Short Answer: Fill recovery cylinders to no more than 80% of their liquid capacity, measured by weight. They are gray with a yellow top, must meet a DOT specification and must be requalified on schedule.
Quick Facts
| Fill limit | 80% liquid capacity, by weight |
|---|---|
| Colour | Gray body, yellow top (AHRI Guideline K) |
| Specification | DOT-4BA or 4BW, commonly |
| Requalification | Often every 5 years (49 CFR 180.209) |
| Never | Refill disposable cylinders or heat with a flame |
Why Recovery Cylinder Rules Matter
When you recover refrigerant you put a pressurised liquid into a steel container. If the cylinder is overfilled and then warms up, liquid expands until there’s no vapour space left. At that point pressure rises very quickly and can rupture the cylinder or open the relief valve. That’s why the rules focus on fill level, cylinder condition and temperature.
The cylinder rules are mostly from the U.S. Department of Transportation (DOT) and industry standards, not Part 82. EPA’s test topics include them under safety and shipping in Core.
The 80% Fill Rule
Fill a refillable recovery cylinder to no more than 80% of its liquid volume. This is a safety practice built into recovery-cylinder design and EPA 608 training.
How to Calculate the Maximum Fill
Each cylinder is stamped with:
- WC (water capacity), the weight of water the cylinder holds
- TW (tare weight), the empty cylinder weight
A commonly taught calculation is:
Maximum gross weight = (WC × 0.8 × specific gravity of the refrigerant) + TW
Refrigerants have different densities, so the safe weight changes with the refrigerant. Many recovery cylinders also have a float switch that shuts off the recovery unit at 80%. Use a scale either way, since float switches can fail.
Temperature Matters
A cylinder filled to 80% at a cool temperature has less vapour space when hot. Store cylinders out of direct sun and don’t leave them in a closed vehicle on hot days. A common guideline is never to let cylinders exceed 125 °F.
Colour Codes
Under AHRI Guideline K, recovery cylinders are gray with a yellow top. The yellow shoulder tells everyone the cylinder contains used, possibly contaminated refrigerant.
New-refrigerant cylinders used to carry a colour for each refrigerant. Industry has moved to a single light green-gray colour for new refrigerant, with the refrigerant shown on the label. Always read the label, not the colour.
DOT Specification and Requalification
Refillable recovery cylinders must be built to a DOT specification. DOT-4BA and DOT-4BW are common for recovery cylinders. The specification and the original test date are stamped on the collar.
Under 49 CFR 180.209, specification cylinders must be requalified (usually a hydrostatic test) at set intervals. For DOT-4BA and 4BW cylinders the interval is commonly 5 years; check the current table in 180.209 for your cylinder spec. Don’t fill a cylinder that is past its requalification date.
Inspecting a Cylinder Before Use
- Check the stamped requalification date.
- Look for dents, gouges, bulges, rust and fire damage.
- Make sure the valve and relief device are intact.
- Confirm it is a recovery cylinder rated for the refrigerant’s pressure. R-410A and other high-pressure refrigerants need cylinders rated for them, often marked 400 psig.
Disposable Cylinders
Disposable (non-refillable) cylinders, such as DOT-39 cylinders that new refrigerant often ships in, must never be refilled and never be used for recovery. When empty:
- Recover any remaining refrigerant to 0 psig.
- Close the valve, then render it useless (for example by puncturing the rupture disc or making the cylinder unusable as the recycler requires).
- Mark it “empty” and recycle it as scrap metal where allowed.
Labelling and Shipping
Recovered refrigerant shipped for reclamation must be labelled to identify the refrigerant and carry the DOT hazard classification. Practical points tested in Core:
- Label each cylinder with the refrigerant type.
- Don’t mix refrigerants in a cylinder. Mixed refrigerant often can’t be reclaimed and may need to be destroyed.
- Follow your reclaimer’s paperwork and the DOT shipping rules.
