CMC · California Mechanical Code

What are 'Valves, Companion or Block' and related valve definitions?

Companion or block valves are paired stop valves used to isolate and join refrigeration sections (defined at §224.0). They let factory or service sections be separated and rejoined safely; refrigerant relief rules (for vessels ≥10 cu ft) require dual reliefs with a three‑way valve unless pumpdown-capable shutoffs and other conditions are met (see §1113.6).

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Last reviewed: July 6, 2026

What the code requires — 2–4 sentences

The California Mechanical Code defines “Valves, Companion or Block” as pairs of mating stop valves used to isolate and join sections of refrigeration systems; the definition is located at § 224.0. These valves are the factory‑or field‑installed stop valves that let two refrigeration sections be joined before opening them or be separated after closing them, and the Code treats them specifically in the refrigeration context. See the Code definition at § 224.0 for the official wording.

In plain English: companion/block valves are a matched pair of stop valves used so two refrigerant-containing sections can be joined or separated safely (closed first, then joined; or joined first, then opened).

Requirements in detail

Key definitions (short)

Valves, Companion or Block — pairs of mating stop valves that valve off refrigeration system sections and are arranged so sections may be joined before opening the valves or separated after closing them (definition: § 224.0).
Valve, Stop — a device in a piping system to shut off flow (defined in § 224.0).
Valve, Pressure‑Relief — a pressure‑actuated valve designed to relieve overpressure (defined in § 224.0).
(Related) Refrigeration system, self‑contained — factory‑assembled unit that may be shipped in sections and that has no refrigerant‑containing field joints other than companion/block valves. This clarifies where companion/block valves are expected to be used.

Decision‑relevant dimensions / choices (table)

Decision item	What to check / value	Code Reference
What is a companion (block) valve?	A pair of mating stop valves arranged so sections can be joined before opening or separated after closing	§ 224.0
Use allowed for field joining of factory sections?	Self‑contained systems may be shipped in sections and joined in the field only with companion/block valves (i.e., field joints by other means are not permitted for “self‑contained” units)	See refrigeration system definition (self‑contained) — (definitions in the code)
When must a three‑way valve be provided?	Dual pressure‑relief valves installed on vessels ≥ 10 cubic feet that discharge to atmosphere must be installed with a three‑way valve for testing/repair	§ 1113.6
When is a single relief valve permitted on ≥10 cu ft vessels?	Only as an exception when: relief valve(s) located on the lowside; the vessel has shutoff valves designed to allow pumpdown; and other vessels are separately protected	§ 1113.6 (exception)
Stop valve references / usage	The term stop and related valve types are defined in § 224.0; stop valves are referenced elsewhere for required shutoffs and service connections (see refrigeration sections)	§ 224.0 and related sections (see Related provisions)

How companion/block valves are intended to be used (practical points)

They are matched pairs located at the mating faces of two refrigerant-containing sections so one section can be isolated (valves closed), the sections separated for transport/maintenance, then rejoined and opened in the proper sequence. The Code definition centers on that sequencing requirement.
For refrigeration machinery or pressure vessels requiring protective arrangements (relief devices), companion/block valves play a role in the Code’s allowed exceptions (for example, permitting pumpdown so a single relief device can be used under specific conditions). See § 1113.6.

Exceptions & special cases

Dual relief valves on vessels of 10 cubic feet (0.28 m³) or more that discharge to atmosphere: the Code requires dual relief valves and that they be installed with a three‑way valve for testing and repair (§ 1113.6). The three‑way valve is required so one relief device can be taken out of service for testing while the other remains effective.
The Code permits a single relief valve on vessels ≥10 cu ft only if ALL exception conditions are met: relief valves located on the lowside of the system; the vessel provided with shutoff valves designed to allow pumpdown of the refrigerant charge; and all other pressure vessels separately protected in accordance with the applicable section (§ 1113.6, exception). Companion/block valves are explicitly relevant to that pumpdown/shutoff capability.
If you need to join factory sections in the field for a “self‑contained” refrigeration unit, the Code contemplates doing so only with companion/block valves (the self‑contained definition notes that field joints other than by companion/block valves are not allowed).

