Flake Ice Machines | Refrigeration System |
Expansion Valve
The expansion valve meters the flow of refrigerant into the evaporator, changing its state from a high pressure liquid to a low pressure liquid. This drop in pressure causes the refrigerant to cool. The cooled refrigerant absorbs heat from the water in
the evaporator.
The flow of refrigerant into the evaporator is controlled by the temperature at the outlet of the evaporator. The expansion valve bulb, which is mounted to the top of the suction line, senses the evaporator outlet temperature causing the valve to open or close. As ice forms in the evaporator the temperature drops and the flow of refrigerant into the evaporator decreases.
The evaporator should become completely flooded (filled with liquid refrigerant). A completely flooded evaporator will form ice in the entire
evaporator. A starved evaporator (not enough liquid refrigerant) will have poor or no ice formation in the evaporator, and the tube exiting the evaporator will not frost.
The tubes in and out of the evaporator should frost within approximately 5 minutes from the time the compressor starts. An expansion valve that is restricted or not opening properly will starve the evaporator causing the suction pressure to be lower than normal. Wet ice or slow production will result.
A low refrigerant charge will also starve the evaporator and cause low suction and discharge pressure. It is important that the refrigerant charge be correct before diagnosing the valve. If not sure of the amount of charge in the system, the refrigerant should be recovered and the correct charge weighed in. If the evaporator is starved but the suction pressure is higher than normal, the compressor may be inefficient.
If the expansion valve sticks open or if the bulb is not making contact with the suction line, the flow of refrigerant into the evaporator will be too great and liquid refrigerant will flood back to the compressor. The evaporator temperature will be higher than normal resulting in wet ice and slow production.
A dual evaporator machine has one expansion valve for each evaporator. If one valve sticks open and the other is operating normally, the suction pressure will be higher than normal and the evaporator with the defective expansion valve will produce less ice than the side with the good valve. If one expansion valve sticks closed and one is operating normally, the suction pressure will be normal or low and the evaporator with the defective expansion valve will produce less ice than the side with the good valve.
Important!
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