A Double Seal Face Cartridge Seal is an integrated, pre-assembled mechanical seal unit with two pairs of sealing faces. It is designed for high-reliability, low-leakage industrial applications, and is widely used in pumps, mixers, and agitators handling toxic, flammable, explosive, or highly corrosive media. The cartridge design allows for quick installation without on-site adjustment, significantly reducing assembly errors.
1. Core Structure & Working Principle
1.1 Basic Structure
| Component |
Function |
| Primary Sealing Faces (2 pairs) |
Consist of rotating and stationary rings (common materials: SiC/SiC, WC/SiC) to block medium leakage |
| Buffer/Isolation Chamber |
The cavity between the two seal faces, filled with buffer fluid or isolation fluid to lubricate the seal faces and block process media |
| Spring/Drive Mechanism |
Provides uniform axial pressure to ensure the sealing faces fit tightly; supports bidirectional rotation |
| Cartridge Housing |
Integrates all components into a single unit; ensures coaxiality of the seal and pump shaft |
| Secondary Seals (O-rings/V-rings) |
Seals between the seal unit and pump shaft/seal chamber; materials are selected based on medium compatibility |
1.2 Working Principle
- The process side seal face blocks the leakage of the conveyed medium into the buffer chamber.
- The atmosphere side seal face prevents the buffer fluid from leaking into the environment, achieving zero leakage of the process medium.
- The buffer fluid pressure is maintained 0.1–0.2 MPa higher than the process medium pressure to ensure the seal faces are tightly attached and form a stable lubricating film.
2. Key Technical Performance Parameters
| Parameter Category |
Typical Value Range |
| Pressure Range |
Vacuum to 4.0 MPa (40 bar); high-pressure versions up to 10 MPa |
| Temperature Range |
-50°C to 350°C (depends on seal face and secondary seal materials) |
| Shaft Speed Limit |
Up to 30 m/s (peripheral speed) |
| Shaft Diameter Range |
20 mm to 200 mm (custom sizes available) |
| Allowable Shaft Runout |
≤0.03 mm (high-precision applications require ≤0.015 mm) |
| Leakage Standard |
Zero visible leakage (buffer fluid circulation normal); meets API 682 emission requirements |
3. Main Types & Application Scenarios
Double seal face cartridge seals are classified by structural layout into two main types:
| Type |
Layout Feature |
Applicable Scenarios |
| Back-to-Back Type |
Two seal faces are arranged in opposite directions; strong resistance to reverse pressure |
High-pressure pumps, chemical reactor agitators, media with variable pressure |
| Tandem Type |
Two seal faces are arranged in the same direction; the process side seal is the primary seal, and the atmosphere side seal is the backup |
Toxic/radioactive media, scenarios requiring redundant safety protection |
3.1 Typical Application Industries
- Petrochemical Industry: Crude oil pumps, hydrocarbon transfer pumps, reactor bottom pumps
- Chemical Industry: Acid/alkali transfer pumps, organic solvent pumps, polymer material mixers
- Pharmaceutical Industry: API (Active Pharmaceutical Ingredient) transfer pumps, sterile process equipment
- Environmental Protection Industry: Wastewater treatment pumps (containing toxic substances), hazardous waste treatment equipment
4. Core Material Selection Guide
| Component |
Material Options |
Applicable Medium Characteristics |
| Seal Faces |
SiC/SiC |
General corrosive media, high wear resistance |
|
WC/SiC |
Media containing solid particles, high abrasiveness |
|
Carbon graphite/SiC |
Low-speed, low-friction requirements |
| Metal Components (Housing/Spring) |
316L Stainless Steel |
Weak corrosive media (water, dilute acids/alkalis) |
|
Hastelloy C276 |
Strong corrosive media (concentrated acids, chlorine-containing media) |
|
Titanium Alloy |
Seawater, chloride-containing media |
| Secondary Seals |
FKM (Viton) |
Most organic solvents, weak acids/alkalis, temperature ≤200°C |
|
FFKM (Perfluoroelastomer) |
Strong oxidizers (concentrated nitric acid, hydrogen peroxide), temperature ≤300°C |
|
PTFE |
Strong corrosive media incompatible with rubber, temperature ≤260°C |
5. Installation & Maintenance Key Points
5.1 Installation Precautions
- Pre-installation Check: Verify that the seal model matches the pump shaft diameter and seal chamber size; check for damage to the seal faces and secondary seals.
- Cleanliness: Ensure the pump shaft, seal chamber, and cartridge seal surface are free of impurities, burrs, or rust.
- Coaxiality Alignment: The seal unit must be installed perpendicular to the pump shaft to avoid eccentric wear of the seal faces.
- No Disassembly: Do not disassemble the pre-assembled cartridge unit to avoid destroying the factory-set compression and coaxiality.
5.2 Daily Maintenance Requirements
- Buffer Fluid System Monitoring: Regularly check the buffer fluid pressure, temperature, and cleanliness; replace the buffer fluid every 3–6 months.
- Leakage Inspection: Use a gas detector or liquid leakage sensor to monitor the atmosphere side for leakage; alarm immediately if abnormal leakage is detected.
- Service Life Management: Under normal operating conditions, the service life is 12,000–20,000 hours; replace the entire seal unit once it reaches the service life, even if no faults are found.
- Storage Requirements: Unused seals should be stored in a dry, ventilated environment; avoid contact with oil, chemicals, or direct sunlight.
6. Key Advantages & Limitations
6.1 Advantages
- Zero Leakage Performance: Effectively prevents toxic/flammable media from leaking, meeting strict environmental and safety standards.
- Easy Installation: Pre-assembled design eliminates on-site adjustment; reduces installation time by 50% compared to split seals.
- High Reliability: Integrated structure reduces the risk of component misalignment; suitable for continuous operation under harsh conditions.
- Reduced Maintenance Cost: The cartridge unit can be replaced as a whole; no need for on-site repair of seal components.
6.2 Limitations
- Higher Initial Cost: More expensive than single-face seals; suitable for scenarios where safety and zero leakage are prioritized.
- Requires Auxiliary System: Must be equipped with a buffer fluid circulation system, increasing the overall equipment investment.
- Space Requirements: Larger radial size than single-face seals; requires the pump seal chamber to have sufficient installation space.
7. Professional Q&A about Double Seal Face Cartridge Seal
Q1: What is the difference between a back-to-back and tandem double seal face cartridge seal?
A: The back-to-back type has two seal faces arranged in opposite directions, which can resist bidirectional pressure and is suitable for variable pressure media. The tandem type has two seal faces arranged in the same direction; the process side seal is the primary seal, and the atmosphere side seal is the backup, which is more suitable for toxic/radioactive media requiring redundant protection.
Q2: How to select the buffer fluid for a double seal face cartridge seal?
A: The buffer fluid should meet the following requirements:
- Chemical compatibility with the process medium (no reaction or contamination).
- Good lubricity and thermal stability to ensure the seal faces are lubricated and cooled.
- For flammable media, use fire-resistant buffer fluid (e.g., water-glycol mixture, synthetic ester).
Q3: Can a double seal face cartridge seal be used for pumps handling media containing solid particles?
A: Yes, but the following configurations are required:
- Select WC/WC or SiC/WC seal face materials with high wear resistance.
- Equip a flushing pipeline to inject clean buffer fluid into the seal chamber, preventing particles from entering the seal faces.
- Install a filter at the buffer fluid inlet to remove impurities in the fluid.
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