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2026
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In winter, the pump valve freezing does not necessarily mean the dryer is at fault.
The air dryer has basically become a standard component on air-braked trucks. Its function is to remove moisture from compressed air, turning it into dry air, ensuring that the air used for truck braking is dry. This prevents brake failure and brake drag faults in winter at low temperatures due to condensation of moisture in the air within the pump and valves.
A dryer is like a sponge; after it is saturated with water, it will also lose its effectiveness. So, is there a way to remove the moisture from the drying particles like wringing a sponge to extend the life of the dryer?
● What is dryer regeneration? It's actually just like wringing a sponge.
Truck enthusiasts who have seen Truck Home dismantle a dryer tank know that the main component inside the dryer tank is a lot of water-absorbing pellets. These pellets can be understood as sponges commonly seen in daily life. You can imagine that a sponge, after being soaked with water, needs to be wrung out before it can absorb water again. The same principle applies to the pellets in the dryer tank; if the absorbed water is not removed in time, they will quickly become saturated and lose their effectiveness. So how can we achieve the goal of removing water?
When the compressed air reaches the specified pressure and the unloading valve releases the load, dry air is used in reverse to blow through the dryer tank, thereby removing the water. This is the reverse blow regeneration device on the dryer tank.
● There are two forms of reverse blowing, both aimed at extending its lifespan.
There are two forms of back-blowing commonly seen on the market. One is the independent cylinder back-blowing, which uses a small independent cylinder with a capacity of 5 liters connected in parallel to the outlet of the dryer. When pressurizing the main cylinder, this small cylinder is also filled with air simultaneously. After reaching the specified pressure, the dryer depressurizes, and the dry air in this small cylinder flows back through the dryer to blow out the moisture inside. This form of back-blowing regeneration is easy to identify; you just need to follow the air circuit to find the small cylinder to recognize it.
Another method is to use the vehicle's own air tanks. After the dryer unloads, a portion of the dried air is returned to blow back through the dryer. A dryer that uses this back-blow method will have a return valve on the dryer valve body, and after unloading, you can see on the pressure gauge that one of the gauges drops about 50 kPa. This is the process of using the air pressure from its own tanks to back-blow the dryer tank.
The goal of both back-blow methods is the same: they both help extend the life of the dryer and make it work more efficiently. But many truck owners have this device, regularly replace the dryer tank, so why is there still water in the air system?
● For the dryer to work efficiently, intake air temperature is crucial.
Forum truck enthusiast 'dssn.01''s Auman LNG tractor has recently been experiencing the issue of the trailer relay valve freezing. His original vehicle was equipped with a recirculating back-blow type dryer, and he suspected that this back-blow design was not effective, so it has now been replaced with an independent back-blow tank type dryer. However, judging from his fault performance and the temperature stickers at the air inlet, the problem of the trailer valve freezing is not closely related to the type of dryer.
The temperature sticker on his device has turned black at the 70-degree mark, which indicates that the intake of his dryer frequently exceeds 70 degrees. The upper limit of the dryer intake temperature is 65 degrees, and only when the intake is within this temperature range can the dryer operate efficiently. Therefore, the root cause of this truck owner's malfunction does not entirely lie in the back-blowing method of the dryer; the excessive intake temperature is actually the core reason for the frozen valve issue. Here, we recommend that the truck owner increase the number of helical pipes to reduce the dryer intake temperature and fundamentally resolve the frozen valve problem.
● Editor's Note
In winter, if the brake pump valves freeze, it either results in no braking or the brakes dragging and not returning to position. Both of these faults seriously affect driving safety. Many repair shops and truck owners do not carefully analyze the root cause of the malfunction and blindly replace the dryer, causing unnecessary economic loss and achieving nothing in terms of fixing the fault. Here, we urge repair shops to correctly and carefully analyze the causes of malfunctions rather than blindly replacing or modifying parts.
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