are extensive prepared in order to obtain the high quality. Therefore also transportation and installation of the filter material have to be done in a way that maintains the high quality.
When filter material will be unloaded from the silo-truck, there is a strong pulsation in the silo and in the blowing out tube, which can lead to abrasion (dust) and can destroy the gravel. The quality impact by the handling gets worse by using long tubes or great ups.
If the blowing out tube is placed in an up and down course like mountain and valley, the problem becomes even more serious. In front of each uphill-course the filter material dams up in the tube and will be then partly destroyed under the air jet pressure. Pneumatically handling and transportation changes the grading curve of the filter material by enrichment of undersized particle; thus also the coefficient of cyclic variation of the filter material changes.
Pneumatic blowing out from the silo truck under simultaneous supply of water with an injector at the silo discharge or at the end of the tube is no sufficient protection from grain destroying, it reduced only the dust formation.
Really careful and at the same time dust free unloading from the silo truck without negative quality impact possible only if the filter material from the water fulfilled silo truck is unloaded hydraulically, thus to be out-washed.
Advantages of hydraulic unloading:
- Reduced abrasion of the filter materials,
- Substantially fewer rubble grains (form the hoses)
- Clearly faster unloading than when pneumatic blowing out
- Small wear of the unloading hoses
- No striking the unloading hoses
- Smaller expenditure with the installation into the filter
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