Processing viscous food products introduces a number of challenges that require careful equipment selection to overcome. Factors like temperature, fat content, and solids loading influence viscosity both across different products and within processes.
To choose the right positive displacement pump for your operations, you need to understand how they work and what their functions mean for your specific application.
How Positive Displacement Pumps Work
A positive displacement pump works by moving a fixed amount of fluid each cycle.
The process starts with drawing fluid into an enclosed pumping chamber. A variety of mechanical designs are used to push the fluid from the inlet to the discharge port. The fixed volume of the pumping chamber means the flow stays steady relative to pump speed.
Positive displacement pumps can feature either rotary or reciprocating designs. Some examples of rotary positive displacement pumps include:
- Sanitary gear pumps
- Rotary lobe pumps
- Screw pumps
- Vane pumps
Reciprocating designs include:
- Piston pumps
- Diaphragm pumps
These designs each have specific features that make them better or worse for particular applications.
In both cases, positive displacement pumps operate under different principles than centrifugal pumps. Instead of having a spinning impeller convert mechanical energy into kinetic energy, positive displacement pumps trap a fixed volume of fluid and move it mechanically from the inlet to the discharge.
How Viscosity Influences Pump Designs
When choosing pumps for your operations, viscosity is among the most important parameters to consider. As viscosity increases, it incurs friction losses at every discharge, elbow, valve, and other pipeline components. More torque is required to maintain the required flow rate. Positive displacement pumps can deliver steady force regardless of pressure when dealing with high-viscosity fluids.
Variation across individual shifts also matters. Temperature and solids loading can dramatically alter viscosity. Positive displacement pumps are made to handle that variation predictably. The flow tracks with pump speed, whereas a centrifugal pump’s output would be much more sensitive to even minor changes.
Pumping high-viscosity fluids rapidly increases both internal loading and heat generation. Solids compound this effect. When selecting a positive displacement pump, therefore, it’s important to account for peak viscosity rather than average. Aiming for lower speed operation with regard to peak parameters helps protect product integrity.
Positive displacement pumps must stand up to harsh real-world service conditions. The design process must carefully evaluate internal mechanisms, clearance, and maximum pressure to ensure optimal performance and safety. Overpressure risk is a serious concern and must be addressed with casing selection and relief path design.
Choosing Pump Technology for Your Application
There are several primary options when it comes to positive displacement pump technology. Rotary pumps deliver low-shear transfer to protect product integrity. The large pumping chambers and gentle action move particulates without crushing. Slip can increase when wear affects clearance, so monitoring and maintenance are essential.
For viscous slurries, progressive cavity pumps can deliver exceptionally smooth flow. The rotor-stator pumping action leads to low pulsation, and output remains stable under changing pressure. Applications that call for precise dosing consistency and protecting product texture can benefit from this design. However, abrasive products can lead to stator wear.
Gear pumps achieve highly accurate dosing and repeatable flow, moving a fixed volume every revolution. These tight internal clearances improve flow consistency, but again, any solids can quickly wear the equipment down.
Reciprocating pumps, such as piston and diaphragm pumps, are ideal for high-pressure operations and precise metering. Dampeners are required in some applications, as the back-and-forth motion can introduce pulsation. Diaphragm pumps are well-suited to protecting the most sensitive formulations.
Matching Positive Displacement Pump Selection to Specific Food Products
Different food-processing applications call for different pump designs. Proteins and other viscous blends necessitate constant flow to feed downstream equipment. Low shear is also critical to avoid damaging product. Progressive cavity pumps are often a good choice to meet both of these goals.
Processing marinades can range from thin brines to thick particulate blends. Rotary lobe pumps work well for these mixtures, transferring product gently while being tolerant of irregular inclusions. The stable flow supports consistent dosing as well.
Complex feeds like slurries can introduce challenges with regard to suction and pressure. Your application may call for a piston pump for consistent transfer. Just make sure to carefully evaluate how pulsation might impact downstream processes.
Choose the Right Positive Displacement Pump for Your Operations
Are you in need of a positive displacement pump for your operations? If so, it’s important to ensure that you’re getting the right equipment for your viscosity range, flow, and product integrity requirements.
The knowledgeable team of experts at FPEC can review your process application to match you with a pump tailored to your needs. Contact us today to get started on the equipment-selection process.