Air Flow Meter

Either in operation or in non-working condition such equipment must be stable, even under the impact of different factors from outside, such as wind, vibrations etc. Correct installation and also consideration of all the factors, which possibly may influence the equipment, becomes a pledge of a successful operation and safety of the operators and workers.

A factor of stability, when calculated for “perfect conditions” (stability of the machine, main load) should as a rule, exceed 1, and is calculated as a ratio of the total moment of all the retention forces to the total moment of the tilting forces with respect to the tipping point. In real life, the operating conditions may turn out to be unpredictable and change in the process of operation, the influencing factors, like wind, may be very unstable and change with the time, from wind speed being equal to zero, to extreme gusts, exceeding the calculated limit value. In addition, the soil, on which machine is installed, e.g. may become uneven when too wet; the inert and tilting forces, wind load impact, may bring to overturn and fall of the cranes. That is why, besides the calculation for “ideal” conditions, it is necessary to carry out the calculations for unfavorable conditions, when additional loads arise. Thus, force of the wind pressure on the leeward surface, force of the wind pressure on the load surface, inert force when starting or stopping the mechanism of lifting the load, the centrifugal force of the load mass, generated by the rotation of the contraction etc. – all this should be taken into consideration. All these additional forces, arising in the process of operation and during the standstill position, may influence the moment of tiling.

From the one hand, the crane is an extremely heavy construction and it seems that wind cannot influence its operation extremely. From the other, underestimation of the wind force is the main mistake which can be made, since wind is a complex movement of the air masses, the speed and direction of which may change within a few seconds. The majority of people think that unless it goes about hurricane and thunderstorm, the “light” wind cannot be a problem. It is a pity, but, wind loads may have a disastrous influence, even without extreme weather conditions. Air is not an “empty” substance, it consists of many particles which are not seen by the human eye, nevertheless when it goes about huge masses of air and quick movements of the masses, the pressure they can exert as a result of the speed increase, may be tremendous.

Since the crane installed in the street is a construction of an impressive height, the wind may influence the controllability of the whole construction and certain parts of it, in particular load, cabin, cargo trolley and the whole crane. In reality, two kinds of influence may be pointed out: immediate or direct, when the crane is ruined or damaged by the wind, and indirect when the load which is lifted is moved not in the right direction and the equilibrium is lost. First, the bigger the height of the machine, the bigger the overturning moment becomes, since there is a big distance between the platform (ground) where the crane stands and the center of itself. Second, speed wind above the ground is much bigger than on the ground. That is why the higher the crane is the more the jib, the load and the cabin may be affected. In addition, it is necessary to remember that wind blows from different directions, from the side, from above, from below, exerting sometimes a way too great force on certain areas of the equipment and on the load. Wind may also change the surface on which the crane is installed, or create the waves in case of offshore equipment, which creates additional problem and difficulties and requires extra training and knowledge in order to prevent tragic outcomes.

Besides the crane itself, wind may influence the load and depending on the character, shape, weight of the load lifted and transported by the crane, the consequences may be quite dangerous as well. The load which under normal conditions would not cause any troubles, may start moving when influenced by the wind and the increase of the radius may lead to increase of the force exerted on the crane, and exceeding of the permissible limits, which results in overturn or load drop.

What can the crane resist the wind force? It depends on the crane and the parts it consists of. It is a complex structure and that is why the producer calculates attentively the loads which each part of the crane can withstand. Once the wind pressure (p) corresponding to a particular wind speed (vs) and the area of the construction which is exposed to the wind are known, the wind force can be calculated, and it is possible to find out which crane can be used for certain loads and under certain conditions. Of course, there are different accepted limits and the permissible wind speed used offshore, or onshore for very heavy loads in the docks is three times higher than the limit for smaller mobile cranes. It is expected that the latter should in reality have their jib lowered when the crane is not in operation, thus, avoiding unnecessary damage in case of strong wind.

The detailed explanation of the particular subject can be found in the regulations ISO 4302-1981 dedicated to wind load. Besides, the European legislation has been paying a lot of attention to improving the safety conditions and a few years ago EN 13000 European standard for mobile machinery came into force. Of course, the influence of nature of the working conditions is unpredictable, but if it is possible to improve the quality of equipment, and to provide education and training for operators on a high level, application of the modern auxiliary devices for monitoring, control and timely reaction in a hazardous situation, it is definitely worth taking it into consideration.

Figuratively speaking, wind may cause a “crane theft”, when the equipment is moved from its place, more than it is permissible. When it may happen is unpredictable, and to provide safe working conditions and avoid the damage of the crane, special sensors may be installed to block the work of some parts, depending on the problem arisen.

One of the auxiliary devices which has been designed to monitor the gusts of wind and their speed, is Air Flow Meter. To use is means to increase the safety of operation and predictability of the possible change of the environmental working conditions. As only the permissible limits are exceeded, the operator gets a signal, as well as the devices and sensors connected. It gives enough time to stop the operation, and take necessary measures of precaution, and, as they say, prevention is better than cure!

The necessary norms and regulations have been created, precise calculations for each particular model can be carried out, modern auxiliary sensors are provided to improve the working conditions and guarantee safety of the operators and personnel involved in the working process. And still, sometimes nature remains beyond the human control. If not to avoid, but to diminish the risks as much as possible, it is necessary not to neglect the all above mentioned measures which, in the long run, not only facilitate the working process, but help to avoid the damages and provide stability, even under the hazardous conditions.