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2026
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When the pump valve freezes in winter, it’s not necessarily caused by the dryer.
An air dryer is basically a standard component on air-braked trucks. Its function is to remove moisture from compressed air, making the air dry, ensuring that the air used for the truck's brakes remains dry, and preventing brake failure and brake drag malfunctions in cold winter conditions due to condensation of moisture in the pump valves.
A desiccant is like a sponge; once it absorbs water, it loses its effectiveness. So is there a way to remove the moisture from the desiccant, like wringing out a sponge, in order to extend the life of the desiccant?
● What is desiccant regeneration? It's actually just like wringing out a sponge.
Truck enthusiasts who have seen the disassembly of a drying tank on Truck Home know that the main component inside the drying tank is many water-absorbing granules. You can think of these granules like the familiar sponges in daily life. You can imagine that a sponge must be wrung out after absorbing water before it can absorb more. The granules in the drying tank work in the same way; if the absorbed moisture is not removed in time, they will quickly become saturated and lose their effectiveness. So how do you remove the moisture?
When the compressed air reaches the specified pressure and the unload valve is activated, dry air is used to blow back through the drying tank to remove the accumulated moisture. This is the back-blow regeneration device on the drying tank.
● There are two forms of back-blow, both aimed at extending the lifespan.
There are two types of back-blowing available on the market. One is the independent cylinder back-blow, which involves a small independent cylinder with a capacity of 5 liters, connected in parallel to the dryer’s outlet. When the cylinder is pressurized, this small cylinder is also filled with air at the same time. Once the regulated pressure is reached, the dryer is depressurized, and the dry air in this small cylinder flows back through the dryer, blowing out the moisture inside. This type of back-blow regeneration is easy to identify; you just need to follow the airflow to locate the small cylinder to confirm it.
Another method is to use the vehicle's own air tank. After unloading the dryer, a portion of the dried air is returned to backflush the dryer. A dryer that uses this backflushing method will have a return valve on the dryer valve body. After unloading, one of the pressure gauges will show a drop of about 50 kPa, indicating the process of using the air pressure from the vehicle's own tank to backflush the drying canister.
The purpose of both backflushing methods is the same: they can extend the life of the dryer and make it operate more efficiently. However, many truck owners have this device and also regularly replace the drying canister, so why is there still water in the air lines?
● Efficient operation of the dryer depends largely on the intake air temperature.
Forum member 'dssn.01's Ouman LNG tractor has recently been experiencing issues with the trailer relay valve freezing. His truck originally had a recirculating blowback-type dryer, and he suspected that this type of blowback was not very effective. It has now been replaced with an independent blowback tank-type dryer. However, judging from the symptoms of the failure 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 dryer shows that the 70°C window has already turned black, which indicates that the air inlet of his dryer often exceeds 70°C, whereas the maximum temperature for the dryer's air inlet is 65°C. Only when the inlet air is within this temperature can the dryer work efficiently. Therefore, the root cause of this truck owner's problem is not entirely related to the dryer's blowback design; the excessive inlet air temperature is the core reason for the frozen valve failure. Here, we suggest that the truck owner reduce the temperature of the dryer's air inlet by adding a spiral pipe to completely resolve the frozen valve issue.
● Editor's Note
In winter, if the brake pump valve freezes, either the brakes don't work at all, or they are delayed and don't return to position. Both of these issues seriously affect driving safety. Many repair shops and truck owners fail to carefully analyze the root cause of the problem and blindly replace the dryer, which leads to unnecessary financial loss and does nothing to eliminate the problem. Here, we call on repair shops to carefully and correctly analyze the causes of failures instead of blindly replacing or modifying parts.
Focus on the research and development of automotive brake systems and pneumatic brake valves to promote the development of the auto parts industry!
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