What happens if the internal pressure of a low-pressure chiller is driven past the rating of its rupture disc?
Correct Answer
D) The disc bursts and the refrigerant charge escapes to the atmosphere
A rupture disc is a one-time device. It is a thin metal diaphragm sized to fail at a set pressure so the shell of the machine is never overpressured, and once it lets go it stays open until someone installs a new one. On a low-pressure chiller the result is that hundreds of pounds of refrigerant leave the machine in a rush. That is a large avoidable release, an expensive loss of scarce refrigerant, and a serious hazard for anyone standing in the machine room at the time.
Why This Is the Correct Answer
Unlike a spring-loaded relief valve, a rupture disc does not reseat. It is designed to burst open and stay open, protecting the shell by dumping everything inside it. Because a low-pressure machine holds a large charge, blowing the disc during careless heating or pressurizing releases that whole charge at once.
Why the Other Options Are Wrong
Option A: The purge unit automatically routes the excess non-condensables outdoors
The purge unit only handles the small quantity of non-condensable gas that collects in the condenser. It has no capacity to relieve an overpressure condition and no connection to the relief path.
Option B: A relief valve lifts and then reseats once the pressure drops back down
Reseating is what a spring-loaded relief valve does. A rupture disc has no spring and no seat, so once the diaphragm tears it cannot close again and the machine keeps venting.
Option C: The compressor unloads and the machine coasts safely to a stop
Compressor controls protect the motor and the bearings, not the shell. On a machine that is shut down for service the compressor is not running at all, yet the disc can still be blown by careless heating or pressurizing.
Memory Technique
A popped balloon does not un-pop: a rupture disc bursts once and stays open until it is replaced.
Reference Hint
Low-pressure appliances are protected by a rupture disc, a non-reseating device; overpressure during service causes a full-charge release.
More epa-608-type-3 Questions
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?
What should a technician do about the water in the chiller tubes before pulling a deep vacuum on the machine?
Which refrigerant was the original factory charge in most low-pressure centrifugal chillers built during the nineteen sixties and seventies?
A running low-pressure chiller develops an opening in a section of shell that is below atmospheric pressure. What passes through that opening?
A technician is assigned to recover the charge from a large water chiller holding nine hundred pounds of R-134a. Which certification does that job require?
Into which appliance category does a machine charged with R-13 for very low temperature service fall?
On a low-pressure centrifugal chiller running at load, how do the evaporator and condenser sit relative to atmospheric pressure?
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