Low and high vacuum area
When low and high vacuum is applied, it is very important to keep drainage parameters under control, in order to regulate the right amount of vacuum needed to perform the most adequate dewatering – not too slow, not too fast or aggressive – in order to save energy.
The right choice of drainage elements – either in ceramic or plastic – is pivotal to obtain the desired, progressive dewatering.
LOW VACUUM AREA
These boxes are installed immediately after the forming zone and are conceived to remove large amounts of water by applying a low vacuum level. The configuration is not standard, but it is defined on the basis of the machine operating parameters so as to guarantee a not aggressive and gradual drainage.
The drainage elements – that can be ceramic or fiberglass-reinforced UHMWPE and may be equipped with draining angle, in order to optimize drainage – are installed on the T-bar, so to allow an easier and precise installation and removal of elements whenever needed.
Plastic deckels are also provided to seal the gaps between elements and keep the box (box) in a vacuum condition.
The box is equipped with an analog vacuum indicator with adequate reading scale and false air valve properly sized to the capacity of the box.
To guarantee the vacuum efficiency, the box must be equipped with an air-water separator to be installed on the drain pipe and it can also take advantage of an automatic VRV-AF valve to perform a more accurate vacuum adjustment.
This box is characterized by an inner double chamber and it is commonly used at the end of the low vacuum area with the purpose of controlling the wet sheet line. The box layout is not standardized, but the best solution is studied considering the drainage system performances, in order to guarantee the wet line stability. This type of box can accommodate ceramic or fiberglass-reinforced UHMWPE drainage elements, but taking into account the considerable vacuum level, it is highly recommended to install ceramic elements to reduce friction and therefore obtain some energy savings.
The drainage elements are installed on the T-bar, so to allow an easier and precise installation and removal of elements whenever needed.
Plastic deckels are also provided to seal the gaps between elements and keep the box in a vacuum condition.
Each vacuum chamber is equipped with an analog vacuum gauge with adequate reading scale and false air valve properly sized to the capacity of the box.
The structure of the stainless steel box is designed to withstand pressures up to around 30kPa.
To guarantee the vacuum efficiency, each vacuum zone must be equipped with an air-water separator to be installed on the drain pipe and it can also take advantage of an automatic VRV-AF valve to perform a more accurate vacuum adjustment of each box room.
HIGH VACUUM AREA
This box is usually installed after the wet line, in the high vacuum zone of the wire. These boxes contain multiple internal chambers (2 or 3) in order to create different zones of progressively increasing vacuum in the flow direction towards the machine, so to prevent the sheet from being subject again to atmospheric pressure as it passes from one vacuum zone to the next with greater vacuum.
This process allows for energy savings and a significant improvement in the final sheet dryness percentage.
Drainage elements are grouped in a single cover which can either be ceramic or fiberglass-reinforced polyethylene, but this last material is strongly discouraged due to the friction generated by the high vacuum levels required by this application.
The ceramic elements are installed on a stainless steel frame that ensures the interchangeability of each of the laths that compose the cover.
The configuration of the cover is customized according to operating parameters.
The structure of the stainless steel box is designed to withstand pressures up to around 50kPa.
Each vacuum chamber is equipped with an analogue vacuum gauge with adequate reading scale and false air valve properly sized to the capacity of the box.
To guarantee the vacuum efficiency, each vacuum zone must be equipped with an air-water separator to be installed on the drain pipe and it can also take advantage of an automatic VRV-AF valve to perform a more accurate vacuum adjustment of each chamber.
