When a tipper trailer fails to dump, we can determine the cause of its malfunction by doing the following.
If there is air in the trailer, check to make sure air is supplied to the control box mounted on the front of the trailer. If there is no air supply to the control box, remove the pressure protection valve next to the air tank and retest.
If air is now present, replace the pressure protection valve. After confirming air, check for power to the terminals connected to the solenoid valve. If there is no power to the terminals, check for proper power wiring. If the power checks out, check the wiring on the back of the outlet to make sure there are no shorts. If there is power to the terminals, check again to make sure the grounding is intact.
If your tipper trailer is equipped with a tarp system locking device, here's what you can do- Make sure the tarp locking device proximity sensor is in the correct position and the tarp is fully open. This is so the electrical signal can reach the solenoid. If the switch is in the active position and there is no power to the solenoid, the proximity sensor may need to be replaced. Depending on the locking system, you may be able to bypass the sensor with the in-box switch.
If it is confirmed that each coil/solenoid is powered and has air, remove the air lines from the hydraulic valves and operate the solenoids through the in-cab switches to ensure that air is supplied through each line to the air shifters on the hydraulic valves. If there is no air to the valve, the coil/solenoid is damaged.
If air is supplied through both lines to the hydraulic valve, the air and electrical parts of the system are working properly. The next step is to check the hydraulic portion of the system.
If the dump trailer seems to tip over, rises a few inches and then stops, then the truck's hydraulic pressure is probably going into the wrong line/coupler. Double check to make sure the pressure line going into the tipper trailer is connected to the coupler on the outermost (closest to the curb) side of the trailer frame.
Sometimes the air shifter on the hydraulic valve can get stuck or may come loose from the spool in the valve. If the connection between the air shifter and the spool is secure, loosen the screws holding the air shifter in place, move the shifter slightly, and retighten the shifter. Pour some tool oil into the air intake and retry the shift valve.
If it still doesn't work, you can remove the cover on the other side of the air shift hydraulic valve. Removing the cover will expose the spool, allowing you to check if the spool has moved. If it moves, retry activating it via the electric switch in the cab. If the trailer still won't dump, the hydraulic valve may need to be replaced.
These are the possible reasons given by LUEN for a tipper trailer fails to dump, if there is anything else you don't understand, ask us, or if you come across something you can't deal with yourself, contact a garage near you!