Mechanical sealing skills

Mechanical Sealing Skills

Source: China Bearing Network | Time: 2013-06-20

Understanding mechanical seals is essential for maintaining the efficiency and reliability of pumps and other rotating equipment. A mechanical seal is a critical component that prevents fluid leakage by using at least one pair of end faces perpendicular to the axis of rotation, under the influence of fluid pressure and a compensating force (such as spring or magnetic force), along with an auxiliary seal.

There are four main components in a mechanical seal:

  1. Primary Seal: Consists of a rotating ring and a stationary ring.
  2. Auxiliary Seal: Typically a rubber or metal gasket that provides additional sealing.
  3. Pressing Parts: Includes springs and push rings that maintain contact between the sealing faces.
  4. Transmission Parts: Such as a gland holder, key, or fixing screw that transfers motion from the shaft to the seal.

When installing a mechanical seal, attention must be given to several key points:

  • Ensure proper alignment of the coupling before tightening the gland. The bolts should be evenly tightened, and the gland face should not be bent. Use a feeler gauge to check for any deviation, which should not exceed 0.05 mm.
  • Check the concentricity between the gland and the outer diameter of the shaft or bushing. The gap should be uniform, and the tolerance should not exceed 0.01 mm.
  • The spring tension should be adjusted according to specifications. Excessive or insufficient tension can affect the sealing performance. The allowable error is typically 2.000 mm.
  • After installing the moving ring, ensure it moves freely on the shaft and can rebound after being pressed against the spring.

When disassembling a mechanical seal:

  • Use caution to avoid damaging the seal elements. Avoid using hammers or flat chisels. Instead, use wire hooks to carefully remove the seal from the drive seat.
  • If the seal is installed on both ends of the pump, take care during disassembly to prevent stretching or damage to the components.
  • If the gland becomes loose and causes the seal to shift, the dynamic ring parts must be replaced. Do not continue using the seal if it has been damaged due to misalignment or wear.

Proper operation and maintenance of mechanical seals are crucial:

  • Before starting the pump, perform a static pressure test to check for leaks. The test pressure is usually 2–3 kg/cm². If leaks persist, disassemble and recheck the installation.
  • Ensure the sealed chamber is filled with liquid before startup. For hot media, preheat the chamber to prevent damage to the soft rings.
  • If the pump starts but shows slight leakage, monitor it for 4 hours. If no improvement occurs, consider shutting down the system for inspection.
  • Maintain stable operating pressure, not exceeding 1 kg/cm². Avoid sudden fluctuations that may cause seal failure.
  • Regularly inspect the seal condition. If the leakage exceeds the standard (5 drops/min for heavy oil, 10 drops/min for light oil), stop the pump and replace the seal if necessary.

For more information on bearings and related technologies, visit our website or explore our articles on bearing quality, angular contact bearings, motor bearing removal, and spindle protection techniques.

Related Bearing Knowledge:

  • How to Distinguish Bearing Quality Correctly
  • NTN/NSK Single Row Angular Contact Bearing Overview
  • How to Remove Motor Bearings Using Hot Oil
  • Spindle Bearing Protection Methods

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