Diesel Electrical Multiple Units (DEMU) fitted with 700 HP were introduced in 1994 by ICF for improving passenger services in non electrified routes. The 1400 HP DEMU was introduced in the year 2002 to replace the slow-moving locomotive hauled push-pull trains in non-electrified routes of metro cities.

  • 1400 HP DEMU (Diesel Electric Multiple Unit) has been inducted in Indian railways to replace the existing slow-moving Loco hauled a passenger train in non-electrified mainline sections and also for low traffic density branch line services.
  • The high acceleration potential of DEMU makes them suitable to work as fast passenger transportation services between cities.
One unit of DEMU consists of four coaches:
  1. Driving power car (DPC),
  2. Trailer car (TC)
  3. Driving trailer car (DTC).
  • Driving power car is a coach that houses the diesel-electric power plant.
  • Around 50% of the coach space is occupied by the plant and balance is for the passengers.
  • It has one control station. The control station is used when the train is moving in the direction where the DPC is leading.

Trailer car (TC) is a simple coach that is meant only for passengers.

  • Driving trailer coach (DTC) is also a coach meant only for the passengers.
  • However, one end of this coach has parallel operator control station.
  • This is used y the operator when the train is moving in the direction where DTC is the leading coach.
  • Multiple operations of DEMU is possible up to 04 units so as to meet varying demands of traffic existing in the section.
  • DEMU is designed for maximum speed of 100 Kmph
  • The power car is provided with the 20 T axle load bogie whereas the trailer car is fitted with 16 T axle load bogies suitable for mainline coaches.
Operating Parameters of DEMU:


Leading Particulars of 1400 HP DEMU Power Car:
  • Length of headstock: 21417 mm
  • Distance between bogie centers: 14783 mm
  • Bogie wheelbase: 2896 mm
  • Wheel diameter: 952 mm (New)
  • Treadwear: 37.5 mm
  • Overall width: 3245 mm
  • Height from rail level to top of roof: 3886 mm
  • Height from rail to floor level: 1282 mm
  • Maximum height of center line of center
  • buffers above rail level for unloaded vehicles. : 1104 mm

Brake System fitted to the Multiple Unit consists of pneumatically controlled straight Air Brake for normal service application together with the Automatic Brake providing a ‘Stand by’ brake for normal service stops if required. The Automatic Brake also provides for emergency application of the brake initiated either by the driver or by a breakaway.

The important characteristics of Air brakes are:
  • The self-lapping pneumatic brake gives flexibility and sensitivity of control to enable the car brakes to be governed accurately to any desired pressure between the maximum and
  • The pressure will be automatically maintained in the car air brake cylinders against normal leakage from them and regardless of variation in piston travel until released
    by the Driver’s Brake Valve.
  • The Car brakes can be graduated on or off with either the automatic or the independent brake valve which can be used for service stops when necessary.
  • Maximum brake force in emergency brake application ensures shortest possible stopping distance. The provision of Emergency Brake Application is available on both brake valves.
  • Traction Power / EP Contactor cut off during emergency braking as well as train parting off on the run.
  • The automatic brake is always available for emergency stops initiated either by the Driver or Guard.
  • The automatic emergency brake is rapidly applied on all cars of a train in case of train parting.

The system ensures Pneumatic Straight Air Brake either independently or in conjunction with car air brakes equipped with Graduated Release Automatic Air Brake Equipment.

The System is a composite one and distinctly comprises of the following elementary Braking features:
  • Independent Straight Air Brakes with multiple unit operations.
  • Twin Pipe (Feed Pipe & Brake Pipe) Graduated Release Automatic Air Brakes operating air brake train with break-in-two feature.

Each driving compartment is fitted with gauges for registering Main Reservoir/Feed Pipe & Brake Pipe by Duplex Pressure Gauge MR/BP, Brake Cylinder BC Gauge, Parking Brake Cylinder by PB Cylinder Pressure Gauge etc.

Driving Power Car system also supplies compressed air for operation of the following auxiliary equipment:
  • Driving Power Car Controls
  • Pneuphonic Horns
  • Pneumatic Wipers
  • Dead man’s ControL
  • Parking Brake Control
  • Other components in use.

In addition, each driving compartment is provided with an indication lamp, batteries, and battery charging equipment, switches, and fuses by the car builders for each Driving Power Car.


The general working/working principles of this brake system are as follows:


Atmospheric air passes through a Suction Strainer as provided with each compressor to ensure that the intake air to the compressor inlet-port is clean. Compressed air as stored in Main Reservoir on the Driver Power Car (DPC) and supplementary Main Reservoirs’ on the trailer cars are fed directly into Main Reservoir Pipe.

