The refrigeration expansion valve, also called the thermostatic expansion valve, is one of the 4 major parts of the refrigeration system(the rest are the compressor, evaporator, and condenser).

The expansion valve is now widely used for Freon and Ammonia refrigeration systems as the throttling mechanism.

The thermostatic expansion valve is a flow adjustment mechanism; it is composed of a signal collector, a signal sender, and a flow regulator.

It can automatically adjust the refrigerant flow to enter the evaporator according to two factors: one is the temperature of the refrigerant that flows out from the evaporator, and the other is the pressure signal.

The thermostatic expansion valve is installed between the liquid receiver and the evaporator to turn the high-pressure and high-temperature liquid refrigerant into low-pressure wet steam by expansion valve throttling, and the low-pressure wet steam will absorb heat when evaporating, so that it will achieve the cooling function.

Internal balance is a pressure balancing method by transferring the outlet pressure of the expansion valve to the power actuator through the internal channel;

External balance is a pressure balance method by transferring the outlet pressure of the expansion valve to the actuator of the valve through the external channel.

It is used to compensate for the pressure drop effect of refrigerant flowing through the distributor and evaporator.

The internal balance expansion valve has a channel in the valve,  to transfer the evaporation pressure P2 at the export of the thermal expansion valve to the diaphragm’s lower cavity and produce a balancing force.

In the externally balanced thermal expansion valve system, the external balance thermal expansion valve transmits the evaporator’s outlet pressure P3, to the lower cavity of the powerhead through the external balance pipe to generate a balance force F2.

Force analysis of valve needle displacement when thermal expansion valve automatically adjusts the flow

Thrust balanced formula

F1=F2+F3-F4+F5

When F1>F2+F3-F4+F5, the superheat will increase, the valve needle will move down, and the valve opening will increase the flow rate.

When F1>F2+F3-F4+F5, the superheat will decrease, and the valve needle will move upward, then close the valve, on this ground, the liquid flow will decrease.

The internal balance expansion valve has a channel to transfer the evaporation Ejection force P2 at the thermal expansion valve export to the lower cavity of the expansion valve diaphragm to generate a balancing force.

In the Thrust Balance Formula:

F1—The upper diaphragm cavity in the powerhead and the temperature sensor have the ejection force between them, and this pressure will cause a thrust.

F2—The evaporating pressure from the expansion valve P2 part will produce a force in the lower cavity of the diaphragm.

The force generated by the external balance expansion valve to the balance pipe to transfer the evaporation pressure of the P3 evaporator outlet to the lower cavity of the diaphragm

F3—The lower part of the valve needle adjusts the preload of the spring.

F4—The thrust generated by the evaporation pressure P2 on the valve needle.

F5—The thrust produced by the inlet pressure P1 on the valve needle.

P1—The pressure when the refrigerant enters the valve port (high pressure)

P2—Evaporating pressure at valve outlet (low pressure)

P3—The evaporator outlet, which is the external pipe, produces the evaporation pressure (low pressure)

S—cross-sectional area of the valve port

F4=P2.S

F5=P1.S

The two thrusts of F4 and F5 are negligible in systems with relatively small cooling capacity, small load changes in the system of the expansion valve, and relatively stable systems.

But the expansion valve with a large cooling capacity (large valve port cross-sectional area) has a large load change and unstable operation. For the system, F4 and F5 affect the opening superheat of the valve.

Miracle, as a trusted refrigeration valve manufacturer and supplier, designs the refrigeration expansion valve.

So that we manage the flow of the refrigerant into the evaporator and maximize its efficiency.

This expansion valve is generally located close to the inlet of the evaporator.

Some main components of refrigeration expansion valves are a sensing bulb filled with refrigerant located in the outlet of an evaporator and connected with a powerhead.

There is a diaphragm that separates the pressure.

After that, there is also an adjustable pressure spring on the bottom of the diaphragm.

The stem rotates clockwise to decrease and counterclockwise to increase the pressure of this spring.

The condensed high-pressure saturated liquid refrigerant enters the expansion valve, passes through the throttling of the valve port, and flows out from the expansion valve outlet.

So how does the evaporator valve control the refrigerant entering the evaporator?

Once the pressure at the top of the powerhead reaches a certain point, the diaphragm is pushed down.

So the expansion valve opens wider, and more liquid refrigerant enters the evaporator.

Absorbs the heat from the surrounding environment to achieve cooling.

In the same way, when the pressure above the diaphragm decreases to a certain point, the valve retracts the refrigerant flow is reduced.

The main function of the expansion valve is to adjust the high and low pressure in the system, and it is a component for gas and liquid conversion.

Miracle expansion valves can be used in the following systems：

• Refrigeration System
• Air Conditioner System
•  HVAC System
• Transportation Refrigeration Systems
• Rail Transit Systems
• Refrigerator, Freezer, and Dehumidifier Systems
• Cold Storage Systems
• Heat Pump Systems
• Energy Storage Systems
• Thermal Management Systems

Install the expansion valve temperature sensor at the outlet of the evaporator.

