When is a discharge pressure switch required?

• A. In all systems.
• B. Only if manual release is used.
• C. Where mechanical system actuation is possible.
• D. For automatic systems only.

Answer: (C)

Discharge pressure switches are used to verify that the discharge piping actually reaches the required pressure when the agent is released and to signal the control system that discharge is underway. This verification is crucial when there is a mechanical means to actuate the release, because mechanical actuation can move a valve without guaranteeing that the agent is flowing to the protected space. The switch provides an independent indication of actual pressurization, enabling proper alarms, interlocks, and fault detection (such as a valve not fully opening, a blocked line, or a leak). If there’s no mechanical actuation path to consider, this extra verification isn’t inherently required, which is why the switch is specified for situations where mechanical actuation is possible rather than for all systems or only automatic systems.