Master-slave hydraulic cylinder pairs are versatile and very practical to handle. As you can see in the drawing below, when the piston rod travels out there is a pressure control in the cylinder pair via a connection line at the piston rod side of the master cylinder. The master cylinder controls the slave cylinder from the piston side with the mineral oil that flows back from the ring piston side, so that both hydraulic cylinders travel out simultaneously. During this procedure the oil volume at the ring piston side of the master cylinder is exactly tuned to the oil volume at the piston side of the slave cylinder. Each time in final position there is an equalisation of the oil volume via a valve in the piston of the master cylinder, so that their synchronous run is also guaranteed after many operating hours.