When lifting bags (also lifting cushions , pneumatic cushion , pressure pad or pneumatic multiplier called) is referred to two at the edges connected (vulcanized or sealed with clamps) rubber / fabric mats or hoses, which can with compressed air to inflate and so for lifting loads can use. Lifting bags are part of flexible compressed air technology with inflatable elements.
There are lifting bags in different designs, including round and semicircular, multi-level and particularly flat (from 2.5 mm, up to 5 bar). In special cases, temperatures of up to 140 ° C and pressures of up to 25 bar are possible. A special lifting bag measuring 25 × 1800 × 2000 mm can lift a load of 60 t to a height of 500 mm. For heavy-duty use, there are lifting bags reinforced with aramid fibers .
Compressed air cushions are another version: They consist of high-quality elastomer fabric in the form of a hose, filled with rubber , mostly NBR, which is closed on both sides by means of a special process with metal clamping plates (steel or stainless steel). They are used in the industrial sector as machine or assembly elements, where high forces are required with low strokes. Their particular advantages are the even surface pressure and the flat installation dimensions (8 to 18 mm), the widths are between 33 and 412.5 mm. At a working pressure of 6 to 8 bar, they can develop forces of up to 50 tons without leakage losses. Their function is comparable to single-acting diaphragm air cylinders or short-stroke cylinders.
Ultra-flat compressed air cushions with a thickness of only 2.5 or 3.5 mm are suitable for pressures of max. 3.5 or 5 bar. These are available in a rectangular, square or trapezoidal shape. The user can choose from a variety of designs and sizes.
For special applications there are vulcanized compressed air bags / lifting bags with a wide variety of uses.
Lifting bags are used for lifting heavy loads, spreading, pressing, aligning heavy components, moving safe, stabilizing, vibration dampers against vibrations (crushers, vibrators), etc. They are filled with compressed air as standard. The use of water pressure is also possible; at high pressures above 10 bar a water / glycol mixture is required; in this case it is recommended to consult the manufacturer.
At least 75% of the area of the lifting bag must be under the load, otherwise it can shoot out under pressure and injure people. It is also important to ensure that the load to be lifted is always secured. This is done, for example, through the permanent substructure with wooden boards and wedges. The assembly instructions of the manufacturer must be followed.
The load that can be lifted with a lifting bag is proportional to the area of the bag and the working pressure. The lifting force in kilograms corresponds to the effective area of the cushion in cm² times the working pressure in bar. The larger the stroke, the lower the force. Accordingly, the greatest force is achieved with the smallest stroke. The manufacturers provide corresponding performance diagrams for their individual types.
Areas of application
Lifting bags and compressed air bags can be used in many ways. Since they can lift enormous masses with great force, they are particularly often used by aid organizations . The fire brigade and technical relief organization (THW) use them, among other things, to free people, after car accidents or after building collapses ( see also earthquakes ). But they are also used in many other industries: shipbuilding , aircraft construction , special trucks, mining , defense technology , track construction, pipelines , transport , civil engineering , quarries , archeology, port facilities, mechanical engineering , conveyor technology, assembly, repair, etc. Compressed air cushions are mainly found in numerous industrial sectors their applications as machine elements for lifting, pressing, clamping, spreading, etc.
Small lifting bags help in the event of a car door locking breakdown or to move heavy furniture a little; Large-volume cylindrical ones, each around 50 cm in diameter and height (balloon or air-cushion car jacks) connected to the exhaust of a car can lift the car on one side even on soft ground, for example to change a wheel.
Advantages and disadvantages
- Since they are very flat, they can easily be placed under the object to be lifted.
- Due to their flexibility , the objects are not damaged as easily as with other tools .
- No manual force is required to lift anything.
- With the compressed air you can easily control lifting and lowering by actuating pneumatic valves.
- Despite the low air pressure (up to 8 bar ), large weights have to be handled (up to 67 t); or more with custom orders.
- They are easy to transport and therefore belong to the standard equipment of assembly teams in the relevant industries.
- Because they are made of rubber, they cannot strike sparks and can therefore also be used in potentially explosive areas (does not apply to compressed air cushions sealed with metal). This applies in particular to compressed air cushions that are vulcanized all around.
- In mechanical engineering, the uniform surface pressure of the compressed air cushions over the entire surface (effective area) is of decisive importance. This has to be seen in connection with large forces, short strokes and flat installation dimensions.
One of the disadvantages is that compressed air is not always available on site; then water pressure can also be used. It is possible to supply on-site by means of a pressure reducing valve through the air from compressed air bottles of compressed air breathing apparatus or through the connection for a compressed air brake system for trailers, which are present in most fire fighting vehicles. This also applies to the compressed air supply for trucks. Exhaust gases cannot be used because the pressures are too low. The cushion can also be damaged by sharp edges, burrs, metal points or broken glass. However, this is largely not the case with the aramid version. By lifting the cushion, the contact area becomes smaller and smaller, so instability can easily arise on shaky ground and large strokes. It is generally not safe to put pillows on top of each other. However, most lifting bag manufacturers allow two pillows or three pillows on top of each other. Here, too, the manufacturer's installation instructions must be carefully observed.
- Lothar Schott, Manfred Ritter: Fire Brigade Basic Course FwDV 2 . 20th edition. Wenzel-Verlag, Marburg 2018, ISBN 978-3-88293-220-1 .
- DIN EN 13731: 2008-02: Lifting bag systems for fire and rescue services - Safety and performance requirements