Polyhedrally shaped screens form the core of TAPIS®. The polyhedron consists of a stainless steel supporting structure which contains the screen surfaces. Whereas the polyhedron sides that are directed to the water surface are equipped with special screens, those sides directed to the ground remain closed to avoid the ingress of debris sediment from the bed of the sea, river or lake.

Inside of the TAPIS® polyhedron there is a spray nozzle system which, due to its special arrangement, and in combination with the geometry of the polyhedron, enables a particularly effective screen backwash by pressurized air pulses. The lower, closed sides of the polyhedron are used as rebounding plates for the expanding pressurized air.

As screen surfaces TAPROGGE uses its special, corrosion-resistant Cling-Free© elements. These screen elements are designed as thick-walled panels and are easy to handle and to exchange. They are fabricated of modified polyamide and provided with holes in the shape of canals. These canals are normally 10 mm in diameter but can also be adjusted to other sizes governed by the requirement of pump protection.

For the discharge of the cleaned water, the polyhedra are connected with the pump well via a pipe or a closed canal.

Filtration Phase:

The driving force for the filtration process through the TAPIS® polyhedra is the static differential pressure between the water level in the pre-screening inlet and that of the pump well. Caused by this level differential the feed water passes through the screen surfaces of the TAPIS® polyhedra. All fouling particles larger in size than the selected perforation of the screen are retained on the exterior sides of the screen surfaces; cleaned water which has passed through the screen surfaces is forced to flow into the pump receiver via a pipe or a closed canal that form the connection between the TAPIS® polyhedra and the pump well.

Air Backwash Phase:

In the course of time fouling accumulates on the screen surfaces. To remove such fouling a backwash cycle is initiated. Controlled by a timer, a signal is given to release the air compressed in the air receiver. Once released, the pressurized air enters from the air receiver via feed pipes directly into the interior of the TAPIS® polyhedra where it abruptly expands via a specially arranged spray nozzle system. The special polyhedron geometry causes a harmonized and thus particularly effective utilization of the pressurized air.

The abrupt expansion displaces the water volume contained in the polyhedron within seconds (air backwash), with the fouling accumulated on the screen surfaces first being vigorously lifted off by the displaced water and then transported away with the expanded air cloud. The canal-shaped holes of the special Cling-Free© filter elements generate a jet effect when being passed by water and air which intensifies the cleaning effectiveness.

The entire air backwash process takes only a few seconds. Filtration continues immediately afterwards, without further interference by the operator, in a natural way (pressure differential between water intake and pump well).

As soon as the release of pressurized air has caused a drop of the static pressure in the air receiver to below a pre-set value, the control emits a signal to close the pressurized air pipe and start the compressor for recharging the air receiver with fresh pressurized air. Once the desired initial pressure has been reached, a new pressurized air charge has been generated, and the compressor switches off. The backwash unit is then ready for another backwash process.