A cylinder holding both liquid and vapor R-134a sits in a 75 °F shop. What mainly determines the pressure inside it?
Refrigeration · EPA 608 Core. The correct answer, and the reasoning behind it.
The refrigeration cycle, refrigerant states and pressures, gauges and leak detection.
The question
A cylinder holding both liquid and vapor R-134a sits in a 75 °F shop. What mainly determines the pressure inside it?
- How full the cylinder is
- The refrigerant's temperatureCorrect answer
- The size of the cylinder
- How long ago it was last filled
Why “The refrigerant's temperature” is correct
When liquid and vapor are both present, the refrigerant is saturated and its pressure is set by its temperature, not by how much is in the cylinder. A nearly empty cylinder and a full one at the same temperature show about the same pressure, which is why weight, not pressure, tells how full a cylinder is.
Source: EPA: Test Topics
Why the other answers are wrong
- How full the cylinder is — As long as some liquid remains, the amount does not set the pressure.
- The size of the cylinder — Cylinder size does not change saturation pressure.
- How long ago it was last filled — Elapsed time matters only because the temperature may have changed.
Practice more of this
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