Must air operated pumps be protected against zero flow rate, and if so, what method of protection is recommended?
A. Air-operated diaphragm pumps are a class of displacement pump featuring flexible membranes in combination with check valves used to move liquids in and out of pumping chambers. These pumps are used extensively in transfer and metering applications requiring flows up to about 1,150 lpm (300 gpm). They are quite versatile, handling a wide variety of liquids including, but not limited to: chemicals, dry powders, food additives, glues, paints, pharmaceutical products, slurries, tailings and wastewater. Air-operated pumps have unique operating characteristics. They are sealless pumps, have no dynamic seals or packing, are self-priming, can run dry indefinitely and can operate at infinitely variable flow rates and pressure within the pressure and flow rate range for the pump. The liquid discharge can be throttled to zero flow indefinitely. The most common type is the double-diaphragm pump (duplex pump), which has two pumping chambers and two flexible diaphragms. The diaphragms are connect
