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STEADY AS SHE TIPS
Page 42
Page 43
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Despite an alarming toll of accidents involving toppling tippers, there are few products on the market aimed at making them more stable. We find out why and look at what is available.
• According to one industry estimate, there are up to 2,000 accidents a year involving tipping vehicles that fall over sideways while discharging their loads. Semi-trailers suffer worst because they tend to be longer than rigids and can be less stable during tipping. Powder tankers are particularly vulnerable because if the load sticks you can't see it. But all tipping vehicles face a similar threat.
Recently, there have been two main approaches to the problem. One involves building a sensor into the tipping mechanism that will detect any sideways movement and halt the tip. The other provides a jacking system that will brace the body against the ground. Sometimes these jacks are mounted on outriggers, like those on mobile cranes, and extend the tipping base sideways. Developments on both fronts are under way, yet there is less activity now than there was even two years ago.
One cause of this slow-down is the concept of product liability. Manufacturers reason that if they provide a safety device for a vehicle, and then that vehicle is involved in an accident they could be held responsible.
With tippers, the problem is particularly acute because it is so difficult to anticipate all the factors that might contribute to an accident — uneven ground, for instance.
In systems where the driver has to raise or lower jacks or other stabilising devices, there is the possibility that he may forget to retract them after use. Then, a system which is meant to prevent an accident could end up being the cause.
In the cost-conscious business of tipper operation, another factor is operator resistance to any device which has no obvious benefit in day-to-day terms. Safety systems involve a weight and cost penalty, and this has deterred many operators. Tipping gear manufacturer Edbro of Bolton, says operator resistance is the chief reason for having discontinued production of its Active Safety Stability System which it launched two years ago.
The Edbro system used hydraulic rams at the back of the chassis to provide a rigid tipping base, and counteract any tendency for the chassis to tilt on its springs. Tipping was halted automatically if the load became imbalanced, and the driver could extend the stabiliser legs to regain stability.
A similar system, unveiled by Drum Engineering of Bradford two years ago, is still available — a batch of 20 sets was supplied to an operator recently. However, Drum is no longer promoting it because it wants to review the implications of current legislation.
The Drum system, priced at around E2,000, also uses a pair of hydraulic jacks, mounted vertically behind the back wheels of the semi-trailer. A safety interlock prevents the body being tipped until the jacks are lowered, and then prevents the jacks being raised until the body is down again. The controls are at the back, another safety feature, which prevents the driver from tipping while in the cab.
Both these systems operate within the width of the vehicle. However, according to George Neville of George Neville Safety Systems, Kirkby-in-Ashfield, the best solution is to extend the tipping base outwards. The company achieves this with a pair of swing-out legs that replace the usual trailer landing legs.
These stabilisers consist of deep, flanged beams which are hinged from the main chassis members and have extending hydraulic legs at the ends. In transit they are folded against the chassis; but when swung out, they increase the usual chassis width from 2.5 metres to around 3.6 metres. Once again, this system is not being actively promoted, but remains available. The tare weight penalty is around 190kg, the price around 21,400 including electro-hydraulic power pack.
A significant feature of the Neville system is its broad, flat feet, which are 300rrun square. Broad feet also feature on a simpler system used by some specialist tanker manufacturers. Typical is Carmichael of Worcester, which fits what is effectively a pair of trailer landing legs at the back of the chassis, behind the wheels. They are extended manually to brace the chassis against the ground.
A different approach has been adopted by Tasker Trailers, which has had a system under development for two years. This uses small hydraulic rams mounted vertically between the trailer axles and the chassis. Their hydraulic circuitry is integrated with the main tipping ram's, and sensors divert fluid into the rams as soon as any tendency to lean is detected.
The system operates on a fixed cycle. As soon as the body tilts more than 1.5° out of the horizontal, tipping stops and the correcting rams come into play. At this point the driver has an opportunity to assess the situation, and stop tipping if he thinks it is unsafe.
Trials have proved promising, according to sales director John Hope. The main bugbear at the moment is air suspension, whose automatic load equalisation tends to counteract the effect of the system. However, Hope is aiming to have a system for mechanically-sprung trailers on the market by the end of the year, priced at about 22,000.
Meanwhile, do the existing systems work? A company that has gained more experience than most is powder-tank specialist Samuel Longson, in Derbyshire. It was one of the first users of the Drum Engineering system, and later bought a batch of Edbro installations. John Hudson, who is behind the exercise, says both systems have shown promise, but neither has been without problems.
"1 wanted a limited tip facility, to allow an existing load-weighing system to come into effect, but the Edbro people never really got the valving for this sorted out. The Drum system does allow it, but on our installation the system involves extending the rams until the back wheels are virtually off the ground."
Longson is currently using a system under development by NCS of Chesterfield. The prototype — which consists of two 70mm diameter, 750nun long, solid rods which fit under the trailer chassis — is manufactured by an Italian company, OMFB of Bresia. Sales engineer Philip Waterfall admits NCS looked at the Edbro system and tried to improve upon it. They have modified the Italian product to Longson's specific requirements.
There is a demand for stability devices and further developments under way. But before they come into widespread use, there are many technical, financial and legislative obstacles to overcome.