Overhead Stirrers

What is an Overhead Stirrer?
Overhead Stirrers are used for standard mixing of the higher viscosity substances, unlike magnetic stirrers. They majorly are mixers, used for suspending, gas intrusion and recirculation. Scientists use these for mixing paint chemicals that are used on cars or for mixing shampoos and other conditioner components. The torque, stirring capacity as well as the viscosity should be reviewed at the time of picking out the correct stirrer for your application.

List of Main Points to Consider While Buying Right Overhead Stirrer
When purchasing an overhead stirrer, it is important to know the application information and the result that needs to be accomplished as this will help to determine the best stirrer fit for the application. The following would be helpful when you are selecting an Overhead stirrer:-

  1. Type of Fluid: On the basis of Product being mixed (liquid/ liquid, Light Oil or liquid/powder) choose the suitable overhead stirrer.
  2. Stirring Capacity: On the basis of how much volume of product needs to mix select an overhead stirrer with suitable maximum stirring volume.
  3. Speed range required: Min and max. Speed is specified for every overhead stirrer. According to the requirement, you can choose the overhead stirrer with suitable stirring speed.
  4. Stirling shaft (Ø X length) & Type of Blade: The size and shape of the mixing vessel help to determine the size and shape of the mixing impeller. Know the ID (inner diameter) of the opening of the vessel as well as the height. Selection of Length of the rod, the diameter of rod and type of paddles and blade depends on sample viscosities and size of the mixing vessel. These are some most commonly used impeller.
  5. Type of Motor used in the stirrer: A brushless DC motor is very efficient and maintenance-free. A brushed motor contains brushes that wear and over time need replacing. Mainly overhead stirrer comes with PMDC Motor, AC/DC Universal motor, AC Brushless, DC Brushless, etc.
  6. Features needed for the application: Digital speed indicator, timer, clockwise and counter-clockwise rotation, a motor that can withstand usage (i.e. 24/7 or once a month)
  7. Sold in kits or individually: Have you purchased everything you need to start mixing? Sometimes stirrers are sold as kits and sometimes the stirrer motor, stand, clamp and mixing impeller accessories are sold separately.

What are the Major Applications of Overhead Stirrer?
Common in both industrial and academic laboratories, mixing is an important part of many tasks. Overhead stirrers are the best fit for high-viscosity applications. There are a variety of overhead stirrer configurations as well as analog and digital options. Mostly overhead stirrers are used for:

  • Tissue grinding to create low and high dose medications
  • Wastewater purification
  • Inks, coatings, glues, and adhesives
  • Plastics, polymers, urethane
  • Media prep
  • Food and beverage production

6 Criteria to Select an Overhead Stirrer

  1. Stirring Speed: Given in revolutions per minute (rpm), this will vary by model.  Most laboratory stirrers provide a speed range, such as 12-1800 rpm or 40-6000 rpm, but there are some single speed options.  Check which speeds are needed for your process and purpose of stirring.  A digital display of speed is an asset if accuracy and repeatability of the speed are needed.
  1. Volume: The stirrer’s volume capacity should meet or exceed your maximum batch size.  Volumes can be 2 L, 25 L, 200 L and anywhere in between.  Maximum volumes typically assume water viscosity unless specified by the manufacturer.
  1. Torque: Torque is the rotational force used to turn the impeller, commonly reported in Newton centimetres (N∙cm) or inch ounces (in-oz).  The higher the torque the better the stirrer is able to sustain impeller rotation in higher viscosity mixtures and when using larger diameter impellers.  A small increase in an impeller diameter (and speed) will cause a great increase in the power required for mixing, as shown in a simplified version of the power equation: Power = rpm3 x Diameter5


    The extra power needed for any increase in diameter and speed will impact your torque needs.  Remember to take this into account.

  1. Viscosity: This refers to dynamic viscosity, which is the fluid’s “thickness” when stirring.  It is an important factor for stirrers mixing batches with viscosities greater than water, or viscosities that change during the mixing.  Higher viscosity mixing will require greater torque from the stirrer motor, and you want to ensure your stirrer can maintain its rpm under changing viscosity conditions.  Be sure the overhead stirrer is able to handle the maximum viscosity of your batches.  Viscosity is reported in centipoise (cP or cps) or millipascal seconds (mPa∙s).  If you do not know the exact viscosity of your products, online viscosity tables of fluids can help provide an estimate.
  1. Options: There are numerous features which may be important to your facility and application.  Stirrer chucks offer a range of diameters so ensure your impeller shafts will fit into the chuck.  Stirrers with through shafts make adjusting the impeller to an optimal height in the vessel easy, and even provide an easy way to move the impeller up out of the way for quick changes to mixing vessels.  Reversible models offer stirring in both clockwise (standard) and counter clockwise directions.  Other features to consider are digital torque and speed display, zero torque, timer, a light, programmable mixing including automatic shutdown, data logging, and external control by a computer.
  1. Operation and Safety: Stirrer controls should be clear and intuitive to operate, especially with multiple users.  Is the stirrer designed for continuous use?   Is the stirrer maintenance free, or does it require scheduling for service?  Some facilities require verification of the speed and torque readings by calibration.  Stirrers with overload or overheat protection automatically shut down to protect the electronics if mixing conditions are outside of operational range.  Is there guarding available to shield from spinning chuck and/or shaft? 

Information Required to quote on a Overhead Stirrer

  1. Do you need a digital or analogue model?
  2. What is the maximum rpm required?
  3. What is the maximum viscosity of your sample?
  4. What torque do you require?
  5. What is the max volume of sample that you will be working with?
  6. Do you need a stirring shaft? Please advise the diameter, length, and type of blade?
  7. Will you be working with acids?
  8. Do you need a stand?
  9. Do you require remote control?


Brochures: Wiggens Brochures: Lab Companion Wiggens Presentation Wiggens Presentation video Overhead Stirrers vs Homogenizers