The vacuum flanges with rubber seal rings used for small-diameter pipeline is known as NW (or KF) flange, and it is widely used in low, medium, and high vacuum systems. Its characteristic is simple use and economical cost, also, it can be repeatedly used. However, the NW flange has two major shortages: 1. limited heat resistance when the equipment is baked. 2. Hydrogen and helium gas permeability problems.
When using the NW flange, a center bracket that has rubber O-ring rubber outside is installed between two NW flanges, and the outer side can be quickly installed and disassembled through the clamp (Figure 1). When using fluorine rubber rings, the baking temperature can reach 150°C.
Figure 1. Schematic diagram of sealing with clamps and center brackets
1. CF/NW adapter flange
3. Center bracket
4. O rubber ring
5. NW adapter flange
The main models and sizes of the NW blind flange are shown in Table 1.
Table 1. Main models and sizes of NW blind flanges