Q.. Explain the working details of tandem master cylinder.


Sketch and explain the construction of a tandem master cylinder. How does It respond when the
brake oil leaks?

Answer !

Tandem Master Cylinder
Tandem master cylinder means a master which contains two pistons placed in line to each other in series within a single
cylinder. Both the pistons are operated with the help of a single pedal This Improves the safety of the braking system when it
is defective. Some of them employ an anti-lock brake system. The main parts of tandem master cylinder are,

(i)Oil reservoir                                                                                        (ii) Primary piston
(iii) Secondary piston
(iv) Brake booster output rod
(v) Springs
(vi) Ports

Primary and secondary pistons (equal or unequal sizes) deliver oil through separate exits under pressure


By depressing the pedal brake, the brake booster output rod pushes the secondary piston and the tension of the
secondary piston spring pushes the primary piston. Due to this, the piston cups close the relief ports A and B and hydraulic
pressure rises on both primary and secondary sides. To compensate the piston stroke, brake oil in the reservoir tank) will Dow
into the port F
Pedal on relcasing both secondary and primary pistons will return to their original position by hydraulic pressure in
the pipes and return force of the piston rings. Remaining fluid is returned through the ports and F to the reservoir tank.


The possible fluid leakages from the system are,
(i)  From the primary system                                                                  (ii) From the secondary system.

 (i).Leakage from the Primary System

The primary piston is pushed by the fluid pressure of the secondary piston and tension of the piston spring
end hits on the cylinder, since the fluid pressure on the primary side does not rise. Hence, the braking is performed by the
pressure on the secondary side.

(ii) leakage from the Secondary System

The secondary piston keeps moving ahead which hits on the end surface of the primary piston so that primary pi
is pushed under same condition as an ordinary rod. Hence, the fluid pressure conducts the braking.


Q.. Draw a neat sketch showing the linkage to operate brake master cylinder and describe the same



When the push od is pressed by the foot pedal through linkage, the punch rod moves the piston to left against the
spring force till it covers the bypass port. Break fluid flow from the resernoir through the byepass or full port into the master
cylinder, supply lines and up to the wheel cylinders. Otherwise, in normal position, the break fluid is always available in the
system and any loss of fluid could be made up by the fluid flow from the master cylinder TVDI

When the brake pedal is depressed the relief port is sealed by the primary cup and in out of the system. The brake fluid
pressure causes the wheel cylinder piston to move outward to operate the brake shoes to ruh against the brake drums. Hence
brakes are applied
When the brake pedal is released the master cylinder’s piston return hack due to spring force. Since the brake fluid
returns slowly, this causes to form vacuum in front of the piston This vacuum c es the brake fluid to flow from res
through the intake port past the piston or through holes in it to fill the vacuum. This makes the complete fluid line filled with
brake fluid. The reservoir cap must be provided with A vent or small hole to ensure that atmospheric pressure acts on the

In hydraulic system, the brake fluid knows by gravity to compensate small loss of brake fluid.


Q… How does an external contracting brake differ from an Internal expanding brake?


External Contracting Brakes

External contracting brakes are sometimes used for parking brakes on motor vehicles for cranes and for controlling the
speed of auxiliary equipment drive shafts
Ter im the brake band (or shoe) of an external contracting brake is tightened around the rotating drum by movin
the husk lever. The brake hand is made of comparatively thin, fexible steel, shaped to fit the drum, with friction
Everest to the inner surface. This flexible hand cannot withstand the high pr required to produce the friction proceeded to
stop a heavily loaded or fast moving vehicle, but it works well as a parking brake or hold brake.
The brake band is anchored opposite to the point where the pressure is applied. In addition to supporting the band, the
anchor allows adjustment of the brake lining clearance. Other adjusting screws and bolts are provided at the ends of the band.

Internal Expanding Brakes

They are used almost exclusively as wheel brakes, but can be found on some cranes. This type of brake permits a more
compact and economical construction The brake shoes and brake operating mechanism are supported on a backing plate or
brake shield attached to the vehicle axle The brake drum. attached to the rotating wheel acts as a cover for the shoe and
operating mechanism and furnishes a frictional surface for the brake shoes
The brake shoe of an internal expanding brake is forced outward against the drum to produce the braking action. One
end of the shoe is hinged to the braking plate by an anchor pin. while the other end is attached and can be moved in its
support by the operating mechanism When force from the operating mechanism is applied to the attached end of the shoe
the shoe expands and brakes the wheel A retracting spring return the shoe to the original position when braking action is no
longer required.




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