Final answer:
A dry pipe valve is installed in a dry standpipe system to automatically permit water into the system when the air pressure drops. When a fire occurs and a sprinkler head is activated, the air in the pipe is released, causing the air pressure to drop and triggering the dry pipe valve to open.
Step-by-step explanation:
A dry pipe valve is installed in a dry standpipe system to automatically permit water into the system when the air pressure drops below a certain point. In a dry standpipe system, the pipes are filled with pressurized air instead of water. When a fire occurs and a sprinkler head is activated, the air in the pipe is released, causing the air pressure to drop. The drop in air pressure triggers the dry pipe valve to open, allowing water to flow into the system and onto the fire.