Correct?The output of a DD pump is not continuous, but pulsatile.  If you put an undamped pressure gage on the discharge, the gage will indicate wild pressure fluctuations until it breaks, which won't take long.  This happens because the diaphragms are alternately pressurized and relieved of air, applied in alternation by a mechanical toggle valve that is triggered by the position of the diaphragms, or the bar linking the two.I am not aware of any air- operated DD pumps that actually include a cycle output, but a pressure transducer and Schmitt trigger could give you a usable square wave.  You would then have to know the discharge volume per cycle; it appears that you might have to measure that for yourself, because the pump manufacturers rate the pumps as if they were continuous discharge devices.  You wouldn't need real fast electronics; DD pumps typically cycle much slower than relays.I've never used 'em as metering pumps myself; they're better adapted as transfer pumps, i.e. pump the entire tote-load into the reactor, and when the discharge pressure drops or an attendant notices the pump speed up (because it's pumping air), shut off the air supply.There exist high purity, high precision, high cost "diaphragm metering pumps" with mechanically driven diaphragms that are intended for metering, and can include some kind of cycle count or rotation count mechanism.I.e., if your mix ratio is other than one entire tote of antifoam per reactor charge, you might consider a different pump technology.The curves provided are for flow vs. total head, not just discharge head. A rotameter will not give a Safety valve stable reading.A paddlewheel might be inaccurate because of constantly accelerating and decelerating.  A true positive displacment flowmeter might be accurate, but might suffer reduced life.Check with your flowmeter supplier.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.

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