understanding viscosity - And Why It Matters When Choosing A Pump
Whether you’re pumping water, chocolate, oil or peanut butter knowing the product’s viscosity is essential to selecting the right pump.
What is Viscosity?
Viscosity is a measure of a liquid or gas’s resistance to flow. It describes how “thick”, “sticky,” or “slimy” a fluid feels or how easily a fluid deforms when an external force is applied.
- Low viscosity: flows easily (like water).
- High viscosity: flows slowly or not at all (like peanut butter).
Viscosity Units
- Dynamic viscosity: measured in centipoise (cP) or Pascal-seconds (Pa·s).
- 1 cP = 1 mPa·s
- Water at 20°C is about 1 cP.
- Kinematic viscosity: measured in centistokes (cSt) or square meters per second (m²/s).
- 1 St = 10⁻⁴ m²/s
Examples of Everyday Products and Viscosities
Here are real world examples to help you visualise viscosity:
| Product | Typical Viscosity (cP) | Notes | Image |
| Water | ~1 cP | Fluid at 20°C |  |
| Milk | 2-3 cP | Slightly thicker than water |  |
| SAE 10 Motor Oil | ~100 cP | Temperature Sensitive |  |
| Olive Oil | 80-100 cP | Temperature Sensitive |  |
| Honey | 2,000 - 10,000 cP | Temperature Sensitive |  |
| Syrup | 5,000 - 10,000 cP | Temperature Sensitive |  |
| Product | Typical Viscosity (cP) | Comments | Image |
| Melted Chocolate | 2,500 - 5,000 cP | Must Be Temperature Controlled |  |
| Ketchup | 50,000 - 5,000 cP | Shear-Thinning |  |
| Toothpaste | 70,000 - 100,000 cP |  |
|
| Peanut Butter | 150,000 - 250,000 cP | Semi-Solid |  |
| Ice Cream | >100,000 cP | Solid Like When Frozen |  |
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Temperature Matters
Viscosity changes with temperature.
- Honey or chocolate: flows easily when warm, thickens when cold.
- Oil: pumps easily in summer, thickens in winter needs heating or insulation outdoors.
- Ice cream: a flowable liquid when melted, solid-like when frozen.
Why Viscosity Matters for Pumping
Getting your pump choice right means:
- Smooth flow
- Energy-efficient operation
- Gentle product handling (avoids damage)
- Fewer clogs or breakdowns
Wrong pump = clogging, shear damage, inefficiency and costly downtime.
Which Pumps Handle Different Viscosities Best?
Our Pumps expert has broken down the different types of pumps, what they can handle and real product examples.
Centrifugal Pumps (CP)
How it works: A high-speed rotating impeller adds kinetic energy to the fluid, converting velocity into flow.
Best for: Low viscosity fluids (1–10 cP)
Product examples:
- Water (~1 cP)
- Milk (~2–3 cP)
- CIP solutions
Pros:
- High flow rates for thin liquids
- Simple, cost-effective design
- Small footprint
- Efficiency drops dramatically with viscous products (>50–100 cP)
- Can shear delicate fluids
- Not self-priming, requires flooded suction
Gear Pumps
How it works: Interlocking gears trap fluid and transfer it from the inlet to the outlet in a controlled, pulsed flow.
Best for: Light to medium oils with viscosities around 50–500 cP.
Product examples:
- Light lubricating oils (~100–300 cP)
Pros:
- Good for moderate viscosity
- Compact and precise flow control
Cons:
- Can shear the product
- Limited solids handling
- Not inherently hygienic
Lobe Pumps
How it works: Rotating lobes create expanding cavities on the inlet side and compressing cavities on the outlet side.
Best for: Food and cosmetic products with viscosities of 1,000-50,000 cP, such as yogurt or sauces.
Product examples:
- Yogurt (~10,000 cP)
- Creamy sauces (~5,000-20,000 cP)
Pros:
- Gentle, low-shear pumping
- Handles soft solids
- Available in hygienic designs
Cons:
- Limited viscosity range compared to screw pumps
Diaphragm Pumps
How it works: A flexible diaphragm moves back and forth, creating suction and discharge to move fluid.
Best for: Abrasive slurries and chemicals with viscosities from 10-2,000 cP.
Product examples:
- Chemical slurries (~1,000 cP)
- Cleaning agents (~100–500 cP)
Pros:
- Self-priming and dry-run capable
- Handles corrosive and abrasive fluids
Cons:
- Produces pulsating flow
- Not suitable for very thick products or high-volume applications
Progressive Cavity (PC) Pumps
How it works: A rotor turning inside a stator forms cavities that progress along the pump, moving the fluid forward.
Best for: Highly viscous materials such as peanut butter and pastes (50,000-250,000+ cP).
Product examples:
- Peanut butter (~150,000 cP)
- Thick sludges (~100,000+ cP)
Pros:
- Low pulsation
- Excellent for thick, sticky products
Cons:
- Large footprint
- Not inherently hygienic
- Limited tolerance for air entrainment
Twin Screw Pumps
How it works: Intermeshing screws rotate to gently move fluid along the pump chamber in a continuous flow.
Best for: Applications involving a wide viscosity range-from thin CIP fluids to thick creams and chocolate.
Product examples:
- Chocolate (~3,000–5,000 cP)
- Creams (~10,000 cP)
- CIP (~1–10 cP)
Pros:
- Handles thin to thick fluids with one pump
- Smooth, gentle flow with low shear
- Bi-directional, self-priming, hygienic design
Cons:
- Higher initial cost
- May be excessive for only thin fluid applications
Summary
Know your product’s viscosity range in CP, and how it changes with temperature.
Think about flow requirements, cleaning, solids, air entrainment and shear sensitivity.
Match the pump type to your product - especially if the process handles different viscosities or needs strict hygiene.
Twin screw pumps are a smart choice when you need one pump for thin and thick fluids, gentle handling, CIP compatibility and reliable flow.
Choosing a trusted Pump Manufacturer
OEM Automatic offers an extensive range of Pumps, with more coming to the portfolio soon, from leading manufacturers Jung Process Systems and Samoa, tailored for diverse industrial applications. Whether your applications require pumping of low or high viscosities or hygienic design, we have the solutions to meet your specific requirements.
Our product specialists can help you identify the ideal pump for your project, ensuring optimum performance and reliability across your operations.
Need Help with a Pumps Application?
Our Pressure & Flow Team is here to help! Whether you need expert advice, product recommendations, or a proof-of-concept demonstration:
Phone support – Call us at 0116 284 9900
Email support – Contact us at [email protected]
Live chat – Available on our website
On-site visits – Our expert sales engineers can provide in-person demos and application support. Email [email protected] to arrange a visit or call us.
Let us help you find the right pump for your application. Contact us today!
Related Products
View our range of twin screw pumps and diaphragm pumps below. We'll be adding more to our pumps portfolio soon! So no matter you're requirement our pumps experts can provide the right solution for you application.
