New class of integral piston diaphragms satisfies the demands that are critical in AODD pump operation
As the parts that are constantly in motion during the operation of an air-operated double-diaphragm (AODD) pump, careful consideration must be taken in regard to diaphragm selection. Any breakdowns or failures can result in undeniably costly and oftentimes hazardous product leaks. Previous experience can assist the operator when selecting a diaphragm, but new applications require research and may warrant the use of third-party assistance in order to determine which diaphragm will most successfully meet the application’s operational parameters.
When selecting a diaphragm, there are generally seven primary factors to consider:
- Chemical Resistance – material compatibility with the fluid being pumped
- Temperature Ranges – capability to remain flexible in low temperatures and not deteriorate in high temperatures
- Abrasion Resistance – ability to withstand wear and friction from contact with solids and particles in the fluid being pumped
- Sanitary Standards – requirements that the diaphragm comply with hygienic or sanitary standards
- Inlet Condition – capacity to pump fluid from one location to another
- Flex Life – expected longevity of the diaphragm before requiring replacement
- Cost – total cost of ownership, including initial price, rated flex life for the application, and costs of downtime and diaphragm replacement labor
Over the years, leading AODD manufacturers realized that improved diaphragm design was the next frontier in achieving better, more reliable pump performance. In fact, Wilden revolved around the shortcomings of the outer-piston. The inner and outer diaphragm pistons, often refereed to as plates, connect the diaphragms to the reciprocating common shaft and seal the liquid side from the air side of the diaphragm.
While outer-piston diaphragms will perform in many common applications, these diaphragms have some worrying characteristics. First, outer-piston abrasion that occurs during normal operation will lead to the formation of leak points. This abrasion is exacerbated by the presence of abrasive particles in the fluid stream that can become trapped and build up between the piston and the diaphragm. Abrasion-caused leaks are expensive from lost product, maintenance and replacement perspectives, and from a safety standpoint if the pump is handling toxic or hazardous liquids.
Taking into account the problems that abrasion wear and material buildup can cause, the industry worked to develop the integral piston diaphragm (IPD). In the IPD design, the piston used to move the diaphragm laterally during the pumping stroke is encapsulated into the interior of the diaphragm itself. IPDs also have a smooth finish with an angle of operation that enhances fluid flow and suction lift while reducing the propensity for material buildup on the outer piston.
Wilden engineers have developed a IPD design that uses the same hardware as standard full-stroke diaphragms, which means there is no tradeoff in performance when using a IPD. Specifically, Wilden has designed two models of IPDs, both of which can achieve a traditional stroke length that will optimize flow rates, suction lift and efficiency.
Chem-Fuse Diaphragms are made for high-volume chemical and industrial liquid-handling applications. Most significantly, elimination of the potential leak point at the outer piston makes Chem-Fuse diaphragms a good choice when the application involves the transfer of critical, dangerous, toxic or hazardous liquids.
Pure-Fuse Diaphragms have been designed specifically for hygienic applications. They feature a one-piece design that eliminates trap areas between the outer piston and the diaphragm, which can encourage the growth of bacteria. The Pure-Fuse design also eliminates the typical abrasion wear caused by the outer piston in a traditional diaphragm, resulting in longer service life. Additionally, no adhesive is used in the Pure-Fuse diaphragm’s construction.