A paddle-type water flow alarm indicator shall be installed only in

Paddle-type (or vane-type) water flow alarm indicators are specifically designed for and restricted to use in wet pipe sprinkler systems. These devices operate via a paddle that is pushed by the movement of water, activating an alarm switch. In dry, deluge, or pre-action systems, the pipes are not normally filled with water. When these systems activate, the sudden and high-velocity inrush of water can damage or break the paddle mechanism. Furthermore, in dry and pre-action systems used in freezing environments, any trapped water could freeze around the paddle, rendering it inoperable.

A. dry systems. The violent inrush of water when the dry pipe valve trips can damage the paddle. Freezing of trapped water can also impede its function.

C. deluge systems. The rapid filling of the pipe network upon system activation can create a water velocity surge sufficient to damage the paddle mechanism.

D. pre-action systems. Similar to dry and deluge systems, the initial surge of water filling the pipes upon activation can damage the paddle.

1. NFPA 13, Standard for the Installation of Sprinkler Systems (2022 Edition). Section 17.11.2.1 explicitly states: "Vane-type or paddle-type waterflow alarm indicators shall be installed in wet pipe systems only." This is a mandatory requirement.

2. Fire Protection Research Foundation, "Sprinkler System Design and Installation Obstructions Report" (October 2018). While discussing overall system reliability, the report implicitly supports the NFPA 13 requirement by differentiating the alarm mechanisms suitable for different system types, noting that pressure switches are used at the valve for dry, preaction, and deluge systems, whereas vane-type flow switches are a local device for wet systems. (Report ID: FPRF-2018-15).

3. Oklahoma State University, School of Fire Protection and Safety Engineering Technology, FSET 3153 Sprinkler and Standpipe Systems Courseware. Course materials consistently teach that vane-type waterflow switches are prohibited in dry-pipe, preaction, and deluge systems due to the potential for damage from the water surge upon system actuation, citing the specific NFPA 13 requirement. (Reference: Module on Sprinkler System Components).