Reclaiming refrigerant and why it matters is covered in Recover vs Recycle vs Reclaim Refrigerant.
Storage and Handling
- Store cylinders upright and secured so they can’t fall.
- Keep them away from heat sources and open flames. Never heat a cylinder with a torch. If you need to warm one to speed charging, use warm water or an approved heating band with temperature control.
- Keep valve caps on when not in use.
- Don’t drop, drag or roll cylinders by the valve.
Evacuating a Recovery Cylinder
Before first use, or when switching refrigerants after reclamation, a recovery cylinder should be evacuated to remove air and non-condensables. Air in the cylinder raises the pressure and reduces recovery efficiency. If cylinder pressure is higher than the saturation pressure for the refrigerant at its temperature, non-condensables are present.
Flammable Refrigerants
A2L and A3 refrigerants need recovery cylinders and equipment suited to flammable refrigerants. Cylinders for flammable refrigerants usually have a red band or marking and left-hand thread valves for some types; check the cylinder and manufacturer instructions. See Refrigerant Types, Classes and A2L Safety.
Quick Reference
| Rule | Figure or standard |
|---|---|
| Maximum fill | 80% liquid volume |
| Recovery cylinder colour | Gray body, yellow top |
| Typical DOT spec | 4BA or 4BW |
| Typical requalification (4BA/4BW) | 5 years (check 49 CFR 180.209) |
| Storage temperature guide | Below 125 °F |
| Disposable cylinders | Never refill or use for recovery |
Test Yourself
Cylinder questions show up in Core. Try the EPA 608 Core Practice Test (2027 Question Bank), or read Refrigerant Safety and Cylinder Handling for the wider safety picture.
Key Terms
- WC (water capacity): the weight of water a cylinder holds, stamped on the collar.
- TW (tare weight): the empty weight of the cylinder.
- Requalification: periodic testing of a DOT cylinder, often hydrostatic.
Common Mistakes on the Job
- Overfilling. Filling past 80% by liquid volume leaves no room for liquid expansion. A hot day or a cylinder left in a vehicle can raise the pressure to the point where the relief device opens.
- Using a disposable cylinder for recovery. Disposable cylinders are not designed to be refilled and must never be used to store recovered refrigerant.
- Mixing refrigerants. A mixed cylinder usually can’t be reclaimed and may need to be sent for destruction.
- Ignoring the test date. Refillable cylinders must be within their requalification date before they are filled or shipped.
- Leaving cylinders unsecured. A cylinder that falls can damage its valve.
Using Weight to Control Fill
The reliable way to stay under 80% is to weigh the cylinder. Many technicians use a scale during recovery, and some recovery machines can work with a cylinder float switch to stop recovery automatically when the cylinder reaches its fill limit.
Steps to Take
- Check the cylinder's DOT specification and test date.
- Weigh it before and during recovery.
- Stop at 80% of the liquid capacity.
- Label the refrigerant type.
- Store and transport it upright and secured.
Frequently Asked Questions
How full can a refrigerant recovery cylinder be?
No more than 80% of its liquid capacity, so there is room for the liquid to expand as temperature rises. Weigh the cylinder on a scale and use its water capacity (WC) and tare weight (TW) to calculate the maximum, or use a recovery unit with an 80% float switch.
What colour is a refrigerant recovery cylinder?
Gray with a yellow top (shoulder), under the AHRI Guideline K colour scheme. New refrigerant cylinders are now generally a single light green-gray colour with the refrigerant identified by the label.
How often must a recovery cylinder be retested?
It depends on the DOT specification. For common DOT-4BA and 4BW recovery cylinders, 49 CFR 180.209 generally sets a 5-year requalification interval. Check the stamped date and the current table in 180.209.
Can I put different refrigerants in one recovery cylinder?
No. Mixing refrigerants can make them impossible to reclaim, and they may then have to be destroyed at high cost. Use a separate, labelled cylinder for each refrigerant.