Common mistakes

Treating any two stop valves as “companion” valves when they are not matched/arranged to allow the prescribed join/isolating sequence — the Code’s definition requires the valves be arranged so sections can be joined before opening or separated after closing (§ 224.0).
Removing or bypassing a required three‑way valve when dual relief valves are installed on large vessels (≥10 cu ft) — the three‑way arrangement is specifically required for servicing/testing of dual relief valves (§ 1113.6).
Assuming that companion/block valves remove the need for proper relief, pumpdown capability, or separate protection of pressure vessels — the Code’s exceptions still demand specific conditions (lowside location, pumpdown-capable shutoff valves, separate protection) before a single relief valve is allowed (§ 1113.6 (exception)).
Failing to follow identification, access, or other refrigeration equipment requirements that interact with valve locations and serviceability (see identification and access sections listed below).

Worked example — concrete scenario

Scenario: You have a refrigeration pressure vessel with internal gross volume = 12 cubic feet. You plan to join a factory section in the field using companion/block valves.

Step 1 — Relief device requirement: Because the vessel is 12 cu ft (> 10 cu ft) and the relief devices will discharge to atmosphere, the Code requires dual pressure‑relief valves or rupture members (not a single valve) and those dual relief valves must be installed with a three‑way valve so one can be isolated for testing while the other protects the vessel (§ 1113.6).

Step 2 — Use of companion/block valves for joining sections: If the factory sections are joined in the field, they must be joined using companion/block valves (definition at § 224.0) so the sections can be joined/isolated in the proper sequence. If you hoped to avoid dual reliefs by relying on pumpdown and a single relief valve, you would need the vessel to have shutoff valves designed to allow pumpdown, the reliefs to be located on the system lowside, and other vessels separately protected — otherwise you must comply with the dual‑valve + three‑way requirement. See § 224.0 and § 1113.6.

Related provisions (select)

§ 224.0 — Definitions: Valves, Companion or Block; Valve, Stop; Valve, Pressure‑Relief (definition source).
§ 1113.6 — Three‑way valve requirement and the exception allowing a single relief when pumpdown is possible and other conditions are met.
§ 1113.3 — Discharge into the lowside of the system and related constraints on use of single relief devices (see refrigeration relief sections).
§ 1113.4–1113.5 — Parallel pressure‑relief devices and discharge capacity rules that interact with relief‑valve installation decisions.
§ 1112.6 — (Referenced in valve listings for stop valves; see Code cross‑references)
§ 1115.0 — Identification requirements for refrigeration equipment and system components, which affect labeling of valves and valve pairs for service.
Definitions and refrigeration system descriptions (self‑contained etc.) — see the refrigeration definitions and system entries in the Code (definitions area and refrigeration chapters) for how companion/block valves are used in that context.

Note: You asked for “controlling sections: 217.0.” In the uploaded CMC text I searched, the explicit Code definition for “Valves, Companion or Block” appears under § 224.0 and related refrigeration valve requirements are in Chapter 11 / § 1113.x as shown above. I did not find a direct, relevant entry for these definitions at § 217.0 in the provided files; if you have a different edition or a specific §217.0 snippet to supply I will incorporate it.

Code references

Grounded in the retrieved California Mechanical Code — click a citation to read the verbatim passage:

CMC § 902.15 High relevance — show source text
VALVE TYPES

Bleed lines for diaphragm-type . . . . . . . . . . . . . .902.15 Companion or block, definition . . . . . . . . . . . . . . .224.0

Pressure relief . . . . . . . . . . . . . . . . . . . . . .224.0, 904.7,

926.4, 1112.0,

1113.0, 1115.4, C 109.1

Safety or relief . . . . . . . . . . . . .1005.0, 1009.0, C 109.1

Shutoff . . . . . . . . . .904.7, 1006.0, 1308.12, 1310.10.1.1,

1310.11, 1312.3.1, 1312.3.2,

1312.5.3, 1312.6, 1406.2.1.5,

C 109.1, D 103.0, D 104.3,

D 110.4, D 112.3

Stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.0, 1112.6

VALVES

For fuel gas piping . . . . . . . . . . . .1308.4.1, 1308.4.7.5,

1308.10.1, 1308.12, 1309.1,

1310.3.3.1, 1310.10.1.1,

1310.11, 1310.14.6,

1312.3.1, 1312.3.2,

1312.5.3, 1312.6, 1312.9,

1313.1.4, 1313.1.5,

D 103.0, D 104.3, D 110.4,

D 112.3, D 113.3

For hydronics . . . . . . . . . . . . . . . . . . . . . . . . . . . .1212.0

For mobile home parks . . . .D 103.0, D 104.3, D 110.4,

D 112.3, D 113.3

For recreational vehicle park . . . . . . .D 103.0, D 104.3,

D 110.4, D 112.3, D 113.3

For refrigeration systems . . . . . . . . . . . .1105.3, 1109.0,

1110.0, 1112.6,

1112.9, 1113.6

VENT

Appliances not requiring vents . . . . . . . . . . . . . .802.2.1 Caps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .802.7.4(3)

Clearance . . . . . . . . . . . . . . .802.7.3.4, Table 303.10.1,

Table 802.7.3.3
CMC § 225.0 High relevance — show source text
Volume, Internal Gross. The volume as determined from internal dimensions of the container, with no allowance for the volume of the internal parts.

