HI Pump FAQs
PD Pumps in Food Processing & Usage of Specific Speed
HYDRAULIC INSTITUTE
| IMAGE 1: Rotary lobe (left) and circumferential piston (right) pumps (Image courtesy of the Hydraulic Institute)
QUESTION
What positive displacement pumps are used in food processing applications?
Applications in the food and beverage segment ensure hygienic and reliable fluid handling in highly regulated, sanitary production environments. Some typical applications include:
- Clean-in-place (CIP) and sanitation
- Beverage transfer
- Ingredient and additive metering
- Food processing and packaging
Some typical pump types include:
- Sanitary rotodynamic pumps
- Rotary lobe, gear, peristaltic and progressing cavity pumps
- Reciprocating diaphragm and metering pumps
Rotary and reciprocating positive displacement (PD) pumps move a fixed volume of fluid during each rotation of the driver shaft or cycle of the reciprocating component. This operating principle makes them particularly well suited for handling:
- Viscous liquids
- Shear-sensitive or delicate foods contained in liquids
- Precise flow applications
These three application considerations are important to many food processing applications, which makes PD pumps a common pump type for this industry.
Additionally, some designs such as the rotary lobe and circumferential piston pumps (Image 1) are easily opened and cleaned, which is an important consideration. For more information on pumps used in market applications and positive displacement pumps, refer to HI’s Introductory Pump & System Training at training.pumps.org.
QUESTION
What is specific speed and how is it used?
Specific speed is an index of pump performance at the pump’s best efficiency point (BEP) rate of flow, with the maximum diameter impeller, and at a given rotative speed. It is used by manufacturers as a hydraulic design parameter.
It is not dimensionless, and standard units are assigned for U.S. and metric conventions; therefore, close attention needs to be paid to the units when calculating and using it for comparison. The equation and unit convention are described with the following equations. For metric units, the symbol “ns” is used and for U.S. units, the symbol “Ns” is used.
In addition to being used by the manufacturer as a hydraulic design parameter, specific speed provides information to the user about impeller type, attainable efficiency, shape of the pump’s total head and pump input power curves as a function of flow rate, as well as the preferred operating region (POR).
For additional information on rotodynamic pump design and application, refer to American National Standards Institute (ANSI)/HI 14.3 Rotodynamic Pumps for Design and Application at pumps.org and HI’s free knowledge resource, the HI Data Tool, at datatool.pumps.org.
HI Pump FAQs® is produced by the Hydraulic Institute as a service to pump users, contractors, distributors, reps and OEMs.
For more information, visit pumps.org.
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