Brakes

Aim - this section provides an overview of the typical operation of the Westinghouse air brake system, and describes the "best" brake settings for Open Rails (OR) WAG and ENG files. Settings are based upon NSWGR standards, which mostly used a single air pipe system.

To convert tons to kN = tons x 9.964 kN.

If you wish to provide any feedback on this page, please use the contact page. It would br great to have some feedback as this helps to ensure the accuracy of the information and models.

Index

Introduction

Overview of Westinghouse Air Brake System

Net Braking Ratio (Braking Percentage)

Effect of Brake Shoe Friction

Brake Code - Structure and layout in Open Rails

Sample Brake Code - Wagon Section

Sample Brake Code - Locomotive - Compressor, Reservoir and Train system

Sample Brake Code - Train and Locomotive Control Valve

Brake Calculators

         Vehicle Maximum Brake and Handbrake Force

         Brake Cylinder Size Calculator

         Brake Pipe Volume

         Reservoir Charging Rate

Generic Brake Design Information

Useful References


Introduction

In the early days of operation trains usually only had brakes fitted to the tender of the locomotive, and special wagons, often called the 'brake van' which were applied by the train guard (also known as the brake man) manually, generally when the locomotive driver sounded a pre-designated whistle code. Sadly as trains were operated at faster speeds, and with heavier loads this method of braking was found to be inadequate due to the slow application and response times to stop, and at the time contributed to a number of accidents, such as the one at Abbots Ripton. As a consequence, there were numerous calls for the introduction of a continuous braking system.

Over the years a number of continuous types of air brakes have been developed and used on trains. These include air and vacuum operated brakes. More recently, electrically operated brakes have been introduced to some rolling stock. Naturally the effort to fit continuous brakes to rolling stock was spread over many years, and often started with passenger stock. In some instances with slower, less important rolling stock air brakes were never fitted throughout the lifetime of the rolling stock. In Australia there wer coal hoppers still in service up to the 1980s that did not have continuous brakes fitted to them.

The Westinghouse brake system was a major break through for the safe operation of trains. It has become the predominant type of brake system used by railways around the world. The Westinghouse system has evolved significantly since its invention in 1873, and there have been many system variations as it has been enhanced to cater for high speed and heavier trains.

There have been many detailed books written describing the design and operation of the brake system, and it is not possible to reproduce this level of detail in this page. Instead the page is designed to provide an overview of the basic features and provide some design rules of thumb that can be used to configure the ENG and WAG files of Open Rails. Naturally it goes without saying that actual prototype information should always be used as the first preference if known.

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Overview of Westinghouse Air Brake System

This information has been extracted from various Westinghouse and NSWGR publications, some of which may be found in the NSWGR Documents Section. Whilst a few different styles and types have been used, the following information should apply in general and give a reasonably close approximation of its operation.

Overview of Brake Systems

In the early days of railway operation, the locomotive and brakevan were the only vehicles fitted with brakes. Train operation required the locomotive driver and brakeman to co-ordinate their activities to control the train. After seeing a wreck in about 1867, a 22 year old George Westinghouse patented a "fail-safe" air brake system. If the pressure in the train brake pipe drops, either because the engineer applies the brakes or the brake pipe is broken for some reason, then the brakes are applied by air pressure from a reservoir in each car. The brakes can only stay open if the compressor is pressurizing the line.

During 1877 some locomotives and passenger cars were imported into the NSWGR from North America fitted with Westinghouse air brakes. From the 1880s Westinghouse Air Brakes were adopted as standard for NSWGR passenger cars. Some older cars were fitted with through air pipes, but no brake equipment. By 1904 most passenger stock was fitted with air brakes. Goods stock followed a similar process. Some privately owned coal hoppers, right up to their retirement in the late 1970s, did not have air brakes fitted. Over the years various refinements have been made to the Westinghouse brake. The overview on this page provides a simplified description of the brake operation and design. For more detailed information refer to the useful links section at the bottom of this page.

Passenger and Freight Car Brake System

The diagram below shows a typical Westinghouse train brake system for an older style passenger or freight wagon, and has been extracted from an Australian Westinghouse publication of the early 1950s.

