13.1 Valves: Types, Operation & Exercising Programs

Valve Types and Applications

Gate Valve Sub-Types

• Resilient wedge (resilient seated) - the modern standard. A rubber-encapsulated wedge seals against a smooth, epoxy-coated body with a full unobstructed waterway; no bottom groove to collect debris.
• Double disc (metal seated) - older design with a bottom groove that accumulates sediment and rock, which is the classic reason a 60-year-old valve will not close the last inch.

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California Spacing Requirements (22 CCR 64577)

At a minimum, isolation valves shall be installed on all new water mains:

1. No farther than 1,320 linear feet apart on mains 12 inches or less in diameter;
2. At each tee or crossing connection between mains 12 inches or less, within 100 feet of that tee or cross with the primary main; and
3. Between the water main and each fire hydrant served by the main.

Practical consequence: at a standard cross in a gridded system there should be valves on three or four legs, so a crew can isolate one block without shutting the intersection. Systems that installed valves only on the main run - a common 1950s and 1960s economy - discover during a break that isolating one segment blacks out a quarter of a neighborhood.

The hydrant isolation valve (item 3) is what allows a hydrant to be repaired or replaced without shutting down the main. A hydrant with no auxiliary valve is a documented deficiency.

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Correct Operating Technique

1. Know the valve before you turn it. Size, type, number of turns to fully close, direction to close, and whether it is a boundary valve between pressure zones.
2. Locate and clean the valve box. Debris in the box is the reason keys slip and stems shear.
3. Count the turns. Record the actual count against the record count. A valve that closes in fewer turns than expected is obstructed; one that never seats has a broken stem or wedge.
4. Operate slowly, especially the last quarter. Closing fast generates water hammer; the surge from a rapidly closed 12-inch valve can break a main elsewhere in the system.
5. Do not force a stuck valve. Excessive torque shears stems and breaks bonnets, turning a stuck valve into a dig. Use a valve exerciser with a torque limit, work the valve back and forth, and consider a valve-turning machine.
6. Reopen slowly and fully, then back off a quarter to half turn from the fully open position so a later operator can tell open from jammed and so thermal expansion does not lock the stem.
7. Flush and sample any segment that was depressurized before returning it to service.

[!WARNING] Never leave a valve partially open as a throttling device. A gate valve throttled for weeks will wire-draw and erode at the disc and seat and may then never seal again. If throttling is needed, install a valve designed for it.

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Valve Exercising

A valve exercising program operates every valve through its full travel on a scheduled cycle - commonly annually for critical and boundary valves and every one to three years for the rest. It is the only way to know a valve works.

What exercising accomplishes:

• Verifies the valve closes - the moment you need that information is the worst possible moment to learn it
• Breaks up scale and tuberculation on the disc and seat
• Confirms and corrects the record - number of turns, direction, actual location
• Finds buried and paved-over valves before the emergency
• Reduces the isolated segment size during an actual break, which reduces customers out of service, the volume lost, and the length of main requiring disinfection

Records to keep for each valve: unique ID, location with GPS coordinates and ties to permanent features, size, type, manufacturer, year installed, direction to close, turns to close, last exercised date, condition notes, and any restriction such as boundary valve - do not operate without authorization.

[!TIP] The performance metric that matters is percentage of valves exercised on schedule and average number of customers affected per isolation. A system with excellent maps but no exercising program will still shut down four blocks to fix one service leak.

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Common Failure Modes

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Boundary and Control Valves

Two categories deserve locked-out handling:

• Pressure zone boundary valves must be tagged and mapped. An accidental opening dumps a high zone into a low zone, blowing out customer plumbing and draining tanks.
• Interties with neighboring agencies are normally closed and often have a backflow assembly and metering. Operating them requires coordination and, usually, a written agreement, because water quality from two different sources mixing at the boundary can cause red water, nitrification, or disinfectant incompatibility - notably chlorine meeting chloramine.

Finally, valve work is where cross-connection risk and contamination risk meet. Any main that has been depressurized must be treated as potentially contaminated: disinfect per AWWA C651-05 and sample for coliform before returning it to service, as 22 CCR 64580 requires.