What type of valve does not have to be removed during hydrostatic testing?

The double block and bleed (DBB) plug valve is specifically designed for situations that require maintenance or testing without needing to remove the valve from the line. This is primarily due to its construction, which allows it to isolate a section of pipe and provide a means for venting, all while remaining in situ.

During hydrostatic testing, it is crucial to ensure that the valve does not allow any fluid past it while maintaining safe operational conditions. The unique design of the DBB valve includes two blocking mechanisms and a bleed port that allows for testing of the section between the two block valves without the need to disassemble the piping system. This not only saves time but also minimizes the risk of leakage and contamination during the testing process.

The other valve types typically require disconnection or removal for testing. For example, resilient liner plug valves and ball valves often don't have the same level of isolation capability as the DBB valve, and gate valves, while effective in shutting off flow, may not provide the necessary bleed function during hydrostatic tests, leading to the potential for trapped pressure and hazardous situations.