Wagon Brakes

The principal elements of the brake system on a wagon are as follows:

Brake pipe

The brake pipe runs the full length of the train and supplies air pressure to the brake systems on each wagon, as well as provides relevant control signals to operate the brakes. Typically the normal operating pressure in the brake pipe is 75 to 80psi on passenger trains and 60 to 70psi on freight trains.

Brake cylinder

Applies force to the brake shoes on the car wheels. The brake cylinders are selected to provide the appropriate brake force for the weight and speed of the wagon.

In some instances for small stock, such as 4 wheel wagons, combined brake cylinder and reservoirs were used. For larger stock separate reservoirs and brake cylinders were typically employed.

Auxiliary reservoir

The auxiliary reservoir was used to supply air to operate the brake cylinder. Typically the auxiliary reservoirs and brake cylinders proportioned that an equalization pressure of 50psi will, be obtained from 70psi auxiliary reservoir pressure (brake pipe pressure). This typically equated to a triple valve ratio of 2.5. In some instances supplementary reservoirs were installed to provide additional air capacity.

Triple Valve

The triple valve has three duties to perform:

An emergency application of the brakes is bought about by the rapid reduction in pressure of the brake pipe. It should be noted that guard of the train had a brake pipe release valve in the brakevan, which could be opened to drop the brake pipe pressure, and stop the train in the case of an emergency.

Brake System Refinements

Over the years a number of enhanced features have been added to the braking systems, and these include the following.

Grade Control

The purpose of the grade control valve is to slow down the rate of exhaust of the brake cylinder finally retaining a small amount of pressure, thus enabling a recharge or the braking system to be obtained on heavy grades without the necessity of using hand brakes to prevent the train accelerating at too fast a rate.

Older wagons typically had no grade control or had manually operated valves. Typically the Grade Control Valves had the following three positions on them:

Load Compensation

The purpose of using this equipment is to use normal braking force when the vehicle is empty, but to provide additional braking force when the vehicle is loaded. Loaded wagons can use larger braking forces as the Adhesive weight of the wagon is higher, and wheel skid is less likely to happen. If the same loaded wagon braking forces were used on empty wagons, it is highly likely, due to the lighte adhesive weights of the wagon, that wheel skid would occur.

Older wagons typically had no grade control or had manually operated valves. Typically Load Compensation Valves had the following two positions on them:

Modern stock tends to have automatic load compensation equipment which uses a proximity switch or pressure switch to differentiate between load and unloaded wagons.

Naturally, as wagons without load compensation used the unloaded (tare) weight for calculating braking forces, special care needed to be taken by the driver, as the braking power of the train was less then that for a loaded train with load compensation.

Miscellaneous Brake System Impacts

Train Pipe Leakage

The brake system tends not to be a perfectly closed syetem, and it is possible for air leaks to develop in the system. The most likely place for leakage is in the couplings due to the seals becoming damaged. Air leakage can result in a slow decline in air pressure in the trainb brake pipe, which will increase the application of the brakes over time. In most brake positions this leakage is compensated for, and air from the reservoir is used to replaced air which leaks out of the system. In older brake systems, such as the A-6-ET system, the LAP position isolated the train brake pipe from the reservoir which prevented air leakage being compensated for, and thus the train brake pipe slowly decreased in pressure. In newer systems the LAP position is often self lapping, ie it compensates for the air leakage.

Most railway companies require the crew to undertake leakage tests when marshalling a train, and this test is deemed a success if the air leakage is less then 5psi/min.

Locomotive Brake System

The diagram below shows a typical Westinghouse train brake system for a locomotive, and has been extracted from an Australian Westinghouse publication of the early 1950s.

Locomotive Brakes

The brake system on the locomotive consisted of two separate components:

The principal elements of the train brake control are as follows:

Compressor

Supplied compressed air as appropriate for the operation of the train brake.

Main Reservoir

Provide air storage for operation of the train brakes. Typically the pressure in the main reservoir was maintained at 100psi.

