What does a technician use to bring a low-pressure machine back up to atmospheric pressure before opening it for tube work?
Correct Answer
A) Dry nitrogen
The vacuum has to be broken before a vessel can be opened, and the gas used should be dry and clean. Dry nitrogen fits: it is inert, contains no moisture, and leaves nothing behind that will cause trouble later. Shop air brings moisture and compressor oil into the machine. Putting refrigerant back in wastes the charge you just recovered and creates an exposure hazard for the crew. Carbon dioxide is neither dry nor appropriate for this use.
Why This Is the Correct Answer
Dry nitrogen is inert and moisture free, so it fills the machine without adding water vapor that would later have to be evacuated. It also gives a clean atmosphere for the crew opening the vessel. This is the standard way to bring a machine that has been under deep vacuum back up to atmospheric pressure.
Why the Other Options Are Wrong
Option B: Shop compressed air from the building's air system
Shop compressed air carries water vapor and often compressor oil mist. Both end up inside the machine and both have to be removed later.
Option C: Refrigerant vapor from the recovery cylinder
Returning refrigerant to the machine wastes the charge that was just recovered and puts refrigerant vapor in the space where the crew will be working.
Option D: Carbon dioxide from a fire extinguisher
Carbon dioxide from an extinguisher is not a clean dry gas for this purpose and can carry propellant residue into the vessel.
Memory Technique
Dry nitrogen in, moisture stays out. If the answer says shop air, it is the wrong answer.
Reference Hint
Break the vacuum on a low-pressure machine with dry nitrogen so no moisture enters before the machine is opened.
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?
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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?
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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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