Liquid refrigerant has to move from the condenser back to the evaporator inside a low-pressure centrifugal chiller. Which device controls that flow?
Correct Answer
B) A float valve or a fixed orifice between the condenser and the evaporator
Centrifugal chillers meter liquid with a float valve, which holds a level in the condenser or an intermediate chamber, or with a fixed orifice sized for the machine. Both are simple devices suited to a flooded machine that runs at a nearly constant pressure difference. Thermostatic expansion valves and capillary tubes belong to direct expansion equipment, where superheat at the evaporator outlet is the control signal, and a chiller's flooded evaporator has no superheat to sense.
Why This Is the Correct Answer
A flooded evaporator keeps the tubes covered in liquid, so there is no superheat signal for an expansion valve to work from. Level control is what the machine needs instead, and a float valve provides it directly. Fixed orifice plates do the same job with no moving parts, relying on the pressure difference between the two vessels to set the flow.
Why the Other Options Are Wrong
Option A: A thermostatic expansion valve sensing superheat at the evaporator outlet
A thermostatic expansion valve controls superheat, and a flooded chiller evaporator does not produce a superheat signal to control.
Option C: A capillary tube sized to the machine's rated tonnage at design conditions
Capillary tubes are used on small factory sealed equipment. Nothing that size would meter the flow required by a centrifugal machine.
Option D: A solenoid valve opened and closed by the machine's leaving water controller
The leaving water controller acts on the compressor's inlet vanes, not on a solenoid metering the refrigerant between the vessels.
Memory Technique
No superheat, no expansion valve. A flooded machine watches its level, not its temperature.
Reference Hint
Low-pressure centrifugal chillers meter liquid with a float valve or a fixed orifice rather than a thermostatic expansion valve.
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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