INBD
LEFT WHEEL WELL SHOWN
FWD
RIGHT WHEEL WELL SIMILAR

B
Antiskid Module Installation
Figure 4

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A

757
MAINTENANCE MANUAL

 (1)  
Two 4-valve antiskid modules are used in the normal brake system. The modules are located in the left and right main wheel well fairing structure, near the wheel well ceiling, just aft of the left and right hydraulic system reservoirs. Each module contains four identical antiskid valves, four hydraulic fuses, a shutoff valve, two inlet filters, a check valve, a restrictor, and a housing with associated parts. The module provides individual wheel control to each main gear. Each module is an LRU and the fuses, shutoff valve, and inlet filters are separate component LRUs. The valves and filters can be removed for inspection without disconnecting hydraulic lines.

 D.
Antiskid Module (Alternate) (Fig.___________________________4)

 (1)  
Two 2-valve antiskid modules are used in the alternate brake system. The modules are located at the keel beam web on a mounting support bracket in left and right main wheel wells. Each module contains two identical antiskid valves, two hydraulic fuses, one inlet filter, a check valve and a housing with associated parts. The module provides laterally paired wheel control to each main gear. Except for configuration differences and quantity of components and wheel control, the alternate 2-valve module functions similarly to the normal 4-valve module.

 E.
Antiskid Module Components (Fig. 4)

__________________________
 (1)  
Antiskid valve

 (a)  
Each valve in the normal or alternate module consists of two stages. The first stage (servo valve assembly) develops hydraulic pressure proportional to the input current. The second stage (slide and sleeve assembly) repeats this pressure at the lower level required for brake control.

 (b)  
The first stage servo valve assembly consists of a torque motor and a hydraulic circuit. The motor, an electromagnetic device, produces an armature deflection proportional to input current which positions the armature between two nozzles, pressure and return.

 (c)  
The second stage slide and sleeve assembly consists primarily of a stop, a quill, and the slide and sleeve. Slide position is controlled by first stage output pressure on one end and pilots brake metered pressure on the other end.

 (d)  
The antiskid valves in both the normal and alternate hydraulic systems operate in the unigain mode. System pressure (3000 psi) is supplied to the first stage providing a constant pressure source by which the second stage is controlled. Through unigain operation, the valve is able to maintain consistent stopping performance through out the braking range, independent of applied brake pressure.

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MAINTENANCE MANUAL

 (2)  
Hydraulic fuses

 (a)  
The fuse prevents hydraulic fluid loss from the brake system if a line should rupture at any point downstream of the fuse. The fuse automatically shuts off all flow if the volume of fluid passing through is too great. The fuse is self-resetting and can be reset within 5 seconds against a pressure differential of 18-30 psi without the aid of reverse flow.

 (b)  
Fuse resetting is done manually by rotating the reset knob. This equalizes the pressure on both sides of fuse and allows the fuse to reset. When the reset knob is released, a spring forces the knob back to normal position. A slot in the knob allows visual verification of bypass valve position.

 (3)  
Hydraulic filters

 (a)  
Two module filters, one at the metered pressure inlet and the other at the system pressure inlet, protect module components against clogging or malfunctioning. The filters provide filtration of hydraulic fluid prior to its entering the module housing.

 (4)  
Shutoff valve

 (a)  
A shutoff valve installed in the normal module prevents system pressure from being supplied to the antiskid valve without pilot metered pressure input of 260 psi or more. When the metered pressure > 260 psi, the valve ports fluid from the system pressure line to the antiskid valve. When the metered pressure < 240 psi, the valve switches and the flow is from the metered pressure line to the antiskid valve. The shutoff valve contains a check valve to allow metered pressure supply to the first stage of the antiskid valve if the shutoff valve closes.

 (5)  
Check valve