Sprinkler Flow Switch and Waterflow Retard on a Wet System
A wet-pipe sprinkler system serves a retail building. The fire alarm panel receives a waterflow signal from a paddle-type flow switch on the riser and a valve tamper switch on the main control valve. During a flow test, opening the inspector's test connection produces a waterflow alarm at the panel after about 90 seconds. The building's alarm contractor says this is 'within retard' and acceptable. The owner complains that a real sprinkler head activation would also take 90 seconds, which is too slow. Separately, during the same visit you find the main control valve partially closed (about one-quarter turn from fully open) and the tamper switch showing 'normal' at the panel. The system is monitored off-site.
1. Evaluate the 90-second waterflow delay. Is 'within retard' a sufficient answer, and what would you check?
Read the worked answer
'Within retard' is not a complete answer. Retard is a deliberate delay to prevent false alarms from pressure surges, but 90 seconds is at the high end and must be justified, not assumed.
What to check:
- Retard setting: flow switches commonly have an adjustable retard (pneumatic or electronic). Verify the actual setting against the manufacturer's listing and the design. If the retard is set near its maximum, that explains the delay.
- Switch adjustment: a paddle switch that is not properly positioned or is binding can add delay independent of the retard setting.
- Test method: the inspector's test connection simulates flow at a specific rate. Confirm the test valve is fully open and the flow rate matches the switch's listed trip point. A partially throttled test valve can stretch the time.
- Code expectation: waterflow must alarm within the time established by the listing and the adopted standard; the goal is prompt notification, not merely 'under the retard limit.'
Judgement: 90 seconds is suspicious. I would verify the retard setting and switch adjustment, and if the device cannot be brought to a prompt, reliable trip, I would require adjustment or replacement and retest.
2. The main control valve is one-quarter turn from fully open but the tamper switch reads normal. What is the significance and what do you require?
Read the worked answer
This is a serious deficiency: a partially closed main control valve can impair or stop waterflow to the system, and the tamper switch failed to report it.
Significance:
- The main control valve must be fully open and supervised so that any closure or partial closure is annunciated. A valve one-quarter turn from open is not in its fully open position and reduces available flow.
- The tamper switch reading 'normal' means supervision is not working - either the switch is misadjusted, bypassed, or the wrong type. This defeats the purpose of tamper supervision.
- Because the system is monitored off-site, a silent tamper failure means no one would know the valve was moved.
What I require:
- Open the valve fully and confirm the open position.
- Adjust or replace the tamper switch so it reports off-normal for any movement away from fully open, and verify the signal at the panel and off-site.
- Functionally test the tamper switch by partially closing the valve and confirming annunciation, then restore.
- Document the deficiency and correction, and check whether the valve was left this way intentionally (e.g., during work) - if so, confirm the work is complete.
A valve that is not fully open with a tamper that reads normal is a compound failure that must be corrected before the system is considered in service.