Hydraulic jacks use pump plungers to move oil through two cylinders. When the plunger is first drawn back with a lift of the handle, it opens the suction valve ball within and draws oil into the pump chamber. As the plunger is pushed forward with a downward press of the handle, the oil moves through an external discharge check valve into the cylinder chamber, and the suction valve closes, which results in pressure building within the cylinder and pushing the jack up. Hydraulic jacks come in two different kinds—bottle jacks and floor jacks. Bottle jacks are compact and easy to store, are easily transportable but frequently won't lift as heavy of loads as a floor jack. Floor jacks, though bulkier, are safe and easy to use, and large ones can lift several tons. However, you need plenty of space around your vehicle or other object you need to lift in order to use a floor jack.