lifter bag is a diving equipment item consisting of a sturdy and airtight bag with rope, which is used to lift heavy objects under water by using buoyancy bag. Heavy objects can be moved horizontally underwater by divers or sent unattended to the surface.
The appropriate bag lifting capacity should match the task. If the lifting bag is too large, the escape or out of control may occur. The commercially available levers can combine the exhaust valve to allow the operator to control buoyancy during the climb, but this is a dangerous operation with high winding risk in uncontrollable lifting or sinking. If a single bag is insufficient, some bags may be used, and should be distributed to fit the load.
There is also a pick up bag used on land as a short lift jack to lift the car or heavy loads or lift the bag used in the machine as a type of pneumatic actuator that provides loads over a wide area. This US/CR type lifting sleeve is for example used in the rollercoaster brake mechanism.
Video Lifting bag
Physical lift floating
The volume of the bag determines its lifting capacity: every liter of air in the bag will lift 1 kilogram weight, or each cubic foot will lift about 62 kilograms. For example, a 100 liter bag (3.5Ã, cuÃ, ft) can lift an underwater object weighing 100 kilograms (220Ã, lb).
A partially filled bag will accelerate as it rises as the air in the pouch expands as the pressure decreases as it rises, following Boyles' law, increasing the buoyancy of the bag, while the full bag will overflow or extinguish excess volume and maintain the same volume and buoyancy provided is not down. A bag that leaks enough to begin to sink will lose the compression volume and become less afloat in the positive feedback loop until it is stopped by the bottom.
Breakout
The force required to lift a submerged object from below can be divided into two main components:
- The real weight, which is the object's weight is less the buoyancy of its displacement.
- Breakout style due to embedment at the bottom, which can be ignored, or in some cases the main part of the load.
Once the object is detached from the base, only the visible weight remains, and the controlled appointment requires a way of managing a sudden drop in resistance to lift. There are three basic ways you can do:
- The use of mechanical or hydraulic excavation to relax the load-bearing sediments.
- The use of "Dead Man Anchor" - a large heavy load - and a retaining cable to prevent the bag from moving too far, so that the buoyancy can be corrected to better match the load.
- Use of shallow bags with long wires to the load to provide an escape, which will only lift a short distance before surfacing, after which the load can be removed further with a staged staging or direct appointment by the near sac.
Load stability
After the load is lifted from the substrate, it will rotate until the center of gravity is in the position of the lowest potential energy. If delayed from one point, the real center of gravity (corrected for attached buoyancy) will be directly below the lift point. If it is not desirable for spinning loads with large corners when leaving the bottom, lift points should be chosen to allow this effect, and multi-section slings or bar spreaders may be needed, and may be necessary for safe sling so they do not slip.
Maps Lifting bag
Type and construction
Underwater lifter bags are lifter tools and thus may be required to comply with safety standards.
Open hand bag (lifting bag)
A parachute lift is open at the bottom. When full, extra or inflated air will spill. The shape of the open lifter bag should distribute the volume vertically rather than the horizontal direction so that the open end of the bag is always under water. If the open end reaches the surface, the air will come out of the bag and may sink.
The simplest version is a two-sided bag, either incorporated on the edge or folded and spliced ​​along two sides. The webbing straps can be stitched onto a multiplier patch which is then glued or welded into a bag on a light duty bag, but in large and heavy duty bags there is usually a strip of bag material tied to a pouch that forms a flat retaining tube for plaited threaded through a tube and can be drawn for care and inspection. the heavy duty open bag is generally cone-shaped with the top of the ponytail or the top of the cut cone, and may have several straps from the rapture point at the bottom, through the guide tubes on its sides, to the crown or steel crown ring at the top, for spread the load evenly over the bag cloth.
The lift parachute bag can not be overloaded and is suitable for elevators where there is a large pressure change, and where it may be necessary to flip (reverse) the bag to stop the oncoming elevator.
Some lift bags can be converted from open to closed by attaching the cover to the bottom opening.
Closed lift bag (camel)
The closed lifter bag has an excess pressure valve to prevent internal pressure from exceeding ambient pressure over a set amount (about 10 kPa, or 1 msw). Closed lift bags are intended for use on or near the surface, as they retain air even in rough seas. They are available in several configurations, including horizontal cylinders, vertical cylinders, teardrops and cushions.
Rapid deployment
The fast dispatching bag has a scuba cylinder mounted on the outside that contains enough air to inflate the bag at the specified depth. The bag can be attached to the load and when it is ready, the valve is opened and the diver swims clearly. If the regulator pressure is set to a lower pressure than the excess pressure relief valve, the enclosed pocket will automatically stop filling before the release valve is opened, but will be filled if it leaks once it reaches the surface. The regulator pressure should consider the difference in hydrostatic pressure between the top and bottom of the bag so that the bag will be completely filled.
Dump valves
The exhaust valve is used to release air from the bag while in the water. They can be operated manually on the valve by a diver or can be operated remotely by a towing strap, which can be operated by a diver or attached to a load that will automatically open the valve if weight is lifted from below. Some exhaust valves can be operated in both ways. One system operates by pressing on top or drawing a line attached to the bottom to move the spring valve. The exhaust valve can be a rapidly changing screw system, and the spring tension can be adjusted.
Use
Dynamic lift
When an empty lift bag is attached to the load and the elevator is made by controlling the inflation air volume called a dynamic elevator.
Direct appointment
Bag or set of bags is used to lift the load directly to the surface. This is simple, but there is a risk if the lifting bag is too large and can not be removed fast enough so that the lift may become out of control and rise so fast that the pockets rupture the surface, upside down and collapse, losing so much air that it can not support heavy loads, and then it will sink back down. If there is a float marker attached it will at least not be lost. A lift bag that is only slightly larger than required to support the load will rise more slowly, and tends not to be reversed on the surface, because excess air will spill continuously during the climb.
