In hydraulic systems, a fuse (or velocity fuse) is a component which prevents the sudden loss of hydraulic fluid pressure. It is a safety feature, designed to allow systems to continue operating, or at least to not fail catastrophically, in the event of a system breach. It does this by stopping or greatly restricting the flow of hydraulic fluid through the fuse if the flow exceeds a threshold. The term "fuse" is used here in analogy with electrical fuses which perform a similar function. Hydraulic systems rely on high pressures (usually over 7000 kPa) to work properly. If a hydraulic system loses fluid pressure, such as due to a burst hydraulic hose, it will become inoperative and components such as actuators may collapse. This is an undesirable condition in life-critical systems such as aircraft or heavy machinery, such as forklifts. Hydraulic fuses help guard against catastrophic failure of a hydraulic system by automatically isolating the defective branch. When a hydraulic system is damaged, there is generally a rapid flow of hydraulic fluid towards the breach. Most hydraulic fuses detect this flow and seal themselves (or restrict flow) if the flow exceeds a predetermined limit. There are many different fuse designs but most involve a passive spring-controlled mechanism which closes when the pressure differential across the fuse becomes excessive. Many gas station pumps are equipped with a velocity fuse to limit gasoline flow. The fuse can be heard to engage with a "click" on some pumps if the nozzle trigger is depressed fully. A slight reduction in fuel flow can be observed. The fuse resets instantly upon releasing the trigger. Types There are two types of hydraulic fuses. The first one acts like a pressure relief valve, venting in case of a pressure surge. The second is more or less like a check valve. The only difference is a check valve is in place to prevent upstream fluid from coming back and venting out. A fuse is in place before the venting area and stops fluid from venting forward of it. Hydraulic fuses are not a perfect solution to fluid loss. They will probably be ineffective against slow, seeping loss of hydraulic fluid, and they may be unable to prevent fluid loss in the event of a catastrophic system failure involving multiple breaches to hydraulic lines. Also, when a fuse activates it is likely that the system will no longer function