‘Hydraulic jack’ and ‘hydraulic jacking systems’ will be topics you are familiar with. But, is strand jack a known topic? Yes, as we mentioned in our previous blogs, a strand jack is a type of hydraulic jack. The strand jacks are mainly used for carrying out heavy lifting and skidding operations. So, is this strand jack utilize hydraulic power? Definitely. Then how does it work? The basic working mechanism is explained in this article for your better understanding.
Let’s start with the beginner level. What is a strand jack? This category of jacks is mostly used for construction and engineering purposes, including offshore structures, refineries, major buildings, power stations, and more. The concept evolved from the concrete post-tensioning principle. Strand jacks are highly applicable if it is required to carry a heavy load for a longer distance, where a hydraulic crane can’t be preferred. By assembling multiple strand jacks, it will be possible to handle loads weighing thousands of tons. The key advantages of strand jack over cranes are pin-point precision, smaller footprint, and the ability for a single operator to control multiple jacks using computerized control.
Now, let's move to the hydraulic strand jack working. The strand jack lifting system utilizes a sequence of locking, pulling, and unlocking mechanisms. A strand jack, which is considered a linear winch includes steel cables or strands running through the hydraulic cylinder, where the cylinder contains an anchor system with wedges above and below. The lifting and lowering operations are performed with the in and out flow pump stocks. The electric or diesel-powered hydraulic power pack will supply power for this operation. The locking mechanism is activated mechanically when the system pressure drops resulting in the automatic close of wedges.
The strand jack is mostly suited for precisely pulling objects and structures horizontally to a longer distance or includes many lifting points. One such application of Strand jack can be found in the offshore mining industry, where the rig is transported from onshore to a barge.
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The important components included in the strand jack lifting system are the strand guide, main hydraulic jack, top and bottom mini-jacks, counterbalance valve, chair, and strand jack wedges. Among these, the main hydraulic jack (cylinder) is considered the heart of the system that extends and retracts with each stroke. The top and bottom mini-jacks with the anchor system are used for locking and unlocking the cables or strands. The strand jack wedges will grip the strands by utilizing the hydraulic pressure applied by mini jacks. Next, the role of the counterbalance valve is to provide smooth and controlled lowering of the load and provide load holding when the hose fails.