This main air supply passes through “After cooler” for reduction of temperature to the reasonable level after being generated by the compressor. The check valve is mounted between the compressor and Main Reservoir to prevent any development of back pressure to the compressor and also to retain main air reservoir pressure
stored for subsequent utilization for brake application and other respective uses in the system.

Safety Valve set at 8.5 ± 0.1 kg/sq cm is provided in the supply line to the Main Reservoir.Feed Valve is mounted on the main Feed Pipe via 1″ Centrifugal Dirt Collector with Drain Cock and the feed pipe is also provided with a gauge for registering the feed pipe pressure. Main Reservoir fitted with Auto Drain Valve type D-I satisfying automatic draining facilities from MR with respective pressure differential & ultimately connected to Compressor Governor (pressure Switch) set at 8 ± 0.1 kg/ closed and 7 ± 0.1 kg/ open via 3 way Magnet Valve (Normally Close type) to maintain the MR pressure between the suitable limits.

All compressor governors on a train of the combination of cars are synchronized so that all compressors should start and stop together. Cooling pipes or aftercoolers to precipitate water vapor is provided by the car builders in this case.


The Straight Air Brake of Driving Power Car is controlled by the operation of SA-9 Independent Brake Valve provided at the single end Cab Control MR/ Feed pipe air pressure is piped to port 30 of SA-9 Independent Brake Valve and Duplex Pressure Gauge in the Cab.

As the SA-9 Brake Valve handles from the brake control is moved towards Application Zone, the Feed Pipe Air, in accordance with the degree of handle movement, will flow through the Port 20 of SA-9 Independent Brake Valve and charge the Brake Cylinders.

In the event of the further increase in the braking demand through SA-9 Brake, Valve handles movement towards Full Service, the Feed Pipe air will further build up the pressure in the Brake Cylinders.

The release of Straight Air Brakes in steps or in full will follow with SA-9 Brake Valve handle being moved towards Release position, which will result in withdrawing the pneumatic braking demand accordingly and the air from the brake cylinder release through the exhaust port of SA-9 Independent Brake Valve to the atmosphere.

Since SA-9 Independent Brake Valve is self-lapping and pressure maintaining type, the brake cylinder pressure will hold, irrespective of the normal leakage from them or the length of the brake cylinder piston travel.


The Graduated Release Automatic Air Brake features in DMU/DPC Brake System are controlled through the operation of A-9 Automatic Brake Valve provided at the single end cab control. MR/Feed pipe air pressure is piped to port 30 of A-9 Automatic Brake Valve which in turn is also piped to the Duplex Pressure (FP-BP) gauge. Feed pipe/ MR air is also piped to the supply port-1 of C2W Relay Valve will charge the entire Brake pipe (BP) line to 5 kg/ and maintain the pressure against leakage.

Port 5 of A-9 Automatic Brake Valve is piped to E- 3 Emergency Application Valve & Magnet Valve (Normally Open) through a pressure switch set to cut-out at 3.2 kg/ & cut-in at 4.2 kg/ for Deadman’s Control.BP air piped to C3W Distributor Valve activates the distributor to assume brake release condition by recharging its Control Reservoir (CR) to 5 kg/ and connecting Brake Cylinder line to exhaust. BP air is also piped to Port 1 of A-9 Automatic Brake Valve.

As the A-9 Brake Valve handle is moved towards the Application Zone the ER pressure according to the degree of handle movement will be destroyed. The C2W Relay, in turn, will destroy the BP air. The C3W Distributor Valve will quickly sense the destruction of BP air and sets itself to application position by first disconnecting BC from an exhaust and then connecting MR air to BC line. However, the distributor will automatically lap as soon as the pressure builds up in BC is in proportion to the BP airdrop. The C3W distributor valve is designed to produce an output of 3.8 ± 0.1 kg/ against a BP air depletion of 1.5 kg/ or more.

This output pressure is again controlled by N1 Reducing Valve set at 1.6 kg/ to the BC line for corresponding brake application. In this context, BC line is set to 1.6 kg/sq cm for composite brake block being used in place of conventional C.I. brake block.

The BC outlet will now act as a pneumatic braking signal which should not exceed more than 1.6 kg/sq cm and N1 Reducing Valve set at 1.6 kg/ is used in this brake-circuit as a precaution in the unlikely event of over braking. All the brake cylinders under the bogies will be charged during this course of brake application as explained under the Straight Air Brake System.

