SAFARI

44 BRAKES 5.5 Brakes on without vacuum (Fig. 48) : In this condi t ion, al l chambers are in atmospheric pressure. When the pedal is depressed, the piston moves forward hitting the rubber reaction disc. In this condition the vacuum brake valve has no boosting action and the output force on the push rod is given as below Output force = Input force on the operating rod – Mechanical loss inside booster The mechanical loss inside booster is mainly due to spring loads and friction due to seals in cover and rear housing. 6. BALANCINGARRANGEMENT : The balancing action of vacuum brake valve is by means of rubber reaction disc arrangement Fig. 43. The input force on the operating rod moves the operating rod assembly, which further exerts force on the rubber reaction disc. The rubber reaction disc acts as a compressed Fig. 48 fluid transmitting the force from the operating rod via. the piston to the push rod. The reaction force from the master cylinder compresses the rubber disc, which further transmits this force to the valve body.The valve body balances this reaction force by moving backwards, closing the air valve. The boost ratio is given by the ratio of the reacting areas on the push rod and the piston i.e Boost ratio = Area of inner diameter of reaction area of push rod / Area of Piston = D 2 /d 2 Where D = Inner diameter of reaction area in push rod d = outer diameter of piston By changing the diameter of piston and the corresponding diameter of valve body, various configurations of boost ratios can be obtained.