Underwater Air Lift Bags Reliable Sealing High Strength Webbing Stable Buoyancy

Designed for the rigorous daily demands of shipyards, dry docks, and port construction, the Hongruntong Marine Pillow Underwater Lifting Bag is the ultimate tool for precision flotation and positioning. Unlike open-bottom lift bags which are dynamic and vent air, our enclosed pillow bags function as static lift devices, providing stable and sustained buoyancy ideal for precision keel block placement, emergency bilge pumping support, or heavy lifting in confined dockside environments.

Constructed from a durable, high-frequency welded PVC composite with a Panama double longitude reinforcement, these bags offer a superior strength-to-weight ratio, making them easy for dockworkers to handle without heavy machinery.

The low-profile "pillow" shape is specifically engineered for operations where vertical clearance is limited. Whether sliding under a dry-docked vessel to adjust blocking or providing lift for a sinking small craft, the bags remain stable and resistant to rolling. Each unit is fitted with robust 3/4" NPT inflation ports and quick-disconnect fittings for rapid deployment, while integrated pressure relief valves safeguard against over-inflation, ensuring operational safety in busy port environments where efficiency is paramount.

During a routine dry-docking of a 70,000-ton bulk carrier, a fractured keel block was discovered directly beneath the hull's engine room section. Replacing the block with the vessel fully docked is impossible, but removing the weight entirely risked structural stress. The yard's marine superintendent utilized four Hongruntong HM-WD07 (8-ton) pillow bags to execute a critical lift.

With the vessel already on blocks, clearance was minimal—less than 30 centimeters. The low-profile design of the Hongruntong bags allowed them to be manually slid into the tight gap on either side of the damaged block. Using a manifold system to ensure equal pressure, the bags were slowly inflated, taking approximately 15 tons of weight off the specific keel block. This slight lift created enough space to safely extract the damaged timber and slide a new, pre-cut block into place. The entire operation, from setup to removal of the bags, took less than four hours—a task that would have otherwise required undocking the vessel, costing the yard and the ship owner millions in lost time and fees. The precision and reliability of the lift prevented any damage to the hull's epoxy coating.

• Low Profile Design for Confined Space Operations
  The defining characteristic of the pillow bag is its geometric efficiency. Where cylindrical pontoons require significant depth to be effective, the pillow bag maximizes surface area while minimizing lift height. This allows for insertion into extremely tight spaces—such as between a ship's hull and the dry dock floor, or under a pipeline just meters above the seabed. The broad, flat surface distributes lifting force evenly, preventing point-loading that could damage sensitive hull structures or concrete foundations.
• Rapid Response Inflation and Deflation System
  Port operations demand speed. Our pillow bags feature large-diameter inflation/deflation ports integrated with high-flow ball valves. This allows for massive volumes of air to be introduced quickly from a standard compressor or, conversely, allows for rapid deflation to demobilize and recover the bag swiftly once the operation is complete. The inclusion of stainless steel quick-disconnect fittings ensures a secure, leak-proof connection that can be made in seconds by divers wearing thick gloves, maximizing bottom time and efficiency.
• Exceptional Abrasion and Tear Resistance
  Shipyard environments are abrasive, with concrete, steel plating, and marine growth posing constant threats to inflatable equipment. Our pillow bags utilize a thicker outer skin of PVC specifically formulated for high abrasion resistance. The material is resistant to common petro-chemicals found in shipyards, such as diesel and hydraulic fluid, preventing degradation from accidental exposure. The RF-welded seams are often stronger than the parent material, ensuring the bag remains intact even when dragged across rough surfaces during positioning.
• Integrated Lifting Harness and Redundant Attachments
  While often used in "loose" applications, many shipyard tasks require securing the bag to the load. Hongruntong pillow bags feature a built-in heavy nylon lifting harness that is an integral part of the bag's construction, not a bolt-on afterthought. This harness, with a safe working ratio of 6:1, provides secure points for shackles and slings. For complex rigging, multiple stainless steel D-rings are placed around the perimeter, allowing the bag to be tethered in multiple directions to prevent shifting during the lift.

