The bonnet knife gate valve is a derivative type of the knife gate valve. By adding a bonnet structure to form a closed cavity, the gate is prevented from being exposed to the external environment. It is designed for high cleanliness, pollution prevention and frequent operation scenarios, and is commonly used in the fields of food, pharmaceuticals and sewage treatment.
1. Structural design
Bonnet assembly
A split or integral bonnet and valve body are combined to form a closed chamber to prevent dust and impurities from adhering to the gate surface and reduce the risk of closing and blocking;
When the valve stem passes through the bonnet, a packing seal (such as graphite, PTFE) is used. The friction resistance is reduced by about 30% compared with the bonnetless knife gate valve, which greatly reduces the operating torque.
Gate and seal
The bottom of the gate retains a knife-shaped bevel cut, which has the ability to cut off fibers and particles. The sealing surface adopts carbide surfacing or O-ring soft seal, which is suitable for high pressure (PN16) and corrosive media;
The elastic gate structure can be selected to compensate for the processing error of the sealing surface through slight deformation to improve the sealing reliability.
2. Comparison of technical advantages
| index | Bonneted knife gate valve | Bonnetless Knife Gate Valve |
|---|---|---|
| Environmental adaptability | Strong anti-pollution performance, suitable for clean workshops and outdoor environments | Susceptible to dust intrusion, need regular cleaning |
| Maintenance costs | The packing replacement cycle is extended by 50%-70% | The gate is exposed and easy to wear, and the maintenance frequency is high |
| Sealing performance | Leakage rate ≤ 0.01% DN (soft seal can reach zero leakage) | Suitable for hard seal, leakage rate is about 0.1% DN |
3. Typical application scenarios
Food industry: Control fluids containing pulp and fiber in dairy and juice production lines to avoid medium contamination;
Environmental protection engineering: Sludge conveying pipelines in sewage treatment plants to ensure that the gates operate without clogging for a long time;
Pharmaceutical industry: Liquid medicine conveying system in sterile workshops to meet GMP cleanliness standards.
