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    • Lifting Bags

    Underwater Lift Bags

    Underwater lift bags are specialised inflatable bags that are used in commercial diving to lift heavy objects from the seabed to the surface. These air lift bags are made of durable materials that can withstand pressure and are designed to be filled with air or other gases to create buoyancy. Each product is carefully tested to ensure it performs reliably under varying load conditions and at depth.

    Our underwater lift bags range includes commercial lift bags suited for remote locations, enclosed flotation bags to float objects close to the surface, and pontoon lift bags ideal for shallow water salvage. Each type is tailored to provide the optimal lifting solution in diverse underwater scenarios, offering dependable performance whether lifting from the seabed or managing buoyancy control at specific depths.

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    Frequently Asked Questions

    Open-bottom parachute bags are shaped like an inverted teardrop with an open base. They are primarily used for lifting objects from deep water directly to the surface. As the bag ascends, the decreasing water pressure causes the air inside to expand. The open bottom allows this excess air to vent naturally, preventing the bag from rupturing. Totally enclosed lift bags, such as cylindrical pontoons or pillow bags, are completely sealed. They are generally used for shallow water salvage, draft reduction, or surface towing, as their enclosed design prevents them from losing buoyancy in rough surface waves.

    When using totally enclosed lift bags, the expanding air during ascent has nowhere to escape. Without intervention, the expanding gas would rapidly stretch and burst the heavy-duty fabric, causing the entire load to drop back to the seabed. To prevent this, enclosed bags are fitted with highly calibrated over-pressure relief (OPR) valves. These mechanical valves automatically vent expanding air once the internal pressure exceeds a safe threshold. This ensures the bag maintains its structural integrity and exact buoyancy rating throughout the entire ascent.

    Salvage pontoons are large, horizontal, totally enclosed lift bags designed specifically for heavy marine salvage and vessel recovery. Unlike standard parachute bags that provide vertical lift from a single top point, pontoons are rigged in pairs alongside the hull of a sunken vessel or a heavy pipeline. This configuration provides massive, distributed lifting force. Because they are enclosed, pontoons can breach the surface of the water without deflating, allowing the salvage team to safely tow the raised vessel into a shallow port for permanent repairs.

    An uncontrolled ascent is one of the most dangerous scenarios in commercial diving. If a bag ascends too quickly, it can break the surface violently, spill its air, and immediately sink. Divers maintain complete control using an inverter line connected to a manual dump valve on the top of the bag. As they pump air into the bag to initiate the lift, the diver can pull this line to manually vent small amounts of air. This allows them to finely tune the buoyancy, ensuring the heavy load rises to the surface at a slow, deliberate, and highly predictable speed.

    Because they handle immense loads above human divers, commercial lift bags are subject to rigorous safety standards, most notably those set by the International Marine Contractors Association (IMCA), such as document IMCA D016. These guidelines dictate that all lift bags must be clearly marked with their Safe Working Load (SWL). They require mandatory pre-dive visual inspections for fabric abrasions and webbing degradation, alongside periodic formal inspections by competent personnel to guarantee the lifting strops and valves remain fully certified for heavy offshore use.