Various materials have been used for insulation purposes in the refrigeration field. It is this equipment that service people are most often called to repair or maintain. It is therefore necessary for the present day repair person to be acquainted with the older types of insulation that may be encountered during the workday.

The success of any refrigeration plant depends largely on the proper design of the refrigeration piping and a thorough understanding of the necessary accessories and their functions in the system. In sizing refrigerant lines, it is necessary to consider the optimum sizes with respect to economics, friction losses, and oil return.

It is desirable to have line sizes as small as possible from the cost standpoint. On the other hand, suction- and discharge-line pressure drops cause a loss of compressor capacity, and excessive liquid line pressure drops may cause flashing of the liquid refrigerant with consequent faulty expansion-valve operation.

Refrigerant piping systems, to operate successfully, should satisfy the following:
• Proper refrigerant feed to the evaporators should be ensured.
• Refrigerant lines should be of sufficient size to prevent an excessive pressure drop.
• An excessive amount of lubricating oil should be prevented from being trapped in any part of the system.
• Liquid refrigerant should be prevented from entering the compressor at all times.

Pressure-Drop Considerations
Pressure drop in liquid lines is not as critical as it is in suction and discharge lines. The important thing to remember is that the pressure drop should not be so great as to cause gas formation in the liquid line and/or insufficient liquid pressure at the liquid-feed device.

A system should normally be designed so that the pressure drop due to friction in the liquid line is not greater than that corresponding to a 1-to 2-degree change in saturation temperature. 

Friction pressure drops in the liquid line include a drop in accessories, such as the solenoid valve, strainer-drier, and hand valves, as well as in the actual pipe and fittings from the receiver outlet to the refrigerant feed device at the evaporator.

Friction pressure drop in the suction line means a loss in system capacity because it forces the compressor to operate at a lower suction pressure to maintain the desired evaporating temperature in the coil. It is usually standard practice to size the suction line to have a pressure drop due to friction no greater than the equivalent of a 1- to 2-degree change in saturation temperature.

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