Chilled water is finding its way into the refrigerant side of a low-pressure chiller. Which failure allows that to happen?
Correct Answer
A) A tube that has corroded through, or a joint where a tube meets the tube sheet
In a shell and tube chiller the water runs inside the tubes and the refrigerant surrounds them, so the only path from one to the other is through a tube wall or through the joint where the tube is rolled into the tube sheet. When either fails, water is pushed into the shell because the water side is at a higher pressure than a machine running in a vacuum. The other failures listed lose water or refrigerant to the room, not across the boundary.
Why This Is the Correct Answer
The tube wall and the tube-to-tube-sheet joint are the entire boundary between the chilled water and the refrigerant. A failure at either point lets water into the shell, and the pressure difference guarantees the flow runs that way rather than the other. That is why make-up water consumption and purge run time rise together when a tube goes.
Why the Other Options Are Wrong
Option B: A waterbox cover gasket that has hardened and is weeping at the flange bolts
A weeping cover gasket puts water on the floor outside the machine. It never crosses into the refrigerant space.
Option C: A purge unit water separator that has filled and has not been drained this season
A full separator is a maintenance item on the purge unit and holds water the purge already removed from the machine.
Option D: A rupture disc that has weakened and is passing at less than its rated pressure
A rupture disc opens to the outside of the machine, so a weak one loses refrigerant rather than admitting water.
Memory Technique
Water inside the tubes, refrigerant outside them. The only door between them is the tube itself.
Reference Hint
The tube wall and the tube-to-tube-sheet joint form the boundary between the water and the refrigerant in a shell and tube chiller.
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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