Solenoid Valves in Refrigeration Systems: Classification and How They Work

Structure of solenoid valve in refrigeration system

Solenoid valve in refrigeration system is designed with a precise structure to withstand high pressure and remain compatible with specific refrigerants. The device comprises 3 main assemblies, each with a distinct function in the overall mechanism.

Solenoid coil

The coil is the part that converts electrical energy into a magnetic field. Conductive wire (copper or aluminium) wound around a magnetic steel core forms an inductor. When 24VAC or 220VAC current flows, a magnetic field appears and pulls the plunger. Coil power consumption is typically 5W to 25W depending on valve size.

Plunger (core)

The plunger is the part that moves directly to open and close the valve port. Common materials are SUS304 or SUS316 stainless steel to resist corrosion in refrigerant environments. The plunger moves axially, with a stroke of typically 3 mm to 15 mm depending on working pressure and pipe diameter.

Valve body

The valve body houses the entire internal mechanism, with an inlet and outlet port for the fluid. The material determines refrigerant compatibility: brass for R22, R404A and R410A; stainless steel or grey cast iron for NH3 (ammonia) and CO₂. Surfaces in contact with the fluid are machined to a tolerance of 0.01 mm to guarantee absolute tightness.

Operating principle of solenoid valve in refrigeration system

Solenoid valve in refrigeration system operates on a basic electromagnetic principle: current through the coil generates a magnetic field, and the magnetic field produces the mechanical force that moves the plunger. Its operating cycle in design and installation refrigeration system proceeds through the following steps:

• Opening phase: When the coil receives an electrical signal from the temperature controller or the central SCADA control system, a magnetic field appears instantly around the steel plunger. This magnetic force is strong enough to overcome the return spring, pulling the plunger along its axis and opening the refrigerant flow path.
• Closing phase: As soon as the electrical signal is cut, the magnetic field disappears. The return spring immediately pushes the plunger back to its default position, closing the valve port. The whole closing action is extremely fast, typically 0.5 to 2 seconds, to keep the refrigeration cycle safe.

The opening/closing cycle of a Solenoid valve in refrigeration system can repeat millions of times over its product life. Service life is typically 3 million to 10 million operating cycles, depending on the brand — reputable names include Danfoss, Castel and Parker.

On Tan Long's real projects, such as the freezing system for GN Food JSC or the NECS automated cold store, the PLC control cabinet calculates and sends the precise ON/OFF signal. Control of the Solenoid valve in refrigeration system is based on actual values for the temperature setpoint, system pressure and the operating status of the refrigeration compressor in order to optimise energy use and protect the equipment.

Why is a solenoid valve essential in a refrigeration system?

Solenoid valve in refrigeration system acts as an intelligent “gatekeeper”, fully resolving the 3 core problems that traditional mechanical valves cannot address in modern automated systems.

• Precise refrigerant flow control: The solenoid valve opens and closes exactly on the controller's command, holding the cold store temperature within ±0.5°C of setpoint. In frozen seafood stores requiring -18°C to -25°C (-0.4°F to -13°F), this accuracy directly affects food quality and safety.
• Full automation of the refrigeration cycle: When integrated with a PLC control system or a SCADA control panel, solenoid valves handle dozens of simultaneous open/close points with no operator intervention. A 5,000 m³ cold storage system may have 15 to 40 solenoid valves operating independently.
• System protection during faults: A normally closed (NC) solenoid valve automatically cuts the refrigerant flow on power loss, protecting the compressor and evaporator from liquid flooding. Tan Long always specifies NC valves on the liquid feed line into the evaporator on every cold store it installs, including the NH3 systems at the FRESCOL Tuna Vietnam seafood plant (Nghe An) and Kyokuyo Vina Foods.

6 common solenoid valve types in refrigeration systems

The industrial refrigeration equipment market in Vietnam currently offers 6 main solenoid valve types. Depending on requirements for default state, body material or pipe connection method, a business can choose the right Solenoid valve in refrigeration system to optimise operating performance.

Normally closed solenoid valve (NC)

Solenoid valve in refrigeration system the normally closed (NC) type is closed when de-energised and only opens on an electrical signal from the controller. This is the most common device, accounting for around 70% of real applications.

Choose an NC valve where safety on power loss matters: the liquid feed line into the evaporator, the suction line back to the compressor on multi-evaporator systems, and flow control points in the cold store. NC valves stop refrigerant flooding into the compressor when the system stops suddenly.

