In a dry pipe system, what event allows water to enter the pipes?

• A. Release of pressurized air
• B. Manual pull station
• C. Automatic temperature trigger
• D. Power failure

Answer: (A)

Dry pipe systems keep the piping dry by using pressurized air. Water can enter the pipes only after that trapped air is released. When a sprinkler is activated, the dry-pipe valve opens and the air is vented, allowing the water supply behind the valve to push water into the piping network. Once the air is displaced, water fills the pipes and reaches the sprinklers. Manual pull stations or automatic temperature triggers may start sprinkler action, but they don’t by themselves release the air; power failure wouldn’t cause water to enter.