Hydraulic Brake Booster: Testing and Inspection

Pressure Test On Brake Booster Circuit

Overview

1. General
2. Pressure gauge connection
3. Tests
4. Nominal values / Notes


1. General

The pressure test on the brake booster circuit tests the following points:

- Freedom from leaks of the booster circuit (any internal leak can thus be localized)

- Gas filling pressure of the pressure accumulator

- Switching points for the booster circuit (brake pressure warning lamp and operating pressure). This is controlled by the pressure warning switch of the pump assembly.


2. Pressure gauge connection




- Depressurize the booster circuit. To do this, disconnect the electrical plug at the pressure pump (pump assembly) and then press the brake pedal approx. 25 times. The system is depressurized as soon as the brake pedal feels hard when operated. In order to disconnect and plug the electrical plug onto the pressure pump, press in the center on the plug locking clip. The cover in the area of the pump unit need not be removed.




- Connect pressure gauge 9509 (No.1) at the screw coupling (mini measuring connection No.3) of the pressure accumulator with the high-pressure measuring line 9509/2 (No.2).

- Bleed the pressure gauge (No.1). To do this, connect a collection bottle to the pressure gauge bleeder valve (No. la) and open the valve.
Move the ignition key to position 1 (necessary for pump operation).
Plug the electrical plug onto the pump. Disconnect the electrical plug and close the bleeder valve as soon as no air bubbles are visible anymore at the transparent bleeder line of the collection bottle.

Note
Before removing the manometer after the test, the booster circuit must be depressurized.


3. Tests





Note
Operation of the pump is regulated by means of the ignition key for testing purposes.

- In ignition key position 0, plug the electrical plug onto the pump. Locate the pressure gauge in a position where it can be seen.

- For the tests, it is expedient to observe the following sequence:

a. Pressure accumulator - Gas filling pressure

b. Switching points for the brake pressure warning lamp

c. Cut-in and cut-out points of the pump

d. Leak test

- Turn the ignition key to position 1 (pump starts up).

a. Gas filling pressure of the pressure accumulator.

Turn the ignition key to position 0 at approx. 100 bar.

Operate the brake pedal several times and observe the pressure gauge. When the indicator falls rapidly towards zero, the filling pressure of the pressure reservoir has been reached. For required values, see Nominal Values table.

Note
Sensitively operate the brake pedal shortly before the gas filling pressure is reached.

b. Checking the switching points for the brake pressure warning lamp.

Pressure build-up:

Start the engine and observe the warning lamp. Immediately turn the ignition key to 0 position at the instant when the warning lamp goes out. Read off the pressure on the pressure gauge.

Pressure reduction:

Produce a system pressure of approx. 140 bar. Disconnect the plug at the pressure pump.
Start the engine
Operate the brake pedal sensitively several times until the warning lamp lights up. Read off the pressure on the pressure gauge. Refer Nominal Values.

c. Checking the switching points of the pressure pump

Cut-out pressure: Turn the ignition key to p0sition 1. The electrical plug must be plugged onto the pressure pump for this.
Read off the pressure on the pressure gauge immediately after independent pump cut-out.

Cut-in pressure: Turn ignition key to position

1. Wait until the pump switches off independently if appropriate. Press the brake pedal as often as required until the pump starts up. Read off the pressure on the pressure gauge at this instant.
Refer to Nominal Values.

d. Checking the pressure loss of the booster circuit.

Turn the ignition key to position 1. Wait until the pump cuts out independently. Press the brake pedal as often as required until the pump starts up again. After independent cutout of the pump, turn the ignition key to position 0 and disconnect the electrical plug at the pump. No longer operate the brake pedal. Measure the pressure drop over the course of time. Refer to Nominal Values for permitted values.

Note
Depressurize the booster circuit before removing the pressure gauge.

4. Nominal values / Notes





Values Table