The market is characterized by the presence of many local and international vendors and as a result appears to be highly fragmented. Local and regional vendors compete with the well-established international players with diversified product portfolios by offering products at a comparatively lower price. Diaphragm pump manufacturers also compete on the basis of several other factors such as quality, reliability, and after-sales services and are mainly focused on differentiating their products by manufacturing customized and energy-efficient pumps.

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Overpressure safety recirculation? If pressure downstream of the pump increases for whatever reason (blockage, narrow restriction, etc.), a recirculation feature, like the one on KNF pumps designated .27, provides safety for the pump and system. This option is field or factory adjustable to open and even run continuously at set pressures from 1 bar gauge (14.5 psig) to greater than 6 bar gauge (87 psig).

From a technological perspective, the installation of the displacement pump significantly simplified the system as control valves and pipes previously required to adapt capacity to requirements were no longer needed. The design of the centrifugal pump meant it had to be set to a delivery volume which was far above the volume needed in order to meet the desired discharge pressure. Excess capacity was drained off and led back, leaving the efficiency of this system at a mere 20%. The new system with the displacement pump on the other hand, achieves an efficiency of more than 90%. Schlüter regards the simplification of the system technology as an additional advantage; removing unnecessary, superfluous complexity.

Diaphragm pumps are categorized as positive displacement pumps that are used mainly in industrial applications, which involve pumping and lifting of heavy fluids, such as sludge, slurry, or mud. Sludge is a semi-solid slurry that is produced following the treatment of wastewater treatment or as a settled suspension from numerous industrial process. 

Energy costs for the pump comes from the consumption of the compressed air required to power the pump. Since compressed air is a relatively costly utility in many plants, requiring compressors and air distribution systems this represents the main running cost for an AODD pump. However, AODD pumps can be used in areas either where electricity simply isn’t available, or in hazardous areas where electrical supplies are forbidden. This enables AODD pumps greater flexibility over centrifugal and positive displacement pumps. AODD pumps are generally environmentally friendly as most of them use oil-free compressed air for pollution-free operation. No oil mist is vented into the atmosphere and also there can be no oil contamination of the pumped fluid. Since there are few components that require maintenance, it is relatively straight forward to refurbish AODD pumps, increasing their lifetime and further decreasing cost of ownership.

There are general guidelines and points to consider when choosing the correct configuration. In parallel with these recommendations, it’s always advisable to check the manufacturer’s specifications and chemical compatibility guides. The first guideline is to remember to identify the temperature limits of all components in the pump. The internal pump components may be rated to an extremely low or high temperature, but that does not imply that the pump body material is rated to the same level, and vice versa. When configuring an AODD pump, it’s important to identify the temperature ratings of all components, by referring closely to the manufacturer’s product specifications. Increasing the working temperature has a significant consequence on material selection. For example, plastic pump bodies are not recommended because cold flow and creep can lead to leaking. As temperatures rise above 80°C, the choice of compatible internal components further decreases. At these elevated temperatures, materials such as ethylene propylene diene monomer rubber (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF) and fluoroelastomer (FKM or Viton®) are preferred. FKM and EPDM have the highest heat resistance, rated to 160°C and 135°C respectively. Next in line are PVDF and PTFE, rated to 107°C and 100°C respectively. At the other end of the thermometer, glycol transfer pumps are required to withstand cold environments down to −20°C, thus requiring aluminum, stainless steel, EPDM, FKM and Santoprene. Key points: • For high temperature applications: Stainless steel or aluminium pumps with FKM, EPDM, PTFE or PVDF wetted materials. • For low temperature applications: Stainless steel or aluminium pumps with EPDM, FKM or Santoprene wetted materials.

Rubber diaphragms are compression molded of synthetic rubber with a nylon fabric mesh positioned within the rubber to improve the diaphragm’s flexing characteristics. The following are the rubber diaphragm materials available:

When considering the use of metal casings lined with corrosion-resistant thermoplastics, special consideration of the service conditions is critical. The following questions should be addressed when selecting the special material: How will the lining hold up under the flow conditions? How abrasion-resistant is the lining material? How significant is the danger of wear or pinholing, which might lead to corrosion of the metal or contamination of the product? These concerns become less significant as lining thickness increases, or with designs that use thick-sectioned, replaceable wet-end components.

Various rubber components are used in the manufacture of diaphragms and a nylon fabric mesh is used for dimensional stability and additional strength. Elastomers such as Neoprene, Buna-N, EPDM, (Nordel) and Viton are the most frequently used. Their chief characteristic is flexibility which allows more volume to be displaced. Thermoplastic materials are also available for manufacturing diaphragms. These are produced by an injection moulding process and require no fabric reinforcement for dimensional stability or tensile strength. The most popular are polyurethane, Hytrel, Santoprene and Teflon. Polyurethane gives excellent general purpose diaphragms which are the most economical of all, with extremely good flex life.

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