to check whether the sealing surface is flat. If the sealing surface is not flat, pressure water will enter the dynamic ring sealing surface of the assembled mechanical seal, separating the dynamic ring and making the mechanical water seal ineffective. If necessary, create tools to perform water pressure test before assembly.

• The working principle of mechanical seals requires that there should be no impurities outside the mechanical seals. Therefore, before assembling the mechanical seals, clean the dynamic ring, stationary ring, and shaft sleeve.

• Check whether there are any defects that affect the sealing performance on the contact surface between the dynamic ring seat and the dynamic ring sealing ring.

• Check whether the compensation spring of the mechanical seal is damaged or deformed and whether the stubborn coefficient has changed.

• Check whether there are defects such as burrs and grooves on the sealing mechanical seal shaft sleeve.

• For mechanical seals equipped with pumping mechanisms, check whether there are defects such as cracks or broken wires in the screw pump's screw.

• Clean and check whether all sealing gaskets have defects such as cracks, pores, etc. and whether the gasket diameter is within the tolerance range.

Calibration of Mechanical Seal Assembly Technology Dimensions

• Measure the size of the dynamic ring sealing surface. This data is used to verify the radial width of the dynamic ring. When using different friction materials, the radial width of the hard material friction surface should be 1-3 mm larger than the soft one. Otherwise, the corners of the hard material end face are prone to embed under the soft material end face, causing damage to the mechanical seal function.

• Check the clearance between the dynamic ring and the mechanical seal shaft or mechanical seal shaft sleeve. The inner diameter of the stationary ring is sometimes larger than the shaft diameter by 1-2 mm. For the dynamic ring, to ensure mobility, the inner diameter is 0.5-1 mm larger than the shaft diameter to compensate for the vibration and deflection of the shaft. However, the clearance should not be too large, otherwise, the dynamic ring sealing ring may be stuck, causing damage to the mechanical seal function.

• Calibration of the compressive force of the mechanical seal. The compressive force we usually refer to as mechanical seal tightness should be appropriate. If it is too large, the friction surface of the mechanical seal will heat up, slow down the wear of the end face, and reduce the friction power. If it is too small, it is easy to leak. The compressive force is determined during the mechanical seal design, and we can only determine it by measuring the compressive force of the mechanical seal during assembly. Usually, the vertical interval between the end surface of the stationary ring and the end surface of the gland after the stationary ring is installed is measured, and then the vertical interval between the end surface of the dynamic ring and the end surface of the gland is measured. The difference between the two is the compressive force of the mechanical seal.

• Measure whether the length of the compensation spring has changed. The change of the function of the spring will indirectly affect the end face pressure of the mechanical seal. In some cases, the length of the spring will be extended after a long period of operation, and the compensation spring will also deform due to the centrifugal force in the dynamic ring mechanical seal.

• Measure the length of the anti-rotation pin of the stationary ring and the depth of the pin hole to avoid the situation where the pin is too long and the stationary ring cannot be assembled in place, which will damage the mechanical seal.