Component Tests: Accumulator

The diaphragm type accumulator is precharged with nitrogen at 80 bar (1160 psi), its function is to store hydraulic energy. Over a period of several years a normal loss of precharge will occur. This procedure will indicate extent to which precharge pressure has fallen.

1. Depressurize brake system fully. See DEPRESSURIZING SYSTEM  under BLEEDING BRAKE SYSTEM.
2. Remove banjo bolt securing high pressure hose, use a second wrench on large hexagon to prevent it being loosened.
3. Fit pressure gauge adaptor, using sealing washers. Connect pressure gauge.
4. Switch ignition on and observe pressure gauge.
5. There should be a rapid rise in pressure to accumulator precharge, point X, of 80 bar (1160 psi), then a slowing down in rate of increase as pressure rises to system pressure, 170 bar (2465 psi). See Fig 1 .
6. Accumulator has lost precharge is point X occurs below 80 bar (1160 psi).
7. Fit new accumulator if point X occurs below 50 bar (725 psi).
8. Depressurize system, remove pressure gauge and adaptor.
9. Fit banjo bolt securing high pressure hose, use NEW sealing washers, tighten to 11 ft. lbs (15 N.m).
10. Bleed pump.
11. Check/top up fluid level.

Fig 1: Checking Accumulator Precharge

Courtesy of LAND ROVER NORTH AMERICA, INC.