Centrifugal pump seals prevent leakage of pumped fluid along the rotating shaft. The choice of seal depends on factors like pressure, temperature, fluid type, and operational conditions.
Mechanical seals are widely used in centrifugal pumps due to their reliability and efficiency. They consist of two primary parts:
Stationary Seal Face (mounted in the pump housing)
Rotating Seal Face (attached to the shaft)
Types of Mechanical Seals:
Single Mechanical Seal
Basic design, cost-effective.
Used for non-hazardous liquids (water, light oils).
Example: ANSI/API 682 Type A
Double (Dual) Mechanical Seal
Two sets of seal faces with a barrier fluid in between.
Used for hazardous, toxic, or high-pressure fluids.
Example: ANSI/API 682 Type C
Cartridge Mechanical Seal
Pre-assembled, easy to install/replace.
Reduces installation errors.
Balanced vs. Unbalanced Seals
Balanced seals handle higher pressures (>200 psi).
Unbalanced seals are for low-pressure applications.
Traditional sealing method using braided rope-like material (e.g., graphite, PTFE).
Requires periodic adjustment and lubrication.
Used in low-pressure, low-speed applications.
Pros:
✔ Low initial cost
✔ Tolerates minor shaft misalignment
Cons:
✖ Higher leakage (controlled weep)
✖ Requires maintenance
Simple, low-cost seals for low-pressure applications.
Used in small pumps, light-duty applications.
| Factor | Mechanical Seal | Packing Seal | Lip Seal |
|---|---|---|---|
| Pressure | High (>200 psi) | Low (<100 psi) | Very Low |
| Temperature | High (up to 500°F) | Moderate | Low |
| Fluid Type | All (including hazardous) | Non-hazardous | Non-abrasive |
| Leakage Control | Minimal | Controlled weep | Some leakage |
| Maintenance | Low (long life) | High (adjustment) | Low |
| Cost | High initial cost | Low initial cost | Very low |
| Failure Mode | Possible Causes | Solutions |
|---|---|---|
| Seal Face Wear | Dry running, abrasive particles | Use hardened faces (SiC, tungsten carbide) |
| Leakage | Misalignment, worn O-rings | Check alignment, replace elastomers |
| Overheating | Lack of flush/cooling | Install flush system (API Plan 11/32) |
| Cracking (Thermal Shock) | Rapid temp changes | Use balanced seals, gradual startup |
| Corrosion | Chemical attack on seal materials | Switch to corrosion-resistant materials (PTFE, ceramic) |
The API 682 standard specifies requirements for mechanical seals in centrifugal pumps in refineries and chemical plants.
Seal Arrangements:
Type A: Single seal
Type B: Unpressurized dual seal
Type C: Pressurized dual seal
Flush Plans: Different cooling/flushing methods (e.g., Plan 11, Plan 32).
For water, light oils, general use → Single mechanical seal
For hazardous, high-pressure fluids → Double mechanical seal
Low-cost, non-critical applications → Gland packing
Small, low-speed pumps → Lip seals
Would you like more details on a specific seal type or application?
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