Describing how roller brake testers work is VLT Test Services director Brian Beacon: “The system is basically a motor working via a gearbox with a chain that drives the rollers. Between the gearbox and the axle rollers, a strain gauge measures the amount of torque on the rollers as the brake is applied. That is converted into digital milliamp signals that is then transferred to the basic brake pressure.”
Despite being robust enough to withstand up to 20t axle loads, roller brake testers (RBTs) are still required to produce precision measurements of braking force day after day. Misuse, and wear and tear, are the biggest maintenance issues that they face, he contends. “The worst thing is when they are driven over at high speed; the shock can damage the measuring equipment.”
There are wearing parts, he adds: the chain wears and stretches, and there are bearings that can wear. Over time, electronic components such as load cells and strain gauges will fail, as will various sensors and perhaps the motor or gearbox, too.
RBTs work best if looked after properly – or as Beacon puts it, “servicing, greasing, cleaning, adjusting and calibration” at six-monthly intervals.
Also keen on servicing is Louis Tunmore, MAHA UK dynamometer and garage equipment specialist. He says: “We check that chains are adjusted and lubricated correctly. It is essential that correct lubricants and quantities are used in both cases. Also, the electronic control side needs a thorough inspection, as, sadly, it’s not unusual to see electrical components damaged by rodents! We thoroughly inspect the control system to ensure that it is all working correctly. Controlling the two-speed motors are various contactors; we also ensure that those are in good health. Along with the reverse direction controls, we check these contactors because they are not so frequently used, and a problem may not be obvious.”
Checking for the latest edition of the DTP database, distributed by DVSA, is essential, as it gives the brake configuration of all trucks tested in the UK. Its technical data includes make, model, maximum axle weights, brake system splits, gvw and other vital information to enable the equipment to apply the correct pass/fail formula.
The rollers themselves “are designed for years of heavy use and don’t see a fraction of their design potential,” he adds. A damaged roller coating is normally caused accidentally or by misuse, adds Tunmore. “If you start losing patches from the rollers and expose bare metal, the coefficient of friction may fall below what is required to record a lock.”
Once the RBTs are in tip-top shape, both men also highlight the importance of calibrating the system, since its results provide safety-related data about vehicle braking performance.
And this requires an outside expert, advises Beacon, such as one of VLT’s 22 mobile technicians, who can get the job done in three to four hours. “Some of the maintenance work [a workshop] could do, but they can’t calibrate it; that has to be done to DVSA standards. It requires a calibration kit, which has to be calibrated to a traceable strain gauge. That’s not something the workshop would have.”
MAHA UK also employs a team of trained mobile engineers. Tunmore adds: “We also recommend that we carry out inspection and maintenance. All of our engineers carry spare parts and dedicated calibration devices, along with a tech dongle for diagnostics. As manufacturers of our product, we have full access to the latest service information and equipment to ensure the job is done correctly.”