Properly installed oil traps are crucial components of a well-designed piping system.
Good piping practices are essential to guarantee a long life and minimal maintenance for refrigeration and freezer equipment. First off, a good system begins with a little planning.

Correct line sizing is imperative to optimize the performance of the system. Undersized lines will result in high pressure drops, diminished capacity, and increased power requirements. An oversized suction line will lead to poor oil return (as oil and refrigerant do not mix) and premature compressor changeouts.

When the capacity of the refrigeration system is reduced, it is usually because of a pressure drop in the refrigeration lines. Therefore, it is important to keep the refrigeration lines as short as possible, use as few fittings as practicable, and be especially careful not to kink the lines.

Keep your layout as simple as possible. Properly support the piping to absorb vibration and the normal expansion and contraction caused by temperature changes.

Note: Some planning may be required to ensure that the piping does not present a safety hazard, obstruct the normal operation of the equipment, or restrict adjoining spaces.


The following pointers will also help you design and install relatively trouble-free piping.

  • Ensuring proper oil return is also part of the piping design. Oil traps (P-traps) installed at the coil outlet, inverted P-traps where the refrigeration lines exit to the roof, and riser traps for risers of more than 20 feet, are crucial ingredients in a well-designed system.

  • It is recommended that only clean, dry, sealed, refrigeration-grade hard copper tubing be used, and that all joints be made with silver alloy-type solders.

  • Other ways to keep the system free of moisture and foreign matter include using only tubing cutters to cut refrigeration lines, using a minimum amount of flux as needed, and feeding a small amount of dry nitrogen into the tubing during brazing operations.

  • Don’t forget to insulate. Well-insulated suction lines minimize the heat absorption, which leads to diminished capacity. Proper insulation also controls condensate that could form on the suction line.

  • Remember to seal all ends, joints, and any other open areas (including slits necessary to fit the insulation tubing over the installed piping) with insulation glue.

    Melvin is senior engineer at Master-Bilt Products, a division of Standex International Corp. Information on the company may be obtained at (website).

    Publication date: 12/02/2002