It is necessary to connect the balance pipe to the intake pipe and make sure the position is near the expansion valve bulb’s back end.

Install the expansion valve body to the liquid pipeline where is the entrance of the evaporator.

Please make sure to install the thermal expansion valve near the evaporator, and not tilt or install it upside down.

Since when the thermal expansion valve work, it has to rely on the temperature sensed according to the temperature sensing bulb.

If the temperature sensing system’s sensitivity is low, the time lag of the transmission signal is large.

It will be easy to cause and fluctuations in the liquid supply. So, the installation is very important.

The thermal expansion valve has two types: internal type and external type expansion valve according to the pressure balance structure.

Please pay attention to the following points for how to install an expansion valve:

Pay attention to the flow direction.

Install the expansion valve body vertically.

The temperature sensing bag should be placed horizontally or head down, and be wrapped with heat-insulating material.

The interface of the outer tube at the outlet of the evaporator should be close to the temperature sensing ball.

When welding the interface, use wet cotton yarn to wrap the expansion valve up to avoid overheating or low temperature, etc., and adjust the evaporation temperature after everything is installed.

Make sure to install the expansion valve’s temperature-sensing bulb on the horizontal pipe.

If the actual situation does not allowed to do that, then it has to ensure the capillary tube points upward

If a vertical pipeline and the capillary point downwards, it may cause the refrigerant to migrate to the thermostatic element, which will cause the expansion valve to malfunction.

When you confirm the expansion valve bulb installation position, you should refer to the suction pipe diameter, which is very important;

It is not correct to install the expansion valve temperature sensor on the end of the evaporator pipe, or you will get a false signal from the compressor oil return.

Make sure to install the expansion valve temperature sensor not close to large components;

The installation position of the expansion valve temperature sensing bulb cannot be at the back end of the heat exchanger;

Do not install the expansion valve temperature sensor in a place where the outside heat/cold area is in contact;

If there is heating flow in the environment of the expansion valve bulb, then it’s better to do the heat insulation treatment on the bulb;

The expansion valve temperature sensor should be installed on the horizontal pipeline.

The Steps to install the temperature sensor with lashing tape.

Step 1: Pass the lashing tape through the notch.

Step 2: Put the expansion valve bulb between the lashing tape and the capillary tube, and tighten the lashing tape.

Step 3: When the correct bend mark enters the groove, bend the tie so that the bolt can pass.

Step 4: Tighten the bolts and fix the expansion valve bulb.

Step 5: Wrap the excess lashing tape.

Principle and Debugging of Expansion Valve Superheat

Superheat Setting:

For getting the best system performance, you should adjust the expansion valve superheat;

The method to lower the superheat is to rotate the rotary rod counterclockwise step by step until a fluctuation is observed;

A difference of ±0.5℃ is not regarded as a fluctuation;

Superheat Measurement:

The superheat degree should refer to the heat degree which is increased on the saturated suction temperature;

Superheat degree=(the suction temperature)-(the saturation temperature caused by the suction pressure);

The thermal expansion valve superheat cannot be less than 6-8℃;

Mostly, you can measure the back-end temperature of the distributor by estimating the evaporation temperature, because the distributor end temperature is the same as the wet suction temperature.

Check what is the degree of superheat for more details.

You should make sure the bent straight pipe’s length is more than 7 times the pipe diameter, otherwise, uneven liquid dispensing will be caused.

Once the system uses a liquid distributor, an externally balanced thermal expansion valve must be used;

The pipe diameter and length of all distributors must be the same.

Otherwise, it is easy to cause uneven liquid distribution.

For valves with replaceable orifices, the refrigerant loss of the power unit is easy to check.

Close the orifice or the orifice assembly to the diaphragm and check the orifice spring’s elasticity.

If the spring is not elastic, the refrigerant is gone.

The elasticity indicates that there is still refrigerant in the power element.

For more refrigerant leak inspection methods, please check how to detect refrigerant gas leaks.

Ensure that the expansion valve temperature sensor and the suction pipe have a good condition, which ensures the sensor has good heat insulation.

When adjusting the superheat, please rotate about a full circle, and then wait five minutes for the input to take effect.

If the valve is unstable, increase the superheat slowly until the valve stops vibrating.

The expansion valve opening degree in the cold storage refrigeration system has a great relationship with the superheat degree.

When the superheat is large, the opening degree is also large; when the degree of superheat is small, the opening degree is also small.

When the degree of superheat decreases to a certain value, the expansion valve just closes at the moment, which is the degree of superheat at which the expansion valve opens.

Here we collected some common failure situations from our own use and our customers’ use; they are all small faults, and you can deal with them by yourself without panic and protect the expansion valve and refrigeration system.

At the same time, increase your skills for dealing with expansion valves to ensure their perfect performance. If there is any analysis that is not clear to you, please contact us for further explanation.