High Viscosity & High Specific Gravity How they Affect Pumping

Viscosity is the measure of a fluid’s thickness, and in particular, it’s ability to resist deformation at a given rate.
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This Article Includes

  • What is Viscosity?
  • What is Specific Gravity?
  • How is Viscosity Measured?
  • Considerations When Pumping High Viscous & High Specific Gravity Fluids
  • EDDY Pump’s Heavy-Duty High Viscosity & High Specific Gravity Pumps

What is Viscosity?

Viscosity is the measure of a fluid’s thickness, and in particular, its ability to resist deformation at a given rate.  Essentially, viscosity indicates a fluid’s ability to resist the forces that tend to produce a flow of that material.  Some other particulars regarding viscosity are that viscosity usually decreases when the temperature of the fluid increases which causes the material to become thinner and flow with less force applied.  The opposite is also true in that when the temperature of the fluid decreases the viscosity increases which causes the material to become thicker and require a greater amount of force to cause the material to flow.  Another important item that must be understood is that higher viscosity fluids cause greater pipe friction loss.  

Temperature’s Role in Pumping High Viscosity Fluids

A key point to keep in mind when pumping high viscosity fluids is that when the highly viscous fluid is exposed to increased temperatures the viscosity has a tendency to decrease.  The converse is also true in that fluids experience an increase in viscosity due to the temperature decreasing.  


What is Specific Gravity?

Specific gravity, also referred to as relative density, is the measure of a fluid’s density compared to the density of water.  For measuring the specific gravity of gases the comparison is usually the density of air.  When a fluid’s specific gravity is greater than 1 Sg the fluid is denser than water, if the specific gravity is less than 1 Sg the fluid is less dense than water.  An interesting fact regarding specific gravity is that if a material has a density less than 1 Sg, and that material is submerged in water it will actually float on the surface of the water.  The opposite is also true in that if the material has a density greater than 1 and is tossed in water it will sink.  

As an example, water has a specific gravity (of 1 Sg, and a typical sand/water mix in dredging ranges from 1.3 Sg to 1.8 Sg. An EDDY Pump specifically designed for slurry applications that involve high viscosity and high specific gravity materials can pump materials that have a greater specific gravity range than most common centrifugal pumps; usually, centrifugal pumps are on the lower specific gravity range compared to an EDDY Pump.

How is Viscosity Measured?

Understanding the accurate viscosity rate of the fluid you are pumping is one of the most important, if not the most important factors for pumping viscous fluids.  Centipoise is a popular method for measuring viscosity and is considered a dynamic viscosity measurement unit.  Water has a viscosity of 1-CPS.  Water is often used as a baseline for comparison.  The formula for measuring viscosity is Shear Stress / Shear Rate = Viscosity expressed in Centipoise (CPS).  

What is the No. 1 Mistake Made When Determining Viscosity for Pumping

Interestingly, the No. 1 mistake made when determining viscosity is AVOIDING the process of determining the correct viscosity, using the proper measure device!  Instead, they do a “guesstimate” which oftentimes leads to an incorrect understanding of the true viscosity of the fluid you want to pump.  

One reason why people avoid determining viscosity is that they are intimidated by the process and the measuring devices required.  This can be a big problem, and a problem that is easily avoided because in reality, using the proper measuring devices and following the correct procedures are very simple and easy to conduct.  

Not knowing the true viscosity of the fluid you are pumping can cause a situation where the pump you purchase does not move the viscous fluid because of such things as insufficient motor power, or the fluid is “settling or pooling” in the liquid path and not moving through the pump.  

The reality is that the measuring devices and processes used to determine a fluid’s viscosity are very simple and easy to perform.  Keep in mind, do not be intimidated by the measuring devices or the processes required to determine viscosity.  

Popular Types of Measuring Devices For Determining Viscosity

There are a number of devices to measure viscosity.  Most often, if the fluid does not change viscosity due to varying flow conditions a Viscometer is used to determine viscosity.  If the viscosity does change due to varying flow conditions then a Rheometer is used to determine viscosity. 


Viscometer – Marsh Funnel Model 201 and Measure Cup Model 202

The Marsh Funnel is very simple to use and can provide on-the-spot measurements that allow engineers to identify sudden changes in the slurry viscosity so that any required corrective action can be taken to avoid issues with viscosity increasing beyond the point that the pump can move.  For more on the Marsh Funnel Model 201 and Measure Cup, Model 202 go to:  https://www.fann.com/fann/products/oil-well-cement-testing/viscosity/marsh-funnel.html#


Fann Model 35 For Measuring Viscosity

For many decades the Fann 35 (model 35) has been the most popular Viscometers on the market and has become “the measure” of what a great Viscometer should be like.  Commonly known as the Standard of the Industry, the Fann 35 is a couette coaxial cylinder rotational viscometer.  This viscometer is the most popular for determining the viscosity for drilling fluid applications.  One reason why the Fann 35 is so popular is due to its ease of use.  This viscometer uses a spring-loaded bob that moves when enough force is applied to the fluid that is being tested.  It is as simple as that; the force required to “shear” or “cut-through” the fluid is the shear rate or CPS (centipoise).  For more on the Fann 35 go to:  https://www.fann.com/fann/products/oil-well-cement-testing/viscosity/df-viscosity.html?nodeId=1_leveltwo_27

This is how the Model 35 works. Another common viscometer used is the type that is fitted with a spindle that is immersed in the fluid that is being measured, and as the spindle rotates it measures the torque required to turn the spindle, which in turn indicates the viscosity of the fluid.  Both types are suited for Newtonian fluids.  