225.0 – W –

Wall Heater. See Vented Wall Furnace.

Warm Air Furnace. An environmental heating appliance designed or arranged to discharge heated air through any duct or ducts. This definition shall not include a unit heater.

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Unusually Tight Construction. Construction where:

(1) Walls and ceilings exposed to the outdoors have a continuous water vapor retarder with a rating of 1 perm or less with openings gasketed or sealed.

(2) Weatherstripping is on openable windows and doors.

(3) Caulking or sealants are applied to areas such as joints around window and door frames, between sole plates and floors, between wall-ceiling joints, between wall panels, and at penetrations for plumbing, electrical, and gas lines and at other openings. Use (Material). The placing in action or making available for service by opening or connecting a container utilized for confinement of material, whether a solid, liquid, or gas.

224.0 – V –

Vacuum. A pressure less than that exerted by the atmosphere. Valve, Pressure-Relief. A pressure-actuated valve held closed by a spring or other means and designed to automatically relieve pressure in excess of its setting. Valve, Stop. A device in a piping system to shut off the flow of the fluid.

Valve, Three-Way-Type Stop. A manually operated valve with one inlet that alternately can stop flow to either of two outlets.

Valves, Companion or Block. Pairs of mating stop valves valving off sections of refrigeration systems and arranged so that these sections may be joined before opening these valves or separated after closing them.

Vent. A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Vent, Type B Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved appliances equipped to burn only gas. Vent, Type B-W Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved gas-fired vented wall furnaces. Vent, Type L Gas. A venting system consisting of listed vent piping and fittings for use with oil-burning appliances listed for use with Type L or with listed gas appliances. Vent, Gas. A passageway composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions for conveying vent gases from appliances or their vent connectors to the outdoors. [NFPA 54:3.3.53] Vent Connector, Gas. That portion of a gas-venting system that connects a listed gas appliance beginning at the draft hood or flue collar to a gas vent and is installed entirely within the space or area in which the appliance is located. Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe. [NFPA 54:3.3.101]

2025 CALIFORNIA MECHANICAL CODE 47

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CMC § 3.3.53 High relevance — show source text
Valves, Companion or Block. Pairs of mating stop valves valving off sections of refrigeration systems and arranged so that these sections may be joined before opening these valves or separated after closing them.

Vent. A pipe or other conduit composed of factory-made components, containing a passageway for conveying combustion products and air to the atmosphere, listed and labeled for use with a specific type or class of appliance. Vent, Type B Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved appliances equipped to burn only gas. Vent, Type B-W Gas. A factory-made gas vent listed by a nationally recognized testing agency for venting listed or approved gas-fired vented wall furnaces. Vent, Type L Gas. A venting system consisting of listed vent piping and fittings for use with oil-burning appliances listed for use with Type L or with listed gas appliances. Vent, Gas. A passageway composed of listed factory-built components assembled in accordance with the manufacturer’s installation instructions for conveying vent gases from appliances or their vent connectors to the outdoors. [NFPA 54:3.3.53] Vent Connector, Gas. That portion of a gas-venting system that connects a listed gas appliance beginning at the draft hood or flue collar to a gas vent and is installed entirely within the space or area in which the appliance is located. Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe. [NFPA 54:3.3.101]

2025 CALIFORNIA MECHANICAL CODE 47

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DEFINITIONS

Water Well. An excavation that is drilled, cored, bored, washed, driven, dug, jetted, or otherwise constructed for the purposes of extracting groundwater, using the geothermal properties of the earth or injecting water into an aquifer or subsurface reservoir.

226.0 – X –

No definitions.

227.0 – Y –

No definitions.

228.0 – Z –

Zeotropic. Blends comprising multiple components of different volatilities that, when used in refrigeration cycles, change volumetric composition and saturation temperatures as they evaporate (boil) or condense at constant pressure.

