NOTE:  An engine pressure ratio indicator reading above 1.00 with engines shut down or no pressure applied to system does not necessarily mean that system is inaccurate or that a component needs replacement. Frictional losses may cause sticking of pointer, and an adjustment/test should be made before changing system components.

(b)  
Close applicable engine EPR circuit breaker on circuit breaker panel (P6).

CAUTION:  ALLOW SYSTEM TO WARM UP FOR 2 MINUTES BEFORE CONDUCTING TEST TO PREVENT DAMAGE TO PRESSURE RATIO TRANSMITTER.
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(c) Apply pressure to inlet and exhaust pressure lines per Table I to obtain 1.50 on the pressure ratio indicator.
ENGINE INLET PRESSURE  ENGINE EXHAUST PRESSURE  PRESSURE RATIO INDICATIONS 
In. Hg Abs PSIA  In. Hg Abs PSIA  Pt7/Pt2 
31.00* 15.23 31.00* 15.23  68.2* 33.50 46.5* 22.84  2.20 + 0.005** 1.5 + 0.005** 

* Correct for barometric pressure
**  The tolerances exclude test equipment accuracy. Test equipment tolerance should be determined and considered cumulative to the test tolerance. Accuracy is for airplanes with digital readout EPR indicator and improved Honeywell EPR transmitter.
TABLE I
(d)  
Open applicable EPR circuit breaker. Engine pressure ratio indicator reading should not change.

(e)  
With circuit breaker open, increase exhaust line pressure to 68.20 inches of mercury absolute (33.50 psia). Engine pressure ratio indicator reading should not change.

(f)  
Close applicable EPR circuit breaker. Pressure ratio indicator should read 2.20.

(g)  
Engine pressure ratio indicator should read both values within tolerances shown in Table I after tapping lightly.

CAUTION:  DO NOT TAP INDICATOR GLASS HARD OR USE RINGS, SCREWDRIVER HANDLES, OR SIMILAR RIGID OBJECTS FOR TAPPING. BROKEN OR SCRATCHED GLASS MAY RESULT.
NOTE:  An engine pressure ratio indicator above 1.00 with the engines shut down or no pressure applied to system is due to the lower mechanical stops in the transmitter which prevent the unit from going below 1.00. In some units due to tolerances in the gear train and location of the mechanical stop, the transmitter is incapable of transmitting a signal of 1.0 to the indicator.
(h)  
Relieve test pressures and remove test pressure lines.

CAUTION:  REDUCE EXHAUST LINE PRESSURE BELOW 50 INCHES OF MERCURY ABSOLUTE (24.56 PSIA) BEFORE REDUCING INLET PRESSURE TO PREVENT TRANSMITTER DAMAGE.

(i)
If other engine pressure ratio system is to be tested repeat steps C and D.

E.  Return Airplane to Normal Configuration
(1)  
Reconnect exhaust pressure line to exhaust pressure manifold outlet elbow.

(2)  
Close engine cowl panel(s).

(3)  
Check inlet pressure nose dome(s) for visual damage.

(4)  
Install nose dome(s) (Ref. 71-11-51).

(5)  
Determine whether there is any further need for electrical power on airplane; if not, remove power.

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Oct 20/85  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  77-11-0 Page 505 

2.  Engine Pressure Ratio Indicating System Test (Alternate Procedure)
A.  General
(1)  The following test procedure will apply during an Engine Pressure Ratio Indicating system accuracy check.
B.  Equipment and Materials
(1)  
A regulated air pressure source.

(2)  
Absolute pressure gage.

(3) 
 Test hose.

(4)  
Shutoff valve (Fig. 502).

C.  Prepare for Test
(1)  
Pull applicable engine START circuit breaker on circuit breaker panel P6-2, and placard circuit breaker with DO NOT CLOSE.

(2)  
Placard thrust reverser controls with DO NOT OPERATE.

WARNING:  SERIOUS INJURY CAN OCCUR IF ENGINE IS STARTED AND/OR THRUST REVERSER IS OPERATED.

(3)  
Open ENGINE-1 and ENGINE-2 EPR circuit breakers on circuit breaker panel P6.

(4)  
Open cowl panels (Ref. Chapter 71).

D.  Test Engine Pressure Ratio Indicating System (Fig. 502)
(1)  
Disconnect PT7 line at the 6 o'clock position of the turbine exhaust case (Fig. 501).

(2)  
Attach test line to engine PT7 line.

(3)  
Obtain barometric pressure from absolute pressure gage and note.

(4)  
Check that regulator valve is backed off and that valve to test line is open.
　
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