Vacuum truck
A suction vehicle (also called suction vehicle or vacuum suction device ) is a utility vehicle with which liquid and pasty materials or fine-grained solids can be extracted by means of a vacuum pump ; it belongs to the tank trucks . In addition, material can also be transported using overpressure - and then blown out again (suction-pressure tanker) .
Transport vehicles for pourable goods (such as grain, wood pellets), some of which also have their own blow-out device, are called silo wagons . Other devices - possibly also mounted on vehicles - that work with a fan and high air speeds instead of a pump are called suction excavators .
Types of vacuum trucks
Vacuum trucks are divided into:
- Standard vacuum trolley
- High-performance suction trolley
- Chemical suction truck
Standard vacuum trucks lift liquids out of shafts or pits. The vehicles can suck up suspensions and pasty materials such as sludge . They are not well suited for dry solids such as sand , gravel and stones, since the usual air throughput of up to 4000 m 3 per hour is not sufficient for this. Depending on the height above sea level, a vacuum of up to 90 percent can be generated.
High-performance suction vehicles have more powerful vacuum pumps and often other filter systems as well. Air throughput is usually between 6500 m 3 / hour. and 21,000 m 3 hours and can vacuum gravel as well as mud. You reach about 85% vacuum. Some suction vehicles can blow gravel onto flat roofs at a height of over 100 meters using the injector principle .
Chemical suction trucks are made of corrosion-resistant materials, seals and fittings and are usually made in accordance with the regulations for the transport of dangerous goods (ADR). For example, the weld seams have to be X-rayed or checked with ultrasound . Depending on the calculation pressure, the tank is subjected to a test pressure of up to 10 bar, in exceptional cases up to 21 bar. The tank is usually made of V4A stainless steel or has an internal coating. Depending on the type approval, there are regulations with regard to the type, number or location of the intake and outlet openings. The tank code indicates the maximum pressure as well as the number and locations of the openings.
All vacuum trucks can be manufactured according to the regulations for dangerous goods (ADR) and equipped with the appropriate safety installations (overpressure safety valves, protective bars). Depending on the country, ADR tests are carried out at different intervals, during which the vehicles are checked for leaks with pressure, among other things.
principle
Components of a vacuum truck:
- tank
Vacuum trucks have a vacuum-resistant tank that can withstand 90% vacuum. It is often made of normal or chrome steel and approx. 5–8 mm thick (more in the case of high-performance suction vehicles to withstand greater wear and tear). Reinforcement rings on the outside wall of the tank increase stability. There is usually a rear tank lid through which the extracted material can be tipped off. Instead, chemical vehicles often only have connections in sizes from 1 ″ to 6 ″. At the top of the tank, a ball held by a cage floats on top of the suctioned material to close the suction opening to the pump when the tank is full. Otherwise, depending on the pump type, over- suction could cause minor or major damage.
- Separator system
The separation system separates the sucked in material from the flow so that it remains in the tank and does not get into the pump:
- Separator chamber: The tank of the suction vehicle forms a simple separator chamber in which liquid media are retained by gravity. This does not stop dust and other fine solids.
- Cyclone: The cyclone or centrifugal separator creates a circulating air flow (similar to a windpipe ). Due to the centrifugal force , the dirt particles move to the outer wall of the container and collect on the bottom. In addition to the ball in the tank, the pump is usually protected by a ball in the cyclone separator.
- Filter bags: As with the air filter of a motor vehicle, the dust that should not get into the pump is held back on the filter walls. The pockets are cleaned manually or automatically using compressed air. Filter bags are mostly only used in high-performance vacuum trucks that suck up dust, sand, gravel, etc.
- pump
The pump creates the vacuum. Due to the pressure difference between the tank and the environment, the material is drawn or pushed into the tank, depending on how it is viewed. The pump types are also available in ATEX design, so that they can be used in potentially explosive areas. There are different types of pumps:
- Water ring pump : A water circuit is necessary for their operation. The water seals the rotor from the outer casing. Due to the sealing water ring, the rotor and the outer housing do not touch. The pump runs very smoothly, is low-wear and has a long service life. For operation at temperatures around 0 ° C, the water must be protected from freezing. The water ring pump is therefore rarely used in very cold countries.
- Lamellar pump: The principle of the lamellar pump is similar to that of the water ring pump: The rotor contains slots around the circumference into which the lamellas are embedded. The lamellae are pressed against the housing by the centrifugal force and thus seal. To reduce wear and tear, oil is added drop by drop. The oil-containing exhaust air must be held in an oil separator . The lamellar pump is more subject to wear than the water ring pump and is significantly louder.
- Rotary lobe pump: Two interlocking gears (two to four teeth) create a vacuum. They are also relatively loud and, in terms of wear and tear, are to be classified between the lamellar and water ring pumps.
When aspirating liquids that hardly contain any solid matter, the rotary lobe pump can also be installed in front of the tank so that the medium to be conveyed is passed through the pump. The tank then does not have to be vacuum-resistant and can be made thinner and lighter as a pure transport tank. Rotary lobe pumps are often used in the chemical and food industry. The gears must be provided with a special alloy in order to be resistant to alkalis, acids, etc. Depending on the type of pump, the maximum solid size is 0.5 cm to 5 cm.
drive
The drive is usually hydraulic or by means of V- belts and multi-ribbed belts. Direct drive via a cardan shaft is rather rare . The loss of power is greatest with the hydraulic system and the smallest with the cardan drive. The V-belt drive has few losses if it is correctly tensioned.
various
- Suction depth: Theoretically, water can be sucked up approx. 9 m deep with a suction vehicle at 90% vacuum (the mean air pressure on earth of 1013 mbar corresponds approximately to a 10 m column of water, this in turn corresponds to the suction depth at a 100% vacuum). Heavy and highly viscous materials such as sludge etc. are sucked off in the air stream. If not enough air gets into the suction hose during suction, additional air can be blown in via a compressor . The greater the suction height, the more air must be added. The stiffer the medium to be extracted and the greater the suction height, the thicker the suction hoses must be and the more important the added air factor becomes .