[ASHRAE 34:3]

Zone. [OSHPD 1, 2, 3, 4 & 5] A space or group of spaces within a building for which the heating, or cooling require- ments are sufficiently similar that desired conditions can be maintained throughout by a single controlling device.

48 2025 CALIFORNIA MECHANICAL CODE

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CALIFORNIA MECHANICAL CODE – MATRIX ADOPTION TABLE

CHAPTER 3 – GENERAL REGULATIONS

(Matrix Adoption Tables are non-regulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)
CMC § 417.0 High relevance — show source text
AIRBORNE INFECTION ISOLATION ROOMS . . .417.0

THERMAL RECOVERY UNIT

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .222.0

TOILETS, GAS FIRED . . . . . . . . . . . . . .928.0, Table 802.4

TYPES OF

Chimneys . . . . . . . . . . . . . . . . . . . . . . . .(see Chimney)

– U –

UMC

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223.0

UNCONSTITUTIONAL . . . . . . . . . . . . . . . . . . . . . . . . .101.4

UNDER-FLOOR SPACE . . . . . . . . . . . . . . . . . .304.4, 608.0

UNIT HEATER . . . . . . . . . .223.0, 916.0, Table E 503.7.1(5)

UNSAFE EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . .102.5

UNUSUALLY TIGHT CONSTRUCTION

Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .223.0

– V –

VALIDITY OF PERMITS . . . . . . . . . . . . . . . . . . . . . .104.4.2

VALVE TYPES

Bleed lines for diaphragm-type . . . . . . . . . . . . . .902.15 Companion or block, definition . . . . . . . . . . . . . . .224.0

Pressure relief . . . . . . . . . . . . . . . . . . . . . .224.0, 904.7,

926.4, 1112.0,

1113.0, 1115.4, C 109.1

Safety or relief . . . . . . . . . . . . .1005.0, 1009.0, C 109.1

Shutoff . . . . . . . . . .904.7, 1006.0, 1308.12, 1310.10.1.1,

1310.11, 1312.3.1, 1312.3.2,

1312.5.3, 1312.6, 1406.2.1.5,

C 109.1, D 103.0, D 104.3,

D 110.4, D 112.3

Stop . . . . . . . . . . . . . . . . . . . . . . . . . . . . .224.0, 1112.6

VALVES

For fuel gas piping . . . . . . . . . . . .1308.4.1, 1308.4.7.5,

1308.10.1, 1308.12, 1309.1,
CMC § 304.8 Medium relevance — show source text
For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa

1112.12.5 Simultaneous Operation. When outlets of two or more relief devices or fusible plugs, which are

TABLE 1112.12.4

ATMOSPHERIC PRESSURE AT NOMINAL INSTALLATION ELEVATION ( Pa )

[ASHRAE 15: TABLE 9-2]

For SI units: 1 foot = 304.8 mm, 1 pound-force per square inch = 6.8947 kPa

244 2025 CALIFORNIA MECHANICAL CODE

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REFRIGERATION

1113.2 Type of Protection. Pressure vessels with an internal gross volume of 3 cubic feet (0.1 m [3] ) or less shall use one or more pressure relief devices or a fusible plug. Pressure vessels of more than 3 cubic feet (0.1 m [3] ) but less than 10 cubic feet (0.28 m [3] ) internal gross volume shall use one or more pressure relief devices. Fusible plugs shall not be used.

[ASHRAE 15:9.7.2.1, 9.7.2.2]

1113.3 Discharging into Lowside of System. For pressure-relief valves discharging into the lowside of the system, a single relief valve (not rupture member) of the required relieving capacity shall not be used on vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume except under the conditions permitted in Section 1112.11.3. [ASHRAE 15:9.7.3]

1113.4 Parallel Pressure-Relief Devices. Two or more

pressure-relief devices in parallel to obtain the required capacity shall be considered as one pressure-relief device. The discharge capacity shall be the sum of the capacities required for each pressure vessel being protected.

1113.5 Discharge Capacity. The minimum required discharge capacity of the pressure-relief device or fusible plug for a pressure vessel shall be determined in accordance with ASHRAE 15.

1113.6 Three-Way Valve. Pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume shall use one or more rupture member(s) or dual pressure-relief valves where discharging to the atmosphere. Dual pressure-relief valves shall be installed with a three-way valve to allow testing or repair. Where dual relief valves are used, the valve shall comply with Section 1113.5.

