Refrigerant Cylinder Filling Ratios & Temperature Compensation (DOT/ISO/GB)

Sun, 20 Sep 2026 · QUZHOU HUAFU NEW REFRIGERATION MATERIAL CO., LTD.

Why a cylinder is never filled to 100%, and how the fill limit is actually calculated.

1. The single fact people get wrong

A refrigerant cylinder is never filled by volume. It is filled by a mass ratio, calculated so that the cylinder does not become liquid-full at the maximum temperature it may encounter.

If a cylinder is liquid-full and the temperature rises, the liquid expands, hydraulic pressure builds, and there is no vapor space to absorb it. For a liquefied compressed gas that is the mechanism behind overpressure rupture — not a slow leak.

2. The two numbers that define the limit

The governing relationship is:

filling_ratio  ≤  (density_of_liquid_at_reference_temp) × (1 − vapor_allowance)

So the limit is a function of the liquid density at the reference temperature, not of the ambient temperature where the cylinder happens to be filled.

3. Temperature compensation — what it actually means

The phrase describes one thing: the limit is derived at a reference temperature set by the framework in question — for example, 49 CFR sets its filling limit against 131 °F / 55 °C, while the Chinese rules work from the maximum service temperature marked on the cylinder — so the mass that may go in is capped by what the liquid will occupy at the warmest condition the framework assumes, not by the temperature at which the cylinder happens to be filled.

• The mass limit is the same for a cold fill. Filling cold product does not change the number the regulation sets: liquid occupies less volume at the fill temperature, and it is the liquid volume at the reference temperature that the limit was calculated against. A low level is therefore not evidence of an under-filled cylinder.
• Level and volume are not controls. Because the liquid volume moves with temperature, the only quantity that can be verified — by the filler and by the receiver — is mass (net = gross − tare). A cylinder “filled to the top”, or topped up by counting gas transferred, says nothing about whether the mass is inside the limit.
• The dangerous case is the warm one. A cylinder that is liquid-full at the fill temperature has no vapour space left, so warming raises pressure hydrostatically instead of along the vapour curve. The limit is set low enough that liquid-full is never reached at the reference temperature.

4. What is physically on the cylinder (and why the marks matter)

A cylinder supplied without a legible WC/TW pair cannot be verified by the receiver — that absence is itself the signal.

5. Why the reference temperature differs by mode

⇒ The regulatory consequence: a cylinder that is compliant under one framework is not automatically compliant under another. The filling limit for a given gas is jurisdiction-specific, and a supplier quoting a single percentage without naming the framework has not given a usable number.

6. The overfill test that matters at receipt

1. Read the stamped WC and TW.
2. Weigh the cylinder (gross).
3. Net product = gross − TW. Compare against the declared net weight.
4. Confirm the declared net weight is consistent with the filling ratio for that gas under the named framework.
5. Confirm UN number / proper shipping name matches the paperwork (receiving checks).

Steps 1–3 are mechanical. Step 4 is where documents and physics have to agree — and where an inconsistency is detectable without opening the cylinder.

7. What this means for procurement

If you are comparing offers on a liquefied gas, the technical question is not “what is the price per tonne” but “net product per cylinder, under which framework’s fill limit, with what declared tare.” Those three answer the only quantity that can be verified on arrival. The connection for the destination market is a separate specification (valve outlets by market), and the stowage rules that apply once the cylinders are in store are a third (storage and segregation).

The operational side of the same subject — what is checked before, during and after a fill, and what the fill record has to carry — is set out separately (filling operation and records).

FAQ

Why is a cylinder never filled to 100 %? Because a liquefied gas expands as it warms. Leaving vapour space is what keeps the pressure below the cylinder’s test pressure at the reference temperature — the fill limit is calculated from the cylinder’s water capacity and the filling ratio for that gas, not estimated.

Which two numbers define the fill limit? Water capacity (WC) and tare weight (TW), both stamped on the cylinder. The fill limit is derived from the water capacity by the filling ratio for the gas under the transport framework in force for the route.

Which standards govern the vessel and which the fill limit? ISO 4706 / ISO 10297 / ISO 18119 / ISO 10460 specify the vessel, the valve and the inspection; the fill limit itself comes from the transport framework in force for the route. For China domestic cylinders the filling rules are GB/T 14193.1-2025 with TSG 23-2021, separate from the cylinder construction standards (GB/T 5100-2020, GB/T 5099.1-2017).

What is the overfill check at receipt? Weigh and compare the net contents against the declared net weight and the fill limit for that gas, and confirm the UN number and proper shipping name on the cylinder match the paperwork.

What we can provide

Who supplies this: QUZHOU HUAFU NEW REFRIGERATION MATERIAL CO., LTD. is a storage-and-filling trading company in Quzhou, Zhejiang — the cylinders are filled and documented at its site, and it does not manufacture refrigerants.

If you need the cylinder-level fill documentation (WC/TW/UN marks, declared net weight, and the framework the fill limit was calculated under) to accompany a shipment, we can supply it as part of the shipping documents. Contact us with the gas, the cylinder type and the destination market.

Sources

• 49 CFR Part 173 (incl. §173.304a) — US DOT filling limits for liquefied compressed gases (PHMSA / eCFR).
• IMDG Code (International Maritime Organization) — liquefied gas filling limits and the Dangerous Goods List.
• IATA Dangerous Goods Regulations (IATA) — air transport of refrigerants.
• ADR (UNECE) — road transport filling limits for liquefied gases; national variants in 49 CFR.
• GB/T 14193.1-2025 — Rules for filling of liquefied gas cylinders — Part 1: Industrial gas cylinders (SAMR/SAC, China; in force, supersedes GB/T 14193-2009).
• TSG 23-2021 — Gas Cylinder Safety Technical Regulation (SAMR, China; in force) — filling rules and periodic inspection cycles.
• GB/T 5100-2020 / GB/T 5099.1-2017 — Steel welded gas cylinders / Seamless steel gas cylinders — the cylinder construction standards, cited only to distinguish them from the filling rules.
• ISO 4706 / ISO 10297 / ISO 18119 / ISO 10460 (ISO) — cylinder, valve and periodic-inspection standards.

Prepared by Quzhou Huafu New Refrigeration Material Co., Ltd — a warehousing and filling operation (storage and cylinder filling/repacking), not a manufacturer.