[darwins]

Looking into possibilities of modelling the Westinghouse-Henry double brake, SME brake or SMEE braking system, I noticed that SMEE braking is very similar to the model of EP only braking that we have in Open Rails:


EP brake has two pipes - brake pipe and main reservoir pipe / SMEE brake has two pipes – brake pipe and straight air pipe

(In USA the brake pipe in the SMEE system is called the 'Emergency Pipe' but it is the 'normal' brake pipe or air train pipe.)

Triple valve and auxiliary reservoir do not change during EP only service braking or during SMEE service braking

Application and release are graduable for both EP only service braking and SMEE service braking

Equalising reservoir is not required for either EP only systems or SMEE systems

Brake application and release are rapid for both EP systems and SMEE systems,
For (twin pipe) EP systems application and release in all cars is 'instant' as it is controlled by electrical signals.
For SMEE application in motor cars is 'instant', but for trailer cars there should be a very small delay for air to arrive from the nearest motor car.


For the EP brake the main reservoir pipe is at main reservoir pressure or as set by AirBrakeMaxMainResPipePressure ( )

For SMEE the atraight air pipe is at brake cylinder pressure


I would like to suggest that a simple model of the SMEE braking system could be added to Open Rails by way of a few mostly cosmetic changes to the present EP only braking model. These are:

Renaming the Main Reservoir Pipe in the HuD as the Straight Air Pipe.

Setting the Pressure in the 'Straight Air Pipe' as equal to the brake cylinder pressure.

Renaming the relevant EP brake tokens as SME (or for Australians SEM) brake tokens bearing in mind that the straight air brake only works if the brake pipe (aka emergency pipe) is fully charged.

TrainBrakesControllerSEMHoldStart = works as TrainBrakesControllerEPHoldStart only if brake pipe pressure = TrainBrakesControllerMaxSystemPressure

TrainBrakesControllerSEMOnlyStart = works as TrainBrakesControllerEPOnlyStart only if brake pipe pressure = TrainBrakesControllerMaxSystemPressure

TrainBrakesControllerSEMFullServiceStart = works as TrainBrakesControllerEPFullServiceStart only if brake pipe pressure = TrainBrakesControllerMaxSystemPressure

it may well be worth also defining a release token

TrainBrakesControllerSEMReleaseStart = Allows air to be rapidly released from brake cylinder = TrainBrakesControllerFullQuickReleaseStart only if brake pipe pressure = TrainBrakesControllerMaxSystemPressure

TrainBrakesControllerMaxSystemPressure ( ) - sets the pressure of the brake pipe (aka emergency pipe)

There is no need for a new item to set the maximum pressure of the straight air pipe as this is set by BrakeCylinderPressureForMaxBrakeBrakeForce ( )


All of should provide a reasonably accurate model of SMEE braking.

It could also be used as a crude model of the the Westinghouse-Henry double brake, or the older SME brake - which would work well for trams, single cars or short trains, but would lack the propagation delays of air travelling along the straight air pipe in longer trains.

Any thoughts? Is it worth a try?