Mechanical seals, also known as end seals, are essential components used to seal rotating shafts in various equipment such as pumps, compressors, and hydraulic systems. These seals consist of a pair of friction faces—one stationary and one rotating—that work together to prevent fluid leakage. The design relies on fluid pressure, elastic force from a compensating mechanism (such as a spring or magnetic force), and auxiliary sealing elements to maintain effective sealing.
One key feature of mechanical seals is the use of an auxiliary seal, often a metal bellows, which allows for compensation under varying operating conditions. This makes them particularly suitable for high-pressure and high-temperature environments where traditional seals may fail.
The main components of a mechanical seal include: the primary seal (moving ring and stationary ring), the auxiliary seal (such as a rubber O-ring), the pressing element (like a spring or push ring), and the transmission part (which includes the gland seat and fixing screws). Each component plays a vital role in ensuring proper operation and long service life.
Mechanical seals can be classified based on several factors. For example, they can be either rotary or static depending on whether the spring rotates with the shaft. They can also be categorized by their location—built-in or external—and by the direction of leakage, which can be internal or external. Additionally, they can be balanced or unbalanced based on how the fluid pressure affects the sealing faces, and single or double-ended depending on the number of sealing faces.
Other classifications include the number of springs used (single or multiple), the type of elastic element (spring or bellows), and the type of non-contact seal (hydrostatic, hydrodynamic, or dry gas). Temperature and pressure ranges also influence the selection of mechanical seals, with options available for high, medium, low, and ultra-high pressure applications.
When installing a mechanical seal, it's crucial to avoid misalignment. Ensure that the gland is properly aligned with the coupling before tightening the bolts evenly. Check for concentricity between the gland and the shaft using a feeler gauge, and ensure the clearance is within 0.01 mm. The spring compression must be adjusted according to specifications, typically within a 2.00 mm tolerance. If the compression is too high or too low, it can lead to excessive wear or poor sealing performance.
During disassembly, care should be taken to avoid damaging the seal components. Use tools like wire hooks to gently remove the seal rather than hammers or flat blades. If the seal has been in operation, the static and dynamic rings should be replaced instead of reusing them, as the friction surfaces may have changed due to wear.
For normal operation, pre-start checks are essential. Ensure all parts are installed correctly and perform a static pressure test at around 2–3 kg/cm² to detect any leaks. Also, manually turn the pump to check for smooth rotation. When starting a hot oil pump, allow the system to cool down before stopping the cooling water to prevent damage to the seal components.
During operation, monitor for any signs of leakage. If minor leakage occurs but does not improve after a few hours, the pump should be stopped for inspection. Keep the operating pressure stable, avoiding fluctuations greater than 1 kg/cm². Avoid running the pump dry, as this can cause severe damage to the sealing surfaces. Regularly check the seal and replace it if the leakage exceeds acceptable limits (e.g., 5 drops per minute for heavy oil and 10 drops per minute for light oil).
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