Pick up an Amerex 322 for the monthly check and the first thing you notice is what isn't there. No pressure gauge, no green area to confirm. On a dry chemical extinguisher the gauge is the heart of the monthly check; on a CO2 unit it doesn't exist — and Amerex is specific about what takes its place.
Carbon dioxide does three things differently from the dry chemical units most owners already have on the wall. The fullness check is a weight. The hydrostatic test comes at five years, not twelve. And the service parts split across two platforms sharing a valve stem and a safety disc but little else.
Fullness is a weight, not a gauge
Amerex's owner's manual handles this in one line: "Carbon Dioxide extinguishers determine fullness by weighing or hefting." The sentence immediately after it covers the rest of the line — "Water Mist, Water, Wet Chemical, Dry Chemical, Dry Powder, Halotron I, Halotron BrX and Halon 1211 extinguisher pressure gauges should be checked."
The CO2 service manual repeats it as item six of the monthly inspection, then at annual maintenance turns it into a measurement: "Weigh the extinguisher and compare with weight printed in the 'Maintenance' section on the nameplate (label). Recharge extinguisher if weight is not within indicated allowable tolerances."
So the full-weight reference and its tolerance live on the extinguisher itself, not in any catalog. The recharge procedure sends the technician back to the same label for "the proper amount of CO2 to be pumped into the extinguisher" — which is why Amerex's first maintenance step is to "Check to make sure that the instruction nameplate is securely fastened and legible."
Five years, not twelve
This is the interval that catches mixed populations. Amerex states it plainly — annual maintenance "will reveal the need for hydrotesting which must be done on Water Mist, Water, Wet Chemical, Foam and Carbon Dioxide every FIVE YEARS and Dry Chemical, Dry Powder, Halotron I and Halon 1211 extinguishers every TWELVE YEARS."
The CO2 service manual gives the same requirement from the cylinder's side — "The agent cylinder must be hydrostatically tested every 5 years to the test pressure indicated on the nameplate in accordance with DOT requirements" — and tells the technician where to find the date: "Check the date of manufacture stamped on the cylinder dome." One knock-on effect is easy to miss: Amerex's six-year maintenance provision applies to "extinguishers requiring a 12 year hydrotest," so it never reaches CO2. A CO2 unit and a 10 lb ABC unit bought the same day never come due together.
The test has a fitment requirement of its own: "Amerex CO2 valve bodies and aluminum cylinders are 1-1/8"-12 UNF straight threads. Use a proper straight thread adapter when hydrostatically testing." That is the 01290, the Parts Book's "Hydro-test Adapter 1-1/8" - 12 UNF X 1/2"-14 NPT." We sell the adapter; a qualified service company performs the test. Our recharge or replace guide works the same arithmetic.
The hand portable line
Amerex describes the agent this way: "CARBON DIOXIDE is discharged as a white cloud of 'snow,' which smothers a fire by displacing oxygen. It is effective for Class B flammable liquids and is electrically non-conductive. Carbon Dioxide is a clean, non-contaminating, odorless gas." Every model below uses a chrome-plated brass valve and rust-free aluminum cylinder, carries a −22°F to 120°F temperature range and 5-year manufacturer's warranty, and has an initial range of 3 to 8 feet.
| Model | Capacity (lbs.) | UL & ULC rating | Design | Height (in.) | Depth (in.) | Discharge time (sec.) |
|---|---|---|---|---|---|---|
| 322 | 5 | 5B:C | Tube & Horn | 17.75 | 5.25 | 9 |
| 322NM | 5 | 5B:C | Tube & Horn | 17.75 | 5.25 | 9 |
| 330 | 10 | 10B:C | Hose & Horn | 24 | 7 | 11 |
| 331 | 15 | 10B:C | Hose & Horn | 30 | 7 | 14.5 |
| 332 | 20 | 10B:C | Hose & Horn | 30 | 8 | 19.2 |
The rating stops climbing at 10 lb. The 330, 331 and 332 all carry 10B:C — size buys discharge time, not a higher rating. Amerex's ABC dry chemical line works the other way, its Class B number climbing from 1A:10B:C on the 2.5 lb B417T to 10A:120B:C on the 20 lb A411; see what UL ratings actually mean.
