What is the dual brake system in the locomotives?

Question

i mean what is the difference between air brakes and vacuum brakes. also tell me the types of electrical braking systems in an electric locomotives.

Answer 1

air brakes supply air to push a piston to apply the brakes,these are double systems with fail safe mod to increase force up to 20%

vacuum systems used up to 1970 used vacuum to pull the piston  but only worked at 14.7 psi ,atmospheric pressure so everything had to be much larger and heavier to increase efficiency

electopneumatic uses electricity to control the brakes so they can all come on at the same time instead of sequentially as in the air only system

dynamic braking is where the drive motor become generators that create torque at the drive wheels to slow the train,the power generated is turned to heat and discharged by fans,not all engines have this system

Answer 2

The only standard equipment on a locomotive manufactured by EMD or GE is the frame.  Assuming a locomotive is equipped with dynamic brake, then there are four braking systems on a locomotive.

The simplest of these is the hand brake, which is comparable to the parking brake in an automobile.  Manually applied and released by operation of a brake wheel or a lever, which tightens a chain to put the brake shoes against the wheel.  When this brake is used, it only applies a brake to one wheel only.

The next is the engine brake, also referred to as "independent" brake, "straight air" or "jam".  The latter term is a hold-over from the first brakes on a locomotive which were "steam-jam" brakes.  These were operated by the engineer and pumped steam into a cylinder to apply the brakes.  The choices were "on" or "off".

Today it is a brake system that puts air into the cylinder via the 6SL brake valve.  This valve operates from full release to full application and variable for any pressure between.  The BC Equalizing Pipe, regulated from this valve, will vary in pressure from 0 to 45psi.  In the air box there is a relay valve called either a J1 (these were found on older locomotives with cast iron brake shoes), which puts a maximum of 45psi into the brake cylinders.  Today we find the J1.6 relay valve, which at full application will put 72psi into the brake cylinder.

The independent brake valve has two other necessary facets.  One is found in the form of the independent pressure switch, or IPS.  Usually around 15psi this switch nullifies the extended range portion of the dynamic brake to avoid sliding the engine's wheels when bringing the train to a stop.  Sliding wheels will create flat spots or thermal cracks.

The other is the ability to keep the engine brakes released while applying the brakes on the cars.  This is done for slack control.  When the brake valve handle is depressed, it puts main reservoir air into the actuating pipe, releasing the brakes on the engine consist.  This action is called "bailing off".

Next we find the automatic brakes.  This a braking system that begins with a fully charged (with air) system, 90psi for freight and 110psi for passenger.  It is controlled by the 26L brake valve.

When air is exausted from the brake pipe, a valve on each car senses the drop in air pressure and slides to open a port from the auxilliary air reservoir on each car to allow air to flow into the brake cylinder, which moves the brake rigging and applies the brake shoes to the wheel.

When applying the brakes with the automatic, the engine brakes will apply as well, unless the engineer "bails off".  If in dynamic brake on an engine equipped with a DBI (dynamic brake interlock), it will also preclude the application of the brakes without the engineer having to bail off.  More insurance against sliding wheels.

Finally there is the dynamic brake.  There are two basic types; flat and taper.  When in dynamic, the propulsion system is reversed, turning the traction motors into generators, which in turn provides retarding effort.  The electricity generated in this fashion is dissipated as heat through grids, that operate just like the ones in a toaster.  In addition, more electricity is used up running the cooling fans above the dynamic brake grids, which makes the familiar "whining" sound, that varies in pitch according to how much dynamic is being used.

Answer 3

Locomotives can adjust the polarity in their electric drive motors for braking.