A chiller has a leaking evaporator tube and the waterboxes have been removed so the tube sheet is exposed. How does the technician identify the individual tube that is leaking?
Correct Answer
A) Bring the refrigerant side up with nitrogen inside the limit and check each tube end for escaping gas
With the waterboxes off and the tube ends exposed, the refrigerant side is brought slightly above atmospheric with dry nitrogen, kept within the low ceiling that applies to these machines, usually with a trace of refrigerant added. Gas then comes out of the leaking tube and shows up on an electronic detector or as bubbles in a soap solution at the tube end. Once found, the tube is plugged at both ends or the bundle is scheduled for replacement.
Why This Is the Correct Answer
The leak path runs from the shell into the tube, so putting pressure on the shell side sends gas out through the failed tube and into the waterbox where it can be detected at the tube sheet. The pressure has to stay under the machine's limit, which is why the nitrogen goes through a regulator with a relief device set below that limit.
Why the Other Options Are Wrong
Option B: Fill each tube with chilled water in turn and watch the shell sight glass for a change in level
Filling tubes one at a time is unworkable on a bundle with hundreds of tubes, and the shell level would not respond usefully to a single tube being wetted.
Option C: Run a light down the tubes and look for the one whose inside surface shows a bright scale line
Scale and pitting look much the same on a sound tube and a failed one, and a visible defect is not proof of the leak path.
Option D: Measure the water flow through each tube and identify the one carrying the lowest flow rate
Flow measurement through individual tubes is not practical, and a leaking tube does not necessarily carry less water than its neighbors.
Memory Technique
Pressure in the shell, detector at the tube end. The leak tells you which tube it is.
Reference Hint
A leaking tube is found by pressurizing the refrigerant side with dry nitrogen, within the appliance's pressure limit, and checking the exposed tube ends.
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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