What makes the vapor phase of recovery from a low-pressure chiller so much slower than from a comparable high-pressure machine?
Correct Answer
A) The vapor sits at very low pressure and density, so little mass moves through the hose at a time
Recovery rate depends on how much refrigerant mass passes through the hose per minute, and that depends on vapor density. In a low-pressure machine the remaining vapor sits near or below atmospheric pressure, where it is very thin. The recovery machine may be moving a healthy volume of gas while transferring only a trickle of actual refrigerant. Large short hoses, full port valves and added heat all help, but the fundamental reason is simply that low pressure vapor carries very little mass.
Why This Is the Correct Answer
Mass flow equals volume flow times density, and the density of vapor at deep vacuum is a small fraction of what a high-pressure machine offers at the same volume flow. The recovery machine works just as hard while moving far fewer pounds, so the job takes far longer even with identical equipment.
Why the Other Options Are Wrong
Option B: The recovery machine has to be stopped every ten minutes to cool down between pulls
Duty cycle limits vary by machine but are not why low-pressure recovery is slow. The density of the vapor being moved dominates, and pauses only add to the elapsed time.
Option C: Low-pressure refrigerant must be passed through a drier before it can be recovered into a cylinder
No drier is required in the recovery path, and adding restriction would only slow an already slow process. Nothing about low-pressure refrigerant calls for filtering before it can be captured.
Option D: All of the oil has to be drained from the machine before any vapor will move out of the shell
Oil is drained for its own reasons during major service, but vapor leaves the machine whether or not the oil has come out. Oil removal is not a precondition for vapor recovery.
Memory Technique
Thin gas, thin results. A hose full of near vacuum carries almost nothing.
Reference Hint
Low-pressure vapor has very low density, so mass flow during vapor recovery is small and the job takes much longer.
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?
People Also Study
Business & Financial Management
120 questions · 70% to pass
Contract Administration
60 questions · 70% to pass
Project Management
60 questions · 70% to pass
Related Study Resources
Previous Question
To what level may a recovery cylinder be filled when refrigerant is taken out of a low-pressure appliance?
Next Question
A chiller has been pressurized with dry nitrogen for a leak test and the technician returns hours later to read it. What has to be accounted for before deciding the machine has lost pressure?