How to Size an Air-Operated Diaphragm Pump

The Weisbach-Darcy equation can be used from first principles and developed onwards. If one goes that way, there is some data missing in order for the particular calculation:

• What is the density of the fluid?
• What is the difference in elevation between the inlet and the outlet of the hose?
• Is it correct to assume the volume unit is the US Gallon and not the Imperial Gallon?
• Is the hose circular in cross-section?
• What is the roughness parameter inside the hose?

However, it may be much simpler than doing a rigorous calculation, given that an air-driven diaphragm pump is the likely candidate for the job.

First the pressure.

A 15ft vertical water column represents a pressure less than 1/2 bar. So, were the fluid to be the same density as water and the hose vertical, a diaphragm pump will have enough pressure to do the job so long as the inlet air pressure exceeds 1/2 bar. An air-driven diaphragm pump is only able to match the air pressure to the fluid pressure through the diahpragm, so, say the air pressure was 6 barg, then the pump will stall when the line pressure reaches 6 barg and draw no more air from the supply. At that point, the flowrate will be zero.

So the first thing is that, provided the air pressure exceeds the head at the outlet end of the hose, it will work after a fashion.

Now for the flowrate.

The diaphragm chest size and the flowrate of the air into the diaphragm chest will determine how fast it is going to run, and whether the pump is capable of moving the fluid at the required flowrate. There is no detail in the post to get a feel for the air network's capabilities, and it may be that the air installation has a greater impact on shifting this fluid than the pump size!

So in summary, it will be the line size for the air network flowing into the pump which is the determining factor for the pump performance, and not necessarily the characteristics of the fluid being pumped and the network down which it is being pumped.

Thanks PWSlack I appreciate your help.

The specific gravity is .96

The fluid is a pre-polymer that will be pumped from a transportation vessel into a mix vessel at the same elevation

You are correct in your assumption of US Gallon

The hose is circular in cross section.

I am not sure of the roughness parameter units. but the hose is a smooth plastic inside.

There is an 1.5" air line with 125 psi (approximately 8.3 bar ) that I can tap into so air supply should not be a factor.

I am making the assumption that if I can determine how much pressure it would take to pump the fluid through the line at 10 gpm I could specify a pump that puts out 10 gpm at that pressure, but I am a chemist by trade and not that confident in my assumption.

Thanks again for your help

Contact Wilden. They have a very good technical support staff that will assist you in determining the best manner to move your product.

http://wildenpump.com/

Or Yamada

http://www.yamadapump.com/

Troy,

I went thru replies you have already received.

None seems to be hitting the nail!

The only data missing in your question is : are you pumping straight vetically up 15' or horizontal distance is 15' over which the pumping has to be done.

Without waiting for your answer,I would like to give the answer:

The pump size is 1/2" x 1/2"

Total frictional loss in pipe line (2" x 15' long) is max 22 psi

If we consider the pipe runs vertical instead of horizontal, the friction loss still is the same but we nned to add the static head of 15' to this.Hence in this case the pressure drop will be 28 psi.

An 1/2" inlet /oulet pump will consume approx 10 CFM air at 87 psi max.

If you have more air pressure - all the better.

Pump could be in Polypropylene or metal like Aluminum.The diaphragm material is best selected by the manufacturer if the liquid details are furnished.Teflon ,of course, will handle any chemical ( barring a few exceptions) but inexpensive elastomer like Nitrile/Buna may do a better job than Teflon which lacks the resilience of elastomers.

The problem of different manufacturers recommending different sizes of pumps is not new.I had a case when a dealer and the manufacturer offered different models using the same selection software!!The crux lies in estimating the pumping needs correctly using the parameters given and asking for some that are essential for selection.

Trust this helps.

Regards

Chuck Cowlagi

Troy,

I know this is not the answer to your question, but I am an energy manager in a large industrial facility. My advice is do not buy an air operated diaphram pump. It requires seven times as much energy to operate a compressed air driven pump as it does to operate an electrically driven pump. There are plenty of pumps available that should do what you want and if you check with any good pump manufacturer their tech support people will probably size it for you.

Jim

send me all three options. Will review and reply.

Hari