The MID has a section dedicated to Rail Weighbridges: The Measuring Instruments (Automatic Rail-weighbridges) Regulations 2006. However, there is no such section for road weighbridges.
There are legal requirements for public weighbridges that do not apply to private ones. After checking on installation, the Trading Standards Officer (TSO) will check (reprove) the weighbridge every six months and give it a stamp. This stamp will be obliterated by the TSO if it fails a test, but will be reinstated if it passes. Any weighbridge certified by the TSO is acceptable to us.
As above, the TSO will stamp the weighbridge on installation. However, from then on it is up to the trade to have the weighbridge re-proved – the TSO will not test the weighbridge as a matter of course and obliterate the stamp if it is found inaccurate. The weighbridge is only acceptable therefore if it has been reproved at least annually.
As with flow meters, there will be accuracy classes of weighbridge, and these are:
| Accuracy Class | Maximum permissible error expressed as a percentage of mass of a single wagon or total train as appropriate |
| 0.2 | + or - 0.2% |
| 0.5 | + or – 0.5% |
| 1 | + or – 1% |
| 2 | + or – 2% |
Rail tank wagons are loaded from the top, often by remote control apparatus that can include a tank-measuring probe (a type of ALG) as well as by measurement by flow meter. The loading system will also include vapour recovery pipes.
Like road tankers, the initial loading is at low flow rates to stop foaming and turbulence that might cause either static or an electrical spark. Loading is then completed at a higher rate. Where a printout is given for the Rail tank wagon it must give the weight of the wagon and its load.
Rail tanks, where checked manually are usually ullaged rather than dipped. However, if automatic equipment fails we may give permission for a rail weighbridge to be used. If this is the case wagons need to be weighed on a certified weighbridge separately, by being uncoupled, both before and after loading.
