Where does the air that collects inside a low-pressure chiller during normal operation come from?
Correct Answer
D) It leaks in through fittings and seals on the parts of the machine that run below atmospheric pressure
Because the evaporator side of a running low-pressure machine sits below atmospheric pressure, any imperfect seal lets room air push its way in. Gaskets, shaft seals, valve stems and service connections all contribute. That air collects in the machine as a non-condensable gas, which is why these machines are built with a purge unit in the first place. High-pressure machines do not need one, because their leaks send refrigerant out rather than drawing air in.
Why This Is the Correct Answer
Atmospheric pressure outside is higher than the pressure inside the low side of the machine, so air flows inward through any leak path. Over months of operation that adds up to a real non-condensable load, which is exactly the problem the purge unit exists to solve.
Why the Other Options Are Wrong
Option A: It is left over from the original factory charging and evacuation, which never cleared the shell completely
A properly evacuated machine starts out clean and the air load builds steadily during operation. That is why purge run time trends upward as seals age instead of falling off after startup.
Option B: It comes out of the compressor oil as that oil breaks down with age and operating heat
Oil breakdown produces acid and sludge, not the steady volume of non-condensable gas a purge unit pulls off day after day. This mistakes a chemical failure for the source of the air.
Option C: It works its way through the tube walls into the shell from the chilled water circuit
Tube walls are solid metal and gas does not migrate through them. A tube that actually failed would bring water into the shell with it, which is a very different and obvious problem.
Memory Technique
The machine breathes in. Every leak on the cold side is a straw into the room.
Reference Hint
Low-pressure machines run below atmospheric pressure on the low side, so leaks admit air, which becomes the non-condensable load.
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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