During the release of Automatic air brake BP pressure is raised in steps or full to its regime pressure of 5 kg/ by bringing A-9 Automatic Brake Valve Handle to the Release position in steps or abruptly, and in turn C3W Distributor Valve will allow the BC air to flow exhaust either in steps or in full. The A-9 Automatic Brake Valve is also provided with emergency venting of BP air.

As the handle is moved to the Emergency position the BP air quickly drops to zero and thereby emergency brakes are applied at the much faster rate through C3W Distributor Valve. Standby Guard’s Emergency Brake Valve is also provided in the brake control cab which when operated will directly vent the BP air to atmosphere and ensure Emergency braking throughout the air brake train in the combination of cars.


Working Principle:

Parking brake control circuit is provided with Magnet Valve 3-way NC type along with a pressure switch cut-out at 2 kg/ and cut-in at 3 kg/ in order to operate Parking Brake Actuators 2 Nos. per bogie i.e. 4 Nos. per coach. These PB Actuators are installed at cross mounting locations one at each side of the Bogie for use in conjunction with brake cylinder type JSL as per the SIL/Schematic Drg No. 08000301.

in case of DMU/DPC & Schematic Drg No.08002201 in case of DMU/DPC underslung coach. 4 Nos. JSL type brake cylinders are mounted per bogie i.e. total 8 Nos. brake cylinder per coach. PB Actuators are coupled with JSL type brake cylinders by way of mechanical levers arrangement as per SIL Drg No. 08001301. This mechanical lever arrangement enables PB Actuator to operate in conjunction with JSL brake cylinders.

When PB Actuator energizes means apply for the position, JSL brake cylinders are brought back to release position ensuring brake release condition. Similarly when PB Actuator de-energises means in ‘release’ position then JSL brake cylinders in conjunction with Actuators are brought to ‘apply’ position in order to ensure brake application.Thus when PB Actuator gauge indicates zero means parking brake is in ‘applied’ position & when the same gauge indicates the full pressure of 3.5 kg/ means parking brake is in ‘release’ position.

A pressure gauge is provided with the underframe of the coach and with the underframe of each Non-driving Trailer car as well which registers Brake Cylinder pressure in addition to the gauge in the Cab. A release valve is also fitted on the underframe of each car to release the Brake Cylinder pressure independently from the rail level. Suitable Dirt collectors, strainers, and isolating cocks are fitted in appropriate positions
throughout the brake system.

The Main Reservoir and brake pipes which are continuous throughout the train are connected to the cars in the rake formation by means of flexible connections. Coupling cocks with long handles arranged for operation and is provided with each end of the connections of MR and BP. Suitable flexible couplings and coupling cocks are fitted to the train pipe at each car end as well as at the ends of the rake.


Ancillary fittings are the pneuphonic horns with accessories, windscreen wiper operating devices, all accessories to Deadman’s Control, fittings and equipment for parking brake control etc. A duplex check valve is mounted in the ancillary supply line to the horn reservoir.

Duplex Check Valve not only ensures a steady controlled air supply for subsequent operation of the aforesaid ancillary fitting all the time but also protects MR pressure for repeated brake applications, if so required, in the unlikely event of MR pressure being severely reduced due to the situation beyond control.


A control governor is provided for interrupting the traction control circuit when an emergency brake application is made. A low-pressure switch is also fitted to interrupt the traction controls, should main reservoir pressure fall below a specified value.These two governors also prevent the train from being moved when the brake pipe is not charged or the main reservoir pressure is inadequate to operate the traction equipment.


Movement of the Driver’s brake valve handle in the operative cab of the rake to Emergency position causes an emergency application. Excessive brake cylinder pressure is released by the brake cylinder safety valve.
Emergency application of the Automatic brake can be made also by opening Guard’s Emergency valve or by a breakaway. In each case, the brake pipe is quickly vented to atmosphere and brake cylinder pressure increases at the highest possible rate causing emergency braking. This is commonly known as brake in-two feature.

If an emergency application is initiated by opening guard’s emergency valve or a breakaway, the driver must move the brake valve handle to Emergency Position to assist the reduction of brake pipe pressure and prevent loss of main reservoir air to the brake pipe through Driver’s Brake Valve. The train must be allowed to stop before an emergency application is released.


Each Traction Controller is fitted with a pilot valve that opens when the traction controller handle is released in an operative position. Thus, should the driver became incapacitated and release the controller handle, the pilot valve in case of BHEL Master Controller or Magnet Valve in case of NGEF Master Controller will open the emergency application valve, which in turn vents the Brake Pipe and makes an emergency application of the Automatic Brake. If the Deadman’s valve is inadvertently released while running, the driver must allow the train to stop before attempting to release the brakes.