When a line from a standpipe operation is shut down, the pressure:

In a standpipe system, when a line is shut down, the pressure must be lowered accordingly to prevent excess water from flowing through the remaining hoselines. This is because a standpipe system is designed to distribute water through several lines, and each line requires a certain pressure for optimal flow.

If one line is closed or shut down, the system is now operating with fewer outlets for the water. If the pressure is not adjusted down, the excess pressure can cause an uncontrolled flow through the remaining hoselines, which could lead to bursts, leaks, or ineffective firefighting operations. Managing the pressure appropriately ensures that the remaining hoselines receive the necessary amount of water without risking damage to the system and maintaining effective control over water delivery during firefighting situations.

Therefore, lowering the pressure is crucial to ensure safe and efficient operation of the standpipe system following a line shutdown.