ELECTRO-PNEUMATIC BRAKES (I.R)

ELECTRO-PNEUMATIC BRAKES (I.R)

A model of E-R Brake System at RCF

The Following Contents from Rail-technical

Please refer to HERE for detailed Explaination

Introduction

Originally designed for subways or metros, the electro-pneumatic brake has more recently been used on main line passenger railways and some specialised freight operations.  Its main advantage over the air brake is its speed of control and quick on-vehicle reaction times, giving instantaneous control of the whole train to the driver.

Even the most modern, purely air brake systems rely on the transmission of an air signal along the brake pipe.  This is initiated from the front of the train and has to be sent to all vehicles along the train to the rear.  There will always be a time lapse (called the propagation rate) between the reaction of the leading vehicle and the reaction of one at the rear.  This time lapse is a considerable restraint on operation.  It causes the braking of vehicles to happen at different times along the train so that while some cars are slowing down, others are still trying to push, unbraked, from the rear.  When releasing, the front of the train is pulling the rear, still braking, and causes stress to the couplers.

Principles of the E-P Brake

There are many types of e-p brake systems is use today and most of them were developed as an "add-on" to the original air brake system and, as a result, incorporated some common principles in their design as follows:

• The e-p brake operates as the service brake while the air brake is retained for emergency use
• The e-p brake does not compromise the fail-safe or "vital" features of the air brake
• The air brake normally remains in the "Release" position, even while the e-p brake is in "Application" and the same brake cylinders are used.
• E-P brakes are invariably used on multiple unit passenger trains.
• E-P brakes use a number of train wires to control the electrically operated brake valves on each car.
• The train wires are connected to a brake "valve" or controller in the driver's cab.
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E-P Brake Release

In the "Release" position (diagram left), both electrically operated valves are de-energised, the application valve being closed and the holding valve being open.  Once the holding valve is open, brake cylinder air can escape and release the brakes.  It is possible to stop the release by energising the holding valve again.  This prevents any more brake cylinder air escaping.  By adjusting the applications and releases of the brake during the stop, the driver is able to get a very precise stopping position.  In addition, the response of the equipment to his commands is instantaneous on every car.  This sort of control is essential for a rapid transit service on a metro line with frequent stops, heavy patronage and short headways.

E-P Application

This diagram shows the operation of the holding and application valves during an e-p brake application.

The application valve is energised and open while the holding valve works the opposite way, being energised and closed.  Main reservoir air feeds through the application valve into the brake cylinder to apply the brakes in the usual way.