A bottle jack uses hydraulic oil under pressure to lift heavy objects. These jacks are primarily used as automotive or truck jacks, but they can also be used for many home and garden equipment lifting tasks as well. When a hydraulic bottle jack is full of oil but will no longer lift properly, air in the mechanism is the most likely cause. Bleeding the air from the hydraulic fluid chamber inside the jack will restore its lifting capabilities.
Open the bottle jack release valve to release the inner pressure, allowing the jack ram to retract into the base.
Unscrew the hydraulic oil filler screw and remove it. Some bottle jacks will be fitted with a finger screw that can be turned, while other types will need either a wrench or a screwdriver to loosen it. Locate these oil filler screws on the body of the jack. Since they are primarily used for adding hydraulic oil, orient the jack so the oil filler screw is on the top. This may mean turning the jack on its side. Once the filler screw is removed, the oil filler hole will be on top. This positioning will allow air to bleed off while not spilling any oil.
Pump the jack handle vigorously once the oil filler screw has been removed. Pump the handle up to 10 times to bleed the air from the hydraulic cylinder. Trapped air may bubble out or squirt under pressure as it leaves the system, so always wear safety glasses and stay out of the way of any escaping fluid.
Replace the oil filler screw tightly after the air has been bled from the system.
Check the oil level in the bottle jack once the oil filler screw has been removed. Fill the oil reservoir before purging the air from the system. For the correct oil level for your particular jack, refer to the instruction manual for specific filling instructions.
Wear rubber gloves when bleeding air from the jack or adding hydraulic oil.