Hydraulic and Pneumatic fuses
A fuse protects a system against component failures. There are actually two distinct types of fuse and their operation, and effects, are totally different.
The first type of fuse protects against plant damage from over-pressurization. Mounted, for example, in a line directly from pump outlet to tank it is a simple thin metal plate which will rupture at a specified pressure. Once ruptured the entire pump delivery goes straight back to the tank, leaving minimal system pressure. Once this type of fuse has blown the system has to be shut down and the fuse replaced. Note, though, that the sudden and catastrophic loss of pressure can cause unwanted movement and safety hazards.
The second type of fuse is common in aircraft and mobile plant hydraulics and protects against a failure of a pipe or connection which results in a major leak. It detects higher than normal flow in a line and shuts to prevent further leakage. Usually the fuse has to be manually reset. Although it does totally shut down one motion it is probable that other motions can still continue, allowing the plant to be brought into a safe state. Whilst working well for major leaks they are not capable of detecting small dripping leaks.
Pneumatic fuses also protect a pneumatic system against major leaks. If a flex- ible hose for a pneumatic tool fails or a coupling becomes detached the sudden very high air flow will cause the hose to thrash around with the potential to cause major injury. Like hydraulic fuses they have to be reset manually once triggered.
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