Exception: A single relief valve shall be permitted on pressure vessels of 10 cubic feet (0.28 m [3] ) or more internal gross volume where in accordance with the following conditions:

(1) The relief valves are located on the lowside of the sys tem.

(2) The vessel is provided with shutoff valves designed to allow pumpdown of the refrigerant charge of the pressure vessel.

(3) Other pressure vessels in the system are separately protected in accordance with Section 1113.1. [ASHRAE 15:9.7.2.3]

1114.0 Special Discharge Requirements.
CMC § 1002.3 Medium relevance — show source text
1002.3 Electric Boilers . . . . . . . . . . . . . . . 217

1002.4 Solid-Fuel-Fired Boilers . . . . . . . . 217

1002.5 Dual Purpose Water Heaters . . . . 217

1003.0 Detailed Requirements . . . . . . . . . 218

1003.1 Safety Requirements . . . . . . . . . . 218

1003.2 Controls . . . . . . . . . . . . . . . . . . . . 218

1003.3 Gauges . . . . . . . . . . . . . . . . . . . . . 218

1003.4 Stack Dampers . . . . . . . . . . . . . . . 218

1003.5 Welding. . . . . . . . . . . . . . . . . . . . . 218

1004.0 Expansion Tanks . . . . . . . . . . . . . 218

1004.1 General. . . . . . . . . . . . . . . . . . . . . 218

1004.2 Open-Type Expansion Tanks . . . . 218

1004.3 Closed-Type Systems . . . . . . . . . 218

1004.4 Minimum Capacity of ClosedType Tank. . . . . . . . . . . . . . . . . . . 218

Table 1004.4(1) Expansion Tank Capacities for Gravity Hot Water Systems . . . . . 219

Table 1004.4(2) Expansion Tank Capacities for Forced Hot Water Systems . . . . . 219

1005.0 Safety or Relief Valve Discharge . . 219

1005.1 General. . . . . . . . . . . . . . . . . . . . . 219

1005.2 Discharge Piping . . . . . . . . . . . . . 219

1005.3 Splash Shield . . . . . . . . . . . . . . . . 219

1005.4 Hazardous Discharge . . . . . . . . . . 219

1005.5 Vacuum Relief Valve . . . . . . . . . . 219

1006.0 Shutoff Valves . . . . . . . . . . . . . . . 219

1006.1 General. . . . . . . . . . . . . . . . . . . . . 219

1007.0 Gas-Pressure Regulators . . . . . . . 219

1007.1 General. . . . . . . . . . . . . . . . . . . . . 219

1008.0 Low-Water Cutoff . . . . . . . . . . . . . 220

1008.1 General. . . . . . . . . . . . . . . . . . . . . 220

1009.0 Combustion Regulators Safety Valves . . . . . . . . . . . . . . . . 220

1009.1 General. . . . . . . . . . . . . . . . . . . . . 220

1010.0 Clearance for Access . . . . . . . . . . 220

1010.1 General. . . . . . . . . . . . . . . . . . . . . 220
CMC § 25270.2 Medium relevance — show source text
as described in Health and Safety Code Section 25270.2(o)(1)(C)(i)._ 3. Piping systems connected to a petroleum hazardous waste tank in an underground area that complies with the hazardous waste tank standards pursuant to the California Code of Regulations, Title 22, Chapter 15, Article 10 (commencing with Section 66265.190), and the facility has been issued a unified program facility permit pursu- ant to Health and Safety Code Section 25404.2 for generation, treatment, accumulation or storage of hazardous waste, as described in Health and Safety Code Section 25270.2(o)(1) (C)(ii).

5703.6.3 Testing. Unless tested in accordance with the applicable section of ASME B31.9, piping, before being covered, enclosed or placed in use, shall be hydrostatically tested to 150 percent of the maximum anticipated pressure of the system, or pneumatically tested to 110 percent of the maximum anticipated pressure of the system, but not less than 5 pounds per square inch gauge (psig) (34.47 kPa) at the highest point of the system. This test shall be maintained for a sufficient time period to complete visual inspection of joints and connections. For not less than 10 minutes, there shall be no leakage or permanent distortion. Care shall be exercised to ensure that these pressures are not applied to vented storage tanks. Such storage tanks shall be tested independently from the piping.

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on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

FLAMMABLE AND COMBUSTIBLE LIQUIDS

5703.6.3.1 Existing piping. Existing piping shall be tested in accordance with this section where the fire code official has reasonable cause to believe that a leak exists. Piping that could contain flammable or combustible liquids shall not be tested pneumatically. Such tests shall be at the expense of the owner or operator.

