A technician has finished pulling the charge out of an R-123 centrifugal chiller and now has to decide when the machine may be opened. What level must the appliance itself reach first?
Correct Answer
C) Twenty-five millimeters of mercury absolute pressure
Low-pressure appliances have their own line in the evacuation table, and it is written as an absolute pressure: 25 millimeters of mercury absolute. That is a deep vacuum, far below anything a compound gauge can resolve, which is why the number is not given in inches of vacuum or in psig. The same figure applies whether the machine is being opened for service or being taken out for scrap. Stopping at zero gauge pressure leaves a large part of the charge still in the shell.
Why This Is the Correct Answer
The evacuation table gives low-pressure appliances a single required level of 25 millimeters of mercury absolute. Absolute means the reading is taken up from a perfect vacuum, so a smaller number is a deeper vacuum. Reaching it is what makes it lawful to open the refrigerant circuit on a chiller charged with R-11, R-113 or R-123.
Why the Other Options Are Wrong
Option A: Zero pounds per square inch on a gauge at the shell
Zero gauge pressure is the required level for a very high-pressure appliance. A low-pressure machine sits at a vacuum even when it is full, so atmospheric pressure would leave most of the charge behind.
Option B: Ten inches of vacuum read on a compound gauge
Ten inches of vacuum belongs to the high-pressure side of the evacuation table. It is nowhere near deep enough for a machine whose refrigerant boils below atmospheric pressure at room temperature.
Option D: Fifteen inches of vacuum read on a compound gauge
Fifteen inches of vacuum is another figure from the high-pressure rows of the evacuation table. Applying a high-pressure number to a chiller is the most common way candidates lose this question.
Memory Technique
Twenty-five millimeters, twenty-five cents, a quarter. A quarter of a hundred millimeters is all the pressure you are allowed to leave in a chiller.
Reference Hint
Low-pressure appliance: 25 millimeters of mercury absolute, the only evacuation level in the table stated as an absolute pressure.
More epa-608-type-3 Questions
Some jobs on a chiller count as a major repair under the refrigerant rules, which changes what a technician is allowed to do with a badly leaking machine. Which job falls into that category?
An owner asks how many pounds of refrigerant the rules allow to be left inside a chiller once the recovery has been signed off. What is the correct answer to give him?
The motor of a hermetic centrifugal chiller sits inside the pressure boundary rather than outside it on a shaft. What follows from that construction?
An oxygen monitor is used to decide whether a chiller machine room is safe to enter after a refrigerant release. Below what oxygen reading is the atmosphere treated as oxygen deficient?
A low-pressure chiller's rupture disc has a discharge line running from it. Where does that line have to terminate?
A refrigerant vapor detector in a chiller machine room reaches its alarm level. Besides sounding, what is that alarm expected to do?
Which piece of equipment requires a technician to hold Type III certification before it may be serviced?
What property of the refrigerant is what actually places an appliance into the low-pressure category?
During normal operation, what condition exists inside the evaporator of a running low-pressure centrifugal chiller?
In what unit is the required final recovery vacuum for a low-pressure appliance normally expressed?
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