5.1 Gauges, Control Valves & Visual Inspection Frequencies

Separate gauge condition, pressure verification, and valve security

Wet-system ITM begins with confirming that the supply is available and the instruments can be trusted. A normal-looking gauge and an “OPEN” indicator are useful observations, but neither proves the full hydraulic capability of a system. NFPA 25 (2023), Chapter 13, assigns different frequencies to gauge condition, pressure verification, and valve security. Read the activity as well as the component name.

Gauge inspection in the 2023 edition

Under 13.2.4, inspect gauges monthly for operability and physical damage. Gauges monitoring water pressure are checked quarterly to verify normal supply pressure. Gauges monitoring air or nitrogen pressure on dry and preaction systems are checked monthly for normal pressure; the specified supervision arrangement connected to a constantly attended location permits the pressure-verification interval to extend to quarterly. This is different from older weekly dry-gauge teaching.

The monthly physical-condition check still matters even when a pressure parameter is remotely supervised. Look for broken crystals, unreadable markings, corrosion, leakage, damaged fittings, a stuck pointer, or a closed gauge connection. Interpret the reading against the normal condition for that gauge location. The water-supply gauge and a gauge above a check valve need not show identical pressure because trapped pressure and elevation can differ.

For freezer systems, make the required monthly comparison between the compressor-side and system-side gas gauges. A QOD gauge where provided should indicate the same pressure as the system-side dry-valve gauge. A normal pressure near the compressor does not establish that gas can reach piping beyond an ice obstruction. Investigate unexplained differences rather than simply adjusting the compressor upward.

Five-year gauge testing or replacement

Gauges must be replaced every five years or compared with a calibrated gauge at that interval. A gauge not accurate within 3% of full scale must be recalibrated or replaced. “Full scale” is the maximum span of the gauge, not the pressure currently displayed.

For a 0–300 psi gauge:

$$\text{Allowable error}=300\times0.03=9\text{ psi}$$

If the reference reads 100 psi and the installed gauge reads 112 psi, the 12 psi error exceeds that allowance. If it reads 106 psi, its six-psi error is within this particular tolerance. That does not excuse a broken case or other defect. Document the comparison or replacement rather than assuming a legible gauge is calibrated.

Do not apply the permanent-gauge tolerance to every field test instrument. Pump performance testing has its own instrument requirements, and the comparison gauge must itself be suitable and calibrated. Isolate and relieve pressure through the proper trim before removal. A supply gauge can remain pressurized while a downstream work section is safely drained.

Control-valve inspection intervals

The normal baseline is weekly inspection. Valves secured with locks or supervised under the applicable provisions may be inspected monthly. Valves that are electrically supervised may be inspected quarterly. A lightweight seal alone is not a lock. Verify what security or supervision actually exists and whether it is functional; do not assign the longer interval from an absent or failed switch.

The interval is permission under the standard's conditions, not an instruction to ignore a valve between visits. A known closure, damaged lock, or off-normal signal needs attention when discovered.

Inspect the actual valve

Confirm the normal open or closed position for that particular function. An OS&Y rising stem, butterfly indicator, or PIV window gives position information, but mechanical failures can make an indicator misleading. Check accessibility, external leaks, identification, and the condition of operating parts. Do not invent a universal 36-inch clearance around every valve; use the applicable access requirements and actual operating space.

A sign identifies what the valve serves, which is especially important where several risers or buildings share a supply. Record missing or misleading signs. A partially closed valve that restricts protection requires action even if its supervisory switch has not operated.

Exercise and supervisory testing

Operate control valves through their full range and return them to normal annually under the coordinated test procedure. Follow manufacturer instructions for operating effort and final position. Do not force a seized valve, use an improvised extension, or apply one fractional back-off to every design. NFPA 25 specifies a quarter-turn return from fully open for PIV and OS&Y valves; identify those actual valve categories and follow the applicable instructions. Clean and lubricate OS&Y stems using the required method and compatible lubricant.

Test valve supervisory switches semiannually. The off-normal signal must occur within the first two handwheel revolutions or one-fifth of travel from normal, whichever is less, under the applicable arrangement. Verify both the signal and its restoration. A missing supervisory signal and a physically closed valve are different findings and both must be reported.

After closing and reopening a supply control valve, perform the required valve-status test to verify that water can pass. Where the main drain is used, follow the proper method and record the result. An indicator that says “OPEN” is not enough when an internal gate can be detached. Restore locks or supervision, confirm pressures and alarms, and leave the system in its intended normal condition.

Source checked October 19, 2026: NFPA 25 (2023), 13.2.4 and 13.3. NFPA 25 edition information.