HYDAC Australia comes to the rescue when a crane manufacturer finds itself unable to operate accumulators within the suspension requirements of its articulated crane.
Some years ago the crane manufacturer embarked on developing a new 40 tonne articulated crane, which is the largest pick-and-carry crane built by the company.
Pick-and-carry cranes versus other cranes
A HYDAC spokesperson says that HYDAC’s input was integral to the construction of the hydraulic system applied to the articulated crane “from the beginning in terms of concept, and how the hydraulic system would work”.
Both a mobile crane and a pick-and-carry crane are designed to travel on public roads, he says
The mobile crane is cable-controlled and mounted on crawlers or rubber-tired carriers or a hydraulic-powered crane with a telescoping boom mounted on truck-type carriers or as self-propelled models.
This type of crane is able to gain a mechanical advantage to lift heavy objects through a combination of simple machines. The mast is supported by a large, heavy base, which helps offset the weight the crane holds at higher heights.
According to the spokesperson, the key difference between a pick-and-carry crane compared to a mobile crane is its ability to pick up a load at a point and carry the suspended load to its destination because it does not have “outriggers” or “stabilising legs” as most other mobile cranes, which only allow for the crane’s reach from the original set-up location.
“A slew-type crane or conventional mobile crane with outriggers would have to be huge to be able to pick up a load at point A and move it to point B, which could be 50 or more metres. This really illustrates the benefits of pick-and-carry cranes.”
The new articulated crane had hydro-pneumatic suspension on board, which “translated” into the crane manufacturer being unable to operate the accumulators within the suspension system’s pressure requirements, the spokesperson says.
The crane company was using a 1.4L diaphragm accumulator on the front suspension and a 1.0L diaphragm accumulator on the rear suspension, he explains.
The problem experienced with the 1.0L accumulator was the fact that it only had an allowable pressure ratio of 4:1 whereas the front suspension 1.4L has a pressure ratio of 8:1.
“Because the 1.0L accumulator only had a 4:1 pressure ratio and a pre-charge pressure of 70 bar it was not possible to take the relief value above 280 bar, which is four times the pre-charge pressure. As a consequence, the crane axle loading on the rear axles meant that the working pressure required for operation was above the allowable accumulator pressure,” the spokesperson says.
HYDAC’S customised solution
HYDAC resolved the “issue” by using the same accumulator as applied to the front axle suspension of the articulated crane, allowing for commonalities of parts.
“The ultimate solution which we ended up doing in Germany was internally modifying the 1.0L accumulator and increasing the pressure ratio, which facilitated increased system relief pressure, enabling the suspension to operate at the desired working pressure,” the spokesperson concludes.
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