How can a technician test a low-pressure machine for leaks without raising its internal pressure at all?
Correct Answer
C) Pull the machine into a vacuum, isolate it, and watch for the pressure to rise
A standing vacuum test uses the pressure difference the machine already has. Pull it down, valve it off, and let it sit with an absolute vacuum gauge connected. If air is leaking in, the pressure climbs. This suits a low-pressure machine perfectly, because the leak path runs inward and because the machine never has to be pressurized anywhere near its rupture disc. It also tests the whole vessel at once rather than one joint at a time.
Why This Is the Correct Answer
Isolating the machine under vacuum turns atmospheric pressure into the test pressure, with the difference driving air inward through any leak. A rising absolute pressure reading proves a leak exists without putting a single psi of positive pressure on a vessel protected by a low rated rupture disc.
Why the Other Options Are Wrong
Option A: Spray soap solution over every joint while the machine is running
Soap bubbles need positive internal pressure to blow a bubble outward. On a machine in a vacuum the flow is inward and the soap gets pulled in instead.
Option B: Hold a halide torch at each flange with the machine sitting in a vacuum
A halide torch detects refrigerant escaping into the air. With the machine in a vacuum there is nothing coming out for the torch to sample.
Option D: Warm the machine with the water pumps until refrigerant vapor escapes at the leak
Warming the machine to force vapor out of the leak means deliberately releasing refrigerant, which is prohibited and would not locate the leak anyway.
Memory Technique
If it will not hold a vacuum, it will not hold a charge. Let atmosphere do the testing for you.
Reference Hint
A standing vacuum test detects leaks on a low-pressure appliance by isolating it under vacuum and watching for pressure rise.
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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