-
2 servovalves,
-
2 safety valves with integral filter,
-1 filter in the manifold pressure supply. The servovalves are supplied with pressure when the pedals are pushed in. When there is no brake regulation, the pressure applied to the brakes is equal to the pressure supplied to the servovalves. The regulation system decreases the pressure at the brake. The current moves a flapper located between two jets. Two coils are installed around the core which is mounted in the gap of a permanent magnet (only coil 1 is used). The attraction of the core by the poles of the magnet is function of the current which passes through the coil. The movement of the flapper modifies the sections of the fluid passage at the jets. Consequently the pressure in the control chambers of the slide valve is modified. The differential action of the pressure moves a slide valve. This fills or drains the brake depending on whether the current decreases or increases. The slide valve is in a balanced position under the action of the pressure supplied on one of the opposite faces of the slide valve. With zero current in the coil, the pressure supplied is equal to the pressure supplied to the servovalve.
(b)
Safety valves (Ref. Fig. 014, 015) The principle of operation is the same as that of the Normal brake safety-valves (Ref AMM 32-42-00 Page Block 1).
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Yellow Pressure Transmitters
Figure 011
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Alternate Brake Servovalve - Location
Figure 012
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Alternate Brake Servovalve - Schematic
Figure 013
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Alternate Brake Safety-Valve P/N C24757000
Figure 014
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Alternate Brake Safety-Valve P/N C25243002-2
Figure 015
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4. Operation/Control and Indicating
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A. Pedal Artificial Feel
(1) Control A hydro-mechanical system transmits control inputs at the pedals. This hydro-mechanical system is installed between the master cylinders and the distribution dual valve (auxiliary low-pressure control-system). The pressure delivered to the Alternate brake servovalves is in relation to the pedal load/angle. Before you get the pressure,
-
the free travel of the pedals, corresponding to the closure of the internal valve of the master cylinders,
-
the displacement of the distribution slide valve to shut off the return and then let the pressure in,
-and the compressibility of the fluid in the low pressure system
must be taken up. Incomplete bleeding of the low pressure system results in a decrease in the load and an increase in the free travel. The brake Yellow-pressure triple-indicator shows the pressure supplied by the distribution dual valve to the LH and RH brakes. This indicator thus shows that the system is supplied with the Yellow pressure. The servovalves can decrease the pressure at the brakes.
(2) Anti Skid Regulation The regulators used for the Normal system are also used for anti skid regulation. (Ref. Fig. 016) The servovalve gets brake release orders.
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Alternate Braking with Anti Skid - Principle
Figure 016
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1. General_______ (Ref. Fig. 001)
The Alternate braking system is a secondary electrohydraulic system. It is manually operated (no autobrake function available) and used to decrease the speed of the aircraft when it moves on the ground with engine power. It gives automatic anti skid protection, if available from BSCU, when the aircraft moves at more than ten meters per second.
The system automatically becomes available during braking if:
-specified failures occur in the Normal braking system (Ref. 32-42-00) and
-the pressure of the Green Main Hydraulic Power System (Ref. 29-11-00) is less than 90 bar (1305 psi).
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