Exception: Vapor-recovery piping is allowed to be tested using an inert gas.

5703.6.4 Protection from vehicles. Guard posts or other approved means shall be provided to protect piping, valves or fittings subject to vehicular damage in accordance with Section 312.

5703.6.5 Protection from external corrosion and galvanic action. Where subject to external corrosion, piping, related fluidhandling components and supports for both underground and above-ground applications shall be fabricated from noncorrosive materials, and coated or provided with corrosion protection. Dissimilar metallic parts that promote galvanic action shall not be joined.

5703.6.6 Valves. Piping systems shall contain a sufficient number of manual control valves and check valves to operate the system properly and to protect the plant under both normal and emergency conditions. Piping systems in connection with pumps shall contain a sufficient number of such valves to control properly the flow of liquids in normal operation and in the event of physical damage or fire exposure.

5703.6.6.1 Backflow protections. Connections to pipelines or piping by which equipment (such as tank cars, tank vehicles or marine vessels) discharges liquids into storage tanks shall be provided with check valves or block valves for automatic protection against backflow where the piping arrangement is such that backflow from the system is possible. Where loading and unloading is done through a common pipe system, a check valve is not required. However, a block valve, located in an area where it is provided with ready access or remotely operable, shall be provided.
California Mechanical Code Medium relevance — show source text

40
68
88|631
402
392
376|345
273
263
245| |15|0
2
5
10
15|0
11
22
29
35|94
69
65
59
53|58
48
45
41
37|0
15
30
40
48|191
136
130
121
112|112
93
87
82
76|0
20
39
51
61|327
226
219
206
195|187
150
142
135
128|0
22
49
64
76|502
339
330
315
301|285
225
217
208
198|0
38
64
84
98|716
475
463
445
429|390
316
300
288
275| |20|0
2
5
10
15
20|0
10
21
28
34
48|97
75
71
64
58
52|61
51
48
44
40
35|0
14
29
38
46
55|202
149
143
133
124
116|119
100
96
89
84
78|0
18
38
50
59
69|349
250
242
229
217
206|202
166
160
150
142
134|0
20
47
62
73
84|540
377
367
351
337
322|307
249
241
228
217
206|0
33
62
81
94
107|776
531
519
499
481
464|430
346
337
321
308
295| |30|0
2
5
10
15
20
30|0
9
21
27
33
56
NA|100
81
77
70
64
58
NA|64
56
54
50
NA
NA
NA|0
13
28
37
44
53
73|213
166
160
150
141
132
113|128
112
108
102
96
90
NA|0
14
36
48
57
66
88|374
283
275
262
249
237
214|220
185
176
171
163
154
NA|0
CMC § 1205.1 Medium relevance — show source text
1205.1 Authorized Personnel . . . . . . . . . .216

1205.2 Outlets . . . . . . . . . . . . . . . . . . . . .216

1206.0 Authority to Disconnect . . . . . . . .216

1206.1 Disconnection . . . . . . . . . . . . . . . .216

1206.2 Notice . . . . . . . . . . . . . . . . . . . . . .216

1206.3 Capped Outlets . . . . . . . . . . . . . . .216

1207.0 Temporary Use of Gas . . . . . . . . .216

1207.1 General . . . . . . . . . . . . . . . . . . . . .216

1208.0 Gas Piping System Design, Materials, and Components . . . . .216

1208.1 Installation of Piping System . . . .216

1208.2 Interconnections Supplying Separate Users . . . . . . . . . . . . . . .216

1208.3 Sizing of Gas Piping Systems . . .216

Table 1208.3.1 Approximate Gas Input for Typical Appliances . . . . . . . . . . . .217

1208.4 Maximum Operating Pressure in Buildings . . . . . . . . . . . . . . . . . .217

1208.5 Acceptable Piping Materials and Joining Methods . . . . . . . . . .217

Table 1208.5.8.2 Specifications for Threading Metallic Pipe . . . . . . . . . . . . . . . . .219

