Power Required For Adjusting The Height Of Yard Ramps

Several people have enquired about the comparative power required to adjust the height of different designs of yard ramp.

The power required is a simple function of the mass of the ramp, the height it is lifted through, the time taken and the mechanical efficiency of the adjustment system. For any meaningful comparison between different designs of yard ramp, the first 3 of these factors would be the same. Therefore the difference comes down to the overall efficiency of the adjustment system itself. Generally this means a comparison between mechanical adjustment done through landing legs and a small gearbox similar to most HGV trailers and a hydraulic system operated through by a hand pump.

In a mechanical system the losses are those occurring in the actual gear unit and those to overcome friction in the landing leg mechanism. For hydraulic systems there are substantial losses to overcome seal friction in both the pump and operating cylinders, losses in valves and hoses and also due to the geometry of the operating cylinder in relation to the arm movement.

The hydraulic system will therefore normally require a greater power input from the operator in order to raise the ramp. However this system has some benefits when lowering the ramp, because the mass of the ramp and gravity are normally sufficient to do the job, whereas a mechanical system still requires at least a reduced input from the operator. Overall the total power input required for the complete cycle is thus going to be fairly similar, and so the choice really comes down to individual preference and reliability considerations etc. The main point is that whichever system is employed, the power required is well within the capability of a normal healthy adult worker and so this should not be an issue.

Very occasionally yard ramps are fitted with motorised adjustment, but the connection of an external power source by a cable or hose compromises their mobility and generally trailing cables or hoses are not considered the best thing for safety. However where motors are fitted, their power has to be determined by the manufacturer on a case by case basis and will vary according to their specific ramp models.

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