39 BRAKES retained inside the diaphragm disc. The operating rod assembly consists of piston, valve rubber cup, operating rod, and valve retaining spring and operating rod return spring. This operating rod assembly is positioned inside the valve body by means of key. The rubber reaction disc is housed inside the push rod, which is retained in place against the valve body by the diaphragm return spring which is resting on the spring retainer. The assembly consists of four chambers namely 1,2,3 & 4 as in figure 2. In all conditions of operation, the chamber 1 and 3 will always be connected through passage A in the valve body and chambers 2 and 4 will be connected through another passage B in the valve body, as shown in figure 2. There is a vacuum passage C in the valve body, which connects the chamber 1 with chamber 4. The 8” diaphragm acts as a seal between chambers 4 and 3, while the 9” diaphragm acts as a seal between chambers 1 and 2. Fig. 43 4. ZERO LOST STROKE (Fig. 43): From Fig. 43(a), we can see that the operating rod sub-assembly is attached to the valve body, by means of key. Due to the opposing force of operating rod return spring, the key is pulled towards the operating rod side, in the sub-assembly, keeping the vacuum valve (X) open. But when the valve body sub-assembly is fitted in the full assembly Fig. 43(b), the fitted force of diaphragm return spring pushes the valve body towards the rear housing, till the key butts against the rear housing. This movement of the valve body, results in the closing of the exhaust travel, thereby closing the vacuum valve and sometimes even opening the air valve (Y). On application of the vacuum, the valve body moves forward just enough to close the air valve (Y) and bring the assembly to a balanced condition. Hence, at normal running condition, both the vacuum and air valve are closed. This feature provides output force at nearly zero lost stroke of the operating rod. Fig. 43a Fig. 43b
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