(3)
The system performance can also be decreased by too much internal leakage when the flight control PCAs are "off null". You must do a check of the internal leakage "off null" ("seal" leakage) and replace components until the leakage is less than the approved limits. The rudder PCAs must not have a difference between the null and the seal leakage of more than 2.0 GPM. The elevator PCAs must not have a difference between the null and the seal leakage of more than 1.0 GPM.
(4)
The valves which follow must have minimum leakage to isolate the system:
(a)
Alternating Current Motor Pump (ACMP) check valves
(b)
Engine Driven Pump (EDP) check valves
(c)
EDP supply shutoff valves
(d)
Power Transfer Unit (PTU) is isolation check valve
(e)
Reserve brake (isolated ACMP) pressure shutoff valve.
(5)
When you do trouble shooting, it is not necessary to do a check of all the systems. In the system with high leakage, feel for hot tubing or actuators and listen for fluid leakage. This method will isolate the defective components in a subsystem which has too much internal leakage. Use approved tools to find heat, vibration, or sound. Before you do an internal leakage check, operate the components to make sure persons will not be injured ro equipment will not be damaged when the component moves.
(6)
There are two techniques to measure flow rates; the multimeter technique and the flowmeter technique.
(a) Multimeter Technique
1) The multimeter technique uses the ACMPs to measure the hydraulic flow rate.
EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. ú
29-11-00
ALL ú ú 07 Page 680B ú Dec 20/94
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
757
MAINTENANCE MANUAL
2) A multimeter connects to a clamp-on ac current probe which you put around one wire at the ACMP ELCU in the P31 or P32 panel. The multimeter with the ac current probe measures the amperage which flows in the one wire to the pump motor. A graph shown in Fig. 605 changes the amperage to a hydraulic flow rate.
(b) Flowmeter Technique
1) The flowmeter technique uses a flowmeter to measure flow rates directly while the system is pressurized with an ACMP or a hydraulic service cart. You install the flowmeter in the pressure line between the pressure source and the pressure filter module.
(7)
Pressurize the three hydraulic systems at the same time during the test with a hydraulic service cart(s) or an ACMP in each system.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：757 AMM 飞机维护手册 液压 CHAPTER 29 - HYDRAULIC POWER 1(145)
