The master cylinder supplies pressure to the hydraulic brake system. When you depress your brake pedal, you activate the master cylinder which transmits the force from your foot to brake fluid in the brake lines.
http://www.ryderfleetproducts.com/master-cylinders-c-9030
Before using any other type of fluid in the booster or in the master cylinder, contactthe Bosch Hydraulic Actaution and Truck Brake Engineering Department.(See inside of front cover).The booster and the master cylinder use two (2) distinctly different incompatiblehydraulic fluids.
http://www.alpinecoachassociation.com/chassis/Bosch%20HydroMax%20Booster%20Manual.pdf
If a fluid leak occurs in one circuit, only two of the wheels will lose their brakes and your car will still be able to stop when you press the brake pedal. The master cylinder supplies pressure to both circuits of the car. It is a remarkable device that uses two pistons in the same cylinder in a way that makes the cylinder relatively failsafe. The combination valve warns the driver if there is a problem with the brake system, and also does a few more things to make your car safer to drive. In this article, we will learn how the master cylinder and combination valve work.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake.htm
The function of the relay is to provide current to thebackup pump when triggered by the flow switch. Flow Switch: The function of the flow switch is to activate the relay when normal hydraulic powersource fluid flow is interrupted, turning on the backup pump. The flow switch has two terminals(A and B). A is positive.
http://www.alpinecoachassociation.com/chassis/Bosch%20HydroMax%20Booster%20Manual.pdf
A booster combined with a master cylinder (refer to Figure 1) forms thehydraulic brake actuation unit. A typical assembly is shown in Figure 1. The booster reduces thepedal effort required to apply the brakes as compared to a non-power system.
http://www.alpinecoachassociation.com/chassis/Bosch%20HydroMax%20Booster%20Manual.pdf
The brake pedal and mechanical linkage must provide enough travel to fully strokeboth booster and master cylinder, i.e., the brake pedal must not bottom on the floorof the vehicle. A pedal ratio of between 2.8:1and 3.3:1 is recommended to providethe desired pedal feel.c. The Hydro-Max TM booster and master cylinder assembly must be mountedhorizontally.d. The reservoir of the master cylinder must be upright.
http://www.alpinecoachassociation.com/chassis/Bosch%20HydroMax%20Booster%20Manual.pdf
Here you can see what happens when one of the circuits develops a leak. When the first circuit leaks, the pressure between the primary and secondary cylinders is lost. This causes the primary cylinder to contact the secondary cylinder. Now the master cylinder behaves as if it has only one piston.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake1.htm
The base brake system in all modern cars is very similar to the hydraulic brake system introduced in the 1920 Duesenberg. Brake testing is simple and straightforward -- only a few hand tools are necessary.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake.htm
The Master Cylinder in Action. When you press the brake pedal, it pushes on the primary piston through a linkage. Pressure builds in the cylinder and lines as the brake pedal is depressed further. The pressure between the primary and secondary piston forces the secondary piston to compress the fluid in its circuit.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake1.htm
See more brake pictures. In the figure below, the plastic tank you see is the brake-fluid reservoir, the master cylinder's brake-fluid source. The electrical connection is a sensor that triggers a warning light when the brake fluid gets low.
http://auto.howstuffworks.com/auto-parts/brakes/brake-types/master-brake1.htm
what is the purpose of a master cylinder in a truck
A master cylinder in a truck supplies pressure to the hydraulic brake system. The purpose of a master cylinder in a truck is to supply pressure to the hydraulic brake system.