Slip Brake testing
Slip brake testing is a long standing method of measuring the braking performance of a vehicle.
The test train usually consists of a locomotive, a Test Car, modified with a specially-piped independent braking system
and fitted with a slip coupling on the rear and the test vehicle.
The test train is accelerated to the desired speed and then the locomotive’s power is eased off and the Test Car brake is
isolated from the test vehicle. The slip coupling is then operated, releasing the test vehicle.
The Test Car and locomotive continue with the brakes released but the test vehicle has now had the brake applied automatically by the separation of the brake pipes and hence begins to decelerate.
Safety lights are fitted to the test vehicle which flash alternatively as long as the vehicle is moving
The test train and test vehicles continue along the line until the test vehicle is observed to have come to a stand by the
change of the flashing lights to a steady indication
After the test vehicle comes to a stand, the test train then sets back to the stopping point in order to re-couple to the test vehicle. The distance of the stopping point from the release point is recorded by instrumentation
carried on the test vehicle and the Test Car.
Following this the whole train is propelled back to the starting point and the test repeated at a different speed.
Tests are conducted in both tare and laden condition.
In this way a comparative record of brake performance is built up for various speeds and loads and the ability of the vehicle
to meet the NR Statutory Braking Curve requirements is shown.
This had been done for a number of years and from the early 1970's the Testing Section always carried out their tests under a total possession on the Down Slow line near Winsford, north of Crewe on the WCML.
This line was straight and level and the train could propel back to the starting point as required during the tests. Altogether an ideal site for braking tests and once completed the train would go forward to Warrington where the loco would run round then head for home.
On the formation of the RTC the test vehicle used for such tests was the former Eastern Region Dynamometer Car No:2, later DB999500 which was inherited from the York CM&EE and became Test Car 2. It was modified with a specially-piped independent braking system and fitted with a slip coupling on the rear.
It had an unfortunate demise in an accident on slip brake testing work in 1974 when the vehicle under test failed to stop and collided with the Test Car at low speed. Fortunately nobody was seriously injured, just shaken but the Dynamometer Car suffered irreparable damage to its sensitive and integral instrumentation. It was dumped at Crewe Coal yard for a number of months before being cut up on site.
Latterly a new Test Car 2 was used. Numerous tests were conducted up until privatisation on freight and passenger vehicles, tare and laden at various speeds
There was an interesting article by Steve Morris of Ty Mawr Publications here which has a number of photos of slip testing and includes latter day testing on the Great Central Railway, Loughborough but the link no longer works
Some photos from 1986
Click on the picture for a bigger image - photos are courtesy Dave Bower
|Class 47 with Test Car 2 and the test vehicle approaching the site|
|Propelling back to pick up the wagon|
Here are a series of photos depicting a typical slip and brake test on a bogie hopper wagon on 13th July 1999 on the Winsford site
Click on the picture for a bigger image - photos are the author's
|Class 47 with Test Car 2 and the test vehicle approaching the site - just past the bridge in the above photo - 13 years later!|
|The power is eased off and the slip coupling pulled. The photo shows the moment after separation|
|The Test Car and locomotive continue unbraked and the test vehicle has now had the brake automatically applied by the separation of the brake pipe - note the safety lights on the test vehicle which flashed alternatively as long as the vehicle was moving|
|The vehicles continue along the line|
|After the test vehicle comes to a stop the train is propelled to the stopping point in order to collect the vehicle|
|The engineers now have the
opportunity the check the instrumentation, brake disc temperatures etc
Once all is re-coupled the test train propels back to the starting point and the test is repeated
More pictures will be added as time permits
For many years, brake tests on freight wagons were
carried out on the national network, latterly between Crewe and Winsford. Up
until 1993, this testing was carried out free of charge to the operator.
However, with the run up to privatisation and with track access
charges/traction hire/traincrew/test staff etc., the cost of a test slot
escalated sharply to several thousands of pounds.
The first testing at 75mile/h on GCR took place in
2008 involving slip brake tests on a WH Davis Super Low 45 wagon. Many tests
have been carried out since and, although GCR has to apply for a letter of
no objection from ORR each time 75mile/h testing is carried out, to date
there have been no problems.
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