Gradual increase
The lift bag is used to carry the load gradually: a long chain or sling is used to connect the load to the lifting bag just below the surface, which is filled to break the load and lift it until the bag reaches the surface, then the second bag is used to carry the load further. This procedure continues until the load has been reasonably improved. The advantages of this method are the more controlled lifts, the facility to use a larger capacity for early breakouts without the risk of breakout. Losses include requirements for divers to work in or near lifting equipment when under load.
Increased floating help
The elevator is controlled by a line from the surface vessel, and the load is reduced by a lift bag with a volume too small to support the full load. This allows faster appointment with the winch. The lift gear should be able to support the load if the bag fails, or should be set to fail safely.
Floating help elevators are a common procedure for recreational divers to aid in a shotline or anchor recovery, which would otherwise be pulled manually. A small lift bag mounted on the shot was partially filled by the last diver to leave the bottom, and after coating the crew drew the line and the air in the pouch expands as it rose, providing more assistance to the crew. In this app, removable elevators are usually not a problem, and bag sizes are not critical.
Static lifts
The lift bag can also be used for static lifts, where the bags anchored in place with rigging, and used as a very high buoyancy point compared to the load, which is then lifted in a controlled manner using a purchase or chain block or suitable lifting device others.
Rigging lifting bag
Lifting bags should not be exhaled too much, and usually can not use a static buoyancy force greater than their safe workload, but rigging can be subject to hook loads, which can be caused by various factors.
- When a bag is used in shallow water and wave or wave motion causes a rapid change in dynamic loading, by pulling the bag from side to side
- When the bag lifts the load onto the surface and the bag is subjected to vertical wave action
- When the lifting bag is not plugged in correctly
- When the lifting bag is stuck, it is free to be harassed when slack is taken.
- When the load is partially supported by the lifting cable and there is a sudden variation in the voltage across the cable due to the movement of the ship or the cable slip.
When lifting with more than one bag, benefits should be made to reduce the filling capacity if the bag is attached so that they press each other.
Incorrect errors can cause load concentrations at attachment points that can exceed SWLs
An inverted or inverted line can be attached to the top of the bag. This line should be long enough and strong enough to attach to an independent anchor point so that if the bag or strap fails the bag will be reversed and air will come out, preventing a loose lift. This procedure is commonly used for close-range transport near the bottom, such as when aligning large components for assembly. With this method, the load will generally hold the bag in an upright position, so the tripping line can be loaded large enough and the bag can not reverse. The inverter line can also be attached to the load, so it will reverse the pocket if it is detached from the load, but this will not stop the escape escape, and the retaining line is used for this purpose.
The retaining line is used to prevent lift bags from loading and floating when used to lift a short distance at the bottom. Suspension is attached to the lifting ring of the bag, or to the load, and must be mounted by a strong cable to the point of an unrevocable anchor. The SWL of the holdback should be at least equal to the lifting capacity of the bag. A barrier and an inverter are often used together.
A spreading bar can be used to distribute lifting loads more evenly between bags or along loads.
When filling the bag, if every bag is fully loaded before starting to fill the next pocket, it is unlikely that the escape will start, as only one bag can increase lift as it rises. It will be the last bag, and the diver will monitor very carefully as they fill it, so it will be more likely to react in time to regain control of the elevator.
The weighted drain line will automatically open the valve to start discharging excess air if weight is lifted from below. This will stop the elevator from rising further if the exhaust valve releases the air fast enough. When the weight is lowered back down by the sinking load, the valve will close again, and must withstand a fixed load. The stability of this system depends on the preload of the valve spring and the valve opening size.
Contents bag
The amount of air needed for the lifting bag depends on the weight of the load and the depth of the bag. About 1 m 3 air at ambient pressure is required per ton lift. The volume of free air follows Boyle's law, and is proportional to absolute ambient pressure in bars or ata.
For example: Raise 5 tons with a bag to be filled at 20 m, requires 5 m 3 air at 3 bar, which is 15 m 3 at surface pressure.
Air fillers are usually supplied from the surface of a low pressure compressor, but for small lifts the diver can carry an air cylinder for that purpose. It is considered bad practice in some jurisdictions to fill lift bags of diver gas tubes, especially if the diver has a decompression duty or just one cylinder because of the risk of using too much air and leaving the divers without sufficient air to safely climb is considered unacceptable.
Bags can be jacked up from safer distances by using water-lance (a rigid pipe that can be inserted into the bag opening).
Danger of use
- Snorkeling diver or umbilical diver or lifeline in lifting equipment, resulting in an uncontrollable quick climb.
- Uses too much air from the scuba diver's gas supply, resulting in an incident outside the air.
- Uses too much volume in the lifter bag, resulting in positive feedback expansion on steady climbing and lifting.
- Leak in lift bag, causing loss of buoyancy and sinking load after removal. The load can sink quickly when the air in the bag is compressing, and may be harmful to the underwater or working on the load on the surface, or the load may be lost.
- Uneven mounting of the lifting gear may cause the load to become unstable after being lifted free from the bottom. enlargement or subsequent load switching can free it from rigging, or damage the load or carrying case. Selected or inadequate lift points in the same way may cause overload of cargo and cause damage.
Gallery
External links
- Lift Size Bag/Volume Calculator - Online calculator to determine the bag lifting capacity and air volume required to recover underwater objects from fresh or saltwater.
References
Media related to Lifting bags on Wikimedia Commons
Source of the article : Wikipedia
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