ENGINES
Duplex. There are also duplex pumps that are a combination of constant displacement and centrifugal pumps. They have both centrifugal impeller and a rotor with carbon vanes. Now that we know some basic fuel pump theory, we can cover some scenarios where the pumps can be damaged.
Corrosion Corrosion can cause external and internal damage to fuel pumps. Externally, corrosion can build up on the pump housing and on the electrical terminals and wiring. Helicopters operated in coastal areas like we see in offshore oil operations are more susceptible to corrosion because
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of the high-salinity in the environment. Corrosion on the housing won’t necessarily cause a pump to fail, but the corrosion should be removed and the area treated during scheduled inspections. Corrosion on the terminals or in the wiring can affect electrical conductivity, and any damaged wiring or terminals should be repaired or replaced as necessary. “Corrosion will build up an electrical resistance in the circuit,” says Briggs. “So you have to push more current through the wire to get the pump to produce same power. With voltage being a constant, if you have a resistance problem in the power or ground, you start increasing current and this increases heat (Ohm’s Law). So look for indications of heat-damaged wiring and terminals when you are inspecting corrosion.” “It helps to apply a good corrosion
preventative such as ACF-50 to the external surface of the pump to prevent any potential problems corrosion can cause,” adds Mike Lotzer, national sales manager for Hartland, WI-based Rapco, Inc.
External fuel pump corrosion Internally, the biggest cause of
corrosion is water. This is especially true with jet fuel, where microbes like to thrive in the boundary area between the water and the fuel, creating a corrosive sludge by-product. Regular and proper fuel sumping will help reduce internal corrosion issues. “You also need to know you are getting good fuel to begin with,” says Briggs. “Fuel trucks should incorporate proper fuel filtering, regular sumping, and treatment with additives such as Prist or Biobor in the recommended mixture ratios.”
Internal fuel pump corrosion 26
HelicopterMaintenanceMagazine.com February | March 2014
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