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AOD Pumps in Parrallel

AOD Pumps in Parrallel

AOD Pumps in Parrallel

(OP)
I need to pump a liquid with a viscosity of 4000cp out of a mixing tank to a holding tank. It is about a 60' vertical then a 15' horizonal run from the bottom of the mix take to the top of the holding tank. The existing pipe is 4". Using one AOD pump it would take a little less than an hour to transfer 47,000lbs of material from the mix tank to holding tank (95gpm). My questions is, could I replace the one AOD pump with two AOD pumps in parrallel to decrease my transfer time? And if so could I stick with the existing 4" pipe?

Material properties:
Viscosity 4000 cp
Density 13 lbs/gallon

RE: AOD Pumps in Parrallel

My first thought is, add a second  pump to the existing pipeline you will try and double the flow, the friction loss will increase drastically and could subsequently reduce the output from the pumps - maybe where will be no increase in overall flow.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

RE: AOD Pumps in Parrallel

We have tried putting AOD pumps in parallel several times.  The increased pressure drop in the suction can cause NPSH problems.  The increased pressure drop in the discharge will add backpressure to the pumpage.  This eats up the driving force between the pressure of the motive air and the pumpage.  This is all calculatable (be sure you include acceleration losses due to surging flow!). You can make changes to overcome the issues I mentioned, but we have never achieved the full increase we calculated!  We have hypothesized the reason for this shortfall is there was no effort to coordinate the air valve stroking of the two pumps.  

May I suggest an electric driven facsimile of the AOD pump?  Google for Abel Pumps.
 

Good luck,
Latexman

RE: AOD Pumps in Parrallel

As Artisi and Latexman already mentioned it will probably not work the way you want. An AOD does not have a stable flow, the flow depends upon the discharge pressure. More flow through the pipe will increase the pressure and this will reduce the capacity of the pump. You can "play" with the air pressure but you will for sure not get approx. twice the flow with two pumps and keeping the pipe as it is.

RE: AOD Pumps in Parrallel

With one AOD pump, you are getting alternating pulses of flow in the suction and discharge lines.

If you could pair the shuttle valves of the two pumps such that one is on suction stroke while the other is on discharge stroke, you might get some extra capacity out of the existing piping system.  I don't know of a pump mfg who makes an AOD pump like that, nor am I aware of any obvious way to do that with the pumps we buy.  

But if both pumps are set to stroke at random or in sync, all you'll do is increase the peak flow and hence the frictional loss.  You'll get more flow, but nowhere nearly double.

RE: AOD Pumps in Parrallel

(OP)
Thanks to all for the advice. Looks like the plant will have to replace the piping or just deal with the transfer time for now. I looked into a pc pump but I am limited on space and the size pump I would need would not fit. Thanks again for the advice

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