Normally open solenoid valve (NO)

A normally open (NO) solenoid valve is open when de-energised and closes on an electrical signal. Its main application is in systems that must maintain flow during a power failure, such as the cooling water feed to the condenser or cooling tower.

NO valves account for around 30% of refrigeration applications. Never use an NO valve on the liquid feed line into the evaporator, because on power loss it opens fully, causing liquid flooding and destroying the compressor.

Brass solenoid valve

Brass solenoid valves are compatible with most common refrigerants: R22, R404A, R410A, R134a and R32. They are the standard choice for food cold stores, blast freezing tunnels, air blast freezers and commercial air conditioning systems. Brass conducts heat well and machines more precisely than stainless steel, at a lower cost

Limitation: brass is not compatible with NH3, because ammonia corrodes copper rapidly. Never use brass valves on NH3 systems under any conditions.

Stainless steel solenoid valve (SUS304/SUS316)

Stainless steel solenoid valves withstand highly corrosive environments such as NH3, CO₂, industrial chemicals and marine environments (high salinity). SUS316 is more durable than SUS304 in chloride environments, making it suitable for coastal seafood processing plants.

Every NH3 refrigeration system Tan Long installs uses SUS304 or SUS316 stainless steel solenoid valves, including the 12,000-ton cold storage system at the FRESCOL Tuna plant (Nghe An) and the IQF conveyor system for C.P. Vietnam (Binh Duong). Stainless steel valves cost 30% to 80% more than brass, but last 2 to 3 times longer in

Threaded connection solenoid valve

Threaded solenoid valves use BSP (British Standard Pipe) or NPT (National Pipe Thread) threads, common on pipe diameters from DN8 (1/4″) to DN40 (1-1/2″). They install quickly, need no welding and are easy to remove and replace. Their main applications are in residential and small commercial refrigeration systems and secondary control points

Check the tightening torque: 15-25 N·m for 1/2″ threads, 25-40 N·m for 1″ threads. Over-tightening cracks the thread or deforms a brass valve body.

Flanged connection solenoid valve

Flanged solenoid valves are used on large pipework, from DN50 (2″) upwards, with working pressures up to 42 bar (609 psi). The bolted flange connection guarantees absolute tightness and allows removal and maintenance without cutting the pipe. This is mandatory for main pipe runs in industrial NH3 cold stores and large-capacity chiller systems.

*NH3 only with stainless steel or grey cast iron valves; never brass.

Technical specifications to know when choosing a solenoid valve

Choosing the right solenoid valve means checking 7 technical parameters against the refrigeration system's actual operating conditions. Missing any one of them can leave the valve operating incorrectly or failing early.

• Working pressure: The valve's working pressure must exceed the system's maximum pressure. An R404A freezer store system typically runs at 16 to 22 bar (232 to 319 psi) on the condensing side and 1.5 to 3 bar (22 to 43 psi) on the evaporating side. Choose a valve whose working pressure is at least 1.5 times the highest pressure in
• Voltage & frequency: In Vietnam, industrial refrigeration systems commonly use 24VAC/50Hz (safe and easy to control from a PLC) or 220VAC/50Hz (for larger valves). When importing equipment from the USA, note the conversion from 60Hz to 50Hz, because a coil designed for 60Hz overheats when run at 50Hz.
• Refrigerant and ambient temperature: A standard solenoid valve operates from -40°C to +80°C (-40°F to +176°F). Deep-freeze stores requiring valves to handle refrigerant down to -45°C (-49°F) need a specialist model with Teflon seals instead of standard NBR.
• Pipe size & flow rate: The nominal diameter (DN) and the flow coefficient Kv (m³/h at a 1 bar pressure drop) determine the valve's flow capacity. Choose an appropriate Kv: too small causes a large pressure drop that hurts system performance; too large makes flow hard to control at low load.
• Refrigerant type: The refrigerant determines the body and seal materials. R410A and R32 run about 60% higher pressure than R22, so the valve needs a working pressure ≥42 bar (609 psi). NH3 requires stainless steel or grey cast iron valves with Neoprene or Teflon seals. CO₂ (R744) in transcritical systems requires valves rated to 130 bar (1,885 psi).
• IP (ingress protection) rating: Installation environments in machine rooms with high humidity and the possibility of condensation need valves rated at least IP65 (fully dust-tight, protected against water jets). Marine environments or seafood processing plants should use IP67 valves (protected against short-term immersion).
• Connection criteria and method: BSP or NPT threads suit small pipework and install quickly. PN16 or PN25 flanges (to EN 1092-1) are mandatory for main pipe runs in industrial NH3 systems. Brazed connections (ODF/ODM) are common in residential and commercial refrigeration systems in Vietnam.

