Vacuum conveyance is a special type of pneumatic conveyance. As the name suggests, an artificially created vacuum within the pipelines is used to pull or suck the medium through the pipeline. Vacuum conveyance can be used to transport all types of materials, as well as for the emptying of all types of containers. Valves used in vacuum conveyance must be designed for operation in a vacuum.
The vacuum within the pipeline is created by a vacuum pump at the end of the conveyor section. The pump is usually located in a separator vessel in which the suction air flows through a filter system to separate the transported goods. The goods are collected in this container and can be transported further or processed once the vacuum has been removed with the aid of valves. After the vacuum pump has been switched off, the pressure inside the pipelines and the separator vessel returns to the ambient pressure.
For the filter system to work at maximum performance, it needs to be regularly freed of any adhesions – so-called filter cakes. This is done by blowing a short blast of air against the filter. Once the adhesions have been blown away, the vacuum pump can continue its work.
In order to ensure that no constrictions or complete blockages occur at the valves in the vacuum pipe other than those desired, the valves in these sections must be suitable for vacuum operation.
Vacuum technology is not only a reliable solution for emptying containers but also has many other positive characteristics. For example, it relieves the physical demands on employees and reduces damaging impacts on health such as the formation of dust or the release of substances.
However, suction lines are also used outside of industrial processes, for example in vacuum cleaners for cars, as are often found in car washes, or in vacuum toilets on trains. Valves are also used to open or shut off the pipelines under vacuum in these systems.
Pinch valves can be installed in various different positions in vacuum conveyance. At the very start of the pipeline system, they can control the emptying of various different containers such as barrels, canisters, silo vehicles or trailers. They can also be installed to control and shut off the flow of the materials within the pipelines under vacuum and fitted as extraction valves at the lower end of the separator container.
To be able to use pinch valves in vacuum conveyance (from > -0.1 bar), they need to be fitted with a control unit that compensates for and thus counteracts the vacuum in the pipeline. This can also be achieved via a bypass that utilises the unpolluted process vacuum from the vacuum pump and guides it via the bleed vent on the solenoid valve to the inside of the pinch valve. If vacuum compensation using a control unit or bypass is not used, the installed sleeve will contract – due to the negative pressure – and will thus no longer ensure a constriction-free flow. In addition, the service life of the sleeve will be significantly reduced due to the increased strain placed on the inside of the sleeve.
AKO Armaturen offers two systems with the AKOVAC Basic and AKOVAC Comfort control units that equip the pinch valves ideally for use in vacuum conveyance. The control unit does not need to be fitted to the pinch valves directly but can be fitted so that it can control the negative pressure centrally and thus control multiple pinch valves at the same time.
AKO has more detailed information about the control units for vacuum transport (AKOVAC) available for you.
Another field of application for pinch valves in vacuum conveyance is in vacuum toilets on trains.
The brewery uses pinch valves with AKOVAC control unit for the vacuum conveyance of diatomaceous earth.
A sweets manufacturer uses pinch valves as control valves in suction pipelines.
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