The most common and most serious defect in fire protection systems is a control valve left shut. It is not an expensive equipment failure; it is a lever left in the wrong position that could be corrected for free.
How it happens
A valve does not close itself. A valve left shut is always an incomplete human action:
- Not reopened after maintenance. A valve closed for a sprinkler change or pipe alteration waits to be reopened and is forgotten.
- Closed during refurbishment. A subcontractor closes it to do their own work and site management is not told.
- Closed because of a leak. It is closed to stop a leak, the repair is deferred, and the valve stays shut.
- Left partly open. The valve looks open but is not fully open, and severely throttles flow. That is more dangerous than fully shut because it goes unnoticed.
- The wrong valve opened. In an unlabelled valve group, the wrong lever is operated.
A partly open valve is the most insidious state. The system shows pressure, the flow switch works and a visual check reveals nothing. It appears only on a main drain test: static pressure normal, residual pressure under flow far below expectation.
How it is detected
| Method | What it shows |
|---|---|
| Tamper switch | A signal to the panel the moment the valve leaves the open position |
| Main drain test | Pressure drop under flow — partial blockage or a partly closed valve |
| Visual check | Lever position, indicator window, stem height |
| Impairment record | Which valve was closed when, and when it was reopened |
| Lock and chain check | Valves that should be locked in the open position |
None of the five is sufficient alone. A tamper switch fitted but not wired to the panel does nothing — an omission found very frequently at inspection.
Checking a tamper switch
- Is the switch physically fitted?
- Is its cable run back to the panel?
- Is the corresponding zone defined at the panel?
- Does a signal arrive when the valve is closed a few turns? (It must signal before full closure.)
- Is the signal transmitted to a continuously monitored point?
- Has the test been recorded?
Item four is critical: the switch must signal shortly after the valve leaves the open position, not when it is fully closed. Otherwise the warning comes far too late.
The impairment procedure
Closing a valve is not forbidden; closing one without managing it is the problem. The procedure covers:
- Authorisation. Authority to close must rest with a defined person.
- Notification. Site management, security, the alarm receiving centre and, where relevant, the insurer are informed.
- Compensating measures. Fire watch, additional extinguishers, a hot work ban, limiting the affected area.
- A physical tag. A visible tag on the closed valve carrying date, time and responsible person.
- Restoration verification. After reopening, confirm by flow test — checking the lever position alone is not enough.
- Record. Start and finish times are recorded.
Five preventive practices
- Number every control valve and display a valve location plan in the pump room.
- Lock or chain valves that must stay open in the open position.
- Physically test tamper switches at least annually.
- Make "valve reopened and verified" the closing step of every maintenance job.
- Keep authority to close valves with site management during subcontractor work.
Frequently Asked Questions
Why is a partly open valve worse than a fully shut one?
The system shows pressure and a visual check reveals nothing, yet flow is severely throttled. It appears only on a main drain test.
When should a tamper switch signal?
Shortly after the valve leaves the open position, not when it is fully closed. Otherwise the warning comes far too late.
Is closing a valve forbidden?
No; closing one without managing it is the problem. Authorisation, notification, compensating measures, tagging, restoration verification and a record are required.
How is reopening verified?
Checking the lever position is not enough; it must be confirmed by flow test.
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Download MEP Calc on the App StoreNFPA 25 · NFPA 13 (2025) · BS EN 12845:2015+A1:2019 · FM Global DS 2-0, DS 2-8, DS 3-2. The findings here are typical defect patterns defined in the standards and survey guidance, not an account of events at any particular site.