Applications of solenoid valves in industrial refrigeration systems

Solenoid valves appear at 4 to 8 different positions within a single complete refrigeration system, each position performing a distinct control role.

• Freezer stores and chill rooms: In industrial cold storage, an NC solenoid valve is fitted on the liquid feed line to each condenser to control the temperature of each store compartment independently. Multi-compartment cold storage systems use multiple solenoid valves with a PLC to keep the temperature difference between compartments within ±1°C, meeting HACCP standards for frozen food storage.
• IQF conveyors and blast freezing tunnels: In IQF flat conveyor belt and wind tunnel, the solenoid valve controls the refrigerant fed to the evaporator through each freezing cycle. When the conveyor stops mid-cycle, the NC valve closes immediately, preventing liquid accumulating in the evaporator and suction line and flooding the compressor at restart.
• Water chiller systems: In water chiller, solenoid valves are fitted in parallel with the pumps on the chilled water supply and return lines. The valve closes at the same time as the pump when the system stops, preventing chilled water continuing to flow into the evaporator and freezing the pipework while the compressor is off.
• Industrial NH3 refrigeration systems: In NH3 (ammonia) systems at seafood and food processing plants, SUS304 stainless steel solenoid valves act as automatic safety valves: when a sensor detects an NH3 concentration in air above 25 ppm (the safe threshold under TCVN 5938), the NC valve immediately closes the whole line, preventing the leak spreading. Tan Long installs this mechanism in
• Evaporative condenser and cooling tower: An NO solenoid valve is fitted on the condenser spray water supply. When the system stops, the valve stays open so water continues cooling the condenser for a further 3 to 5 minutes before closing fully, bringing the refrigerant below a safe condensing temperature and extending compressor life.

How to install a solenoid valve correctly in a refrigeration system

Correct installation determines 60% of a solenoid valve's service life and operating performance in a refrigeration system. These are the principles Tan Long applies consistently across every refrigeration installation project.

• Determine the flow direction: The valve body carries an arrow showing the flow direction. Fitting it backwards leaves the valve unable to open even when energised (because the differential pressure holds the plunger shut), or open but unable to close because residual pressure holds the plunger off its seat. Check the arrow on the body carefully before brazing or tightening threads.
• Installation position: The coil must point upwards or sit horizontally, within ±90° of vertical. Never install the coil pointing downwards, because lubricating oil and debris from the pipework can settle in the plunger clearance and cause sticking over time. The minimum spacing between two adjacent valves is 50 mm to allow coil heat dissipation.
• Fit a strainer upstream of the valve: Every solenoid valve requires a Y-type or T-type strainer at the inlet with an 80 mesh screen (0.18 mm apertures) to keep brazing debris, metal fragments and contaminants out of the plunger clearance. Contaminants as small as 0.1 mm are enough to hold the plunger partly open, causing continuous leakage and refrigerant loss.
• Electrical connection and earthing: The supply cable to the coil must be rated for at least 105°C. The connector must have a gasket rated IP65 or better in machine room environments. Earthing of the valve body to IEC 60364 is mandatory to prevent electric shock and PLC signal interference.
• Post-installation checks: Before charging refrigerant, test the valve with nitrogen (N₂) at 1.5 times working pressure. Check tightness with soapy water at every joint. After charging, check the coil voltage with a multimeter: the actual voltage must not deviate more than ±10% from the rated voltage on the valve label.

Common solenoid valve faults in refrigeration systems and how to fix them

From experience maintaining hundreds of refrigeration systems, Tan Long's technical team records the 5 most common solenoid valve faults under real operating conditions in Vietnam.

