Blog Article

Although most decanters made in Spain are circulars, there are several rectangular water treatment plants because they incorporate lamellas.

In these cases, the scraper is a rectangular model with 2 o 4 axes, depending of the installation needs:

– The model 2-Shaft it refers to typical rectangular sludge scraper, consisting in 2 Shafts moving the whole system of bottom trawling, but only cleans the decanter’s bottom.

– The model 4-Shaft it refers to a scraper that cleans both sludge from the bottom and scum on the surface, in this case are called 4 Shafts Scrapers.

This kind of rectangular scrapers have the great advantage that they don’t have corrosion, because they are made almost entirely in thermoplastic components,  which makes it perfect for the applications in the field of Water Treatment, both WWTP’s and DWTP’s.

The only inconvenients are:

Abrasion: depending on the sand quantity present in the water to be treated, the wear is accentuated in some of the parts of the scraper. The parts most often subject to wear, use to be the wear shoes of the scraper’s flygts and the bottom rails.

– The misalignment of the flygts: this is one of more common problems in this kind of rectangular scrapers and depending of the scraper’s brand, the problem is exacerbated. This is mainly due to the traction system equipment, when gears and chains are incorrectly designed: Small chain pitch are used with couplings to gear in the sprocket, this fact causes sometimes do not mesh properly and ending misaligned. Also, the manufacturers had to devise an alarm system to indicate when the system was misaligned and stopped the installation to prevent the scraper from derailing.

– Improper installation or setup of the rectangular scraper: It is really important to follow the protocol’s installation to avoid such problems. Almost all manufacturers of rectangular scrapers deliver an installation manual that perfectly describes the most critical points of the system to prevent these problems happening. However, for us, one of the most important aspects is the chain tensioning system. Both models designed by TecnoConverting Engineering an models supplied by our company DEWA, have a self-tensioning system. With this system the possibility of chain derailment is avoided, especially when the scraper has a considerable length, between 40 and 90 meters. When the scraper is so long, is extremely necessary to incorporate a self tensioning to avoid disarrangements in the chain.