Final answer:
In general, a sprinkler system's main control valve should always be locked in the open position, except during temporary maintenance or repairs.
Step-by-step explanation:
In general, it is not acceptable for a sprinkler system's main control valve to not be locked into the open position.
This is because the main control valve is responsible for supplying water to the sprinkler system, and it needs to be open to ensure that water can flow to the sprinklers in case of a fire.
However, there is one situation where it may be acceptable for the main control valve to not be locked into the open position, and that is during maintenance or repairs. During these times, the main control valve may need to be closed temporarily to allow for work to be done on the system. Once the maintenance or repairs are complete, the main control valve should be locked into the open position again.
It is important to note that this exception only applies to temporary situations during maintenance or repairs. In all other cases, the main control valve should be locked into the open position to ensure the effectiveness of the sprinkler system.