Dry pipes systems are used in unheated buildings, but the valve room must be heated,
- Dry pipe systems are more difficult to design than wet pipe systems and are harder to restore.
- Pipes are not filled with water (but with pressurized gas or air),
- Heat from a fire opens a sprinkler head
- Usually only one or two heads open
- Air pressure drops in the piping and opens a water valve (the dry-pipe valve),
- Water fills the pipes and exits through an open sprinkler head(s
- Pipes in protected space are filled with air or inert gas; an opening sprinkler head, triggers the system by releasing the air or gas, which allows water to flow into the pipes and then out through the open sprinkler head,
- A dry pipe valve keeps pressurized air above the supply water pressure
- The clapper valve has a locking mechanism to keep the clapper open until it is reset, by draining the system, opening the dry pipe valve cover and resetting the lock