• Dry Dock Maintenance and Blocking
  Adjusting keel blocks and side supports during a dry-docking operation is a high-precision task. Hongruntong pillow bags act as temporary, adjustable jacks. They can be placed under a vessel to take the weight off a specific section, allowing for the reconfiguration of the blocking arrangement. This is essential for accessing hull plating for repair, conducting underwater inspections, or correcting the vessel's trim inside the dock.
• Emergency Small Craft Salvage
  For marinas and ports, a sinking yacht or workboat is a common emergency. Our smaller capacity pillow bags are ideal for rapid response. They can be quickly attached to the sinking vessel's hull or slipped into the cockpit to provide emergency buoyancy, preventing it from capsizing or sinking completely. This swift action saves the vessel and prevents pollution from fuel leaks.
• Pontoon and Float Installation
  When installing floating docks, breakwaters, or modular pontoons, our bags provide the necessary buoyancy to maneuver heavy concrete or steel sections from the transport barge to their final position. By temporarily attaching pillow bags to the structure, it becomes nearly weightless in the water, allowing for precise positioning with small tugs before the bags are removed and the structure is permanently fixed.

• Integration with Industry Standards (IMDA ABS)
  We design our products to align with the operational guidelines set by the International Marine Contractors Association (IMCA) and the American Bureau of Shipping (ABS). This means our bags are built to the same standards expected by the world's most professional diving contractors and offshore operators. When you choose Hongruntong, you are selecting equipment that meets the stringent requirements of the commercial diving industry, ensuring compatibility with established safety protocols.
• Proven Track Record in Global Ports
  With a client base spanning over 800 customers in more than 30 countries, our products are field-tested in the world's busiest ports and most challenging marine environments. This global footprint provides us with a unique insight into regional operational challenges, allowing us to continuously refine our designs. Our bags are trusted by harbor masters, salvage foremen, and marine engineers who require equipment that performs consistently, day in and day out.
• Comprehensive In House Manufacturing Control
  Unlike companies that outsource production, we maintain full control over our manufacturing process at our Beijing facility. From sourcing raw polymer resins to weaving the reinforcing scrim and final RF welding, we oversee every step. This vertical integration ensures absolute quality control, traceability of materials, and the flexibility to make on-the-fly adjustments for custom orders without third-party delays.
• Responsive Global Logistics and Support
  Downtime in a shipyard is expensive. We understand that when a bag is needed, it is needed immediately. Our logistics team is experienced in managing international freight to ensure products clear customs and arrive on-site as quickly as possible. We maintain a stock of standard sizes and critical spare parts, allowing for immediate dispatch to keep your projects on schedule.

• Can your pillow bags be used to lift a vessel that is partially submerged but still afloat?
  Yes, this is a common application known as "camel" lifting. The enclosed bags can be attached to the side of a listing vessel and inflated to act as outriggers or sponsons. This provides additional stability and righting moment, preventing capsizing while the vessel is under tow or during pumping operations to dewater the hull.
• What air source is required to operate these bags in a shipyard setting?
  Most shipyard operations utilize standard low-pressure, high-volume air compressors (typically 7-10 bar). Our bags are designed for working pressures between 50-100 kPa. A standard shop air compressor is sufficient for smaller bags, while larger lifts may require a diesel-driven screw compressor. We do not recommend using high-pressure diving bottles for large-volume bags, as it is inefficient and can be dangerous without a proper pressure regulator.
• How do I prevent the bag from slipping out from under the load during the lift?
  For applications where the bag is not rigged with straps, surface friction is your friend. The PVC material has a natural coefficient of friction against clean steel and concrete. For angled lifts or if there is significant water current, our bags feature molded tie-down points and integrated harnesses that allow you to secure the bag directly to the object using ropes or straps, preventing any lateral movement.
• Are these bags suitable for use in potable water or environmentally sensitive areas?
  Absolutely. The PVC material we use is non-toxic and does not leach chemicals into the water. They are safe for use in reservoirs, lakes, and other environmentally sensitive areas. Unlike oil-filled hydraulic jacks, there is zero risk of fluid pollution should a bag fail, making them the environmentally preferred choice for lifting in clean water.
• What is the warranty period and what does it cover?
  We offer a standard 36-month warranty. This covers defects in materials and workmanship, including seam integrity, valve function, and material degradation under normal use. The warranty does not cover damage caused by gross over-pressurization, severe puncture from obvious misuse, or improper storage.