What pressure would the shell be at?
Refrigeration · EPA 608 Type III. The correct answer, and the reasoning behind it.
Purge units and pressure-temperature behaviour of low-pressure refrigerants.
The question
An idle R-11 chiller sits in a 70 °F equipment room, with the refrigerant at room temperature. What pressure would the shell be at?
- Slightly below atmospheric, a small vacuumCorrect answer
- About 70 psig
- Exactly 0 psig, as for any idle chiller
- About 15 psig, the rupture disc setting
Why “Slightly below atmospheric, a small vacuum” is correct
R-11 boils at about 75 °F at atmospheric pressure. At 70 °F its saturation pressure is a little below atmospheric, so the idle chiller holds a slight vacuum, which is why leaks draw air in even when it is off.
Source: EPA: Test Topics; Hudson Technologies R-123 and R-11 P-T charts
Why the other answers are wrong
- About 70 psig — 70 psig is typical of a medium- or high-pressure refrigerant, not R-11.
- Exactly 0 psig, as for any idle chiller — Pressure depends on the refrigerant's temperature; it is not always 0 psig.
- About 15 psig, the rupture disc setting — An idle R-11 chiller at 70 °F is nowhere near 15 psig.
Practice more of this
More EPA 608 Type III practice questions, or see every EPA 608 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.