Drivers control stand

Typically NSWGR steam locomotioves were fitted with A-6-ET (Engine and Tender) brake equipment, whereas older diesels were fitted with A-7-EL brake valves. This equipment allowed independent operation of the locomotive and tender brake compared to the rest of the train. The locomotive brake may be applied or released, in whole or in part, with or independently of the train brakes, and this without regard to the position of the locomotive in the train. This allowed the driver some flexibility in applying light brake applications or in some circumstances holding the locomotive and tender brakes on after releasing the train brake.

The brake valve stand contained two brake valves, an automatic brake (controls all cars in the train). and an independent brake which controlled the locomotive and tender brakes only. A typical brake valve stand is shown in the diagram below, with the automatic brake on the left hand side, and the independent brake on the right hand side.

Brake Stand

The operating positions of the A-6 and A-7 brake valve are shown in the diagrams below. The Automatic brake valve (Train brake) is shown on the left hand side of the diagram, whilst the Independent brake valve (Engine Brake) is shown on the right side of the respective diagrams.

A6 Brake ValveA-6 Brake Valve.

A7 Brake ValveA-7 Brake Valve.

Automatic brake valve (Train Brake)

The automatic brake valve, which controlled the train brakes had 5 positions of operation as follows:

Independent brake valve (Locomotive and Tender Brake)

The independent brake valve, which controlled the engine and tender brakes had 5 positions of operation as follows:

When releasing the brakes, a "graduated" approach can be used, so that small increases in brake pipe pressure will result in a small release of the brakes.

More Info

If you want information on other types of brake valves, such as the Westinghouse 26-L or 24-RL models, see alternate brake valves page. For more information on the BrakeControl tokens used by Open Rails to model the different types of brake valves, see BrakeControllers page.

Double Heading of Locomotives

When multiple locomotives are being used on the one train, regardless of where they are in the train, except for the lead locomotive, the brake Valve Isolating cocks must be closed, and bothg brake valves should be in the Running position. This will allow the lead locomotive to operate it brakes. It should be noted that the main reservoir on all but the lead locomotive will remain at full pressure.

Prototype NSW brake settings

In setting the brakes as accurately as possible the following prototypical information has been considered. This information has been compiled from various New South Wales Government Railways (NSWGR) publications. You may however substitute information from any other railway systems to achieve a more localised rolling stock setting.

The brakes were set up to graduate off, and but not on.

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Net Braking Ratio (Braking Percentage)

Train Brake

The "net braking ratio" (NBR) of a vehicle is defined as the ratio of the total force applied to the brake block (shoe) on the wheels, proportional to the total weight of the vehicle.

When this is expressed as a percentage it is known as the "braking percentage" and is the figure used to express the braking value of a vehicle. In the case of goods vehicles the usual figure is 60 - 75% of tare (empty) weight and for passenger cars 75 - 90%.

When expressed as a formula:

Net Braking Ratio (NBR) = Brake Force (BF) / Tare (unloaded) Vehicle Weight (W)

Thus to determine the ideal Brake Force applied to the wagon wheel brake shoe, we have the following:

BF = NBR * W

This provides the force applied by the rolling stock brake cylinder and brake levers. To find the actual force applied to the wheels, we need to take into account the co-efficient of friction of the brake shoe, thus the above figure also needs to be multiplied by co-efficient of friction. Refer to the next section "Effect of Brake Shoe Friction" for a more detailed explanation on friction coefficient.

If imperial figures, such as tons are used, then we may wish to convert them to kN for the purposes of including them in the WAG file. (1 ton = 9.964016384 kN ).This calculated figure should be done for each wagon or loco and then inserted as the MaxBrakeForce.

High values of NBR will result in high brake forces being applied to the wheels of the rolling stock, causing the wheels to "lock up" and to skid along the tracks. Various publications provide guidance on the desired values for NBR under different brake configuration scenarios. The following values are examples of the values recommended:

It should be remembered that OR only models the direct brake force applied to the wheels of the wagon.

Rules of Thumb -

Typically, for NSWGR stock, we will assume NBR values of 60% for Goods cars, 80% for Passenger Carriages, 60% for Locomotive Tenders, and 75% for locomotives.

For NSW we can assume that most pre-1970 stock will have cast iron shoes, and thus a value of 20% for the co-efficient of friction was considered appropriate.

For more current NBR recommendated values refer to pg 14 of ARTC - Freight Vehicle Specific Interface Requirements WOS 01.400 .

