Early wagon brakes were operated by a simple lever and acted on only a single wheel, however from the 1880s the handbrake design by Morton that we see on many of our wagons was developed.
The brake lever extended upwards from a centrally mounted ‘V hanger’ and brake blocks were pressed against the wheels by push-rods which passed through metal supporting loops called ‘brake hangers’. The long brake lever allowed the shunter to exert a considerable force on the brakes. Levers generally extended up towards the right hand end of the body and the handle on the end of the brake lever was usually painted white to make it more visible.
Whilst early wagons had single push blocks on one side of the wagon only, as the weight of wagons and their loads increased so did the amount of braking effort required. Greater braking effort came from using brake blocks on both sides of the wagon and later by using clasp brakes which have two blocks per wheel.
Various designs evolved to transmit and multiply the applied lever effort to the brake blocks to ensure that sufficient brake force could be easily applied to hold a loaded wagon on a gradient. A cam or slotted link arrangement is used so that the handbrake on either side of the wagon operates the brakes on both sides via the transverse shaft.
Handbrakes can also be used during the operation of partially fitted or unfitted freight trains which have no means for the driver to brake the unfitted wagons when he needed to slow down or stop the train. The guard ‘Pins Down’ the handbrakes at ‘Stop and pin down wagon brakes’ locations (usually prior to a severe downhill section of track and known by train crew as part of their route knowledge) so that the handbrakes help ensure that the driver retains control of the train on the downhill section. The train then stops again at the bottom of the incline to allow the guard to ‘take up’ the handbrakes (release them).
The effectiveness of the handbrake on a new design of railway vehicle is established by conducting a static test, whereby the force needed to move a vehicle along the rails, with its handbrake applied, is measured. This resulting force is used to determine the gradient on which the handbrake will hold the vehicle.
In order to move the test vehicle along the rails, a hydraulic ram fitted with a calibrated ‘Load Cell’ is installed between the drawgear of the vehicle under test and an anchor vehicle on the same line. The anchor vehicle was parked with its brakes fully applied and chocks placed tightly under each wheel.
A test is not valid if the wheels slide along the rails, therefore it is important to carry out a test within a workshop, where the rails are clean, dry and preferably level. To ensure a consistent and representative application of the handbrake lever, weights are attached the lever that are equivalent to the standard level of effort that could normally be applied at the lever end by the average person weighing about 60kg applying the handbrake. The test is always repeated to assess the performance of the handbrake when applied from both sides of the vehicle.
The acceptability of the performance of a parking brake was assessed by establishing the gradient on which the vehicle under test could be held without rolling away. The British Railways standard requirement for the design of freight wagon handbrakes is such that each wagon must be able to hold its fully laden weight stationary on a gradient of 1 in 40.
The hydraulic ram is operated either by a hand pump or by an electrically powered hydraulic pump in order to haul the vehicle under test for a distance of between 8and10inches along the rails. The measurements taken from the load cell of the peak value of resisting force are used to calculate the equivalent holding gradient result as follows:-
After each test is completed it is necessary to return the vehicle back to its original position ready to start the next test.
Many locomotives, coaching stock vehicles and newer designs of wagons are fitted with a handwheel & screw type method of applying the handbrake.
The principle and method of testing is very similar however instead of using weights applied to the handbrake lever, a specified level of torque is used when applying the handwheel. This is calculated and applied with a calibrated torque wrench based on the diameter of the handwheel and the standard level of effort of 500Newtons applied at the handwheel rim.
An example of the table of results produced during a handbrake test on a wagon fitted with a handwheel type handbrake.
In general the handbrakes fitted to freight wagons are more than sufficient to hold a loaded wagon on a steep gradient when applied fully; therefore when they are applied to an empty wagon their effectiveness is significantly increased. As such, if an empty wagon is moved with its handbrake ‘ON’ then the effectiveness of the brake will cause the wheels to lock and slide; this can very quickly cause significant damage to the wheelsets in the form of wheel-flats and cavities that are costly to rectify.
This is an example of wheel tread damage caused by operating a vehicle with a handbrake on.