Vane-type water flow switches can be used in dry sprinkler pipes.

Vane-type water flow switches can be used in dry sprinkler pipes.

• A. True
• B. False
• C. Sometimes
• D. Depends on configuration

Answer: (B)

Vane-type water flow switches need water flowing past a vane to push it and generate a signal. In a dry sprinkler system, the pipes are filled with air under pressure and only become filled with water after the dry valve releases. That air-filled condition means there isn’t a steady, fully water-filled path for the vane to sense, so the vane may not move reliably, or it may respond erratically as air slugs move through. The result is unreliable flow indication or nuisance alarms, which is why vane-type switches aren’t used in dry-pipe systems. Instead, devices designed for dry-pipe service or switches placed on the dry valve are used to detect actual water flow.

Vane-type water flow switches need water flowing past a vane to push it and generate a signal. In a dry sprinkler system, the pipes are filled with air under pressure and only become filled with water after the dry valve releases. That air-filled condition means there isn’t a steady, fully water-filled path for the vane to sense, so the vane may not move reliably, or it may respond erratically as air slugs move through. The result is unreliable flow indication or nuisance alarms, which is why vane-type switches aren’t used in dry-pipe systems. Instead, devices designed for dry-pipe service or switches placed on the dry valve are used to detect actual water flow.