Weighbridge Test Wagons

[Jerome West]

Can anyone give some feedback on these wagons?

IMG_2040.jpg (49.87 KiB) Viewed 2589 times

IMG_2041.jpg (51.63 KiB) Viewed 2589 times

[Craig Duckham]

Possibly used to test the weigh bridges around the country, for setting them correctly. Common to find them at a grain mill and such places.

[Steve Appleton]

Hi Jerome,
I do not know about these particular test wagons. However, many years ago, in a previous lfe, I worked in the then Rhodesia (now Zimbabwe) with a company that, amongst a wide variety of industrial and medical electronic products, supplied digital electronic weighbridge equipment to industrial concerns.
These were the amongst first to be installed anywhere in Africa built entirely in-situ using reinforced concrete construction instead of prefabricated steel beams, steel plate and complicated mechanical levers at the time still used by the opposition firms. Unlike mechanical weighbridges, these decks incurred essentially no vertical movement, were much more robust; the mass on top being determined by digitally measuring and summing the outputs of btween four and eight electronic load cells (a form of strain guage) placed under the deck's beams.
Being used in trade, these weighbridges, like all others, had to be extremely accurately calibrated and then assized by a government trade inspector. To do that required the placement of assized weights onto the deck starting with a few and building up to the full certified mass that the bridge was permitted to weigh. In the case of a rail bridge this could be some 150 tonnes or more.
The weights we used belonged to the government, came in 10kg and 20kg steel blocks, each having been indivdually calibrated and certified by them. As you can imagine, this meant the use of lots and lots of weights and lots of labour over several days to stack them on and off the weighbridge, often several times over, to get the calibration adjusted to within permitted tolerances whilst weighing from as little as 100kg right up to 150,000kg.
The weights themselves came in two short railway wagons very simlar to those pictured although they were not gaudily painted like those. Nonetheless, they did have 'no fly shunting' and 'shunt with care' signs on them.
I developed various techniques and short cuts to speed up the process, which usually started with me being the test weight and standing at various points all over the deck. Yes, I only weighed (or rather had a mass of) exactly 70kg in those days and this provided a very quick way to get the zero point and the start of the calibration curve correct. Later, we would stack some weights on the bridge, calibrate and then move them around to ensure that the mass read the same at every point on the deck. Of course there were not enough weights to reach the total capacity of such a weighbridge, so once sufficiently accurately calibrated to about 60 tonnes or so we would use the wagons themselves as a base or tare test weight, then adding the indivdual loose weights back onto the deck to reach the full load. That meant moving the wagons on and off the bridge several times, and I became an expert at bleeding of the vacuum brakes and using a pry-bar ('gwala' in local parlance) to move the wagons just where I wanted them.
Finally, it was necessary to run short trains over the bridge to ensure that after such an event the bridge deck was still perfectly alingned and accurate. Being in a pit under such a massive concrete structure, relying on only six load-cells to hold it up, with nowhere to go should it colapse whilst a diesel loco runs over it takes a leap of faith in the design engineers and their calculations.
Once complete, we would have to repeat the whole exercise a day or two later for the benefit of the government assize inspectors.