For filter press operations, this technology offers a solid solution that incorporates a number of characteristic benefits.
by Peter Schüten
August 5, 2016

Additionally, the increased pressure resulting from these air pressure amplifiers, or “boosters,” pulsates strongly and can influence the product’s flow. Boosters also seem to reach their limits in maintaining pressure (for example, during repressing) because the devices are almost always too small. They yield the required end pressure but may require a longer filling time.

Functional principle of an air-operated double diaphragm pumpFigure 1. Functional principle of an air-operated double diaphragm pump with a feed pressure of 15 bar

The third variant is a pump with internal pressure conversion. Figure 1 shows how this technical solution applies compressed air to a differential piston along with the diaphragms. The increased surface area—typically twice as large or more—causes the compressed air to generate a corresponding amount of increased force. This converted force acts on the feed diaphragms with increased (double) pressure.

The entire construction is designed for the high strain caused by the maximum amount of pressure, as well as the strain caused by the typically abrasive sludge. For this reason, the pump housing is built from materials such as stainless steel or polyethylene (PE UHMW). This tough material is a decisive factor in the durability of the pump.

Wear factors based on the sand-slurry processImage 2. Wear factors based on the sand-slurry process: PE UHMW = 1 (top); PP = 7 (middle); steel = 1.6 (bottom)

Using compressed air to power a pump is effective because of constructive measures. The pump operates with minimal dead space—the space inside the pump that must be filled without serving the actual feed process. As a result, the pump always has sufficient power reserves to handle large volumes of wastewater.

A New Generation of Pumps

With the introduction of a new generation of high-pressure AODD pumps, there is an additional variant that combines the highly robust housing of the pressure-converting pump with an air section where no conversion takes place. This version is suitable for all applications under heavy load conditions, ranging from low-feed pressures to high-pressure applications of up to 15 bar (218 pounds per square inch gauge). If users operate a pump at such high air pressure—whether it is from an external booster or directly from the compressor—they can be assured that the pump is structurally designed for such pressure ranges and need not be held together by external reinforcements.

On these new pumps, the diaphragms are equipped with specially developed heavy-duty diaphragms with an integrated metal core that provides a long service life and the ability to handle heavy loads. The diaphragm’s vulcanized core supports extremely thick layers of elastomer. To transfer the suction forces, the core is reinforced with a special textile that is barely flexible in any direction.

In addition, these pumps can be combined with a sensor that responds to the diaphragm’s movement and allows the cycle to easily be monitored. The slow stroke frequency that accompanies a full press rarely triggers a signal. If a programmable logic controller is used to program a time window within which a stroke should take place, a full chamber filter press is indicated by the fact that these rare signals no longer occur within this time window. The compressed air can be switched off and a signal can be set for the operator to empty the press. This method functions purely by physical means and is independent of sensitive pressure gauges and contaminating sensors in the wastewater current.

When selecting pumps for filter press operations, AODD pumps are a solid solution that incorporates a number of characteristic advantages. Conventional displacement pumps with electric drive and control elements do not have these properties that are specific to the design of these pumps, which include run-dry capability, good controllability and a gasketless mechanical design.

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