Thus to calculate the MaxBrakeForce -

MaxBrakeForce = {(0.6 or 0.8) * Tare (or empty) Weight (tons)+ * 9.964016384} x Coefficient of Friction (20%)++ kN

Note:
+
- Wagons fitted with load adjustment capability will have two their MaxBrakeForce calculated with the Tare weight, as well as the fully laden weight.
++ - May need to be varied from this value when implementing brakeshoe curves in OR.

The above formula has been incorporated into the MaxBrakeForce calculator below.

Handbrake

The NBR for a handbrake in rolling stock specifications is between 13 - 28% of the fully loaded weight of the vehicle. Typically we will assume a NBR figure of 20% for both Goods and Passenger Stock.

Thus -

MaxHandBrakeForce = {0.20 * Fully Loaded Weight (tons) * 9.964016384} x Coefficient of Friction (20%) kN

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Effect of Brake Shoe Friction

As the wheel on a wagon rotates, the amount of stopping force that can be applied will be dependent upon the construction and material type of the brakeshoes installed on the wagon. The brakeshoes will have a certain amount of friction (or adhesion) which will reduce the amount of stopping force that is actually applied to the wheel. For example, a single cast iron brakeshoe, will have a friction coefficient of approximately 50% (or 0.5), so that the braking force calculated in the formula above will be effectively halved. The friction of a brakeshoe also varies with the speed of the train. The diagram below demonstrates the impacts of speed, and brakeshoe type on the coefficient of friction.

brake shoe friction

In the diagram, the curves show reprsent the following:

Thus trains travelling at higher speeds, due to the reduced values of friction, will require more force to be applied to the brakeshoe then at lower speeds. For example, if a brake cylinder force of 10,000lbf is applied to a cast iron brakeshoe with the train travelling at say 5mph, then from the diagram above with a coefficient of friction of 0.288, approximately 2880lbf of stopping force will be applied to the wheel. If the same brake cylinder force is applied at 40mph, then as the friction value has reduced to 0.142, the corresponding stopping force applied to the wheel will only be 1420lbf, or approximately 50% of the force applied at the lower speed.

This means that train drivers will need to exercise great care when their trains are travelling at high speeds, as it is possible for the train to become "uncontrollable", and not stop in the desired time to avoid an accident.

When the retarding force between brakeshoe and wheel becomes greater than the adhesion force between wheel and rail the wheel will skid, and as the co-efficient of friction is high at low speeds, wheels are more likely to be skidded at slow speeds. In most cases skidding takes place when the vehicle is moved from rest with the brake applied, when, since the speed of the wheel relative to the brake shoe is zero, the co-efficient of friction is at its highest value. This would, of course, occur only due to failure of brakes to release, to a hand brake being applied, or to any other cause which may prevent the wheel from rotating.

Open Rails Implementation

Open Rails supports the variation of brakeshoe friction with speed, and comes with a default friction curve included (see the diagram in the section above), this curve can be customised as follows:

Note: When calculating the brake force for stock without load compensation, use the Tare (unloaded) weight of the wagon for both full and empty wagons. For wagons fitted with load compensation calculate the loaded and unloaded brake forces separately, and apply then to the relevant loaded and unloaded wagons.

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Brake Code - Structure and layout in Open Rails

In OR, code to define the braking capabilities of the rolling stock is defined in a number of separate locations as follows:

  • WAG files (Non-powered stock) - contain all the braking parameters relevant to the braking equipment usually located on the wagon.
  • ENG files (Powered or Locomotive Stock) - contains all the relevant braking information for the locomotive and train as follows:
    • Wagon sub-section - contains the parameters for the locomotives "own" brake equipment
    • Engine sub-section - train & engine brake operation - contains the parameters for the compressor, general brake system, train and engine brake operation.
    • Engine sub-section - control levers - contains information for the control levers that operate the various brakes.

For consistency of overall operation, braking parameters should be set the same between all common types of rolling stock and only a small number of stock specific parameters should need to be changed.

