It is directly mounted on the wall. When positive pressure builds up inside the duct, the baffle opens automatically. Valve body thickness: as required by design (L = 50–350 mm)
Technical Parameters：
| Specification (mm) | Exhaust Air Volume | 1 mmH20 | 2 mmH20 | 3 mmH20 |
| 300x200 | 120 | 420 | 600 |
| 400x300 | 150 | 560 | 900 |
| 500x400 | 200 | 630 | 1000 |
| 600x00 | 260 | 900 | 1500 |