types of flow control

A fundamental and indispensable component of any refrigeration system is to control flow or pressure relief device. Its main purposes are:1. Maintain the pressure and boiling point appropriate in the evaporator to handle the heat load required.2. Permit the flow of refrigerant to the evaporator at a rate as to remove heat from the load.The pressure reducing device is one of the points dividing the system.The principal means for controlling refrigerant flow in the first years of refrigeration, a manual valve was basic.Having seen his work and his team, the first operators to ice plants and similar operations with constant load, knew how to open the manual valve according to the work that had to do. However, in modern applications often have varying loads, this is not practical, because the adjustment of the manual valve have to be changed according to the load variation.The five main types of pressure relief devices that are used today in various stages of cooling are:1. Automatic expansion valve2. Thermostatic expansion valve3. Capillary4. Low side float5. High side float.All of them are used to reduce the pressure of liquid coolant, and in some cases to control the flow.The manual valve, of course, is not suitable for automatic operation, because any variation in needs requires manual adjustment, for it was reached by the automatic valve.Automatic expansion valve, or constant pressure, shown in Figure R6-33, maintains a constant pressure in the cooling coil while the compressor. In this expansion valve diaphragm type constant pressure, evaporator pressure effects movement of the diaphragm, which is fixed to the needle assembly.Stability is necessary in the coolant flow and evaporation to work correctly in the expansion valve of constant pressure.