Mechanical Sealing Skills
Understanding mechanical sealing is essential for maintaining the efficiency and longevity of rotating equipment. A mechanical seal is a critical component designed to prevent fluid leakage by using at least one pair of end faces perpendicular to the axis of rotation. These faces are kept in contact under the influence of fluid pressure, elastic force (or magnetic force), and the cooperation of an auxiliary seal.
The basic structure of a mechanical seal includes four main components: the primary seal (consisting of a rotating ring and a stationary ring), the auxiliary seal (such as a seal ring), the pressing elements (like springs or push rings), and the transmission parts (including the gland and key or fixing screw). Proper installation and maintenance of these parts are crucial for effective sealing performance.
Installation Considerations
When installing a mechanical seal, several important steps should be followed:
- Ensure that the coupling is properly aligned before tightening the gland. The bolts should be evenly tightened, and the gland's end face should remain flat. Use a feeler gauge to check for any deviations, which should not exceed 0.05 mm.
- Check the concentricity between the gland and the shaft or bushing. The gap should be uniform, with no more than 0.01 mm deviation measured with a feeler gauge.
- Adjust the spring tension according to specifications. Too much or too little can affect the sealing performance. The required error range 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.
Disassembly Tips
When disassembling a mechanical seal, take care not to damage the components:
- Avoid using hammers or flat tools. Instead, use wire hooks to gently pull out the seal from the drive seat.
- If the seal is installed on both sides of a pump, handle each side carefully to avoid misalignment or stretching.
- If the gland becomes loose during operation, the dynamic ring may need replacement. Do not continue using it, as this can lead to damage and further leaks.
Operation and Maintenance
Proper operation and regular maintenance are vital for the long-term performance of mechanical seals:
- Before starting the pump, perform a static pressure test to check for leaks. The test pressure is usually between 2 to 3 kg/cm². If leaks persist, disassemble and recheck the system.
- Fill the sealed chamber with liquid before starting, especially when handling condensable media. Heat the chamber if necessary to prevent damage to the soft ring.
- For pumps with external sealing oil systems, start the oil system first and stop it last. After stopping a hot oil pump, allow the cooling water to run until the seal temperature drops below 80°C.
- Monitor the pump’s operation regularly. If there is minor leakage, observe for 4 hours. If the leak does not reduce, consider shutting down the system for inspection.
- Keep the operating pressure stable, ideally not exceeding 1 kg/cm². Avoid sudden pressure changes that could cause seal failure.
- Inspect the sealing condition frequently. For heavy oils, leakage should not exceed 5 drops per minute; for light oils, 10 drops per minute. If no improvement occurs within 2-3 days, shut down the pump and inspect the seal.
Mechanical sealing is a complex but essential process in many industrial applications. With proper installation, operation, and maintenance, mechanical seals can significantly enhance equipment performance and reduce downtime.
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This article was originally published on China Bearing Network.
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