Typical Failures in Resistive Fuel Quantity Systems
As previously stated the indicator in this type of system is quite simple, typically nothing more than a meter movement mounted within a case. A meter movement consists of a spool of wire mounted on a pivot and jewel housed within a frame. The frame is in fact a large powerful magnet.
As electrical current flows through the wire spool it interacts with the magnetic field of the frame causing the spool to rotate on its pivot and jewel.
A pivot is nothing more than a miniature axle. A jewel is a finely ground glass cup within which the ends of the pivot are supported and allowed to rotate. Over time and with constant movement the ends of the pivot will begin to wear down similar to the point on a pencil. Eventually the pivot will become so worn that it can no longer rotate easily. It needs to be sharpened or replaced.
As previously stated, a jewel is nothing more than a finely ground miniature glass cup. Glass is fragile; it breaks very easily when mishandled. The glass also becomes worn from the pivot constantly rotating within it. Eventually the glass will become rough and will need to be re-ground or replaced.
The frame of the meter movement is a large magnet. A magnet is nothing more than a piece of steel within which all of the electrons, sub-atomic particles, have been aligned within a specific pattern. Eventually the electrons move and return to their original locations according to the laws of physics. With the loss of alignment the magnet loses its magnetic power.
However while the magnet is still operating properly it, like all magnets, attracts other ferrous metals. The pivot, manufactured with ferrous metal, is in close proximity to the magnet and it is wearing down from rotating within the jewel. As the pivot wears it throws off tiny particles of metal which are attracted to the magnet. Eventually enough of these particles will become lodged between the magnet and wire spool so as to inhibit free movement of the meter. The unit needs to be completely disassembled and thoroughly cleaned.
As previously described the resistive element is subject to wear from the constant movement of the wiper across its surface. Once it is overly worn or broken it must be replaced. There is no possibility of repair
The floats are very often nothing more than hollow metal balls. These sometimes spring leaks. The fuel must be drained and the float must be resealed.
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