According to the principle of pneumatic transport each material can be carried when it is suspended in the atmosphere. Air volume has to be bigger than the volume of the sediment, because there is a huge difference between the specific weight of the air and the sediment.
The applications of this principle are in the building, sewer and road maintenance. Since about ten years, in Italy, the application of air in maintenance works is more and more frequent and widespread. The technology uses a powerful turbine aspirator, named suction excavator, mounted on vehicles and self-moving machines. Main features of these machines are their speed in finishing operations and the reduction of manual works. The equipment is required in delicate contexts and where there are several technical difficulties because of the narrowness and typology of space. It is particularly useful where some conditions rule out the use or limit the use of mechanical machines.
DIGGINGS WITH SUCTION EXCAVATOR
One of the most important problem to the maintenance of water, phone, gas utilities is the excavation in urban areas. Every yard implies problems to the traffic, noise pollution, restoration of the paving, and it is difficult to preserve the pre-existing constructions. The problem is bigger and bigger when there is the necessity of many small diggings. This kind of work implies the use of more companies able to operate twenty-four hours a day and this is very expensive. To operate and solve the various problems of waterworks maintenance Gerotto Federico s.r.l. company proposes to municipalities and administration bodies the method of the suction excavation to achieve the following aims:
-Time reduction of the excavation (70% than traditional methods)
-Excavation volume reduction
-Reduction of the space occupied in the working area
-Complete absence of debris and muddy material around and in the excavation site.
- The paving is cut with the traditional pneumatic tools given with the equipment.
- The dug earth, through suction, is removed and carried, through the suction hose, in a storage tank, while the air is put back to the atmosphere.
Main Components of PneumaticTransport Equipment:
- Air generator: a heat engine or electromotor starts a fan, a booster which creates an air flow.
- Product carrier: when the suction operation begins the material that has to be carried begins to move towards its destination inside a pipe.
- Extraction system of the product from the air: products are collected in a dump storage tank, while the air is put back to the atmosphere.
- In this system the dug earth is torn up and carried through an air flow at high speed.
- Air flow QMF (mc/s or mc/h) describes the air volume per unit of time to ensure the flow of the material.
- Dug earth capacity QMP (kg/s or kg/h or T/h) describes the quantity of the material carried per unit of time.
- Cm concentration describes the relation between the air and the material flow:
- Air speed VF (m/s) describes the average speed of air needed to carry in a specific point and in a particular moment. It is difficult to calculate directly the speed; generally it is calculated knowing the capacity.
- Functioning depression P (17000 Pa) it is the depression used by the equipment.
The readings of these parameters are changed thanks to the experience with this equipment and at the moment they are as follows:
- Nominal capacity of operation: 2500 mc/h
- Minimum theoretical speed of air in the flexible hose: 500km/h
- Flexible hose diameter: 250 mm
Components of the System:
- Motorization and transmission with the engine of the vehicle. In this solution there is a gearbox on the transmission shaft which can be disconnected. This system has the advantage to reduce the weight and space occupied by the vehicle, to make easier the maintenance, and to decrease the price.
Storage and settling tank:
- The capacity, about 8mc, has been adopted to solve the initial problem of having many small diggings in urban areas together with operations from the edge of the excavation.
- Thanks to this solution the material is unloaded by a dump tank, without any manual operating.
The settling tank could not perfectly filter the sucked fluid, so it has been necessary to conceive a filter system to respect the regulation about the emission into the atmosphere.
The flexible hose chosen has the following features:
Low weight to be easy to maintain flexibility and resistance to knocks and abrasions also at low atmospheric temperature
Low sensibility to obstructions at its end it has a steel element of a smaller diameter which can be removed. The entry of sucked materials in the tank is conceived to avoid obstructions. The length depends on the condition of the work. The hose is supported by a telescopic arm radio controlled (up and down) rotating on an axis.
The sucking hose together with the arm is conceived to be placed in the correct position for the traffic without removing the hose. An ergonomic wheel with all the controls is fixed in the hose in a removable way in order to handle it in every situations from the edge of the excavation.
The advantages in the use of the suction excavator are various and some of them cannot be directly measured. For instance:
- Small risk to damage underground pipes;
- Less disturbance to residents who lives and pass in the area;
- More efficiency;
- More supply of excavators;
- The possibility to make preventive operations.
The only elements that can be measured are based above all not only on the decrease of dug earth volume but also the surface of the paving that has to be restored.
Several studies in this field concern with the comparison between the cost of a yard which uses the method of the suction excavation and the techniques of operations from the edge of the digging, and the cost of the same yard using the traditional method. After an analysis of the different elements, such as the hour profit per yard and the profit rate, results that the saving is significant and it can reach a value of about 30%-60% and more for some works.
1. Manual excavation, normal soil conditions, presence of buried cables and pipes
Employing Suction Excavator for removing
2. Heavy soil, presence of buried cables and pipes
3. Dry and heavy soil
4. Wet and heavy soil or clay
5. Moderately heavy soil
6. Muddy soil, gravel and crushed rock
7. Sandy soil
- Vehicle transfer speed;
- Reduction of the space occupied in the working area;
- Reduction of the excavation volume (from 40% to 60%);
- Working time reduction (from 40% to 70%);
- Excavation, loading and carrying with only one machine;
- Suction of every kind of materials (dry, liquid, muddy, gravelly);
- No use of shovel;
- No damages to underground pipes and lines;
- Dry excavation even in the presence of seepage from other channels;
- Machine supplied with many tools (air compressor, demolishing hammer, rammer, pneumatic air jet lance, “lombrico” mini- digger);
- Complete absence of debris and muddy material around and in the excavation site;
- Each operation is made by a radio control at the edge of the hole;
- Possibility to unload the dug earth on dump containers;
- Excavation speed proportional to the friability of the materials;
- Practicalness to silting-up excavations to drillings and Inspections to the condition of channels, connections, joints;
- Many operations can be acted even with networks operating;
- Reduction of insurance costs (no breaks-no franchise);
Maximum safety in the presence of gas and sewer exhalation.