Master Magnetic Chip Detector Hand-Removable Probe
 Figure 012
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 E E Feb 01/98 E E ECES E E 56-5B E E E (2) Scavenge pump (Ref. Fig. 004, 008) After lubrication, the 4 scavenge pumps scavenge the air/oil mixture from the 2 engine sumps and gearboxes through 4 tubes external to the lubrication unit. The 4 scavenge elements of the 5-gerotor-type-positive displacement pumps are powered by the same AGB-driven single drive shaft as the supply element (pump). They have the same technology and principle of operation as those described for the supply pump. (Ref. Fig. 008)

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 (3) Master Magnetic Chip Detector. (Ref. Fig. 002, 004, 011, 012) The flows from the 4 scavenge pumps are mixed together at the master chip detector inlet. This detector consists of the following :
 (a) One cross shaped hydraulic housing with 2 square flanges:

 - One for attachment to the lubrication unit housing (oil inlet flange)

 - One for attachment to a tube which connects with the servo-fuel heather (oil outlet flange).

 (b) A check valve, part of the hydraulic housing, to prevent oil spills when the electrical chip detector is removed.

 (c) A hand-removable chip detector probe, locked on the hydraulic housing by a bayonet attachment system. From its outer end to tip, the probe is equipped with:

 - One back-up seal for safety purposes

 - One o-ring seal

 - Two magnets, separated by a gap. These identical magnets function as normally-open electrical contacts. When metal particles contaminate the scavenged oil, they bridge the magnetic gap and close the contacts formed by the 2 magnets.

 (d) A two-wire, shielded electrical cable and its 28 VDC interface connector. The master magnetic chip detector is connected to a master chip detector indicator. A pop out information, in the fan case compartment at the master chip detector indicator, is given after chip detection.

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 (4) Main Oil/fuel heat exchanger (Ref. Fig. 001, 004, 007, 009, 010) From the discharge side of the master magnetic chip detector housing, the scavenged oil flows through a pipe, outside of the lubrication unit, to the servo-fuel heater, then to the main oil/fuel heat exchanger, and then back to the oil tank.

 (a) General The main oil/fuel heat exchanger cools the oil by using fuel as a cooling medium. The main oil/fuel heat exchanger is installed on the fuel pump housing, between the AGB aft face and piggiback on the servo-fuel heater at the 7:30 o'clock position, approximately, aft looking forward.

 (b) Description (Ref. Fig. 007, 009, 010) The oil/fuel heat exchanger is of tubular type. It consists of a removable core, housing and cover.

 1 The core consists of a cylinder, end plates, and fuel tubes.
_ The fuel tubes are attached to the end plates. Two inner baffles lengthen the oil circulation path around the fuel inlet tubes.
 2 The housing contains the core of the oil/fuel heat exchanger.
_ The following items are located on the outside of the oil/fuel heat exchanger housing :
 - One oil pressure relief valve and one fuel pressure relief valve.

 - One drain port which collects possible fuel leaks from core end inter-seal cavities and prevents fuel from leaking into the oil cavity and contaminating the oil system.

 - One port for a fuel-out temperature probe (optional).

 - One attaching flange for the servo fuel heater.

 - One flange for attachment to the fuel pump.

 - One port on fuel-in for fuel returned from HMU after circulating through the IDG oil cooler.

 3 The cover provides access to the oil/fuel heat exchanger for
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 core installation.

 (c) Operation (Ref. Fig. 007, 009, 010) The oil to fuel heat transfer is achieved through conduction and convection within the exchanger where both fluids are circulated.
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 Fuel from the fuel pump and from HMU enters the inlet. It flows in one direction through one half of the core tubes to the end cover. At the end cover, the fuel flows around the baffle and back through the other half of the core tubes to the fuel outlet. While passing through the exchanger, the fuel gets heated. The fuel portion of the exchanger is equipped with a pressure relief valve which bypasses fuel around the exchanger if core clogging impedes fuel flow. Oil from the scavenge system enters the oil inlet. The oil flows around the fuel tubes, as routed by interior baffles, and exits at the oil outlet after being cooled. The oil portion of the exchanger is equipped with a pressure relief valve which bypasses oil through the exchanger if core clogging impedes oil flow.
　
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