5.1 Valve Requirements: Source, Main Line, Riser, Service & In-Line Valves
Key Takeaways
New or replacement shutoff valves must be quarter-turn to off, meet minimum Cv values, show whether they are open or closed, be serviceable in line, be cleaned for oxygen if used for pressure gases, and have threaded purge ports on both sides.
Every valve except those in zone valve box assemblies must be secured: in a secured area, locked or latched in its operating position, or above a ceiling where it stays accessible and unobstructed.
A source valve sits at the immediate connection of each central supply system so the entire source, including dryers and final line regulators, can be isolated.
A main line valve is required inside the building unless the source and its source valve are inside, or the source is mounted on the building wall with the pipeline entering right beside the source valve.
Each riser needs a riser valve next to the main; each branch off a riser needs one service valve ahead of all zone valve boxes on that branch.
Why Shutoff Valves Exist
NFPA 99 requires shutoff valves to isolate sections of the distribution system for maintenance, repair, and planned future expansion, and to make periodic testing possible. Because a closed valve can stop oxygen to an ICU, valve selection, location, security, and labeling are all regulated.
Requirements for Any New or Replacement Valve
A valve may be of any design as long as it meets every condition below:
- Has at least the minimum Cv in NFPA 99's tables
- Turns a quarter turn to off
- Is made of materials suitable for the service
- Comes with copper tube extensions from the manufacturer for brazing, or with CMT fittings
- Shows the operator whether it is open or closed
- Permits in-line serviceability
- Is cleaned for oxygen service by the manufacturer if used for any positive-pressure service
- Has threaded purge ports on both the patient side and the source side
- Has a minimum working pressure at least equal to the setting of the relief valve protecting that piping, for positive-pressure service
- Has replaceable seals that meet the central supply materials rules (NFPA 99-2024)
Minimum Cv (full open)
| Valve size | Positive-pressure gases | Vacuum and WAGD |
|---|---|---|
| 1/2 in. | 17 | 17 |
| 3/4 in. | 31 | 31 |
| 1 in. | 60 | 60 |
| 1-1/4 in. | 110 | 110 |
| 1-1/2 in. | 169 | 169 |
| 2 in. | 357 | 357 |
| 2-1/2 in. | 390 | 196 |
| 3 in. | 912 | 302 |
| 4 in. | 1837 | 600 |
The vacuum table continues to 5 in. (1022), 6 in. (1579), and 8 in. (3136).
Security and Labeling
Every valve except those in zone valve box assemblies must be secured in one of three ways:
- Located in a secured area
- Locked or latched in its operating position
- Located above a ceiling, as long as it stays accessible and unobstructed
Every valve must be labeled with the gas it supplies and the area or areas it controls. Section 5.5 gives the required wording.
The Valve Hierarchy
| Valve | Where it goes | What it does |
|---|---|---|
| Source valve | At the immediate connection of each central supply system to the distribution piping, in the immediate vicinity of the source | Isolates the entire central supply system, including accessories such as air dryers and final line regulators |
| Main line valve | In the main supply line inside the building, on the facility side of the source valve and outside the source room or enclosure, or where the main first enters the building | Shuts off the whole building's supply from inside the building |
| Riser valve | In each riser, next to the main line | Isolates one riser |
| Service valve | In the branch (lateral) off a riser, ahead of any zone valve box on that branch | Lets a branch be serviced or modified without shutting down the main, the riser, or the facility |
| Zone valve | Outside the area it controls (Section 5.2) | Controls the gas to one zone |
| In-line valve | Optional | Isolates piping to individual rooms or areas for service |
When a main line valve is not required
A main line valve is not required where either of these applies:
- The source and its source valve are inside the building served.
- The source system is physically mounted to the wall of the building served, and the pipeline enters the building right next to the source valve.
Service valves: one per branch
Only one service valve is required for each branch off a riser, regardless of how many zone valve boxes are on that lateral. It must be placed in the branch before any zone valve box on that branch.
Other Valves and Connections
- Valves for future connections must be labeled as to gas content. The downstream piping is closed with a brazed cap, leaving enough tube to cut off the cap and braze again later.
- In-line check valves, new or replacement, must be brass or bronze with brazed extensions. They must be serviceable in line, have no threaded connections, and have 1/8 in. NPT purge points. They must be sized so flow velocity stays within the manufacturer's recommendation.
- Relief valves: plumbing codes that extract NFPA 99, such as the Uniform Plumbing Code's health care chapter, state that a pressure relief valve may not be isolated from its intended use by a valve.
- Auxiliary source connection (cryogenic systems): every cryogenic fluid central supply system must have an auxiliary source connection. It is the same size as the main line, located immediately on the patient side of the source valve, and consists of a tee, a valve, and a removable plug or cap. The valve is normally closed and secured. NFPA 99-2024 also requires an access point for a temporary or supplemental supply on other systems, located in the main line on the patient side of the source valve.
Walking the Hierarchy in an Emergency
Suppose a leak develops in a ceiling above a 4th-floor patient corridor. Staff close the zone valve for the affected rooms first, which stops gas to the fewest patients. If the leak is upstream of the zone valve, in the branch, the service valve for that lateral isolates it without touching other branches. A leak in the riser needs the riser valve. Only a main or source problem calls for the main line valve or source valve. That would cut supply to the whole building, so emergency plans arrange portable supplies first. This is why NFPA 99 wants every level of valve present, accessible to the right people, and secured against everyone else.
The diagram after this text shows the hierarchy.
A lateral branch off a riser serves five zone valve boxes. How many service valves does NFPA 99 require on that branch, and where?
One for each zone valve box, each located just upstream of that box
One for the branch, placed before any zone valve box on that branch
None, because the riser valve serves that purpose
Two, one at each end of the branch
A medical gas valve is installed above a lay-in ceiling in a corridor. Which condition satisfies NFPA 99's security requirement for this valve?
It is painted to match the ceiling grid
It has a clear plastic tamper cover snapped over the handle
It remains accessible and unobstructed above the ceiling
It is installed with its handle removed
A hospital's medical air compressor package sits inside the hospital's own mechanical room, along with its source valve. What does NFPA 99 say about a main line valve?
None is required, since the source and source valve are inside the building
A main line valve is required where the pipe leaves the mechanical room wall
A main line valve is required on every floor
A main line valve must replace the source valve whenever the source is located indoors
Sections you finish are checked off in the contents.