Vacuum Truck

There are a few critical points which should be evaluated when choosing a vacuum truck:

The air flow of the unit. The material is transported by the air.The normal is approx 8 000 m3/h. Remember that a person shall hold the suction hose. A person can work with a 6" hose when handling large heaps of material more or less standing still. For work when moving around is a 4" hose often used. Smaller 2,5" floor cleaning hoses can be used but the air / material  velociity is very high giving high hose wear when operating with high rpm on the unit.

The vacuum of the unit. The normal max vacuum is approx 800 mbar for a vacuum loader. The vacuum is the factor that overcome the pressure drop when sucking air through the suction system and pulling the plug of material in the air stream. The smaller the hose the higher the pressure drop and wear. A larger diameter hose will have smaller velociy of air/material than a smaller diameter hose. The air velocity must however be sufficient to carry material so it cannot fall out from the air stream and possibly create a blocking in the suction hose.

Always ask for the vacuum pump diagram from the original vacuum pump manufacturer. There are vacuum truck manufacturers that increase the rpm above recommended rpm by the the pump manufactuer and thereby show higher air volume due to higher rpm than permitted. The temperature increase over the vacuum pump itself is also an important factor.

Noise level is today very important. Ask for a noise level statement of the unit. Often is a test made at operational rpm  and operational vacuum measured on a number of points at a 7 m distance. The mean value for these measurement are often used. The noise from the truck engine is also to be considered.

Is a suck only unit required or a suck and blow unit required? With the blow funtion must the material collected be sieved at the receival point as it may contain bolts, nuts etc. Many times it is sufficient to have a suck only unit and install a pre separtor which empties material back to a receival point in the production process without blowing as blowing will create dust clouds if not filtered.

Recovery of valuable material back to production is the often the most vital economic reason for investing in a vacuum truck. Lower maintenance costs, minimizing operation stand still at break down and better internal and external environmental conditions are others.

The volume of the material container. This is often stated wrongly. Clarify the actual filling volume based on dimensions of the container and the inlet pipe level and outlet pipe position in the container. Make a calculation of the actual usable payload volume based on this and not the gross air (water) volume in a container. The inlet design and how the material is ditributed inside the container is also a factor of the real payload volume. Does the stated container volume include the volume in the filter section?

The filter system in the unit. The filter area in comparison to air flow to be evalueated. The filter media used and the pressuere drop control for filter cleaning system. A filter cleaning system with back flow of atmospheric air is often recommended. Compressed air solutions demand often a larger air volume on the clean air side. Cartridge filters as main filters block often easily when used as main filters in a vacuum truck. A safety filter which is often a cartridge filter must always be installed after the main filter to safeguard the vacuum pump from filter leakage in the main filter.

There are vacuum trucks with the drive of the vacuum pump truck from the truck engine. These can be mounted on a 6x4 truck if the front axle is 9 ton and the container approx 10 m3. There are vacuum trucks with drive of the vacuum pump by a separate diesel engine. These can only be used on a 8x4 truck and if the container is 12 m3 or larger. Units with containers of 14 - 16 m3 needs 3 axles on the bogie otherwise it will be very heavy overloads..

Ask always for a weight distribution calculation and it will show what is possible to load in a cointainer of material without infterfering with the warranty of the truck axles. Many units are overloaded. Cement is often calcluated to have a volume weight of 1,5 ton per m3 material.

Many work with a vacuum truck on a hose only basis. This is very costly and inefficient as hoses has to be dragged through the plant to where the matrial is located with a high external and internal wear as a result. Build a static system where the vacuum truck is connected outside and work can be made with smaller hose lengths efficiently inside in the areas of operation. Minimize mobilization time, increase effciency and reduce the cost of excpensive suction hoses.

The strange thing is that very few reflects or test a vacuum truck of what is promised and what is delivered. A user buy a vacuum truck which shall transport material with an air stream. The working tool is the air volume. This can easily be tested at various vacuum levels at the hose inlet position of a unit. It is easy to state a large air volume but if one build a unit with small air channels, small filters and small silencers on the air inlet and outlet side which creates a high pressure drop over the unit itself. This will reducie the air volume and vacuum available for the actual work it is purchased for  - to suck material efficiently.

Just a few points of recommendation from my 40 years in the vacuum industry.

Thank you very much, your answer covered everything about the technical specification of vacuum cleaner. I think I can know study all the offers and select one of them.

Thanks again

Best Regards

David 

Hello mr. Karl

A supplier offered a vacuum unit with 6000 m3/h and informed me that 8000 m3/h air flowrate is very high for cement industry and not recomanded. He added ''vacuum unit with 8000 m3/h flowrate only can be used for heavy industry like copper or steel industry".

what do you think about it, is vacuum unit with 6000 m3/h air flow rate has an enough power for cleaning cement industry and as a result reducing the vacuum unit price?

Regarding blowing the material up, don't you think blow the collected material up to silo is a good solution to recycle leaked material? (dust problem can be controlled by the silo bag filter).

Regards

Nael