Lifting bag
Encyclopedia
A lifting bag is an item of diving equipment
consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy
. The heavy object can either be moved horizontally underwater by the diver
or sent unaccompanied to the surface.
The volume
of the bag determines its lifting capacity: a 100 litres (4 cu ft) bag can lift a 100 kilograms (220.5 lb) underwater object.
The shape of the bag should distribute the volume in a vertical rather than a horizontal direction so that the open end of the bag always remains underwater. If the open end reaches the surface, air will escape from the bag and it may re-descend. A partially filled bag will accelerate as it ascends because the air in the bag expands as the pressure reduces on the ascent, following Boyles law, increasing the bag's buoyancy
.
It is advisable to select a lift bag with an appropriate capacity for the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may also incorporate dump valves to allow the operator to control the bags buoyancy during ascent.
Diving equipment
Diving equipment is equipment used by underwater divers for the purpose of facilitating diving activities. This may be equipment primarily intended for this purpose, or equipment intended for other puprposes which is found to be suitable for diving use....
consisting of a robust and air-tight bag with straps, which is used to lift heavy objects underwater by means of the bag's buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
. The heavy object can either be moved horizontally underwater by the diver
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
or sent unaccompanied to the surface.
The volume
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
of the bag determines its lifting capacity: a 100 litres (4 cu ft) bag can lift a 100 kilograms (220.5 lb) underwater object.
The shape of the bag should distribute the volume in a vertical rather than a horizontal direction so that the open end of the bag always remains underwater. If the open end reaches the surface, air will escape from the bag and it may re-descend. A partially filled bag will accelerate as it ascends because the air in the bag expands as the pressure reduces on the ascent, following Boyles law, increasing the bag's buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
.
It is advisable to select a lift bag with an appropriate capacity for the task at hand. If the lift bag is grossly oversized a runaway or otherwise out of control ascent may result. Commercially available lifting bags may also incorporate dump valves to allow the operator to control the bags buoyancy during ascent.