How to Select Industrial Liquid Handling Pumps

How to Select "Pumps"

I remember doing a brief research report on an introduction to pumps back in college. I remember starting my research with a simple Google Images search of "pumps", expecting to obtain some visuals of the most commonly used types. My results looked something like this:

Good start I thought to myself. (Source: theglamorouswoman.com)

Even after discarding expensive women's shoes from the mix, I find that pump selection can be a daunting task - especially to a newcomer. There are a surprising number of ways to move liquid from point A to point B, but finding the best one for the job requires a more rigorous process than matching designer shoes to an outfit.

Pumps by Type

To start, the engineer will need to determine what type of pump to use. There are way to many to list, so in this brief introduction let's just look at the two broadest categories: dynamic and positive displacement.

(An assortment of pump types - Source: Dewallace Technical -->)

Dynamic pumps are pumps which use fluid velocity (kinetic energy) to build and maintain momentum in the system. Centrifugal pumps are dynamic pumps which use centrifugal force from an impeller to induce this velocity. The flow rates generated by centrifugal pumps is variable depending on the head (or resistance) of the system. Because these pumps can generate large flow rates, they are the standard for most industrial applications.

Positive displacement pumps are specialty pumps which use expanding and contracting chambers to push fluid through the system. These pumps are further labeled either rotary or reciprocating based on how these chambers move. They provide constant flow and some (e.g. piston/plunger pumps) can generate much higher pressures than centrifugal pumps while others (screw/diaphragm) are labeled more efficient. However, they often lack the flow rate output needed for industry use.

GlobalSpec's pumps section has over 40 different pumps areas, which goes to show how many different specific types exist. As such, it would be pointless to just list them all, but here's a table that gives an overview of the basic types mentioned above:

Pumps by Specs

The process for "speccing" a pump differs based on the type of pump.

Centrifugal pumps have performance curves provided by the manufacturer detailing pump head vs. flow rate. The operating point of the pump is the point at which the performance curve intersects the system curve (detailing system head at various flow rates). A pump whose operating point matches or is close to the pump's rated best efficiency point (BEP) is often a good choice.

Here's a simplified map of what these curves will look like:

For positive displacement pumps, the process is a little different. Manufacturers usually provide specifications regarding a pump's maximum pressure and flow rate. Engineers must be sure the pressure of the system is below the pressure ratings of the pump and that the pump's flow rate is sufficient for the application.

An ideal pump will generate the performance needed in the right package - this means taking into account the pump's footprint and power requirements. Keep in mind that a more efficient pump is not always the best choice when considering energy costs. For example, a pump that runs at 40% efficiency would be a better choice than one in the same family which is 60% efficient but requires twice the power.

For custom pump designs, engineers will often provide a list of system requirements and allow the manufacturer to design a pump whose performance best fits the application.

Pumps by… Everything Else

This is just a sampling of the most basic and essential elements of pump selection. Industrial buyers may need to consider a number of other factors in the process, including pump construction (sizing, materials, impeller types, etc.) and pump compatibility with the media and outside environment.

For a more detailed run-down on this process, check out GlobalSpec's Industrial Liquid Handling Pumps Selection Guide. And if you're already a pro in this arena, feel free to divulge your own experiences on selecting pumps. Just steer clear of high-heeled shoes.