The 322NM is the specialty build: Amerex lists it as "independently tested and approved for use in MRI facilities to 11.7 Tesla," with "a sanitary white paint finish (easy to clean)." Amerex notes the line "meets many hospital medical equipment requirements," and offers as an option "USCG approved with bracket listed on UL label." The catalog spec table shows the 322NM as the line's only nonmagnetic model, but it is not the only one Amerex builds: the 2026 item list carries item 6902, "FE 331 15. CO2 NON MAG," model 331, rated 10B:C — a 15 lb nonmagnetic CO2 that the catalog page does not print.
Two parts platforms, one shared core
The break is not by capacity, it is by discharge design. The 5 lb 322 uses a discharge tube and horn — Amerex notes "The Amerex 2 1/2 & 5 lb CO2 diffuser is built into the discharge tube," and that the tube-and-horn design "has a swivel and once aimed will maintain that same fixed position and is not required to be held during discharge." The 330, 331 and 332 use a hose and horn assembly, with the hose connection made at an elbow.
| Component | 322 platform (tube & horn) | 330 / 331 / 332 platform (hose & horn) |
|---|---|---|
| Valve assembly | 03090-P | 26846 |
| Discharge path | 01769-P discharge tube | 01782 hose & horn (330); 01705-P hose & horn (331, 332) |
| Horn only | 01772-P | 00572-P (330); 00593 (331, 332) |
| Downtube | 00533 | 00564 (330); 00589 (331, 332) |
| Elbow / elbow O-ring | 02735-P elbow with O-ring, 05689-P O-ring | Elbow referenced in the service manual; none listed as a replacement part here |
| Horn strap and pin | Not listed | 00594-P U-pin; 20570-P strap & clip (330, 331); 20571-P strap & clip (332) |
| Wall hanger bracket | 00546-P (322); 17737 (322NM) | 00575-P (330, 331); 22290 (332) |
| Shared, both platforms | 04000-P safety disc, gasket and nut · 01539-P valve stem assembly · 00501-P spring · 00503-P retainer · 01124-P collar O-ring 1 1/8" · 00160-P ring pin (non-magnetic 06901-P on the 2½/5 lb list, 06901 on the 10–20 lb list) · 00532-P nylon chain · 01387-P lock wire seal · 09020 handle & rivets · 07762 lever & rivet · 01316 fill adapter · 01290 hydro-test adapter | |
The hangers are worth a note, because Amerex names them twice. The Parts Book lists them as part numbers — 00546-P for the 322, 17737 for the 322NM, 00575-P for the 330 and 331, 22290 for the 332 — while the catalog's extinguishers at-a-glance chart lists the same positions by bracket model: 801 Wall, 801SS Wall, 802 Wall, and "20# CO2 Wall." Amerex's 2026 item list joins the two, describing 00546-P as "BKT WALL 801," 17737 as "BKT WALL 801 5.0 CO2 SS STAINLESS STEEL," 00575-P as "BKT WALL 802" and 22290 as "BKT WALL 20 CO2 RD." Same hardware, two naming conventions — which matters most on the nonmagnetic units, covered in CO2 vs Halotron BrX for Class C.
A note on the 2½/5 lb parts list prevents a common double-order: "All Valve Assemblies include Valve Body, Valve Stem Assembly, Spring, Retainer, Safety Disc, Lever and Handle." The 10–20 lb list carries the same contents, shortened to "Stem Assembly." Buy a 03090-P or a 26846 and the stem, spring, retainer, disc, lever and handle are already in the box. One exception: the Parts Book qualifies the 03090-P as a "Valve Assembly - 322, (Does not include elbow or downtube)," so those stay separate line items. The 322 parts list also covers the 2½ lb 321M military model, which takes its own numbers for safety disc, ring pin, lever, handle, discharge tube, horn and downtube.
One fill adapter serves the whole hand portable range. Amerex lists the 01316 under "Carbon Dioxide - All CO2 Hand Portable Extinguishers," and it "Installs on 2 1/2lb., 5lb. Discharge Tube ... Install on 10lb.,15lb., 20lb. CO2 Elbow or valve outlet after 07/2020." Our fill adapter guide maps the rest of the line.
