PIPING DESIGN FOR HORIZONTAL AND VERTICAL LINES

  Horizontal suction and discharge lines should be pitched downward in the direction of flow to aid in oil drainage, with a downward pith of at least  ​1⁄2 inch in 10 feet. Refrigerant lines should always be as short and should run as directly as possible.

  Piping should be located so that access to system components is not hindered, and so that any components, which could possibly  require future maintenance are easily accessible. If piping must be run through boiler rooms or other areas where they will be exposed to abnormally high temperatures, it may be necessary to insulate both the suction and liquid line to prevent excessive  heat transfer into the lines.

  Every vertical suction riser greater than 3 to 4 feet in height should have a ¨P¨ trap at the base to facilitate oil return up the riser as shown in figure. To avoid the accumulation of large quantities of oil, the trap should be of minimum depth and the horizontal section should be as short as possible. Prefabricated wrought copper traps are available, or a trap can be made by using two street ells and one regular ell. Traps at the foot of hot gas riser are normally not required because of the easier movement of oil at higher temperatures. However it is recommend that discharge line from the compressor be looped to the floor prior to being run vertically upward to prevent the drainage of oil back to the compressor head during shut down periods.

  For long vertical risers in both suction and discharge lines, additional traps are recommended for each full length of pipe (approximately 20 feet) to insure proper oil movement.

  In general, trapped section of the suction line should be avoided except where necessary for oil return. Oil or liquid refrigerant accumulating in the suction line during the off cycle can return to the compressor at high velocity as liquid slugs on start up, and can break compressor valves or cause other damage.