Refrigerator Expansions Valves: Functions and Types

The expansion valve is usually connected between the receiver and the evaporator.

A receiver is a vessel that holds the liquid refrigerant from the condenser before it supplies it to the evaporator via the expansion valve.

The expansion valve, just like the other parts of a refrigeration system, it’s very important in completing the refrigeration cycle.

You can read the article below if you want to know how the refrigeration system works.

You might like this: Vapour Absorption Refrigeration System: Working Principle

For you to understand the significance of an expansion valve in a refrigeration system, I will have to share its function.

Without wasting time, let me give you what you need to know about refrigeration expansion valves.

Functions of expansion valves;

1. Expanding liquid refrigerant.

This is one of the functions of expansion valves. Expansion valves expand liquid refrigerant that comes from the condenser under high pressure.

The liquid refrigerant leaves the condenser and a high temperature and pressure.

The condenser only cools the liquid refrigerant partially, and this means it will still be under high temperature even when it leaves the condenser.

It’s the function of the expansion valve to expand the liquid refrigerant to give it room to cool before it’s taken to the evaporator.

For the refrigeration system to work effectively the liquid refrigerant has to be at the temperature that it was before it left the evaporator.

The refrigerant is in low temperatures as possible will enable it to absorb heat effectively thus making the refrigeration system efficient.

2. Controls the flow of refrigerant to the evaporator.

It’s the function of the expansion valve to control the flow of liquid refrigerant into the evaporator.

The liquid refrigerant wouldn’t just enter the evaporator like when you are pouring water into a bottle.

It has to enter the evaporator under a controllable amount.

The rate of the liquid refrigerant entering the evaporator depends on the load that it can handle.

That is why we need the expansion valve to control the flow of refrigerant into the evaporator.

An uncontrolled flow of refrigerant into the evaporator would end up decreasing the efficiency of the refrigeration system.

3. Reduces the pressure of the refrigerant entering the evaporator.

The expansion valves contain the desired pressure between the high-pressure side and the low-pressure side of the refrigeration cycle.

It’s the function of the expansion valve to ensure that the liquid refrigerant is in the correct pressure for to vaporize into the evaporator.

The liquid refrigerant will only vaporize into the evaporator under the pressures that the evaporator was designed to handle.

The whole process of controlling the amount of liquid refrigerant as it flows to the evaporator is to ensure that the pressure that the liquid refrigerant had is significantly reduced.

This throttling process will reduce the velocity at which the refrigerant flows with from the condenser to the evaporator.

For the refrigeration process to take place, the refrigerant has to be under low pressure (pressure that was designed for the evaporator) to be able to absorb heat from the body being cooled.

And that will only happen if the refrigerant will be under the desired pressure.

Types of expansion valves;

1. Capillary tube.

It’s a small tube which is connected from the condenser to the evaporator.

This tube is usually coiled and it has a very small diameter.

The capillary tube creates suction to draw the liquid refrigerant from the condenser due to the friction between the refrigerant and the surfaces of the capillary tube walls.

The refrigerant is cooled as it moves along the capillary tube.

Also, as the liquid refrigerant flows under a high velocity within the capillary tube, its pressure is reduced when it reaches the evaporator.

The capillary tube shouldn’t be too wide or too narrow, it being too wide will end up flooding the evaporator and being too narrow will starve the evaporator.

In most domestic refrigerators, the capillary tube is the most commonly used because of the following advantages;

It has a lower initial cost compared to the other expansion valves.
It does not permit leakages because its ends are soldered.

It eliminated the use of service valves in refrigeration systems.
It also permits the use of starting torque because the tube doesn’t close.
It rarely needs maintenance because it doesn’t have any moving parts.

The way the capillary tube is designed makes it very sensitive, if there is a single detail about it that is not correct it won’t work.

Also, when the thermostat is switched off, the refrigerant will be sucked into the evaporator, which will end up defrosting the food kept in the refrigerator.

When this happens, the compressor will end up overloading the motor too.

The refrigerators that use capillary tubes usually handle a very small amount of refrigerant so that when it’s switched off only a small amount will enter the evaporator.

2. Hand expansion valve.

From its name, we all know that this type of expansion valve is operated manually.

This type of expansion valve is used in areas where a constant cooling capacity is needed for a long period.

It operates under constant loads. If there is a change that needs to be done to the cooling capacity, an operator will just adjust it by hand and that is done.

This type of expansion valve is used in ice-making plants and large cold storage areas.

It’s not used in areas where variations of temperatures are needed.

3. Thermostatic expansion valve/constant superheat valve.

This type of expansion valve maintains superheat temperature of the refrigerants at the end of the evaporator by having a bulb with a refrigerant in it.

The opening and closing of the valve depends on the forces following forces;

Spring pressure.
Evaporator press.
Bulb press

The bulb press and the superheat temperature reduce and lower the pressure transmitted to the diaphragm thus it moves upwards, closing the valve thus controlling the flow of the refrigerant entering the evaporator until the desired pressure is achieved.

4. Externally equalized.

This is an ordinary thermostatic expansion valve that assumes that the pressure at the outlet of the evaporator is equal to the input.

This is definitely one of the rules that allows it to only receive a refrigerant back to the evaporator which has a pressure that is designed for the evaporator.

If the pressure of the refrigerant entering the evaporator is not the same as that of the outlet then it won’t enter.

This type of expansion valve is ineffective because the friction between the refrigerant and the evaporator walls results in a pressure drop.

When this happens, the pressure in the outlet won’t be equal to the one inlet.

To fix this issue, externally equalized is used.

5. Constant pressure expansion valve.

This valve works by maintaining a constant pressure in the evaporator as its name suggests.

The opening and closing of the valve depending on the evaporator press and the diaphragm movement.

There is a spring that exerts pressure on the diaphragm to make it move up and down.

Refrigerant expands at the top and exerts pressure on the diaphragm, which causes it to move downwards, opening the valve and allowing refrigerant to enter the valve until the evaporator press is achieved.

The evaporator press, moves the diaphragm upwards thus reducing the opening of the valve, which ends up reducing the flow of refrigerant to the evaporator until the desired pressure is achieved.

If the pressure is reduced to the required rate the press will be achieved and the process will be repeated again.

This type of expansion valve is mostly used in large refrigerant plants.

Final thoughts.

These are the types of expansion valves used in refrigeration systems.

They operate differently but their functions are similar.

If you have any questions about this topic don’t be afraid to leave your question.

Thanks for reading and I will see you in my next article.