CRST Piping, Tubing & Brazing Techniques 2

Question 1

In refrigeration copper tubing work, what does the term 'swaging' refer to?

Accepted Answer

Expanding the end of a tube so another tube of the same diameter can be inserted for a brazed connection

Answer

Swaging mechanically expands the end of a copper tube to accept another tube of the same nominal size, allowing a direct brazed joint without a separate coupling fitting.

Question 2

In what direction should horizontal suction lines be sloped to promote oil return?

Accepted Answer

1/4 inch per foot sloping toward the compressor

Answer

Horizontal suction lines should slope 1/4 inch per foot toward the compressor so that gravity assists oil in draining back toward the suction inlet.

Question 3

Which gas is the recommended medium for pressure-testing refrigerant piping after brazing is complete?

Accepted Answer

Dry nitrogen

Answer

Dry nitrogen is inert, oil-free, moisture-free, and non-reactive, making it the safe and industry-accepted gas for pressure-testing refrigerant piping without contaminating the system.

Question 4

Why must oxygen NEVER be used to pressure-test or purge a refrigeration system?

Accepted Answer

Oxygen combined with compressor oil under pressure creates an explosive mixture capable of detonation

Answer

Oxygen in contact with petroleum-based compressor oil under pressure can form a highly explosive mixture—similar to a diesel engine—posing a severe fire and detonation hazard.

Question 5

What is the recommended minimum bend radius for ACR copper tubing to prevent kinking, flattening, or cracking during bending?

Accepted Answer

3 times the tube outside diameter

Answer

Bending copper tubing to a radius of at least 3 times the outside diameter distributes stress gradually enough to prevent the tube wall from kinking, collapsing, or cracking.

(CRST) Certified Refrigeration Service Technician Practice Test

(CRST) Certified Refrigeration Service Technician Practice Test

CRST Piping, Tubing & Brazing Techniques 2