1208.6 Gas Meters . . . . . . . . . . . . . . . . . .220

1208.7 Gas Pressure Regulators . . . . . . .221

1208.8 Overpressure Protection Required . . . . . . . . . . . . . . . . . . . .221

1208.9 Overpressure Protection Devices . . . . . . . . . . . . . . . . . . . . .221

1208.10 Pressure Limitation

Requirements . . . . . . . . . . . . . . . .222

1208.11 Backpressure Protection . . . . . . .222

1208.12 Low-Pressure Protection . . . . . . .222

1208.13 Shutoff Valves . . . . . . . . . . . . . . .222

1208.14 Expansion and Flexibility . . . . . . .222

1208.15 Pressure Regulator and Pressure Control Venting . . . . . . .222

Table 1208.13 Manual Gas Valve Standards . . . .223

1209.0 Excess Flow Valve . . . . . . . . . . . .223

1209.1 General . . . . . . . . . . . . . . . . . . . . .223

1210.0 Gas Piping Installation . . . . . . . . .223

1210.1 Piping Underground . . . . . . . . . . .223

1210.2 CSST Piping Systems . . . . . . . . .225

1210.3 Installation of Aboveground Piping . . . . . . . . . . . . . . . . . . . . . .225
CMC § 0.00625 Medium relevance — show source text
** Refrigerants that are highly flammable having a LFL of not more than 0.00625 lb/ft [3] (0.10012 kg/m [3] ) at 140°F (60°C) and 14.7 psia (101 kPa) or a heat of combustion not less than 8169 Btu/lb (1.8988 E+07 J/kg). Toxicity Classification. Refrigerants shall be classified for the toxicity in accordance with one of the following: Class A. Refrigerants have an occupational exposure limit (OEL) of not less than 400 parts per million (ppm). Class B. Refrigerants have an OEL of less than 400

ppm. Refrigeration Machinery Room. A room designed to house compressors and refrigerant pressure vessels. Refrigeration Room or Space. A room or space in which an evaporator or brine coil is located for the purpose of reducing or controlling the temperature within the room or space to less than 68°F (20°C). Refrigeration System, Absorption. A heat-operated closed refrigeration cycle in which a secondary fluid, the absorbent, absorbs a primary fluid, the refrigerant that has been vaporized in the evaporator. Refrigeration System, Direct. A system in which the evaporator or condenser of the refrigerating system is in direct contact with the air or other substances to be cooled or heated.

[ASHRAE 15:5.1.1]

Refrigeration System, Indirect. A system in which a secondary coolant cooled or heated by the refrigerating system is circulated to the air or other substance to be cooled or heated. Indirect systems are distinguished by the method of application given below. [ASHRAE 15:5.1.2] Double Indirect Open Spray System. A system in which the secondary substance for an indirect open spray system is heated or cooled by the secondary coolant circulated from a second enclosure. [ASHRAE 15:5.1.2.2] Indirect Closed System. A system in which a secondary coolant passes through a closed circuit in the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.3] Indirect Open Spray System. A system in which a secondary coolant is in direct contact with the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.1] Refrigeration System, Mechanical. A combination of interconnected refrigerant-containing parts constituting one closed refrigerant circuit in which a refrigerant is circulated for the purpose of extracting heat and in which a compressor(s) is/are used for compressing the refrigerant vapor.

Refrigeration System, Self-Contained. A complete factory-assembled and tested system that is shipped in one or more sections and has no refrigerant-containing parts that are joined in the field by other than companion or block valves.

Registered Design Professional. An individual who is registered or licensed by the laws of the state to perform such design work in the jurisdiction.

Relief Valve, Vacuum. A device which automatically opens or closes for relieving a vacuum with the system, depending on whether the vacuum is above or below a predetermined value.

Removable. Capable of being transferred to another location with a limited application of effort and tools. [NFPA 96:3.3.42]

Replacement Air. See Air, Makeup.
CMC § 5.1.2 Medium relevance — show source text
[ASHRAE 15:5.1.2] Double Indirect Open Spray System. A system in which the secondary substance for an indirect open spray system is heated or cooled by the secondary coolant circulated from a second enclosure. [ASHRAE 15:5.1.2.2] Indirect Closed System. A system in which a secondary coolant passes through a closed circuit in the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.3] Indirect Open Spray System. A system in which a secondary coolant is in direct contact with the air or other substance to be cooled or heated. [ASHRAE 15:5.1.2.1] Refrigeration System, Mechanical. A combination of interconnected refrigerant-containing parts constituting one closed refrigerant circuit in which a refrigerant is circulated for the purpose of extracting heat and in which a compressor(s) is/are used for compressing the refrigerant vapor.

Refrigeration System, Self-Contained. A complete factory-assembled and tested system that is shipped in one or more sections and has no refrigerant-containing parts that are joined in the field by other than companion or block valves.

