Hydraulic jacks are normally used to raise objects off the ground. There are times however, where using a jack horizontally is necessary. Projects like straightening out a door jamb benefit from using a jack to spread the opening. Bottle jacks are the only jack that operate in this way. Using a hydraulic jack in a horizontal position requires that the pump be lower than the piston. This prevents the hydraulic fluid from leaking into the piston reservoir and causing a loss of pressure.
Twist the release valve counterclockwise using the notch on the end of the jack handle to lower the piston completely. Turn the valve clockwise once the piston is down.
Place the jack on its side with the pump below the reservoir. The reservoir is the cylinder that contains the jack piston and the pump is where you insert the handle.
Hold the jack in a straight horizontal position with one hand and use the handle to operate the pump. Pump the handle side to side until the base of the jack and the face of the piston are against the object you are repairing.