More Info

Note: It is good practice to put notes into the ENG and WAG files to act as reminder for any assumptions made. These notes can be made with comment statements as shown below:

Comment (Assume Main Reservoir of 9.549 cu ft and air compressor of 8in)

The following sections provide a suggested brake configuration to closely approximate the model the A-6-ET type of brake in Open Rails. As at v1.0 it appears that Open Rails does not support the implmentation of this type of brake. For example, the independent brake only operates on the locomotive at the moment and not the tender. (Note: As from X3202 the engine brake works on both of the locomotive and tender together, some other features of the A-6-ET have still not been fully implemented.)

The key parameters that impact upon the performance of a steam locomotive are described on the following web page.

Standard Air Brake Parameters for ENG and WAG Files (updated August 2016)

The Brake Calculators can be used to calculate some of the relevant values that are required for entry in the WAG files.

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Sample Brake Code - Wagon Section

The brake configuration on this page represents the brake configuration generally used by the NSWGR pre-1950, which did not have emergency or supplementary reservoirs on the wagons.

This type of code goes into the WAG file or the wagon section of the ENG file.

Typically the lines shown in red text are the only ones that would need to be changed to suit individual wagons.

Use the
Brake Calculators to calculate some of the relevant values that are required for entry in the WAG files. Additional information is also available in the Generic Brake Design Section.

WAG File or wagon section of ENG file

Comment ( *************** Brakes - Wagon Section - General ********************** )
    BrakeEquipmentType ( "Triple_valve, Auxilary_reservoir, Handbrake" )
    BrakeSystemType ( "Air_single_pipe" )
    MaxBrakeForce ( 24.95kN )      Comment ( Empty weight - 6.5t-uk, NBR - 0.6, Friction - 0.5 )
    MaxHandbrakeForce ( 12.45kN )
    EmergencyResVolumeMultiplier ( 1.0 )
    TripleValveRatio ( 2.5 )
    MaxReleaseRate ( 50.0 )
    MaxApplicationRate ( 50.0 )
    MaxAuxilaryChargingRate ( 20.0 )
    EmergencyResChargingRate ( 20.0 )
    BrakeCylinderPressureForMaxBrakeBrakeForce ( 50.0 )
    EmergencyResCapacity ( 2.064ft^3 )
    BrakePipeVolume ( 0.386ft^3 )
    ORTSBrakeShoeFriction ( 0.0 0.49 8.0 0.436 16.1 0.4 24.1 0.371 32.2 0.35 40.2 0.336 48.3 0.325 56.3 0.318 64.4 0.309 72.2 0.304 80.5 0.298 88.5 0.295 96.6 0.289 104.6 0.288)      Comment ( == COBRA Brakeshoes == )

Non-Air Rolling Stock

Non-air rolling stock can be modelled by using the following 'abbreviated' code instead of the full code above. For vehicles not fitted with air brakes set the BrakeSystemType to "Air-piped".

Comment ( *************** Brakes - Wagon Section - General ********************** )
    BrakeEquipmentType ( "Triple_valve, Auxilary_reservoir, Handbrake" )
    BrakeSystemType ( "Air_piped" ) Comment (Wagons not fitted with air brakes)
    MaxHandbrakeForce ( 7.971kN )      Comment ( Empty weight - 6.5t-uk, NBR - 0.6, Friction - 0.5 )
    BrakePipeVolume ( 0.145ft^3 )
    ORTSBrakeShoeFriction ( 0.0 0.50 8.0 0.288 16.1 0.241 24.1 0.211 32.2 0.187 40.2 0.173 48.3 0.161 56.3 0.150 64.4 0.142 72.2 0.139 80.5 0.134 88.5 0.129 96.6 0.125 104.6 0.123 112.7 0.121)    Comment ( == Cast Iron Brakeshoes == )

Typically these types of wagons had handbrakes fitted. It was also normal operating practice to 'pin' down (or apply) a number of handbrakes on non-air trains when they were descending steep gradients to maintain control of the train. Once at the bottom of the grade the handbrakes were released.

Make sure that you test your settings with the brake tests described on the testing page.

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Sample Brake Code - Locomotive - Compressor, Reservoir and Train system

This type of code describes the configuration and operation of the compressor, train reservoir and the train braking system, and is located in the engine section of the ENG file.

