MASTER CYLINDER in Automobile Engineering

The master cylinder is the main component of the system. When the brake pedal is depressed, fluid in the brake master cylinder, under pressure, flows out of it and into the fluid lines leading to the wheel cylinders. It is divided into two parts, namely, fluid reservoir and compression chamber. When the pedal is depressed, the piston at the end of the pedal rod moves to the left, against the force of the spring, until it covers the bypass port. Further movement of the piston causes an increase in pressure in the compression chamber.

As pressure increases, the internal rubber cup of the fluid check valve flexes, forcing fluid into lines under pressure. Fluid enters the wheel cylinder and moves the piston inward, thus activating the brakes. When the pedal is released, the spring causes the piston to move to the far right position. The force of the spring also keeps the fluid check valve pressed in its seat for some time. The fluid returns from the lines to the compression chamber and some delay occurs due to inertia.

This creates a vacuum in the compression chamber which must be destroyed immediately. When the vacuum is created, the air tries to occupy the space and negatively affects the operation of the brakes as the air is compressible.

As soon as a vacuum is created, atmospheric pressure in the fluid reservoir pushes fluid through the suction port and piston holes into the compression chamber. This destroys the void. The liquid returns to the tank by lifting the liquid check valve from its seat. Fluid in the compression chamber becomes excessive and this excess fluid returns to the reservoir through the bypass port. Excess fluid, if allowed to remain in the compression chamber, causes the fluid to move to the lines.

Fluid is trapped in the lines and even a slight application of the brakes causes heat to be generated. This would cause fluid to expand in the lines and eventually block the brakes. The master cylinder is equipped with a rubber cover at the end of the pedal rod. This does not allow dust to enter the chamber through the opening of the pedal shaft. There is an opening at the top. The opening is used to maintain the fluid level according to the plant requirements. The opening is equipped with a screw cap which makes it airtight.

TANDEM Master Cylinder

It has primary and secondary cylinders in a row. These are equipped with individual pistons and have their own return springs. The return spring holds the primary piston cup slightly behind the bypass port to keep the cylinder full of fluid. The return spring also helps return the brake pedal to its original position when the driver takes his foot off.

There are two separate lines, one connects the front wheels and the other connects the rear wheels. In a normal situation, when the pedal stem is depressed, both pistons move into the right brake fluid which is supplied to the lines and the brakes are activated on all four wheels. In the event of a line failure, say a front line, the secondary piston moves until it reaches the cylinder wall.

Subsequently, pressure begins to build up in the space between the two pistons and fluid is supplied to the rear wheels. The rear wheel brakes are activated. In another situation, where there is a failure in the rear fluid supply, the primary piston moves until it collides with the secondary piston. Thereafter, the two pistons move together supplying fluid to the front wheels, thus activating the brakes on the front wheels.