A refillable recovery cylinder carries the stamping DOT-4BA400 in the metal of its collar. What does the number at the end of that marking tell the technician?
Correct Answer
A) The service pressure in pounds per square inch that the cylinder was built for
A DOT cylinder marking names the specification the cylinder was built to and then its service pressure. On DOT-4BA400 the 4BA is the specification and the 400 is a service pressure of four hundred pounds per square inch. That figure decides which refrigerants the cylinder may hold, and it is the reason a cylinder suitable for R-134a may be unsuitable for R-410A. The water capacity and the tare weight are stamped separately, and the requalification date appears as its own stamp with the month and year.
Why This Is the Correct Answer
The stamped marking reads as a specification followed by a service pressure. Four hundred means the cylinder was manufactured and tested for four hundred pounds per square inch of service pressure, and refrigerants developing higher saturation pressures at expected storage temperatures belong in a cylinder rated above that. Reading the collar before a job is how a technician avoids putting a high pressure refrigerant into a cylinder that cannot take it.
Why the Other Options Are Wrong
Option B: The water capacity of the cylinder in pounds, used to work out the fill limit
Water capacity is stamped separately, usually marked WC, and is used with the tare weight to work out how much refrigerant the fill limit permits.
Option C: The year the cylinder was manufactured, counted from the start of the century
Manufacture and requalification dates appear as their own stamps in month and year form, not as part of the specification marking.
Option D: The number of months remaining before the cylinder's next hydrostatic retest
Requalification intervals are shown by the date stamps on the collar rather than by a countdown built into the specification number.
Memory Technique
Letters say how it was built. The number says how hard you may push it.
Reference Hint
DOT cylinder markings give the specification followed by the service pressure in pounds per square inch.
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Two technicians recover from identical refrigerators with working compressors, one using a 1991 recovery machine and the other a 2015 machine. Why do their required recovery levels differ?
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