Hydraulic loads on filter units
It is important to be aware that a filter system is designed for a given flow of water with a given characteristic. If either less or more water than the filter unit is designed to treat is used, the filter will not functional optimally. The ability of a filter to toler-ate varying water flows, for example when tapping down a fish tank, depends on its design. Equipment using settling as a principle is especially intolerant of variations in the water flow, particularly high flows. For a mechanical filter, variations in load are normally not so critical. However, if the loads are too high the filter cloth may become so clogged that breakdown can occur.
A common fault on aquaculture facilities is that the tanks and outlet pipes are the incorrect design and size, so settling of particles occurs in the system. Shock drainage of the outlet system is used, often once or twice a day, to remove settled particles and avoid total blockage. If shock drainage is necessary to keep the outlet pipes open, something is wrong with the design and construction of the outlet. When shock draining the fish production tanks, the water flow in the outlet pipes is increased and so is the particle concentration, because particles that had settled in the outlet system will now go into suspension as a result of the higher velocity. If the filter system does not toler-ate variation in water flow, reduced purification results. This is critical, because it is in these situations that the number of particles is highest, and where good purification is necessary. Here the importance of choosing an appropriate filter system, and of doing everything correctly before the filter system, is apparent. It is also necessary to be aware of the interaction between the different parts in the farming system.