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.

You may want to switch pumps as MikeHalloran suggested.  You will be happier with something like an LMI pump for real small flows or a Pulsafeeder pump for larger flows.  Then control based on the number of strokes, or time which ever is easier for you.   The diaphragm pump is not going to give you what you want.  Maybe you could fill an intermediate tank from the tote and then pump the whole intermediate tank into the reactor but that is more operator intensive.

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