Lotus 2004 ELISE Service Notes page 231

Lotus Service Notes
Pressure Balance
Further pressure on the brake pedal opens the atmospheric port and bleeds atmospheric pressure into
the left hand chamber. This pressure imbalance causes the driving piston to move to the right, adding assistance
to the force applied directly to the output rod (and the master cylinder) via contact between the input and output
rods. When the force produced by the pressure differential across the diaphragm balances the reaction force
of the main spring and master cylinder, movement of the driving piston ceases, with both control valve ports
closed, and the system once again in equilibrium.
From this position of equilibrium, further pressure on the pedal will tend to open the atmospheric port and
allow pressure in the left hand chamber to increase, and move the driving piston to the right before again
stabilising. Any reduction in pedal pressure will tend to open the vacuum port and allow the higher pressure in
the left hand chamber to bleed off into the right hand chamber, whose depression is kept constant by its
connection with the intake plenum. The pressure imbalance is reduced, and the driving piston will move to the
left under the action of the main spring, until equilibrium is again restored.
Input from
brake pedal
Page 16
Higher pressure
balances manifold
pressure plus
spring
Atmospheric port
Section JJ
Low pressure
from intake
manifold
Vacuum port
Output to
master
cylinder
j147c