The normal brakes come from the right hand hydraulic system and fluid can transfer across the brake shuttle valves. Pressurising the r/h side first and depressurising last stops the brake shuttle valves from moving across and allowing any (albeit small) fluid transfer.
If you set the parking brake in one of the conditions below, and then release the brake with only the center system pressurized, the fluid can move to the centre system:
(1) The right and centre systems pressurized
(2) Only the right system pressurized
(3) No hydraulic system pressurized.
If you set the parking brake with only the centre system pressurized, and then release the brake in one of the conditions below, the fluid can move to the right system:
(1) The right and center systems pressurized
(2) Only the right system pressurized
(3) No hydraulic system pressurized.
To keep the movement of the fluid between the right and centre hydraulic systems to a minimum, the conditions which follow are important:
(1) Pressurize the right hydraulic system first.
(2) Remove the pressure from the right hydraulic system last.
Last edited by gas path; 26th April 2005 at 16:15.