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SESK: Stuff Everyone Should Know · sesk.info/epa-80-percent-fill

What is the maximum a refrigerant cylinder should be filled, by volume?

80 percent, no more.

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  1. 80 percent ✔
  2. 90 percent
  3. 100 percent

Why: Liquid refrigerant expands as it warms. Leaving about 20 percent of the cylinder empty gives room for expansion and head pressure. An overfilled cylinder can burst.

Huh, didn't know that: The empty 20 percent of a cylinder is sometimes called head pressure room.

The dad joke
Why do refrigerants make such terrible comedians? Because they always crack under pressure!
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References

Answer: 80 percent. Liquid refrigerant expands as it warms. Leaving about 20 percent of the cylinder empty gives room for expansion and head pressure. An overfilled cylinder can burst.

  1. Section 608 Technician Certification Test Topics, US EPA www.epa.gov/section608/section-608-technician-certification-test-topics
    Risks of filling cylinders more than 80 percent full
    Checked 2026-10-10.
  2. Robinair RG6 Recovery Unit Operating Manual robinair.com/sites/default/files/documents/567912.pdf
    The remaining 20% is called head pressure room.
    Checked 2026-10-10.

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