Mechanical seal design steps
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Mechanical Seal Design Process
When designing a mechanical seal, the first step is to thoroughly understand and analyze the operating conditions and requirements. This ensures that the seal will perform reliably under the specific application environment.
(1) Key Design Conditions for Mechanical Seals
1. Identify the type of pump and the location of the shaft seal.
2. Operating parameters such as pressure, temperature, and peripheral speed (based on shaft diameter and rotational speed).
3. Characteristics of the medium being sealed, including density, viscosity, vapor pressure, solid particle size and concentration, corrosivity (pH), and potential for crystallization, polymerization, or decomposition.
4. Host machine working characteristics, such as continuous operation, number of start-stop cycles, cycle time, and direction of rotation.
5. Environmental conditions, such as whether it's indoors or outdoors, ambient temperature and pressure, presence of pollutants, corrosion, vibration, available coolant, lubricant, and the position of the seal.
(2) Requirements for Mechanical Seals
1. Define acceptable leakage levels, leakage points, and directions (internal or external) to ensure safe and reliable performance.
2. Long service life is essential, especially in petrochemical applications, where the seal must support continuous production.
3. Ensure high reliability and stability of the mechanical seal.
4. Consider the dimensions and structural constraints imposed by the main equipment.
5. Optimize energy and material efficiency.
6. Support stable and efficient operation of the production process.
7. Evaluate material options and cost-effectiveness.
After gathering all the necessary information, the next step is to develop a design plan. This includes selecting the appropriate structure type, determining materials, and defining the dimensions of auxiliary components like lubrication, cooling, and flushing systems. It also involves comparing existing product series. Then, the main components—such as the sealing face, secondary seals, elastic elements, and fasteners—are designed and calculated. Finally, a complete set of drawings is created, along with key technical specifications.
Structural Selection of Mechanical Seals
(1) Based on Working Parameters: Pressure (P), Velocity (V), Temperature (T)
1. The working pressure (P) refers to the pressure of the fluid inside the sealed chamber. This may differ from the pump’s discharge pressure depending on the pump type. For example, in single-stage cantilever pumps, balance holes reduce the seal pressure by allowing some fluid to flow back. In multi-stage pumps, the pressure distribution across stages needs to be estimated. High-pressure applications may require multi-stage or multi-end seals to manage the pressure effectively.
2. The peripheral velocity (v) affects the choice between rotating and stationary spring designs. At lower speeds (<20–30 m/s), rotating springs are preferred, while at higher speeds (>25 m/s), stationary springs are more suitable to avoid vibration and heat issues. Hydrostatic or hydrodynamic seals are recommended for high-pressure and high-speed conditions.
3. The operating temperature (t) determines the selection of materials for the secondary seal and cooling methods. For volatile media, the temperature should be kept below the boiling point by at least 14°C to maintain a stable liquid film. Seals operating above 150°C are considered high-temperature seals and require special cooling measures. Low-temperature seals (<-50°C) may use metal bellows instead of rubber or PTFE.
(2) Based on Medium Properties
For less corrosive media, built-in mechanical seals are typically used due to their better end force control and leakage direction. For highly corrosive media, externally mounted seals or Teflon bellows seals are often chosen, though they are limited to medium pressure ranges (0.2–0.3 MPa). For viscous or crystallizing media, a single large spring design is preferable to prevent clogging. For flammable, explosive, or toxic fluids, double or cascade seals with a barrier fluid are required for absolute sealing.
(3) Based on Shaft Diameter
Seals with a shaft diameter over 120 mm are classified as large-diameter, while those below 25 mm are considered small-diameter. Non-standard seals require additional design considerations.
Our main products include:
- Packing series: carbon packing, PTFE packing, graphite packing, high-water-based packing, aramid packing, split wire PTFE packing, and more.
- Gasket series: PTFE gaskets, metal wound gaskets, asbestos gaskets, and custom-made seals.
- Rubber products: silicone, fluororubber, nitrile rubber, and other specialty shapes.
- PTFE products: rods, belts, membranes, mats, and more. 