Type 21
The Type 21 mechanical seal is a versatile, general-purpose seal that has become an industry standard for many OEM designers and end users. Originally designed by John Crane, the Type 21 seal provides reliable sealing performance for a wide range of rotating equipment, including centrifugal pumps, mixers, agitators, and compressors.
The Type 21 seal features a robust, stainless steel construction and an elastomer bellows design that allows the seal to automatically adjust for shaft misalignment and axial movement. The bellows is hydraulically balanced, minimizing heat generation and face loads for extended seal life.
Mechancial seal drawing
Mechancial seal Chart
| Model | d1 (Inch) | d3 | d7 | l3 | l1 |
|---|---|---|---|---|---|
| Type 21–1/2" | 12.7 | 23.88 | 25.4 | 7.92 | 20.82 |
| Type 21–5/8" | 15.875 | 26.7 | 31.75 | 10.29 | 22.43 |
| Type 21–3/4" | 19.05 | 30.09 | 34.93 | 10.29 | 22.43 |
| Type 21–7/8" | 22.225 | 33.4 | 38.1 | 10.29 | 24 |
| Type 21–1" | 25.4 | 36.78 | 41.28 | 11.1 | 25.6 |
| Type 21–1 1/8" | 28.575 | 40.26 | 44.45 | 11.1 | 27.17 |
| Type 21–1 1/4" | 31.75 | 43.74 | 47.63 | 11.1 | 27.17 |
| Type 21–1 3/8" | 34.925 | 47.32 | 50.8 | 11.1 | 28.78 |
| Type 21–1 1/2" | 38.1 | 50.8 | 53.98 | 11.1 | 28.78 |
| Type 21–1 5/8" | 41.275 | 54.29 | 60.33 | 12.7 | 35.13 |
| Type 21–1 3/4" | 44.45 | 57.87 | 63.5 | 12.7 | 35.13 |
| Type 21–1 7/8" | 47.625 | 61.46 | 66.68 | 12.7 | 38.3 |
| Type 21–2" | 50.8 | 65.04 | 69.85 | 12.7 | 38.3 |
| Type 21–2 1/8" | 53.9 | 68.63 | 76.2 | 14.27 | 43.05 |
| Type 21–2 1/4" | 57.1 | 72.22 | 79.38 | 14.27 | 43.05 |
| Type 21–2 3/8" | 60.3 | 75.81 | 82.55 | 14.27 | 46.25 |
| Type 21–2 1/2" | 63.5 | 79.4 | 85.73 | 14.27 | 46.25 |
| Type 21–2 5/8" | 66.6 | 82.99 | 88.73 | 15.9 | 49.4 |
| Type 21–2 3/4" | 69.8 | 86.58 | 91.95 | 15.9 | 49.4 |
| Type 21–2 7/8" | 73 | 90.17 | 95.25 | 15.9 | 52.57 |
| Type 21–3" | 76.2 | 93.76 | 98.43 | 15.9 | 52.57 |
Key features
- Elastomer bellows design automatically compensates for shaft misalignment and axial movement
- Stainless steel construction provides corrosion resistance and durability
- Single coil spring improves tolerance to clogging and provides consistent face loading
- Positive drive mechanism protects the bellows from over-extension and minimizes shaft fretting
- Simple, modular design allows for easy installation, maintenance, and repair
Materials of construction
- Seal faces: Carbon, Silicon Carbide, Tungsten Carbide
- Elastomers: Viton, Nitrile (Buna-N), EPDM
- Metal parts: 316 Stainless Steel
- Springs: Hastelloy C
Operating limits
- Temperature: -40°F to 400°F (-40°C to 205°C), depending on materials
- Pressure: Up to 150 psig (10 barg)
- Speed: Up to 2500 fpm (13 m/s), depending on size and configuration
Applications
- Centrifugal pumps
- Rotary pumps
- Turbine pumps
- Mixers and agitators
- Compressors
- Blenders
- Chillers
Interchangeability
- John Crane Type 21
- AES P04/P04T
- Pac-Seal Type 215
- Sealol Type 43
FAQs
The Type 2100 is an updated, cartridge version of the Type 21, offering the same features in a more compact, pre-assembled design
While the elastomer bellows provides some tolerance for abrasives, a double seal arrangement or a seal specifically designed for abrasive service may be more suitable for highly abrasive applications
