What type of valve is specifically used for achieving absolute tightness around the valve stem?

The diaphragm valve is specifically designed to achieve absolute tightness around the valve stem, making it ideal for applications where preventing leakage is critical. This type of valve uses a flexible diaphragm that, when moved, either opens or closes the flow path. Since the diaphragm forms a seal directly against the valve body, it eliminates the possibility of any fluid leakage through the stem area. This construction is particularly beneficial in applications involving corrosive substances or scenarios where cleanliness is paramount.

In contrast, ball valves and butterfly valves, while effective for many applications, don’t provide the same level of stem sealing as a diaphragm valve. Gate valves, on the other hand, are also not designed for tight sealing; they are more suited for applications where full flow is necessary without pressure drop, and they can have issues with leakage around the stem.