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TECHNICAL DETAILS PAGE |
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| This section looks at hoe hydraulic booms work. It deals only with the boom versions of Coles cranes around 1974, primarily because I have no information about any others, however the basic principles are the same |
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) The above Hydra 70T boom was the first basic boom introduced on the very first Hydra 7 ton crane. It is in three sections but only the middle section is powered. The outer casing has the lifting rams attached cable drum and hydraulic pipes attached.
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| Hold cursor over diagram above to see animation The main extension ram inside the boom (red) is attached to the rear end of the outer casing. This ram pushes out the middle section of the boom (dark blue), it is this section that can extend or retract under power, even while carrying load. The third section (green) is extended manually by using the ram to extend then hold the third section with a holding bar while the ram retracts. The third section is then pinned to the middle section. When the ram is extended again the middle take the top section with it. |
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| The boom for the Hydra 150T needed to extend further than the single ram allowed. This Boom had four sections. A system was developed that used an internal chain to pull the third section out while only using one hydraulic ram. |
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| Hold cursor over diagram above to see animation The chain (black) was fixed at the base of the outer Boom casing (dark blue) along with the foot of the ram. The chain ran over the end of the ram (red) back down to a wheel at the foot of the second boom section (light blue) , it went over this wheel and was fixed to the inside top of the outer boom. As the ram, fixed to the third boom section (green), pushed out the third boom, the chain pulled the second section out via the wheel at its base. The fourth top section (orange) when required was extended by hand as on the 70T above. |
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The Hydra 300T had an even longer boom and could not use the chain system as the chain effectively halved the ram useful ram extension. Double extension was achieved on the 300 by using two rams (shown red) inside the main boom casing. This allowed two powered extensions with a far greater reach. In modern cranes multiple rams are the normal configuration, using computer control and self locking boom extensions, booms with five or six powered section are achievable. |
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