• Fault 1: Valve does not open when energised: The most common cause is a broken coil or insufficient supply voltage. Measure the voltage at the coil terminals: if it is below 90% of rated, check the supply and the wiring. If the voltage is correct but the valve does not open, check the plunger by removing the coil and using a magnet to pull it: if the plunger moves freely, the coil has failed; if it is stuck fast,
• Fault 2: Valve does not close when de-energised: The plunger is stuck open because of accumulated contaminants or a return spring weakened after years of service. Check the inlet strainer first. If the strainer is clean, remove the valve and soak the plunger in a solvent compatible with the body material (acetone for stainless steel; never acetone on valves with NBR seals), then check spring elasticity. Replace the spring if its compression
• Fault 3: Coil overheating: An overheating coil (surface temperature above 90°C/194°F) usually results from excessive supply voltage or the coil being energised 100% of the time with no rest period. Check whether the valve is being energised continuously against the design. If the system requires the valve to stay open continuously,
• Fault 4: Refrigerant leaking through a closed valve: The seal is worn, or chemicals in the refrigerant have swollen the seal material. NBR seals are compatible with R22 and R134a but swell in the synthetic POE oil used with R410A. Check the seal material's compatibility with the refrigerant and oil type. Replace seals every 3 to 5 years, or immediately when a leak is found.
• Fault 5: Valve opening/closing at the wrong time: The cause is usually interference on the control signal from the PLC, or a loose wiring connection. Check the signal by measuring voltage fluctuation at the coil terminals during operation. If voltage fluctuation above ±15% is found, check the earthing and add an EMI filter on the signal cable.

Solenoid valve maintenance guide for refrigeration systems

Maintenance on schedule extends solenoid valve life to 10 to 15 years, instead of the 5 to 7 years it lasts when run without servicing.

• Six-monthly inspection: Clean the inlet strainer, check the coil voltage, and listen to the valve opening and closing (a healthy valve gives a clear, consistent “click”). Record the coil surface temperature and compare it with the previous reading. A rise of more than 5°C since the last measurement is a sign the coil is starting to degrade.
• Annual inspection: Remove the valve from the pipework (only with the system shut down and the refrigerant recovered). Visually inspect the plunger and seal: wear on the plunger above 0.1 mm, or a discoloured or swollen seal, requires immediate replacement. Replace the coil if the measured resistance deviates more than ±5% from the rated value on the label.
• Scheduled replacement: Seals: 3 to 5 years, or when a leak is found. Coil: 8 to 10 years under normal operating conditions. Whole valve: 12 to 15 years or after 5 million open/close cycles, whichever comes first.

The solenoid valve is a small control device, but it determines the stability of the entire refrigeration cycle. Choosing the right type, installing it in the right position and flow direction, and maintaining it on schedule are the 3 conditions for a refrigeration system to run efficiently and safely throughout the equipment's life.

With more than 20 years of experience designing, installing and operating industrial refrigeration systems — from seafood cold stores to IQF freezing lines — Tan Long provides technical advice on selecting the right solenoid valve for each specific application. Contact our technical team on 0933 357 058 (Mr. Thinh) for support

Frequently asked questions about solenoid valves in refrigeration systems

Which is safer for a cold store, an NC or an NO solenoid valve?

NC (normally closed) valves are safer for most cold storage applications because they automatically cut the refrigerant flow on power loss, preventing liquid flooding and refrigerant leaks. Tan Long always specifies NC valves on the liquid feed line into the evaporator across every cold storage project it installs.

Can brass solenoid valves be used on NH3 systems?

No. Ammonia (NH3) strongly corrodes copper alloys, including brass and copper. NH3 refrigeration systems must use SUS304 or SUS316 stainless steel solenoid valves with Neoprene or Teflon (PTFE) seals, not standard NBR seals.

Why do solenoid valve coils burn out quickly?

The three most common causes: supply voltage more than 10% above rated; the coil energised continuously for more than 8 hours when designed for intermittent duty; and an ambient installation temperature above 50°C leaving the coil unable to dissipate heat. Check the supply voltage and

Is 24V or 220V more suitable for a cold store solenoid valve?

24VAC/DC is more suitable for industrial cold storage because it is electrically safer (low voltage reduces shock risk during maintenance), integrates directly with PLC outputs without an intermediate relay, and is less affected by mains voltage fluctuation. 220VAC is used for larger valves (DN50 and above) where greater magnetic force is needed to operate at high pressure.

How often does a solenoid valve need replacing?

The coil should be replaced after 8 to 10 years, or when its resistance deviates more than ±5% from the rated value. Seals after 3 to 5 years. The whole valve after 12 to 15 years or 5 million open/close cycles. Actual life depends on refrigerant quality (free of contaminants), a stable supply voltage, and maintenance on schedule.