Abstract: Focusing on different medium characteristics such as high temperature, easy vaporization, solid particle content, and corrosiveness, this article provides professional recommendations for mechanical seal selection.
In petrochemical and refining units, pumped media vary widely, requiring condition-specific sealing solutions. Below are response strategies for several typical operating conditions.
1. Seals for High-Temperature Medium Pumps
High-temperature oil pumps (such as tower bottom hot oil pumps, heat transfer oil pumps, residue oil pumps, asphalt pumps, etc.) pose severe challenges to seals. Recommended solutions:
- Hard-to-hard friction pairs, suitable for high-temperature media containing solid particles
- Welded metal bellows mechanical seals, adapting to thermal expansion and contraction under different pressures
- Shaft seal box cooling jackets or fin cooling structures to reduce seal chamber temperature
- Double mechanical seals + enhanced flushing
2. Seals for Easy-Vaporizing Medium Pumps
Light hydrocarbon pumps, LPG pumps, liquid ammonia pumps, etc., handle media with low boiling points that vaporize easily. Countermeasures:
- Enhanced flushing to ensure stable seal chamber pressure and temperature, maintaining the seal in liquid phase state
- Adoption of hydrodynamic pressure seals for good lubrication
- Heating methods to enable stable vapor phase operation
- Tandem mechanical seal designs
3. Seals for Solid Particle-Containing Medium Pumps
Solid particles entering friction pairs accelerate wear, while fibers can easily cause leakage. Solutions:
- Double mechanical seal or tandem seal structures
- Flushing fluid filtration to prevent particles from entering seal end faces
- Selection of wear-resistant material combinations
4. Seals for Corrosive Medium Pumps
Acid and alkali pump seals require comprehensive consideration of material corrosion resistance and galvanic corrosion issues. Recommendations:
- Corrosion-resistant friction pair materials: ceramics, filled PTFE, silicon nitride, corrosion-resistant cemented carbide
- Auxiliary seals: fluororubber, polytetrafluoroethylene
- Structural optimization: externally mounted bellows, internally mounted seals where springs do not contact the medium
- High-risk media: double mechanical seals + barrier fluid isolation
5. Seals for Easy-Solidifying/Easy-Crystallizing Medium Pumps
High-viscosity or easy-crystallizing media tend to cause end face sticking or excessive wear. Recommendations:
- Cemented carbide to copper alloy friction pairs
- Stationary seal structures with reinforced stationary ring anti-rotation
- Heated seal chambers to maintain medium above crystallization temperature
- Use of solvents at back cooling to dissolve crystals