A Rheometer is a very precise device that measures a fluid’s response to forces applied to the fluid which causes the fluid or material to “sheer” which determines the viscosity.  Rheometers are the device of choice for more complex fluids that cannot be defined by a single value or characteristic.  There are two types of Rheometers; Shear Rheometers that apply shear stresses, and Extensional Rheometers that apply extensional stress.  Suited for Non-Newtonian fluids.

Three Primary Viscosity Categories

With the wide range of viscosities that exist there have been three categories developed to enable easy reference to another liquid with similar or dissimilar viscosity.  


  • Water is in this category, along with all other thin liquids that have a similar fluidity as water.  Water is 1 CPS at 70ºF (21ºC).


  • In this category, liquids are thicker than the liquids that are in the Thin Category.  An example of liquids in this category are maple syrup or motor oil (SAE 30).  Motor oil (SAE 30) is 150-200 CPS.


  • The category for viscous liquids has a greater range than the other two categories.  Also, the liquids in this category can have viscosities as high as tens of thousands of CPS.  
  • An example of liquids in this category are molasses at 5,000 to 10,000 CPS, and peanut butter that has a viscosity range of 150,000 to 250,000 CPS.  Another challenge associated with pumping peanut butter is that besides the material being such a high centipoise at 250,000 CPS, pumping peanut butter also occurs in a food manufacturing factory and the water content of the peanut butter is extremely low.  Extremely low moisture content is outside the capabilities of what most other centrifugal pumps can move.  

Considerations When Pumping High Viscous

Viscosities and specific gravity are both very important characteristics of a given fluid that must be factored into the decision when purchasing a pump for your job. One of the most important factors when pumping high viscous and high specific gravity fluids is to ensure that the pump, piping, and any other pump system components are sized to handle the degree of viscosity and specific gravity for all combined materials to be pumped. This is a crucial step in the process and might require some calls to material manufacturers to ensure that you have the correct specific gravity and viscosity for all materials. The unit of measure for viscosity is centipoise (CPS), and the unit of measure commonly used for specific gravity is g/cm³ or lbs/gal.

An Example of Centipoise Rating

The following viscosity information is to be used as a comparison example to understand the different level of viscosity for each of the materials listed below.

Material Viscosity in Centipoise (CPS)
Water 1 CPS
Milk 3 CPS
SAE 30 Motor Oil 150-200 CPS
Bauxite (red mud) 1,000 CPS
* Honey 10,000 CPS
*Ketchup 50,000 CPS
*Peanut Butter 250,000 CPS

*Typically ultra centipoise applications like this require a positive displacement pump.

Fann Mud Balance Model 140 For Measuring Specific Gravity

One of the most popular conventional mud balanced used, the Fann Model 140 is one of the most simple and accurate measurement devices for determining density or weight-per-unit volume (specific gravity).  The advantage of this particular mud balance is that the temperature related to the sample of the material being used to measure specific gravity does not substantially affect the accuracy of the readings, which makes determining viscosity even easier because the temperature is, essentially, removed from the equation.  For more on the Fann Mud Balance Model 140 go to:  https://www.fann.com/fann/products/drilling-fluids-testing/mud-balances/mud-balance-m140.html?nodeId=1_leveltwo_16&pageId=Products

The following is an example of two scenarios when determining the specific gravity of a slurry with a 50/50 blend of two mixed materials; 1) scenario is knowing the specific gravity of both materials, and 2) when the specific gravity of both materials is unknown and the specific gravity for both materials must be determined using a specific gravity measuring device.  

Another very important consideration for a pumping application is the specific gravity or the weight of the fluid to be pumped.  Specific gravity when combining multiple materials to create a slurry is very important to ensure that the pump is capable of pumping the material.  Something to keep in mind regarding determining specific gravity is that it is actually very simple – anybody can do it with the proper measuring device and a little understanding of the measuring process.  

Scenario 1 – When You Don’t know the Specific Gravity of Each Fluid/Material

Not knowing the specific gravity of a material can be very intimidating but keep in mind that measuring viscosity is very simple when using the correct measuring device for the task.  For this scenario we suggest using a conventional mud balance like the Fann Model 140 which is extremely easy to use.  

