Why This Matters Now
In marine recovery, research, and emergency situations, knowing how underwater lift bags work isn’t just useful—it’s essential. Imagine your commercial vessel sheds equipment; a diver needs to recover it safely and quickly. Or picture a research team retrieving delicate archaeological artifacts, where a sudden drop or surge could destroy centuries-old history. For companies like Sunhelm, which specialize in underwater lifting solutions, having advanced knowledge of lifting bags underwater and underwater lifting bags is mission-critical.
What Are Underwater Lift Bags?
Underwater lift bags are air‑filled, sealed, or open-bottom underwater balloons that provide buoyancy to lift submerged objects to the surface.
They come in two main types:
- Open (parachute) bags: open at the bottom so extra air can escape as pressure changes during the ascent.
- Closed (camel/pillow) bags: sealed with overpressure valves, designed for surface-level or rough water use.
How They Work: The Physics Behind the Lift
Boyle’s law explains it: as air expands with decreasing pressure, each liter of air displaces roughly 1 kg (or 62 lb/ ft³) of water, generating buoyant lift beneath the bag.
For instance, a 100 L bag can lift about 100 kg underwater.
Divers fill bags using low-pressure hoses or secondary regulators, not primary breathing air, to maintain control and diver safety.
The Step-by-Step Process
- Attach the bag securely to the submerged object, using straps and rigging to ensure stable engagement.
- Inflate slowly to neutral buoyancy—just enough to “break” the object free from sediment.
- Control ascent, venting extra air via dump valves or manually “burping” the bag, preventing runaway lifts.
- Surface hookup: Once at the surface, secure the load to the boat crew, deflate, and lift aboard.
Why It’s Urgent & Important
Neglecting proper technique can result in:
- Uncontrolled ascents that risk bag bursting or diver injury.
- Rapid burping, letting the load plummet back to the bottom.
- Divers in harm’s way, due to entanglement or air loss.
Companies like Sunhelm stay ahead with high-quality underwater lift bag systems and rigorous training, reducing these risks.
Continue Reading
Keep scrolling to learn more about key gear selections, risk management, and why Sunhelm stands out in safety and innovation.
FAQ
How do I choose the right capacity lift bag?
Choose a lift bag with buoyancy greater than the object’s weight in water, plus a 20% safety margin.
What is the difference between open and closed lift bags?
Open bags vent excess air during ascent; closed bags are sealed and used near the surface.
Can lift bags cause uncontrolled “runaway” ascents?
Yes. Overinflation or poor venting can make the bag rise too fast, risking damage or injury.
How are lift bags inflated—what air source is used?
Divers use low-pressure hoses or spare air tanks—not their primary breathing system.
What safety steps should divers take during a lift?
Always secure the load, inflate slowly, control ascent with dump valves, and stay clear of entanglement.