Piping, Brazing & Leak Detection Flashcards

What is the purpose of an oil trap (inverted P-trap) installed at the base of a vertical refrigerant suction riser?

Answer: To collect oil that drains down during the off-cycle and return it to the compressor

During the off-cycle, oil drains to the lowest point of the riser; the oil trap collects it and re-entrains it in the suction gas flow so it is carried back to the compressor when the system restarts.

What is the maximum recommended refrigerant velocity in a liquid line to prevent flashing ahead of the metering device?

Answer: 3 m/s

Liquid line velocities above approximately 3 m/s create sufficient pressure drop that subcooled liquid may flash to vapour before reaching the metering device, causing capacity loss.

Per the Canadian Refrigeration Code, what is the maximum recommended support spacing for horizontal copper refrigerant suction lines?

Answer: 3 m (10 ft)

The Canadian Refrigeration Code and ASHRAE recommend maximum support intervals of approximately 3 m (10 ft) for copper refrigerant lines to prevent sagging, vibration fatigue, and stress on brazed joints.

Why is reaming the inside of copper tubing after cutting with a wheel cutter a mandatory step?

Answer: To remove the internal burr that restricts flow and can contaminate the system

A wheel cutter leaves a raised internal burr that restricts refrigerant and oil flow, and can break off to contaminate metering devices, compressor valves, and strainers.

When sizing refrigerant suction lines, the design goal is to:

Answer: Balance minimum velocity for oil return with minimum pressure drop

Suction line design requires maintaining sufficient velocity to carry oil back to the compressor (especially in vertical risers) while keeping pressure drop low enough not to reduce system capacity and efficiency.

Outdoor refrigerant line set insulation must be protected primarily against:

Answer: UV degradation of insulation and mechanical damage from wind-induced vibration

Solar UV radiation breaks down foam and elastomeric insulation materials over time, and wind-induced vibration causes fatigue failure at supports and joints — both leading to moisture ingress and energy loss.

Which type of mechanical fitting is preferred for refrigerant piping connections that must be disassembled for service?

Answer: SAE 45° flare fittings

SAE 45° flare fittings are designed for repeated field disassembly and reassembly and are the standard choice wherever a serviceable mechanical joint is required, such as at service valves and gauge ports.