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

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

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

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, so the mass that may go in is capped by what the liquid will occupy at the warmest condition the framework assumes (typically 55 °C / 131 °F), 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).

What we can provide

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 cylinders (SAMR/SAC, China).
• TSG 23-2021 — Gas Cylinder Safety Technical Regulation (SAMR, China) — 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 6406 / 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.