In a vacuum exhaust system, which of the following cannot be used to isolate the pumps?

In a vacuum exhaust system, the use of a grooved joint does not serve the purpose of isolating the pumps. A grooved joint is primarily designed for joining pipes and allows for easy assembly and disassembly. While it provides a reliable connection between two sections of pipe, it does not function as a means to stop or isolate the flow of gas or vacuum from the pumps.

In contrast, the other options, such as a blind flange, check valve, and manual valve, are specifically designed to control fluid or gas flow. A blind flange can fully seal off a pipe's end, effectively isolating it from the system. A check valve allows flow in one direction while preventing reverse flow, which can help isolate pressure in certain scenarios. A manual valve can be opened or closed by an operator to isolate sections of the piping system.

Therefore, while grooved joints are valuable for their structural function, they are not suitable for isolating pumps in a vacuum exhaust system.