Sanitary valve stem nut must have certain strength because it directly bears the axial force of the valve stem during the opening and closing processes of the valve. Meanwhile, valve stem nut and valve stem are thread driven, requiring a small friction coefficient and no rust.
1. Copper alloy
The friction coefficient of copper alloy is small and it doesn’t rust, so it is currently one of the most widely used materials. For low pressure valves, ZHMn58-2-2 cast brass can be used. For medium pressure valves, ZQAL9-4 tin-free bronze can be used. For high pressure valves, ZHAL66-6-3-2 cast brass can be used.
When the working condition doesn’t allow the use of copper alloy, high-quality carbon steel and stainless acid-resistant steel can be used.
What working condition doesn’t allow are the following two situations:
1. When it is used in electric valve, and the valve stem nut is with a melon-shaped clutch, it needs to undergo heat treatment to obtain high hardness or surface hardness.
2. When the working medium or surroundings are not suitable for the use of copper alloy, such as ammonia medium that corrodes copper.