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Preventing Damage From Raise Lower Valves

Raise Lower (Docking) valves are used to bring the trailer deck height in line with loading bays, and Hendrickson offer a series of recommendations on preventing damage from raise lower valves. They are very useful when dealing with various height loading bays. However, the valves can also cause considerable damage if not installed or used correctly.

Raise Lower (Docking) valves work by bypassing the height control valve to set trailer height. This means that the operator could inadvertently put full system air pressure into the air springs.  

So, an air spring that may usually see a maximum of around 70 psi, could be pressurised up to 140 psi, if left in the raise position. This excess pressure could damage air springs, shock absorbers and mountings if left in this state.

To prevent this kind of damage, all genuine Hendrickson Raise Lower valve kits contain a pre-set protective pressure regulator. However, if installing an aftermarket Raise Lower valve, then you should supply and install a pressure regulator set to a maximum of 80 psi. It is vital that these regulators be installed in the air supply line to the Raise Lower valve, which will minimise accidental component damage from over-pressurisation.

80 psi Pressure Regulator. (Image: Prime Creative Media)

What can make the situation worse, is when drivers set the deck height and then accidentally drive off with the trailer raised. The suspension will now bump against the extended shock absorbers, which can severely damage limit straps, shocks and mountings. This can be bad enough with a regulator set 80 psi, but without a regulator the results will be catastrophic to the components involved.

Some trucks have an option called RtR (Reset to Ride Height), which resets the ride height on account of a speed related signal from the EBS (or ABS) systems. This built in override is a great addition and is usually set to operate when vehicle speed reaches around 6 to 15 kmh. Even with an RtR, it is still important for the driver to manually set the Raise Lower valve back to standard before driving off.

There are two reasons for this practice. Firstly, it takes time for the suspension to react and drop down. By that time the driver could have already caused some damage. More importantly the RtR will not operate if the EBS is not operating properly. This could be due to an electrical wiring fault, malfunctioning EBS unit or a disconnected wiring harness. This is probably the worst-case scenario because the driver will be unaware that there is any problem until it is too late.

That is why driver education must be included as part of the solution to preventing damage due to Raise Lower valves. Driver education should include warning of the possible consequences of leaving the Raise Lower valve set high and to not simply rely on the RtR to prevent any damage.

In summary, preventing air spring, shock, shock clevis and mounting damage caused by Raise Lower valves can be prevented by incorporating several actions:

Install an 80 psi maximum regulator before the Raise Lower valve.
Install Raise Lower valves with RtR (Reset to Ride Height).
Educate drivers of the likely results of leaving the Raise Lower valve in the high position.


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