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SPOTCHECKSAFETY


Figure 3


the trailer manufacturer’s manual for loads with a high centre of gravity (CoG). Company ‘A’ also instructed the trailer operator (party ‘B’) to use a spirit level during all phases of the transport operation in order to closely monitor the horizontal position of the trailer bed at all times and, if necessary, to compensate for the level setting of the trailer bed with the hydraulic suspension system.


Negligence claim


As party ‘A’, at the client’s request, had insured the reactor against damage during transportation, the insurance company of ‘A’ – which claimed that the cause of the accident was the negligence of party ‘B’ – claimed the cost of the accident against party ‘B’. Party ‘B’ rejected the claim and said that the supervisor at ‘A’ had given the wrong instructions and that the trailer should have been set at a three-point suspension system instead of a four-point suspension system. It was claimed that the level position of the trailer on a four-point suspension system could not be controlled and had caused the load to tip over. Party ‘A’ also claimed that the suspension system of the trailer in this accident was not the cause of the accident, but the trailer bed had not been levelled when negotiating the 2.8° camber and this had been the contributing factor. Party ‘B’


60 July/August 2013


denied this suggestion and a court case was instigated to settle the matter. To fully understand what had happened, here is a little bit more about hydraulic platform trailers. A platform trailer in principle consists of a rigid steel frame, in which individual axles are mounted and each axle is suspended by a hydraulic cylinder. All these hydraulic cylinders are connected with each other by means of hydraulic lines and with valves one can create individual suspension points consisting of two or more suspension cylinders. In this way a so-called three-point or four-point suspension system is formed. Figure 2 shows a three-point suspension system. The four cylinders at the front of the trailer are connected with each other as one suspension point, whereby the six rear cylinders are separated into two individual suspension points each consisting of three cylinders connected with each other. In this way a three-point suspension system is created. Provided the CoG of the load is placed exactly in the centre of the trailer, each axle will have the same load (hydraulic pressure in each suspension point is equal). Another great advantage of the hydraulic platform trailer is that the trailer can be raised by means of a separate diesel driven hydraulic pump. In most cases the maximum stroke is limited to 600 mm. Because of this hydraulic suspension system,


uneven road surfaces can be coped with and still guarantee an equal load on each individual axle (see Figure 3).


Spring system


In non-hydraulic trailers this is achieved by a spring system or by means of swivelling rocker arms applied to each set of axles. The more axles and the longer the trailer is, the more difficult it becomes to guarantee equal load distribution on all axles. This is where the hydraulic platform trailer offers an ideal solution. By coupling individual trailer units with each other longitudinally or side by side, we can create platform trailers capable of handling loads up to several hundreds and even several thousands of tonnes. Of course, the hydraulic lines between each trailer must be connected with each other and opening and closing the correct valves should create a three or four-point suspension system.


The horizontal level of the trailer can be adjusted as well, which comes in handy when the road has a certain camber. Each individual suspension point can be raised or lowered by means of the diesel driven hydraulic pump.


In the case under the microscope, the transport saddles were 12 m apart and the saddle loads were acting on the forward and aft part of the trailer, which was composed of


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