Registered Design Professional. An individual who is registered or licensed by the laws of the state to perform such design work in the jurisdiction.

Relief Valve, Vacuum. A device which automatically opens or closes for relieving a vacuum with the system, depending on whether the vacuum is above or below a predetermined value.

Removable. Capable of being transferred to another location with a limited application of effort and tools. [NFPA 96:3.3.42]

Replacement Air. See Air, Makeup.

Residential Building. A building or portion thereof designed or used for human habitation.

Riser Heat Pipe. A duct that extends at an angle of 45 degrees (0.79 rad) from the horizontal. This definition shall not include any boot connection.

Room Heater. A freestanding, nonrecessed, environmental heating appliance installed in the space being heated and not connected to ducts.

Room Heater, Unvented. An unvented, self-contained, freestanding, nonrecessed, fuel gas-burning appliance for furnishing warm air by gravity or fan circulation to the space in which installed, directly from the heater without duct connection. [NFPA 54:3.3.56.6]

Rupture Member. A pressure-relief device that operates by the rupture of a diaphragm within the device on a rise to a predetermined pressure.

221.0 – S –

Seam, Welded. See Joint, Welded.

Secondary Filtration. Fume incinerators, thermal recovery units, air pollution control devices or other filtration media installed in ducts or hoods located in the path of travel of exhaust products after the initial filtration.

Self-Contained. Having all essential working parts, except energy and control connections, so contained in a case or framework that they do not depend on appliances or fastenings outside of the machine.

Service Corridor. A fully enclosed passage used for transporting hazardous production materials and purposes other than required exiting.

Service Piping. The piping and equipment between the street gas main and the gas piping system inlet that is installed by, and is under the control and maintenance of, the serving gas supplier.
CMC § 2.25 Medium relevance — show source text
00|2.25|0.70|DR|3.70|1.05|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|3.85|1.45|DR|DR|3.40|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|33 mil cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|3.40|DR|DR|DR|2.70|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|12|3.00|1.80|DR|DR|3.00|0.65|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|16|3.00|1.00|DR|DR|2.85|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#8 Screw|Steel thick-
ness plus 3
threads|24|2.85|DR|DR|DR|2.20|DR|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|12|4.00|3.85|2.80|1.80|4.00|3.05|1.50|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|16|4.00|3.30|1.95|0.60|4.00|2.25|DR|DR| |Minimum 33
mil steel
furring or
minimum
1x wood
furringc|43 mil or
thicker cold-
formed steel
stud|#10 screw|Steel thick-
ness plus 3
threads|24|4.00|2.25|DR|DR|4.00|0.65|DR|DR| |For SI: 1 inch = 25.4 mm, 1 pound per square foot (psf) = 0.0479 kPa, 1 pound per square inch = 0.00689 MPa.
DR = Design Required, o.c. = on center.
a. Wood furring shall be spruce-pine-fir or any softwood species with a specific gravity of 0.42 or greater.

Frequently asked questions

What exactly qualifies as a "companion" valve pair?

A companion (block) valve pair is two mating stop valves arranged so the two refrigerant sections can be joined before opening the valves or separated after closing them — the Code definition is at § 224.0.

Can companion/block valves replace pressure‑relief valves?

No. Companion/block valves are for sectional joining/isolation. Relief‑valve requirements (single vs dual, three‑way valve for dual devices on larger vessels) are set in the refrigeration relief sections (see § 1113.6). Companion valves may support pumpdown procedures that are part of an allowed exception, but they do not substitute for relief devices.

When is a three‑way valve required?

When dual pressure‑relief valves are installed on pressure vessels 10 cu ft (0.28 m³) or larger that discharge to atmosphere; the dual relief valves must be installed with a three‑way valve for testing/repair (§ 1113.6).

If I see two stop valves, how can I confirm they are acceptable companion valves?

Verify they are a matched/mating pair arranged and labeled to allow the join‑then‑open / close‑then‑separate sequence the Code describes; also confirm any service or relief exceptions that rely on pumpdown are satisfied per the refrigeration sections. The Code definition and refrigeration sections should be used for confirmation (§ 224.0, § 1113.6).

Where to look next in the CMC for valve‑related service requirements?

See the refrigeration chapter relief device rules and the definitions chapter for valve types: § 1113.x (relief devices and three‑way valve requirements) and § 224.0 (valve definitions).

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What is an 'Absorption Unit' and common refrigeration-definition terms?

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Equipment, refrigeration and valve definitions frequently referenced

California Mechanical Code