Positioning Accuracy of Iris Diaphragm Control Valves under Real Conditions

At the Brightwater wastewater treatment plant in King County, Washington State, northeast of Seattle, 12 Iris Diaphragm Control Valves are used for the airflow control of the aeration tanks. Nine 8” Iris valves control maximum air flows of up to 4000 SCFM (6500 Nm³/h), while the three smaller Egger 6” valves control flows of up to 1500 SCFM (2400 Nm³/h). All Iris control valves were supplied as a Process Control Kit with inlet and outlet sections and feature a precise mass flow measuring system located upstream of the valve, centered in the flow axis.

In a large-scale field test, the repeatability of the aeration airflow control system with the diaphragm control valve was tested by the plant operator in the presence of the design engineering company Brown & Caldwell from Seattle.

In each case, the air volumes to be controlled were measured at three different opening degrees of the valve in different basin zones. After a short period, the valve was returned into the same position. The results were convincing: the measured quantities showed only a minimal quantity deviation of less than one percent.

The diagram above shows the very high reproducibility of the operating characteristic curve of the aeration air volume control achieved by the Iris control valve in basin 2, zone 1 (orange dots).

How can Egger Iris Diaphragm Control Valves produce such high control accuracy and reproducibility?
The robust drive mechanism, spindle-mounted and supported at both ends, enables a very precise positioning of the control segments. The drive spindle is dimensioned for process control operation at high cycle frequencies. Due to the high number of threads with low thread angle, the maintenance-free spindle enables particularly high positioning accuracy and reproducibility.