TPMS.
In the dictionary, under "Corrosion", the explanation "damage to metals"
A more comprehensive definition is "a process in which a material, especially a metal, is broken down or digested by a chemical reaction."
The presence of oxygen, along with a humid environment, is enough to initiate this process. Sometimes this effect is enhanced by other factors in the immediate vicinity. In the Netherlands with a relatively humid maritime climate, road salt in the winter on the roads, aggressive rim cleaning agents, there are “supporting” factors to accelerate this corrosion process considerably.
With TPMS sensors, these conditions are an excellent breeding ground to ensure that the TPMS valve part will be affected. The most common form of corrosion with TPMS valves is that of galvanic corrosion, which does not depend on which part of the world the vehicle is located, although local conditions can speed up or slow down the process.
Galvanic corrosion is caused by the presence of the following conditions:
- Different types of metal.
- They must be able to come into contact with each other.
- There must be an electrolytic conductor.
If 2 different metals come into contact with each other to form a galvanic coupling, one type of material will act as an Anode and the other type of material will act as a Cathode. The Anode is the "giving" side and the Cathode the "receiving" side. Either material transfer will take place from the anode to the cathode. With the TPMS sensor with an aluminum valve part, the valve body will function as an Anode and the copper inner valve as a Cathode. The necessary electrolyte is formed by moisture in the form of e.g. water, or any liquid, as long as it is moist.
The corrosion process will proceed as follows:
The valve body aluminum will slowly dissolve in the electrolyte present as a conductor and deposit on the material of the inner valve. During this process, the valve body material will become thinner and weaken and lose its strength. Ultimately, this will result in the valve housing breaking off, precisely where the inner valve has the largest contact surface with the valve housing.
This "aging process" will be accelerated if an extra Cathode is added in the form of a metal valve cap, which will affect the valve housing and the screw thread on the outside, but also on the inside.
Because these valves are designed in this way, this corrosion with the associated consequences will occur regularly and therefore the "breakdown" problem will continue to exist.
The TPMS sensor comes from the factory with a copper inner valve that is provided with a nickel coating. This nickel coating acts as an insulator or barrier between the 2 different materials. Furthermore, the sensor also comes with a valve cap from the factory, which is equipped with a rubber sealing ring, which will prevent moisture from entering the valve housing. As a result, if the inner valve is tightened to the specified torque and a correct valve cap has been used or fitted to achieve the required sealing ring, there will be very little to no corrosion of the valve body.
The disadvantage is that in daily practice it often goes wrong by doing the wrong thing.
The TPMS sensor with a “snap-in” valve does not have the above problems, but only a small part of the total market in which they are applied.
As long as the automotive industry continues to use aluminum valve bodies, the necessary maintenance actions will be required to prevent "breakdown" problems in the future.