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The 80 percent fill rule for recovery cylinders

A refillable recovery cylinder may be no more than 80 percent full of liquid, which you check by weight on a scale. Liquid refrigerant expands as it warms, and a cylinder full of liquid has no room left: a small rise in temperature can then burst it. The empty space is what keeps it safe.

From the lesson Cylinder Handling and the 80 Percent Fill Rule

Why it matters on the exam

Cylinder safety is a Core topic, and the exam asks about the fill limit, the cylinder colours and the retest interval. They are quick marks if you know them.

Key points

  • Checked by weight. The limit is 80 percent of the cylinder's volume as liquid. You check it on a scale: the cylinder is stamped with its tare weight and water capacity, and the refrigerant's density turns those into a maximum weight.
  • Gray and yellow. A refillable recovery cylinder has a gray body and a yellow shoulder.
  • Five years. Refillable cylinders are hydrostatically retested every five years.
  • No flame. Never heat a cylinder with a torch, and never store one above 125°F.

Common trap

Filling by eye, or by one rule of thumb for every refrigerant. The safe weight depends on the refrigerant's density, so weigh the cylinder and work its limit out from its tare weight, its water capacity and the refrigerant in it.

Question 1 of 5

Why must a recovery cylinder never be filled past 80 percent of its capacity?

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Tap an answer and I’ll tell you why.

Question 1 is written for this page and checked by a person. The others are practice questions from the MindMax app. None are from a past exam.

Where it comes from

Lesson 2 in Safety, Cylinders and Shipping · Core Section

Cylinder Handling and the 80 Percent Fill Rule

  1. State the 80 percent fill limit by weight and explain the hydrostatic expansion hazard behind it
  2. Determine whether a cylinder is overfilled using tare weight and water capacity
  3. Identify a DOT-approved recovery cylinder by its gray body and yellow shoulder
  4. State the five-year hydrostatic retest requirement for refillable cylinders
  5. State the prohibitions on heating a cylinder with a torch, refilling disposable cylinders and storing cylinders above 125 degrees Fahrenheit
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Key terms in this lesson

80 percent fill rule
A refillable cylinder may be filled to at most 80 percent of its volume with liquid, checked on a scale, leaving room for the liquid to expand.

Learn more

FAQ

Liquid refrigerant expands as it warms. Past 80 percent, a small rise in temperature can leave the liquid no room, and the pressure can burst the cylinder. The space left over is the safety margin.

By weight, on a scale. Work the maximum out from the cylinder’s stamped water capacity and tare weight and the refrigerant’s density, then stop when the scale reaches it.

A gray body with a yellow shoulder. It is retested every five years, and should never be heated with a torch or stored above 125°F.

Keep reading

Loading the clip…

Here's a recovery cylinder sitting on a scale, still empty, and the scale already reads seventeen pounds. That's the tare weight stamped on the collar. Now watch the gauge as refrigerant flows in: the needle barely moves, because pressure follows temperature, not how full the tank is. A sight glass, or the heft in your arms, can't tell seventy percent from ninety. For this cylinder, eighty percent works out to twenty-four pounds of refrigerant, so you stop when the scale reads forty-one. That last twenty percent is vapor space, which leaves the liquid room to swell on a hot truck.

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