EXPANSION VALVES &
Question answers make the concept
absolutely clear. The basic principles
become easily applied to practical
List the various types of expansion devices with their practical applications.
Various types of expansion devices are
This tube is very small diameter ( fraction of a mm) tube with no moving parts. Thus, is extremely simple and least expensive: Used in small refrigeration units like
Window air conditioners,
Deep freezers etc.
2. Automatic Expansion Valve (A.E.V.)
Used in plants where cooling load is almost constant like in ice plants.
These expansion valves are not suitable where cooling loads vary. Because these increase the flow of refrigerant when the heat load on the evaporator is less. Further decrease the flow of refrigerant through the evaporator when the heat load on the evaporator is high. It is, thus, contradictory. These are very less in use.
3.Thermostatic Expansion Valve (T.E.V.)
Maintains a constant degree of super-heat at the outlet of the evaporator. It is under all conditions of heat loads on the evaporator. Flow decreases when the load on the evaporator is less and vice versa. T.E.V. is most common expansion valve.
4. Low Side Float Valve
This float valve is located in the evaporator itself. It is cheap and simple. Used only in big industrial units.
5. High Side Float Valve
That the float valve is located in the condenser itself. It is also cheap and simple. Used only in big industrial units.
CONTROLS IN REFRIGERATION AND AIR CONDITIONING
NEED: CONTROLS MAKE THE OPERATION OF A REFRIGERATING MACHINE FULLY AUTOMATIC.
Small cooling units are for a single application. It is to be fully automatic. Most of the usefulness of a domestic/commercial system would be lost if the operation is not fully automatic. The larger units are for a single/multi application. The single application units are to be fully automatic . Multi application unit is not fully automatic. It has different requirements at different times. There is always a technician available to take care.
VARIOUS CONTROLS FOR AUTOMATIC OPERATION
(i) Liquid refrigerant flow controls
(ii) On and off motor and compressor controls
(iii) Condensing medium flow controls
(iv) Safety controls
(v) Controls for special applications