Which valve must NEVER be fully closed during reverse osmosis treatment while in operation?

During reverse osmosis treatment, the brine or reject valve plays a crucial role in maintaining the proper operational dynamics of the system. This valve controls the flow of the concentrated solution that is rejected by the membrane process. If the brine or reject valve is fully closed during operation, it can lead to a dangerous buildup of pressure within the system. This pressure increase can cause damage to the membrane and other components of the reverse osmosis system, potentially leading to system failure or leaks.

In contrast, the other valves involved in the process serve different purposes. The feed water valve is important for allowing water into the system, while the concentrate and permeate valves deal with the water that has either passed through the membrane or is left behind. However, these components do not carry the same risk of system damage that a fully closed brine or reject valve poses. Therefore, it is critical to ensure that the brine or reject valve remains open to allow for proper pressure regulation and to prevent any complications during the reverse osmosis treatment process.