What is the primary job of the purge unit fitted to a low-pressure centrifugal chiller?
Correct Answer
D) Removing air and other non-condensable gases from the machine
Because a low-pressure chiller runs in a vacuum, air works its way in through seals, gaskets, and service connections. Air does not condense at the temperatures inside the machine, so it collects in the top of the condenser, takes up condensing surface, and pushes head pressure up. That costs efficiency and can trip the machine off. The purge unit continuously pulls that pocket of non-condensable gas out and vents it, while doing its best to hold on to the refrigerant that comes along with it.
Why This Is the Correct Answer
Non-condensable gases, mostly air pulled in through the low side, gather in the condenser where they blanket the tubes and raise head pressure. The purge unit's whole purpose is to draw off that mixture, separate out and return as much refrigerant as it can, and release the air. Every low-pressure chiller has one for this reason.
Why the Other Options Are Wrong
Option A: Adding makeup oil to the compressor sump during operation
Oil is added through the oil charging system and the sump, not the purge. The purge unit handles gases at the top of the condenser and has no role in lubrication.
Option B: Filtering scale and particulates out of the chilled water loop
The chilled water loop is filtered and treated by the water side of the plant, with strainers and chemical treatment. The purge unit is connected to the refrigerant circuit only.
Option C: Boosting evaporator pressure whenever the machine runs at light load
The purge unit does not add pressure or control capacity. Machine capacity at light load is handled by inlet vanes or a variable speed drive, not by the purge.
Memory Technique
Purge the air, not the charge: the purge unit is the machine's nose, blowing out the air that leaked in.
Reference Hint
Purge units remove non-condensable gases from low-pressure appliances; their efficiency and run time are regulated service concerns under Subpart F.
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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