Use the
Brake Calculators to calculate some of the relevant values that are required for entry in the WAG files. Additional information is also available in the Generic Brake Design Section.

Comment ( *** Braking system *** )

Comment ( == Compressor, Reservoir and General == )
    AirBrakesMainMaxAirPressure( 107.0 )
    AirBrakesCompressorRestartPressure( 90.0 )
    ORTSBrakePipeChargingRate ( 40.0 )
    AirBrakesMainResVolume( 11.0ft^3 )
    ORTSMainResChargingRate ( 0.575 )
    TrainPipeLeakRate ( 0.0833 )

Comment ( == Automatic Brake valve - Train == )
    TrainBrakesControllerMaxSystemPressure( 70 )
    TrainBrakesControllerMaxReleaseRate( 1.0 )
    TrainBrakesControllerMaxQuickReleaseRate( 20.0 )
    TrainBrakesControllerMaxApplicationRate( 1.0 )
    TrainBrakesControllerEmergencyApplicationRate( 30.0 )
    TrainBrakesControllerFullServicePressureDrop( 25.0 )
    TrainBrakesControllerMinPressureReduction( 7.0 )

Comment ( == Independent Brake valve - Engine & Tender == )
    EngineBrakesControllerMaxSystemPressure( 70 )
    EngineBrakesControllerMaxReleaseRate( 1.0 )
    EngineBrakesControllerMaxQuickReleaseRate( 20.0 )
    EngineBrakesControllerMaxApplicationRate( 1.0 )
    EngineBrakesControllerEmergencyApplicationRate( 30.0 )
    EngineBrakesControllerFullServicePressureDrop( 25.0 )
    EngineBrakesControllerMinPressureReduction( 7.0 )

Make sure that you test your settings with the brake tests described on the testing page.

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Sample Brake Code - Train and Locomotive Control Valve

Note: It is recommended that graduation operation be selected with this brake configuration. For graduated operation of the brakes, it will be necessary to select the relevant menu option tickbox in Open Rails before starting.

This type of code describes the controller (brake valves) in the locomotive.

Comment ( *** Brake control equipment *** )
Brake_Engine ( 0 1 0.01 0.25
    NumNotches ( 5
       Notch( 0.0 0 TrainBrakesControllerFullQuickReleaseStart )
       Notch( 0.25 0 TrainBrakesControllerRunningStart )
       Notch( 0.50 0 TrainBrakesControllerHoldStart )
       Notch( 0.75 0 TrainBrakesControllerFullServiceStart )
       Notch( 1.0 0 TrainBrakesControllerEmergencyStart )
       )
    )

Brake_Train ( 0 1 0.01 0.25
    NumNotches ( 5
       Notch( 0.0 0 TrainBrakesControllerReleaseStart )
       Notch( 0.25 0 TrainBrakesControllerRunningStart )
       Notch( 0.50 0 TrainBrakesControllerHoldStart )
       Notch( 0.75 0 TrainBrakesControllerFullServiceStart )
       Notch( 1.0 0 TrainBrakesControllerEmergencyStart )
       )
    )

Brake_Hand ( 0 1 0.0125 0        Comment ( Note: some locomotives were not fitted with handbrakes. )
       NumNotches( 0 )
    )

Make sure that you test your settings with the brake tests described on the testing page.

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Brake Calculators

Vehicle Maximum Brake and Handbrake Force

To use this calculator:

More Info

If you need to convert any numbers on this page for input into the following calculators, then use the conversions page.

Tare (Empty) Weight:

Select input units:
tons (UK) tons (US) tonnes (Metric)

Coefficient of friction (Automatic Brake): Coefficient of friction (Handbrake):

NBR - Passenger: NBR - Goods: NBR - Locomotive: NBR - Tender: NBR - Handbrake:

Results

The following values represent the force applied to the wheels by the brake shoes, and are the values used by OR to calculate a wagon's braking force.

Weight (Tons UK):    Weight (Tons US):     Weight (Tonne Metric):

Goods - Brake Force (kN):     Handbrake Force (kN):    

Passenger - Brake Force (kN):     Handbrake Force (kN):

Locomotive - Brake Force (kN):    

Tender - Brake Force (kN):     Handbrake Force (kN):

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Brake Pipe Volume

The appropriate values can then be entered into the relevant input boxes below. The calculator makes allowance for the brake hose connection between the cars (two per car). The exterior length of the car (excluding the couplers) should be entered into the calculator.

