The main reason for the freezing of pneumatic valves
The fundamental reason for freezing is the rapid decrease in moisture and temperature. Specifically, the key factors are:

Moisture in compressed air: This is the core reason.
The atmosphere naturally contains water vapor. When an air compressor compresses air, it also compresses this water vapor. As the pressure increases, the dew point temperature of the air (the temperature at which water vapor begins to condense into liquid water) will also rise.
When compressed air leaves the compressor and passes through the pipeline, its temperature will decrease. Once the temperature drops below the dew point, water vapor will condense into liquid water.
If the air drying system of the factory (such as freeze dryer, desiccant dryer) is inefficient or malfunctions, a large amount of liquid water and water vapor may enter the pneumatic system.

Throttle expansion effect (Joule Thomson effect):
This is the most direct physical process that causes the valve itself to freeze.
When compressed air passes through restrictive components such as the exhaust port of pneumatic actuators or positioners and speed control valves, it immediately expands from high pressure to atmospheric pressure.
This rapid expansion process absorbs a large amount of heat, causing a sharp drop in local temperature. If there is moisture in the air, it will immediately condense and freeze, forming ice crystals.
This process is similar to the compressed air tank used to clean the keyboard becoming very cold.

Parts that are prone to freezing
Exhaust port of actuator: When the valve runs rapidly, a large amount of air is discharged here, making it the most likely place for throttling expansion and freezing.
The throttle hole and air channel in the locator: The locator has precise throttle holes, which are easily blocked by ice, leading to control failures.
Speed control valve (speed controller): The component used to regulate the opening/closing speed of the valve is also a limiting point.
The pilot hole and exhaust port of the solenoid valve: The internal passage of the solenoid valve is narrow and easily blocked by ice.

The consequences of freezing
Slow or stuck valve operation: Ice blocks the air passage or mechanical transmission components, causing the valve to fail to open or close properly.
Out of control: Freezing of the locator or solenoid valve can cause the valve to lose control signal and remain in one position.
Process interruption: Valve failure can directly interrupt the production process, causing economic losses.

Equipment damage: In extreme cases, forced freezing valve operation may damage components such as diaphragms and connecting rods.
High quality air handling system:
Ensure that the air dryer is functioning properly and provides dry compressed air with a sufficiently low dew point (e.g. -20 ° C or lower). This is the most fundamental solution.
Install a gas storage tank after the compressor to cool and separate most of the liquid water, and regularly drain it.
Use high-efficiency filters (FRL filters, regulators, lubricators) in air treatment units and regularly perform manual or automatic drainage.

Insulation and heat tracing of air pipelines:
Insulate air pipelines, pneumatic actuators, positioners, and other critical components exposed outdoors.
In extremely cold regions, it is necessary to install electric heat tracing belts on gas supply pipelines, storage tanks, and even valves themselves, and cover them with insulation layers to maintain system temperatures above freezing point.

Use antifreeze:
Add specialized pneumatic system antifreeze to the lubricator of the air handling unit (FRL).
Antifreeze is carried by air flow and forms a protective film at restricted points, lowering the freezing point of water and preventing freezing. Attention: Use professional products compatible with sealing materials.

Design optimization:
Whenever possible, install pneumatic valves indoors or in insulated enclosures.
For critical valves, consider designing a compressed air blowing system that continuously blows a small amount of dry air into the valve casing to prevent cold air from entering.

Emergency response measures:
Safety first: Before handling, ensure that the process is in a safe state.
External heating: Use steam tracing, hot water, or a safe hot air gun (note: avoid local overheating to prevent damage to seals and paint) to slowly heat and melt frozen parts.
Inject antifreeze: If conditions permit, inject a small amount of antifreeze into the system through an air pipeline connection to help melt the ice.
Do not use force: Do not strike with hard objects or heat directly with an open flame, as this can easily damage precision components.
summary
Whether the pneumatic valve freezes in winter depends on the dryness of the compressed air and the ambient temperature. As long as there is moisture in the air, there is a risk of icing when the valve expands due to throttling during operation. By ensuring a dry air supply, insulation and heat tracing pipelines, and using antifreeze, this problem can be effectively prevented.