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.
We build most John Crane seals, not only Type 21. Send the seal part number, a drawing or the old seal. All are equivalents, not sold as genuine OEM parts.
Operating limits
Drawing & dimensions
Mechanical seal Chart
Dimensions in mm by shaft diameter d1. Letters match the section drawing. Standard sizes shown; other sizes are built from a drawing or the old seal.
| 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 | 31.09 | 34.93 | 10.29 | 22.43 |
| Type 21–7/8" | 22.225 | 33.4 | 38.1 | 10.29 | 24 |
| Type 21–1" | 25.4 | 43.18 | 41.28 | 11.1 | 25.6 |
| Type 21–1 1/8" | 28.575 | 46.28 | 44.45 | 11.1 | 27.17 |
| Type 21–1 1/4" | 31.75 | 49.4 | 47.63 | 11.1 | 27.17 |
| Type 21–1 3/8" | 34.925 | 52.58 | 50.8 | 11.1 | 28.78 |
| Type 21–1 1/2" | 38.1 | 55.8 | 53.98 | 11.1 | 28.78 |
| Type 21–1 5/8" | 41.275 | 62.2 | 60.33 | 12.7 | 35.13 |
| Type 21–1 3/4" | 44.45 | 66 | 63.5 | 12.7 | 35.13 |
| Type 21–1 7/8" | 47.625 | 66.6 | 66.68 | 12.7 | 38.3 |
| Type 21–2" | 50.8 | 73 | 69.85 | 12.7 | 38.3 |
| Type 21–2 1/8" | 53.9 | 73.3 | 76.2 | 14.27 | 43.05 |
| Type 21–2 1/4" | 57.1 | 78.41 | 79.38 | 14.27 | 43.05 |
| Type 21–2 3/8" | 60.3 | 82 | 82.55 | 14.27 | 46.25 |
| Type 21–2 1/2" | 63.5 | 84.87 | 85.73 | 14.27 | 46.25 |
| Type 21–2 5/8" | 66.6 | 88.4 | 85.73 | 15.9 | 49.4 |
| Type 21–2 3/4" | 69.8 | 92.58 | 88.9 | 15.9 | 49.4 |
| Type 21–2 7/8" | 73 | 94.85 | 95.25 | 15.9 | 52.57 |
| Type 21–3" | 76.2 | 101.9 | 98.43 | 15.9 | 52.57 |
Design
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
Materials of construction
- Seal faces
- Carbon, Silicon Carbide, Tungsten Carbide
- Elastomers
- Viton, Nitrile (Buna-N), EPDM
- Metal parts
- 316 Stainless Steel
- Springs
- Hastelloy C
Applications
Cross-reference
Interchangeability
- John Crane Type 21
- AES P04/P04T
- Pac-Seal Type 215
- Sealol Type 43
FAQ
FAQs
What is the difference between a Type 21 and Type 2100 seal?
Both are John Crane elastomer bellows seals. The Type 2100 is the shorter, more compact design, so check the working length before swapping one for the other. Send the old seal or its part number and we match the right one.
Can the Type 21 seal handle abrasive media?
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
Request a quote
Send the brand and part number, the seal drawing or a sample of the old seal. As the manufacturer we quote drop-in equivalents, custom and private-label seals at low minimums.