79-32-01
 ALL  ú ú N01 Page 408 ú Jun 18/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
LOW OIL PRESSURE WARNING SYSTEM - DESCRIPTION AND OPERATION
___________________________________________________________
 1.  General
_______
 A.  The low oil pressure warning system uses a pressure switch, with advisory and status messages in the flight compartment, to show when the oil pressure downstream of the fuel/oil cooler is too low to sufficiently supply the engine bearings with engine oil.
 2.  Low Oil Pressure Warning Switch (Fig. 1)
_______________________________
 A.  The low oil pressure warning switch is installed on the left side of the engine just aft of the intermediate case at the 10 o'clock position. The low oil pressure warning switch is a hydraulically actuated and mechanically operated snap-action switch.
 B.  The low oil pressure warning switch senses the pressure differential between the oil pressure downstream of the fuel/oil cooler and the breather air pressure from the main bearing compartment.
 3.  Low Oil Pressure Warning Indication
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 A.  An EICAS advisory message ENG (1, 2, 3, or 4) OIL PRESS will show on the main EICAS display when engine oil pressure decreases to less than 70 |2 psid with the engine in operation. (An EICAS status message ENG (1, 2, 3, or 4) OIL PRESS will also show on the auxiliary EICAS display if the STAT key is pushed.)
 4.  Operation (Fig. 2)
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 A.  Functional Description
 (1)  
The oil pressure downstream of the fuel/oil cooler is supplied to the high pressure side of the warning switch for the low oil pressure. Breather air pressure from the main bearing compartment is supplied to the low pressure side of the switch. With power supplied to the system and the engine not in operation, the low oil pressure warning switch is in the closed position.

 (2)  
During an engine start, and until the oil pressure differential across the switch is more than 80 psid, the switch stays closed. When the oil pressure differential is more than 80 psid, the switch opens.

 (3)  
If the oil pressure differential decreases below 70 |2 psid and the engines are at or above idle, the ENG (1, 2, 3, or 4) OIL PRESS EICAS advisory message will show. This shows that the oil system pressure is below a safe limit.

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 79-33-00
 ALL  ú ú N01 Page 1 ú Feb 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
SEE A
LOW OIL PRESSURE WARNING SWITCH
FWD
INTERMEDIATE CASE (REF)
ENGINES WITHOUT SB 79-2036
A
Low Oil Pressure Warning Switch Location Figure 1 (Sheet 1)
 E18774
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 79-33-00
 ALL  ú ú N01 Page 2 ú Jun 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
LOW OIL PRESSURE WARNING SWITCH
FWD
ENGINES WITH SB 79-2036 A
Low Oil Pressure Warning Switch Location Figure 1 (Sheet 2)
E18776
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 79-33-00
 ALL  ú ú N02 Page 3 ú Jun 10/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES /MAINTENANCE MANUAL ////////////////////////
DM7353
M7353 EIU-3 DM7352
M7352 EIU-2

DS1584
DM7351
P
M7351 EIU-1

E2-6 EIU RACK S1584 ENGINE LOW OIL PRESSURE WARNING SWITCH

Low Oil Pressure Warning System Simplified Schematic
Figure 2

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