RotaBolt's Tension Control System Saves Time and Money in the Middle East

Every amateur mechanic knows the importance of the correct and careful tensioning of cylinder heads and casings. Fragile castings can be so easily damaged with just that extra twist where it wasn't needed. But when the cylinder casings are worth upwards of $80,000 a piece, and the application is fundamental to the efficient operation of the plant, precise control is even more important.

The National Marine Dredging Company, operating in Abu Dhabi, uses a large marine diesel engine to power their dredge pump. The engine drives a 2.5 meter impeller and the continuity of the operation is dependent on its faultless performance. If the unit fails, dredging stops, and time and money are lost.

Although the engine itself performs very well during normal operation, National Marine Dredging have had difficulties during maintenance. On a number of occasions, the cylinder casings have cracked due to lack of precise tension control on re-assembly. The company has used hydraulic tensioners in the past . . . however, the accuracy of this method is solely dependent on the accuracy of the pressure gauge. When loads are critical, accidents can happen - and do.

To solve the problem, National Marine Dredging chose to convert the existing bolts to RotaBolt 2 tension control fasteners. The RotaBolt 2 conversion enables the load on each bolt to be set accurately by measuring the stretch of the bolt's material, not the load applied by the tightening tool. This fundamental change in measurement method eliminates the reliance on gauges and avoids variations caused by corrosion or contaminants.

The RotaBolt 2 is a precision conversion of a standard bolt to include twin, positively anchored pins, each with its own cap that can be rotated between finger and thumb. The two Rotas are set to the upper and lower load levels for the specific application. National Marine Dredging set the RotaBolts to an upper limit of 44.7 tons and a lower limit of 39.6 tons. When the lower limit is reached the inner Rota locks but the outer Rota still spins freely. Only when the upper limit approaches will any resistance be felt on the outer Rota, warning the engineer that damage may result beyond that point.

The result is an accurate, simple system of tensioning without need for special tools or skills. National Marine Dredging is now able to apply the correct load to all parts of the cylinder head, eliminating the risk of distortion caused by uneven stresses. When in operation, the whole assembly can be checked precisely in a few seconds.

National Marine Dredging is delighted with the results from the use of RotaBolt 2. Since introducing this method of tension control there has been no re-occurrence of the original problem.

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