Proportioning Valve: Operation

1. Operation before the split point
   • Piston is held by spring so that valve is kept away from valve seat.

     Under this condition, fluid pressure "P₃ " to rear wheel cylinders equals fluid pressure "P₂ " from master cylinder.

     Fig 1: Identifying Proportioning Valve Ports

     
2. Operation near the split point
   • Force "f₁ ", applied to piston by spring, is spring force "F". In other words, "f₁ " = "F".
   • Force "f₂ " is also applied to piston in the direction opposite to spring force "F" due to fluid pressure "P₂ " generated by master cylinder according to cross sectional area "A".
   • Force "f_2" increases respondingly with fluid pressure "P₂ ". When "f₂ " is greater than "f₁ ", piston moves in direction opposite to spring force "F". This causes valve to come in contact with valve seat, blocking fluid passage.
     Fig 2: Proportioning Valve - Operation Near The Split Point

     
3. Immediately before fluid passage is closed, fluid pressure "P₂ " is held equal to pressure "P₃ ".

When brake pedal is depressed to increase fluid pressure "P₂ ", piston moves in the same direction as spring force "F", opening fluid passage.

However, since fluid passage is closed again immediately after pressure "P₂ " equals "P₂ ", pressure "P₃ " is held at a value of less than pressure "P₂ ".