What should be done as the final step to take a DPV out of service?

Taking a Deluge Preaction Valve (DPV) out of service requires that the system is properly isolated to prevent unintended activation while maintenance or testing is being performed. Closing the DPV system control valve is the crucial final step because it physically stops the flow of water to the system, ensuring that no water will exit the valve and potentially activate the fire protection system.

This action is fundamental because it establishes a clear boundary to isolate the water supply from the DPV, effectively allowing technicians to safely perform any necessary work without the risk of accidental discharge. Other actions, while important in the overall process of putting the system out of service, do not provide the same level of assurance that the control of water flow has been securely managed. Thus, closing the control valve is essential for compliance with safety protocols and operational procedures in fire protection systems.