This device is also known as a Rupture Valve in some parts of the world . A device known as a rupture valve is often attached to the hydraulic inlet\/outlet of the piston and can be adjusted for a maximum flow rate . If a pipe or hose were to break ( rupture ) , the flow rate of the rupture valve will surpass a set limit and mechanically stop the outlet flow of hydraulic fluid , thus stopping the piston and the car in the down direction .