An operator asks how the required low-pressure recovery level compares with the vacuum scale printed on an ordinary compound gauge. Roughly how far below atmospheric pressure does that level sit at sea level?
Correct Answer
D) About twenty-nine inches of mercury below atmospheric pressure
Atmospheric pressure at sea level is close to thirty inches of mercury. The required level of twenty-five millimeters of mercury absolute is about one inch of mercury above a perfect vacuum, so it sits roughly twenty-nine inches below atmospheric. That is right at the far end of a compound gauge's scale, where the needle can no longer be read with any accuracy, and it is the reason the requirement is written as an absolute pressure and verified with an electronic gauge instead.
Why This Is the Correct Answer
Sea level atmospheric pressure is about thirty inches of mercury, and the required absolute pressure of twenty-five millimeters is about one inch of mercury. Subtracting leaves roughly twenty-nine inches of vacuum. Understanding that the target sits almost at the bottom of the gauge explains why a compound gauge is useless for proving compliance on a chiller.
Why the Other Options Are Wrong
Option A: About ten inches of mercury below atmospheric pressure
Ten inches of vacuum is a high-pressure appliance figure. On a chiller it would leave the shell nearly two thirds of the way up to atmospheric pressure with most of the charge still inside.
Option B: About fifteen inches of mercury below atmospheric pressure
Fifteen inches of vacuum also comes from the high-pressure rows of the evacuation table, and it is only about half the depth a low-pressure machine has to reach.
Option C: About twenty-two inches of mercury below atmospheric pressure
Twenty-two inches sounds deep enough to a technician used to high-pressure work, but it still leaves several inches of mercury of pressure in the shell and a great deal of refrigerant with it.
Memory Technique
Thirty minus one is twenty-nine. The chiller has to give up all but the last inch of the atmosphere sitting inside it.
Reference Hint
Twenty-five millimeters of mercury absolute is about one inch of mercury absolute, which is about twenty-nine inches of vacuum at sea level.
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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