The safety disc, and why substitutes fail here
Amerex's troubleshooting guide names the safety relief nut as one of six CO2 leak points; the corrective action is a whole-assembly swap: "Replace with new Amerex safety nut, disc and gasket assembly. Tighten assembly to 250 in-lbs [28.25 Nm] maximum of torque." The maintenance procedure repeats it with emphasis — "replace with complete Amerex factory assembled safety relief assembly ... DO NOT SUBSTITUTE." The Parts Book warns catalog-wide that "To protect the UL listing and to keep the warranty in effect Amerex replacement parts must be used." That part is the 04000-P, the same number on both platforms. Amerex also caps valve installation at "100 ft. lbs. [135.58 Nm] maximum torque": "Over-tightening can damage both valve and cylinder."
A test the 322 never needs
Because the 330, 331 and 332 carry a hose, they pick up an annual step the 322 does not have. Amerex: "Carbon dioxide hose assemblies have a continuous metal braid that connects to both couplings to minimize static shock. A hose continuity test shall be performed using a basic conductivity tester ... (NFPA 10)." Amerex also directs the technician to "Replace the horn if brittle, cracked or deformed" — so we stock horns separately: the 01772-P for the 322, the 00572-P for the 330, the 00593 for the 331 and 332 — or the complete 01782 on the 330 and 01705-P on the 331 and 332 when the hose goes too.
Where Amerex points CO2 — and where it doesn't
CO2's selling point is what it leaves behind — Amerex lists "Leaves no residue" among the line's features. On Amerex's application chart, carbon dioxide is pointed at welding shops, auto repair shops, manufacturing facilities and high-voltage electrical distribution, while data server rooms are pointed at the HT Series instead. The warnings deserve equal weight: used "in an unventilated space, such as a small room, closet or other confined area, prolonged occupancy of that space can result in loss of consciousness due to oxygen deficiency," and "Hold horn on hand grip only—grasping the horn or swivel discharge tube could cause cold burn." Amerex's own instruction is direct: "Persons expected to use this extinguisher shall be trained in initiating its operation and in the proper fire fighting technique."
What we stock
Hand portables — the 322 5 lb, the MRI-rated 322NM, and the hose-and-horn 330, 331 and 332 in the CO2 collection; 50 lb and 100 lb units in wheeled CO2.
Valves and internals — the 03090-P and 26846 valve assemblies and the 04000-P safety disc assembly, plus stems, springs, retainers, O-rings and downtubes in valves, gauges and downtubes.
Horns, hoses and adapters — the 01772-P, 00572-P and 00593 horns and the 01782 and 01705-P hose and horn assemblies, with U-pins and horn straps, in hoses, nozzles and horns; the 01316 fill adapter, 01290 hydro-test adapter and CO2 wall hangers in mounting parts and hardware. If the bracket is the open question, start with which Amerex bracket fits your extinguisher.
Sizing CO2, or matching parts to units already in service? Send models and quantities and we'll come back with options, availability and lead time — request a quote.
Sources
Ratings, capacities, discharge times, dimensions, temperature range, agent description and application guidance are from Amerex Corporation's Portable Fire Extinguisher Catalog. Inspection, maintenance, recharge, hydrostatic test and troubleshooting language is from Amerex service manual PN 05603, Carbon Dioxide Portable Extinguishers — Models 321M, 322, 322NM, 330, 331, 332, and PN 27794, Owner's Manual Hand Portable. Part numbers, platform groupings, wall hanger fitment and adapter fitment are from the Amerex Portable & Wheeled Parts Book, PN 27277 Rev C. The bracket part-number-to-model mapping and the nonmagnetic 331 come from Amerex's 2026 published item list. Two differences between Amerex documents are worth knowing: PN 05603 lists 15 and 19 second discharge times for the 331 and 332 where the catalog lists 14.5 and 19.2 (the catalog figures are used above), and PN 05603 places the date of manufacture on the cylinder dome while the catalog puts it on the cylinder shoulder. Confirm any critical rating, charge weight, test interval or part number against the extinguisher's own nameplate and Amerex's current documentation, and confirm inspection and hydrostatic test requirements with a qualified fire protection professional, NFPA 10 and your authority having jurisdiction.
ShopAmerex.com is owned and operated by Centurion Holdings Group LLC, an independent authorized distributor of Amerex Corporation products. We sell equipment and factory OEM service parts — we do not perform inspection, service, hydrostatic testing or recharging.