Air-Operated Double Diaphragm Pump Sizing
Whenever sizing an Air-Operated Double Diaphragm pump (or any pump in that matter), do you size for just the discarge head? Or do you size the pump (determine operating point on pump curve) by using:Head=Discharge head-Suction head
We use a lot of these pumps. Almost all of ours are 1" pumps. We use them in all kinds of intermitant services. We have pressure regulators on the compressed air to the pumps. That controls the total allowable discharce pressure (Discharge=Supply) and we also have a ball valve on the air line that we throttle to slow or speed up the pump. It is pretty crude but effective for what we do. If you actually have a standard application maybe you would be more interested in a vane pump or centrifugal pump but for miscellaneous pumping needs the 1" or 2" diaphragm pumps work well.I only look at the required discharge pressure and the volume I want to pump to pick the pump size. It is not like a centrifugal pump because in most cases you do not have a stable NPHS to work with. Lets say you are just pumping out of the bottom of a full tank to the bottom of an empty tank. In the beginning you have lots of NPHS and Butterfly Valve low head. That situation slowly reverses as the suction side tank empties until you are pumping air. So the sizing of the pump is not that critical because it is a transient operating point.Maybe if you explain to me in detail what you want to do I can help you a lot more.The pump is going to pump antifoam from an tote into an empty reactor with about 5 psig pressure in it. Don't have the piping configuration yet, but we can place the pump pretty closeto the tote (within 5 feet). The maximum level of the tote above the pump suction is about 5 feet. Which would coincide to about 2.1 psig of head from the tank level. This is going to decrease until the tote is about completely empty. So it would decrease. So I guess you would be correct as to just use the discharge pressure head to size it.
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