Why must a recovery cylinder never be filled to more than 80 percent of its capacity?
Because liquid refrigerant expands as it warms. A cylinder filled too far can become completely full of liquid, and further warming then builds pressure very quickly and can rupture it.
- The recovery machine cannot push refrigerant above 80 percent
- Warming liquid expands and could burst the cylinderCorrect answer
- Refrigerant above 80 percent turns to vapor and vents
- DOT allows only 80 percent so the cylinder weighs less
Why “Warming liquid expands and could burst the cylinder” is correct
As temperature rises, liquid refrigerant expands. A cylinder that is too full can become completely liquid-filled, and further warming then builds pressure very quickly and can rupture it. Leaving at least 20 percent vapor space prevents this.
Source: EPA: Test Topics
Why the other answers are wrong
- The recovery machine cannot push refrigerant above 80 percent — The limit is about cylinder safety, not machine capacity.
- Refrigerant above 80 percent turns to vapor and vents — Refrigerant above 80 percent does not simply vent; the danger is hydrostatic pressure.
- DOT allows only 80 percent so the cylinder weighs less — The limit protects against rupture, not shipping weight.
The source, word for word
Risks of filling cylinders more than 80 percent full
This one rests partly on trade knowledge. EPA's outline lists the risk of filling past 80 percent as a safety topic but doesn't explain it. The explanation of liquid expansion here is standard physics and trade practice, not wording from the rule.
How to stay under the limit
Pressure will not tell you how full a cylinder is, because its pressure follows temperature as long as any liquid is left. Weigh it instead, on a scale, while you recover.
Other cylinder rules on the same outline
EPA's safety topics also cover the cylinder itself.
- Recovery cylinders are reusable and DOT-approved, with a yellow and gray color code.
- Disposable cylinders are never refilled.
- Shipped cylinders need labels naming the refrigerant, plus a DOT classification tag.
Keep practicing
- What sets the pressure inside a cylinder
- What a shipped cylinder must show
- Why emptying a recovery cylinder outdoors is venting
- EPA 608 Core practice test
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.