- Competitor suction dredger: In recent years the suction dredger has developed as a competitor to suction trucks. However, the basic area of application of the suction excavator is different from that of the suction truck. The suction excavator was originally intended as a replacement for an excavator . In the beginning it was mainly used in civil engineering for the gentle, risk-free suction of earth material when repairs to water pipes, power lines etc. The suction dredger is used wherever there is a high risk of damaging a pipe with the excavator. A suction dredger has hose dimensions between 200 mm and 300 mm, which is why it is able to extract larger media. However, the suction excavator is not intended for wet media, as its filter system is actually designed for dry media. Furthermore, it does not meet the requirements for the transport of dangerous media as extensively as a vacuum tank (suction excavators have cubic tanks). The suction excavator is, so to speak, intended more for dry, large, heavy media. Furthermore, for weight reasons, it is usually not allowed to drive loaded on public roads. Since baffles must be present for liquid transports over 7500 liters (or a maximum of 20% or a minimum of 80% load must prevail, which is not possible because it is then too heavy in terms of total weight), it remains on the construction site. It has to be reloaded in troughs that are removed by other trucks. Furthermore, the hourly rates are relatively very high.
- Transport tank : These tanks are mostly not vacuum-resistant, but often overpressure-resistant. Some tanks (ADR) are tested according to L4BH; This means that they can withstand an internal overpressure of 4 bar, are intended for liquid media, have three openings and are considered airtight. These tanks usually do not have a pump or a rotary lobe pump through which the cargo flows. Vehicles without a pump are usually filled from above using a free fall. When filling and emptying the tanks, it must always be ensured that the maximum pressure conditions are maintained. Otherwise such a tank could contract or it could explode / burst.
- Driving behavior: Most vacuum trucks have a high center of gravity. Therefore, great caution is always advisable when cornering and during evasive maneuvers. Most accidents happen while swerving or cornering. The dangerous thing is that you have no clues as to when the vehicle will start to tip over. The vehicle leans slightly to one side and remains there for a long time. Suddenly and without warning, the vehicle tips over. In evasive maneuvers, the abrupt changes in direction are the greatest potential hazard. The jerky evasive action can cause the vehicle to rock and tip over. Usually the first evasive curve can still be implemented, but the second change in direction causes the vehicle to tip over because the energy of the first evasive maneuver builds up and then becomes too big when the vehicle is caught and discharges. Thus the vehicle tips over. The risk of tipping over is lower with tank trailers than with 2-, 3-, 4-, 5-axle vacuum trucks. This has been proven several times in circular tests.
- Operation: No training is required by law to operate such a vehicle. Usually one receives internal training, or these are carried out by the manufacturer. Special training of the driver is required for dangerous goods (ADR). The vehicle must be built, checked and registered according to ADR in order to be able to carry out such ADR transports.
- Safety: The higher the regulations and requirements, the more safety measures are built into dangerous goods vehicles (ADR). These can include dead man's switches, for example. The legal regulations are massively tightened when entering dangerous goods (ADR). Therefore, consider carefully whether you need such a vehicle. Personal protective equipment is of course also part of safety. Depending on the hazardous material, more extensive protective measures must be taken. These are noted in the written instructions and documents. There are no regulations for normal vacuum and high-performance vacuum vehicles. Whether with or without hand and face protection is not required, unless the customer applies his own operating rules.
- Cleaning the tanks: The tanks are cleaned by machine or by hand. With machine cleaning, a device with spray nozzles is inserted into the chamber and thus cleans the tank walls. If this is not possible or the degree of cleaning is insufficient, it must be cleaned by hand. To do this, the tank is cleaned using "high pressure cleaning". What also always has to be cleaned are the piping of the inlet and outlet devices to the tank. After cleaning, a certificate is issued stating when, where, how etc. the tank was cleaned. Depending on the customer, this certificate may be requested before loading. With normal vacuum trucks, the tank is cleaned either by a water hose or a high-pressure hose.
- Hoses and fittings: The suction hoses of the individual vehicles are very different. While the upright vacuum truck uses normal suction hoses, the high-performance vacuum truck needs either very thick-walled, but heavy, hoses (which last longer) or thin-walled, but light, hoses (which wear out quickly). The chemical suction truck requires different hoses depending on the load. For example, NBR materials are more suitable for oily waste, whereas EPDM, Viton or carbon are more suitable for acids and alkalis. There is no one mix that can be used for everything. Most connections and fittings are made of stainless steel. Stainless steel has a high resistance to acids, alkalis, etc. Normal galvanized steel or Chorm steel is often used for normal vacuum trucks. Since these vehicles do not transport acids, alkalis or the like, fittings in chrome steel are not an issue.
literature
- Helmut Orth: Suction vehicle for picking up and transporting liquids and viscous sludge with its own filling system and additional deep suction device in Hösel, Schenkel, Schnurer: Müll-Handbuch , Verlag Erich Schmidt, Berlin 1991.
Individual evidence
- ↑ Bernd Bilitewski, Klaus Marek, Georg Härdtle: Waste management: manual for practice and teaching . 3. Edition. Springer, Berlin / Heidelberg 2000, ISBN 3-540-64276-5 , pp. 116, 125 (729 p., Limited preview in Google Book search).
- ↑ Regulations in Switzerland ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