The train brake pipes vary depending upon whether the braking system is Air or Vacuum. Air systems typically use 1.25" pipes, whilst Vacuum systems use 2.0" pipes. Select the correct brake system type.

If you need to convert any numbers on this page for input into the following calculators, then please use the conversions page.

Car Length (ft):

Select car brake type:

Vacuum Air

Results

Pipe Volume (cu ft):

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Reservoir Charging Rate

The charging rate for a reservoir can be determined by the following formula:

Charging time (min) = [ Reservoir Vol (cu ft) * (Max Press (psi) - Min Press (psi)) ] / [(Free air (scfm) * Atm Press (psi) ]

Where scfm = Standard cubic feet per minute

The outcome of this formula is then converted to a charging rate per sec for inclusion into open Rails.

This calculator can be used to determine the charging rates for various air reservoir type devices as follows:

The appropriate values can then be entered into the relevant input boxes below.

If you need to convert any numbers on thsi page for input into the following calculators, then please use the conversions page.

Starting Pressure (psi):     Max Resevoir Pressure (psi):     Main Resevoir Volume (cu ft):     Compressor Free Air (cu ft / min):    

Results

Charging Time (mins):     Charging Rate (psi/sec):    

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Brake Cylinder Size Calculator

To calculate the size of the necessary brake cylinder size for the stock in question the following equation can be used as a rule of thumb.

Brake Cylinder Force (lbf) = {Max Brake Force (kN) / Leverage ratio} (kN)

Leverage ratio - The connection from the brake cylinder to the brake-shoes is made by beams and levers, or their equivalents. Leverage ratio is a measure of the mechanical leverage of the levers in the braking system. Typically it will be somewhere between 7 and 9.

These values can then be entered into the appropriate code lines below.

If you need to convert any numbers on this page for input into the following calculators, then please use the conversions page.

Max Brake Force (kN):     Leverage ratio:    

Results

Brake Cylinder Force (kN):    

Once the required brake Brake Cylinder Forece is determined, then the appropriate brake cylinder size can be found, and then the corresponding auxiliary cylinder size selected.

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Generic Brake Design Information

For instances were specific brake parameters are not know the following information may be used instead to ascertain an appropriate approximation for some brake parameters. Always use known information where available. In the tables below some values have been calculated based upon other values in the table, and are shown in green figures in the table.

Standard Brake Cylinder Size

The following table shows the maximum force exerted by the cylinder when the pressure in the cylinder is fully charged to 50psi. The required brake cylinder force can be calculated with the wagon brake force and the brake cylinder size calculators above. Once this is done an estimation can be made of the brake cylinders that need to be fitted to a locomotive, carriage or wagon, by comparing the kN force result with the closest relevant figure in the right hand column of the table below. If the calculated value exceeds the value shown in the right column, as may be the case for some heavy stock such as a locomotive of modern bulk hoppers, then multiple brake cylinders can be used to achieve the most appropriate result. For example, a NSW C38 class locomotive was fitted with 2 x 15" Brake Cylinders, whilst the tender had 2 x 12" brake cylinders. For multiple brake cylinders multiple the brake cylinder force by the relevant number of cylinders required, ie 2 off 12" = 50.264kN. Cars and wagons can have can have brake cylinders mounted on each bogie (truck).

Brake Cylinder Size

Force exerted

Cylinder capacity (@ 8" travel)

(in)

(lbf)

(tonf)

(kN)

(cu in)

(cu ft)

6

1,400

0.625

6.227

226.2

0.131

8

2,500

1.116

11.120

450

0.260

10

3,900

1.741

17.348

675

0.391

12

5,650

2.522

25.132

950

0.550

14

7,700

3.437

34.251

1,280

0.741

16

10,000

4.464

44.482

1,650

0.955

18

12,700

5.670

56.492

2,085

1,206

For locomotives, the suggested size of brake cylinder used for different weights on driving wheels is as follows: