Freight Wagon Information

Some basic information about goods wagons

Q 1 - How do you tell the ‘A’ end from the ‘B’ end?

When modelling or photographing wagons, it is a good idea to know which end of a wagon is what! As the drawing indicates the relationship of equipment is basically the same on all rollingstock.

On both 4 Wheel and bogie wagons, the direction of the brake cylinder piston always points to the handbrake wheel, which is always fitted on or towards the ‘B’ end of a wagon.

The brake equipment is laid out underneath the wagon, along the centerline on 4 Wheel wagons and off to the right-hand side on bogie vehicles.

On bogie hopper wagons, all brake equipment is arranged on the ‘B’ end platform. The handbrake is usually mounted on that end too, but exceptions do exist.

The latest bogie wagons, such as well wagons and multi-pack vehicles have bogie mounted brake equipment. They only have a

Multi-compartment air reservoir/triple valve attached to the chassis.

Q 2 – How does the air brake system work?

The basic principal of the air brake system is that air pressure is used to keep the brakes released. Any reduction of pressure in the system will cause the brakes to apply. The driver applying the brakes from the locomotive can make this reduction, a burst train brake hose or any other event that causes the separation of brake hoses, derailment etc.

Each wagon is fitted with a:

- ‘Brake Pipe’ which travels the full length of the vehicle At each end there is a flexible brake hose and shut-off tap.

- ‘Auxiliary Reservoir’, which stores air under pressure

- ‘Triple Valve’, this is the brain of the air brake system. It perform 3 processes (CAR),

o Charges the auxiliary reservoir from the BP,

o Applies the brakes by directing air from the aux reservoir to the BC and,

o Releases the brakes by directing the air in the BC via a grade control valve or choke to atmosphere.

- ‘Brake Cylinder’, which turns air pressure force, via a piston into mechanical movement of the brake shoes thru brake rigging.

- and a ‘Handbrake’, that is used to secure a wagon for extended periods.

Basic Automatic Train Brake Operation –

Once all the brake hoses along the train are coupled together, and to the locomotive, the driver places his brake handle into the release position and train brake pipe is charged from the locomotive’s ‘Main Reservoir’ (MR) to full brake pipe pressure (BPP). The brakes release as the BP is fully charges.

The Triple Valve (TV) is basically a pressurized, horizontal cylinder with a piston inside. On the left-hand side of the piston there is brake pipe pressure (BPP), on the right-hand side there is auxiliary reservoir pressure. The TV allows the charging of the auxiliary reservoir from the brake pipe when the BP is being charged. This is done by the inrush of brake pipe pressure on the left being greater than aux reservoir pressure on the right, thus moving the piston to the right, this opens a port to the reservoir and charges it to full BPP. When both pressures are at full BPP, they are termed ‘equalized’ and the piston rests in mid position.

When the driver moves his brake handle to apply the brakes, BPP escapes to atmosphere and the train BPP is reduced. The TV piston slides to the left as the auxiliary pressure becomes greater than BPP. This movement of the piston opens a port, which then allows auxiliary reservoir pressure to flow into the brake cylinder. This pushes out the piston inside the BC and forces the brake shoes against the tire of the wheel. As the pressure inside the auxiliary reservoir drops, the piston inside the TV returns to the middle as both pressures equalize, this in turn closes the port to the BC.

The driver can make a further reduction in BPP if needed, and the process will repeat again.

When the driver moves his brake handle to the release position, air again flows into the BP, and inside the TV, the BP now being greater than auxiliary reservoir pressure, slides the piston to the right. This opens a port to allow BP to flow into the aux reservoir to recharge it. Another port is opened which allows the air in the BC to escape via grade control valve or choke to atmosphere to release the brakes.

Q 3 – How is brake equipment laid out on different types of vehicles?

The short answer is that all vehicles had equipment laid out differently!

However, there are common versions of brake layout design.

This drawing shows the most basic form of air brake design used on NSW rollingstock. The principal design was used on both 4 Wheelers and early (till mid-1950’s) bogie wagons. It is suitable for vehicles that weigh up to 70t gross or run up to 65 km/h. The drawing does not show the typical connection between the brake cylinder piston and the brake shoe. This is done by a system of levers and rodding.

The next drawing shows how the basic system was improved as trains became heavier and longer. The main addition is the supplementary reservoir; it supplies a larger volume of air to apply the brakes. It is used on vehicles that weigh over 75t gross and operate up to 80 km/h

This design, introduced the use of main reservoir air from the locomotive to assist in recharging the supplementary reservoir on the vehicle. These wagons are fitted with a brake hose as well as main reservoir hoses on the wagon headstock.

Air from the supplementary reservoir is also used for other pneumatic equipment such as bottom discharge door/roof hatch opening systems, where fitted. This design is used on wagons with a maximum speed of 115 km/h.

The next ‘big leap’ in air brake design was the use of bogies with the brake equipment mounted in them. In Australia, it has been used from 1995 on newly built long container wagons and other body types that do not allow ‘traditional’ designs to be used, such a multi-pack well wagons.

All air delivery to the brake cylinder is via flexible hoses to each bogie.

Q 4 – What is Grade Control?

Q 5 – What is Load Compensation?

This equipment compensates for the weight of the payload on a wagon. When a wagon is running empty, the amount of braking force needed to slow the wagon is less than that is required when the wagon is running around loaded. The compensator reduces the air pressure that enters the BC when the wagon is empty and supplies normal pressure when the wagon is loaded.

The Load compensator is changed manually, as shown by the two types in the picture.

Most modern wagons are changed automatically using a pressure switch mounted on the body or on the bogie bolster. The switch is activated when it strikes the bogie side frame as the body/bolster lowers when the wagon is loaded. Wagons fitted with Load Compensation equipment have a square on the body side or codeboards on each side. Automatic Load Compensation equipped vehicles have ‘ALC’ marked on the wagon codeboards.