Throttle valve (Expansion Valve) is the device that regulates refrigerant flow before the evaporator while dropping the pressure from the high side (condensing pressure) to the low side (evaporating pressure). It is one of the four essential components in the refrigeration cycle, alongside the compressor, condenser and evaporator.
The expansion valve determines how much refrigerant enters the evaporator. Too much, and liquid returns to the compressor and damages it. Too little, and cooling capacity falls and the store never reaches the required temperature. This article analyses the construction, types, operating principle, selection criteria and maintenance of expansion valves in industrial refrigeration systems. Tan Long has compiled it from more than 20 years of experience designing and installing cold stores and freezing tunnels in Vietnam.
How is an expansion valve constructed?
Technically speaking, throttle valve is built from specialised parts to ensure pressure reduction and refrigerant metering happen accurately. A standard throttle valve comprises the following key components:
- Valve body: This is the main load-bearing part, usually made of high-quality brass or stainless steel for corrosion resistance. The valve body withstands high operating pressures, commonly 2.5 MPa to 4.5 MPa (362 to 652 psi), suiting the standards of today's industrial cold storage systems.
- Orifice: This is the “heart” of the device, where the abrupt pressure drop turns high-pressure liquid refrigerant into a low-pressure liquid-vapour mixture. The orifice area typically ranges from 0.4 mm to 5 mm depending on the system's cooling capacity. On thermostatic expansion valves (TXV) or electronic expansion valves (EEV), this size varies flexibly with the actual cooling load. On a capillary tube, by contrast, the area is fixed and cannot be adjusted.
- Adjustment mechanism: This part determines how intelligent and responsive the valve is. There are three common adjustment mechanisms today:
- Thermal sensing diaphragm: used in thermostatic valves to modulate based on superheat.
- Electronic stepper motor: used in EEVs to control flow extremely accurately from an electrical signal.
- Manual adjusting screw: used in manual valves for simple systems.
Understanding the construction of an throttle valve helps Tan Long's engineers calculate and select the most suitable equipment when delivering cold storage installation for customers, keeping the system stable and optimising electricity costs.
If you are looking for replacement components or need deeper advice on the specifications of refrigeration compressor combined with a modern expansion arrangement, contact our technical team now.
How does an expansion valve work?
Technically, an throttle valve works on the principle of pressure reduction as flow passes through a narrow orifice, creating a very large pressure difference across the device. High-pressure liquid refrigerant from the condenser enters the valve inlet. Passing through the orifice, its pressure is pulled down to industrial refrigeration.
The full operating sequence of an throttle valve is controlled by Tan Long's engineers through four consecutive technical steps:
- Step 1: Liquid refrigerant arrives at the valve from the condenser at high pressure, typically 1.2 MPa to 2.0 MPa (174–290 psi) with R404A or R22.
- Step 2: The refrigerant passes through the narrow orifice. Flow velocity rises sharply and pressure drops abruptly (the Joule-Thomson effect).
- Step 3: Pressure after the valve falls to around 0.3–0.5 MPa (43–72 psi), corresponding to a boiling point of minus 40°C to minus 15°C depending on the refrigerant.
- Step 4: The refrigerant evaporates in the cooling coil, absorbing heat from the air or the product to be cooled, completing the refrigeration cycle.
On the thermostatic type (TXV), a sensing bulb throttle valve is fitted at the evaporator outlet to measure the superheat of the suction vapour. When it detects rising superheat (vapour too dry), the valve's adjustment mechanism opens further to add refrigerant. Conversely, if superheat falls (vapour still wet, with a risk of liquid returning to the refrigeration compressor), the valve closes down automatically to protect the equipment.
The standard superheat Tan Long always recommends holding for cold storage systems is 5K to 8K, i.e. a temperature difference of 5°C to 8°C above the actual boiling point.
What types of expansion valve are used in refrigeration systems?
Industrial refrigeration systems use four main expansion valve types, distinguished by control mechanism and degree of automation.
Capillary tube
A capillary tube is a length of copper tube with an internal bore of 0.4 mm to 2 mm and a length of 0.5 m to 5 m (1.6 ft to 16.4 ft), coiled to save space. Its operation is entirely passive: refrigerant flow depends on the fixed pressure difference between the condenser and the evaporator.
Capillary tubes suit small domestic equipment below 5 kW (17,000 BTU/h): household refrigerators and mini split air conditioners. The advantages are no moving parts, no maintenance and low cost. The limitation is that they cannot adjust when the cooling load changes, and they block easily if the system contains contaminants.
Thermostatic expansion valve (TXV)
The TXV is the most common valve in industrial refrigeration systems from 5 kW to 200 kW (17,000 BTU/h to 682,000 BTU/h). It adjusts flow automatically based on the superheat measured at the compressor suction, using a thermal sensing bulb and a pressure balancing diaphragm.
TXVs come in two configurations: internal equaliser and external equaliser. The external equaliser suits evaporators with a pressure drop above 0.02 MPa (2.9 psi). Danfoss offers TXVs from model T2 to T5 with capacities from 1 kW to 30 kW (3,400–102,000 BTU/h) for each refrigerant: R22, R404A,
Electronic expansion valve (EEV)
The EEV uses a stepper motor or solenoid valve together with a central controller (a PLC or dedicated controller) to adjust valve opening in real time. Adjustment resolution reaches 0.1% of maximum flow, 10 to 50 times faster than a TXV.
The EEV holds standard superheat at 8.3K, sensing a minimum pressure differential of 1 bar (14.5 psi) to ensure enough liquid reaches the evaporator. Systems fitted with EEVs consume 10% to 25% less electricity than TXV systems under the same varying load conditions, according to data from Danfoss and Emerson Climate Technologies.
The EEV is mandatory for: chillers above 100 kW (341,000 BTU/h), automated cold stores integrated with SCADA/PLC, multi-coil VRV/VRF systems, and cold rooms requiring temperature control within ±0.5°C.
Manual expansion valve
A manual valve adjusts flow by turning the needle by hand. The orifice area varies from zero to maximum according to the number of turns. It does not self-adjust to the cooling load, so it suits only test rigs, steady-load systems, or use as a bypass valve in an auxiliary circuit.
Comparing the common expansion valve types in refrigeration
To optimise performance for a freezing system or cold storage installation, choosing the right metering device is essential. The comparison below gives you an overview of the throttle valve Currently:
| Comparison criteria | Capillary tube | Thermostatic expansion valve (TXV) | Electronic expansion valve (EEV) | Manual expansion valve |
| Suitable capacity | Below 5 kW | 5 to 200 kW | Above 50 kW | Any capacity (auxiliary circuits) |
| Self-adjusting capability | None | By superheat | By electronic signal | Manual adjustment |
| Operating accuracy | Low | Medium | Very high | Depends on the operator |
| Investment costs | Low | Medium | High | Low |
| Maintenance requirement | Low | Medium | High | Low |
| Energy saving | Least | Good | Best | Least |
| Typical applications | Refrigerators, residential air conditioning | Industrial cold storage | Chiller systems, cold stores | Test rigs |
If you are unsure about the specifications or need help calculating the optimal throttle valve for your project, contact Tan Long's engineering team for a survey and detailed advice.
How do you choose the right expansion valve for a refrigeration system?
Calculating and selecting the right throttle valve is decisive for the energy efficiency and durability of the whole machine set. At Tan Long we always base equipment selection on the following five core technical criteria:
- Cooling capacity and refrigerant type: Each line throttle valve an is built for a specific capacity range and is compatible only with a certain group of refrigerants. Using the wrong refrigerant can block the valve port, destabilise the temperature and shorten system life. For example, the Danfoss TE2 TXV is optimised specifically for R404A or R507 and must never be used with R41
- Operating pressure and temperature: the technician must check the equipment's maximum working pressure (MWP) carefully. For systems using R410A, with pressures up to 4.2 MPa (609 psi), you must throttle valve with an MWP of at least 4.5 MPa (652 psi) for technical safety.
- Degree of automation: If your industrial cold storage system integrates SCADA monitoring technology or PLC control, an electronic expansion valve (EEV) is mandatory to receive signals from the central controller. Conversely, standalone systems need only a TXV to optimise investment cost.
- Evaporator pressure balance: On industrial refrigeration with several parallel circuits or long pipe runs, pressure losses are usually high. When the loss exceeds 0.02 MPa (2.9 psi), you must use an throttle valve of the external equaliser type so the valve can read the actual evaporating pressure at the coil outlet accurately.
- Brand and spare parts: Favour brands with genuine distribution and service networks in Vietnam, such as Danfoss, Sporlan, ALCO Controls or Emerson. Choosing major brands makes it easy to look up detailed capacity tables and ensures replacement parts are always available refrigeration compressor.
The optimal installation position for an expansion valve
In a standard refrigeration cycle, the exact installation position of the metering device determines the heat rejection capability and efficiency of the refrigeration compressor. Below is detailed technical guidance from Tan Long's engineering team:
- General position: Device throttle valve the is always installed between the condenser and the evaporator, specifically on the liquid line. This position is the critical boundary separating the high-pressure and low-pressure sides of the system.
- Notes for thermostatic expansion valves (TXV): On this type, the sensing bulb must be fixed precisely at the evaporator suction line outlet, 15 cm to 30 cm (6 to 12 inches) from the coil flange. The bulb must contact the pipe wall directly, preferably at the 4 o'clock or 8 o'clock position for the most accurate suction vapour temperature reading. throttle valve reading the wrong value, losing control of refrigerant flow and adversely affecting the industrial refrigeration.
- Notes for electronic expansion valves (EEV): In modern systems using SCADA and PLC technology, this throttle valve connects to pressure and temperature sensors through signal cables running back to the central controller. The cabling must be protected in specialist moisture-proof conduit, which matters especially when carrying out cold storage construction with deep sub-zero ranges below minus 20 degrees C.
What faults are common with expansion valves?
An expansion valve working incorrectly shows up as four typical faults.
- Valve plugging: contaminants, oil residue or moisture freezing at the orifice reduce or completely block the refrigerant flow. Symptoms: abnormally low suction pressure, store failing to reach temperature. Remedy: fit a filter drier properly and replace it every 6 to 12 months.
- Flooding: the valve opens too far and liquid refrigerant returns to the compressor, damaging the pistons and valves. Symptoms: sweating or frost on the suction line, knocking from the compressor. Main causes: the TXV sensing bulb wrongly positioned or making poor contact, or the superheat setting
- Stuck closed: the valve will not open because contaminants have jammed the needle. Symptoms: suction pressure falling to near 0 bar, compressor running but producing no cooling. The valve must be removed, cleaned or replaced.
- Incorrect superheat: a valve not set to the right superheat leaves the system both inefficient and unable to protect the compressor. On a TXV, check and adjust the adjusting spring. On an EEV, check the setpoint on the controller and calibrate the sensors.
Expansion valve maintenance guide for industrial refrigeration systems
Maintaining the throttle valve at least every 6 months is key to sustaining energy efficiency and preventing faults in the refrigeration compressor. From real experience on major projects such as the NECS and AJ Total cold stores, the inspection should focus on the following three key technical items:
- Operating pressure analysis: the technician checks the compressor's suction and discharge pressures while the system is running and compares them with the original design values. If suction pressure is 0.05 MPa below design throttle valve is short of flow. Conversely, high suction pressure together with frost on the suction line shows the valve is overfeeding refrigerant into the industrial refrigeration.
- Sensing bulb inspection (TXV): On mechanical valves, ensure the bulb clamp is always secure and in full contact around the suction pipe. In particular, the bulb's insulation must be intact. If the insulation is damaged, the bulb reads the ambient temperature instead of the actual refrigerant temperature, and control of the whole device is lost throttle valve.
- Filter drier inspection: This is an important step in Tan Long's maintenance and warranty procedure. Measure the temperature difference before and after the filter. If the difference exceeds 2 degrees C (3.6 degrees F) or moisture appears on the filter shell, the filter is saturated and must be replaced immediately to avoid blocking the throttle valve.
How expansion valves differ between cold stores and industrial freezing tunnels
Selecting and designing the throttle valve depends entirely on the intended use and the system's operating temperature range. Below is a detailed analysis of the difference between storage rooms and deep-freeze systems:
- For storage cold rooms: In systems at above-zero temperatures from 0 to 10 degrees C, R404A or R134a is normally used with evaporating pressure held at 0.3 MPa to 0.5 MPa (43 to 72 psi). In this segment, an internally equalised thermostatic throttle valve (TXV) with a capacity range of 5 kW to 50 kW (17,000 to 170,000 BTU/h) is the common choice, giving stable performance for the heat exchangers.
- For IQF freezing tunnels and industrial freezing cabinets: The characteristic of an IQF conveyor or air blast freezer is a requirement for extremely low evaporating temperatures, down to minus 45 degrees C, which can bring evaporating pressure below 0.1 MPa (14.5 psi). Under these severe conditions the system must use an externally equalised thermostatic throttle valve , or ideally an electronic throttle valve (EEV). The valve materials must meet high technical standards to withstand continuous deep sub-zero temperatures without becoming brittle or seizing the metering mechanism.
- Energy optimisation solution: For cold storage construction or freezing tunnels with a cooling load that varies continuously by production shift, applying an electronic throttle valve EEV together with a PLC control cabinet system is the leading solution. This combination optimises the refrigerant fed to the coil, saving considerable electricity and holding temperature stable throughout the food preservation cycle.
How does Tan Long advise on and supply expansion valves?
Tan Long advises on expansion valve selection as part of an overall refrigeration system solution, not as an isolated component. The process has three steps: gathering system parameters (capacity, refrigerant, evaporating temperature), calculating the valve capacity for actual operating conditions, and selecting a suitable model from Danfoss, Sporlan or ALCO.
With more than 20 years of experience designing and installing industrial refrigeration systems in Vietnam, Tan Long has delivered many cold storage projects from 100 tons to several thousand tons of goods, in which expansion valve selection is a technical step calculated in detail from the design stage onwards. Contact Tan Long's technical team for advice on the right expansion valve specification for your system.
Tan Long provides comprehensive industrial refrigeration solutions: from design and equipment selection to installation and maintenance. Contact us for detailed technical advice on expansion valves and the other equipment in your refrigeration system.
Frequently asked questions about expansion valves
How does an expansion valve differ from a capillary tube?
“Expansion valve” is the general name for every device that reduces refrigerant pressure, of which the capillary tube is the simplest, with a fixed bore. The thermostatic expansion valve (TXV) and electronic expansion valve (EEV) have flexible adjustment mechanisms that vary flow automatically with the actual cooling load.
Why does an expansion valve freeze up?
An expansion valve freezes up because moisture has entered the system. As the moisture passes through the orifice, the abrupt temperature drop freezes it and blocks the refrigerant flow. The remedy is to evacuate the system under vacuum and fit a new filter drier.
How should an expansion valve be chosen for an R410A system?
R410A operates at pressures about 60% higher than R22. An expansion valve for R410A must have a maximum working pressure (MWP) of at least 4.5 MPa (652 psi) and be designed specifically for that refrigerant. A valve designed for R22 cannot be used with R410A.
Do electronic expansion valves need maintenance?
An EEV needs periodic checks of its electrical side: sensor wiring connections, signal cables and the setpoint on the controller. The mechanical part of an EEV fails less often than a TXV because there is no mechanical sensing bulb. However, the stepper motor can fail after years of continuous operation in a humid environment, so an annual check is needed.
Frequently asked questions about expansion valves
What is a throttle valve?
An expansion valve is the device that drops liquid refrigerant pressure from the high side to the low side before the evaporator, while metering the refrigerant supplied to the evaporator according to the actual cooling load.
What types of expansion valve are there?
The common types are the capillary tube, the manual expansion valve, the thermostatic expansion valve (TXV) in internally and externally equalised versions, and the electronic expansion valve (EEV) controlled by a signal from a controller.
How do thermostatic and electronic expansion valves differ?
The thermostatic valve meters by superheat sensed through a bulb; it is low in cost and needs no power supply. The electronic valve meters more accurately from sensor signals, allowing lower condensing pressure and energy savings, but requires a controller.
Where is the expansion valve installed?
Fitted on the liquid line immediately before the evaporator. On an externally equalised valve, the equaliser line and the sensing bulb must be fitted in the correct positions on the suction line leaving the evaporator for it to work accurately.
On what criteria is an expansion valve chosen?
The refrigerant type, the evaporator's cooling capacity, the design evaporating temperature and the pressure drop across the valve. Choosing a valve that is too large causes liquid to return to the compressor; too small leaves the evaporator short of refrigerant and unable to reach temperature.
Related pages
- Solenoid Valves in Refrigeration Systems: Classification and How They Work
- How to adjust the cold storage throttle valve accurately and effectively
- Principles and procedures for standard refrigeration system gas charging
- What are refrigerants? Concept, classification, and applications.
- turnkey NH3 refrigeration systems
Doanh Nghiệp Đang Cần Khảo Sát, Nâng Cấp Hoặc Thiết Kế Mới Hệ Thống Lạnh Công Nghiệp?
Đội ngũ kỹ sư Cơ Điện Lạnh Tân Long với hơn 18 năm kinh nghiệm thực chiến chỉ đạo hơn 29 đại dự án quốc gia, cam kết tư vấn tính toán phụ tải nhiệt chuẩn xác, tối ưu hóa hệ số hiệu suất COP, chuyển dịch môi chất tự nhiên NH3/CO2 và tiết kiệm 20–30% chi phí điện năng vận hành.
Kỹ sư Nguyễn Toàn Thịnh (Giám đốc Kỹ thuật)
Hơn 18 năm kinh nghiệm thực chiến chỉ đạo tư vấn thiết kế và thi công hệ thống lạnh công nghiệp nặng, kho tự động ASRS và cấp đông IQF qua hơn 29 đại dự án quốc gia.
