Hydraulic leveling jacks for RVs are devices attached to the covers or sides of the vehicle that are used to ensure that the RV sits level on the ground. Jacks are only designed for use when the RV is stationary and should be retracted before moving the vehicle.
Some hydraulic jacks need to be raised and lowered manually using a hand crank or drill to turn the internal mechanism. Other jacks are automatic and are raised and lowered using a group of buttons on the instrument panel inside the vehicle. When an RV is level, appliances inside such as the refrigerator tend to work better and beds tend to be more comfortable.