  1. The Fann Model 140 is constructed with an easy-to-read beam that is graduated into four scales:  pounds per gallon, specific gravity, pounds per cubic foot, pounds per square inch per 1,000 feet per depth.  
  2. One end of the beam has a cup attached that is used to fill with the fluid to be measured.  
  3. Fill the cup attached to the beam with the fluid to be measured.
  4. Place the beam with the fluid-filled cup back onto the beam balance, and moving the ryder along the graduated beam, find the exact location on the graduated beam where the balance is achieved which is indicated by the “bubble” on the beam being centered.  
  5. Once this previous step is completed, the numbers on the graduated scale are used to perform a simple calculation that will produce the exact specific gravity of the fluid.  

NOTE:  For a more concise description of this process of using the Fann Model 140 to determine viscosity go to the following Fann instructional video:  https://www.youtube.com/watch?v=8wNEN6SOa7M

Scenario 2 – When You Know the Specific Gravity of Each Fluid/Material

To determine the specific gravity of a slurry mixture for this scenario the specific gravity for each of the materials must be known.  To obtain the specific gravity of each material, if the specific gravity is not located on the packaging of the material, then contact the manufacturer of each material.  First, check the packaging; sometimes manufacturers include specific gravity on the packaging. Something else you can do is take a look at the manufacturer’s website; sometimes they include important characteristics of the product such as specific gravity on their materials.  

Once you have the specific gravity per each given material, the specific gravity for all the materials combined can be determined.  The following is an example of how to determine the specific gravity of combined multiple materials.  For this example, we will use dry crushed rock and water.  

  1. Specific gravity is the average weight of the water and the material being pumped.
  2. To determine the specific gravity of a slurry:
    1. Using the specific gravity of the crushed rock which for this example is 2.5 Sg, and the specific gravity of water which is, and begin calculating specific gravity for the materials combined as a 50/50 blend (50% water, and 50% crushed rock).
    2. Calculation:
      1. Crushed Rock – Multiply 2.5 Sg by 0.5 = 1.25 Sg
      2. Water – Multiply 1 Sg by 0.5 = 0.5 Sg
      3. Then add the specific gravity of both materials which would be 1.25 Sg + 0.5 Sg = 1.75 Sg for the combined 50/50 blend of crushed rock and water.
    3. One thing to always keep in mind is that the higher the specific gravity, the greater pumping force required to pump the material.  

EDDY Pump’s Heavy-Duty High Viscosity and High Specific Gravity Pumps

The EDDY Pump is considered one of the premier high viscosity and high specific gravity pumps in the world.  The EDDY Pump Engineering Team has well over three decades of experience developing and creating pumps that are specifically designed for the challenges associated with pumping high viscosity and high specific gravity fluids and slurries.  

The EDDY Pump is a non-clogging pump design that includes an enlarged wetted path and a recessed rotor for moving large amounts of materials through the pump without issue.  The design of the rotor and the way the pump displaces fluid is very unique in that the spinning action of the rotor creates something called an Eddy Current.  An Eddy Current is a circular current of fluid that produces a vortex that extends down into the inlet of the pump; this creates suction strong enough for solid particles to travel upwards into the volute

Another benefit to the unique design of the rotor is that it helps to keep solids in suspension.  Maintaining suspension of the solids keeps the high viscosity and high specific gravity fluids efficiently moving through the wetted path without settling at the bottom of the volute.  This unique aspect of the EDDY Pump design also makes it a great pump for transferring large solids as well.  The EDDY Pump’s ability to pump concentrated solids is perfect for moving viscous materials with as much as 40-70% solids by volume; an impossible task for a lot of traditional pump types.  

The EDDY Pump is made of the highest quality materials and is extremely rugged, chemically compatible with most fluids, and capable of withstanding a great deal of punishment that is typically inherent in abrasive, high viscosity, and high specific gravity applications.  

Features & Benefits

  • Non-Clogging Design
  • High Solids Handling
  • High Viscosity and Specific Gravity Handling
  • No Critical Tolerances
  • Low Maintenance
  • Minimal Downtime
  • Low Cost of Ownership
  • 40-70% Solids Pumping by Volume
  • Capable of pumping objects almost the size of the liquid inlet and discharge port sizes.
  • Easily moves rags, stringy material, rocks, and other types of media.
  • 100% American Made

For more information on the EDDY Heavy-Duty High Viscosity and High Specific Gravity pump go to https://eddypump.com/ or give us a call today!

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    • Hydraulic Power Units (HPU)

If you are pumping slurry, brines, high solids, extremely viscous material, paste, high abrasives (sand & gravel), and material filled with solids, then you found the best-suited pump for the job.  Go to:  https://eddypump.com/  or Call Us!

Mining, Fly Ash, Coal Ash, Oil, Fracking, Gas, Wastewater, Pulp and Paper, Chemical, Energy, Water Municipalities, Irrigation, and Dredging Companies.  For Access to Complete Product Line Go to: https://eddypump.com/products/ 

Eddy Pump For High Viscosity

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