Central Valve (Brake Cylinder)
Well, if your first reaction when looking at the (enlarged) image is: 'The compensation bores are missing'. You are right, and this is precisely the reason for the introduction of the central valve, which has the master
cylinder otherwise left as it was. In the period before ABS the system was depressurized at the moving back of the brake pedal.
You probably have experienced even the intervention of ABS. As you are fully on the brake pedal while this pumping in very rapid intervals. Here are under severe pressure on the primary cup seal. Should then be found,
unfortunately, In the area of the replenishing bore it would partially pushed in there and possibly damaged.
Here you can see an elongated recess in the intermediate or floating piston. A rod is visible behind the spring, on which a valve in the right part depends far ahead from the primary cup seal. The recess is for the pin
below, passing through the piston, but rigidly connected with the housing. Its task is to open the valve via the plunger rod on the right side of the piston, if it is in its rest position. By this the brake circuit and the
compensating tank are connected via the replenishing bore.
To better illustrate the function, the two rods and the valve together with the spring are drawn into the intermediate piston. Thus makes clear the possible flow of the brake fluid at completely depressurized system. The
central valve may be installed only at the intermediate piston, too. 03/16
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