One of the best kept secrets in pumping technology
What's a flexible impeller pump? This is one of the first questions most people ask.
In the food industry, the most common pump types are centrifugal pumps, rotary lobe pumps, rotary piston pumps (often referred to as external circumferential piston or ECP), air-operated double diaphragm pumps (AODD), peristaltic or hose pumps, and many others. However, flexible impeller pumps (FIP) are a lesser-known pump type. Those in the dairy industry may already know that the pump on the back of a milk collection truck is a flexible impeller pump. This article explores FIPs, including how they work and how they are used in the food industry.
History of the Flexible Impeller Pump
The FIP was invented in 1938 by Jack Streeter and Art Briggs in Burbank, Calif., as a condensate removal pump on a simple air conditioning system and was patented in 1940. They used their initials to create the name of the first company to produce this pump, JABSCO Pump Company. Since then, the pump has been used in many applications including marine engine cooling. Through the years, the pump has been developed and improved, using different impeller and body materials, and in the early 1960s, sanitary versions became available.
How Do FIPs Work?
An FIP, as its name suggests, is a pump with a flexible impeller. To be more precise, it is a flexing vane pump. The impeller is made of rubber and is fitted into a concentric bore. See Figure 1. Inside the bore, between the suction and discharge ports, is a smaller diameter bore (cam).
As the impeller rotates and the vane moves down a ramp from the small diameter bore to the larger diameter bore (Figure 1, Section 1), the cell formed between two vanes enlarges and consequently product is drawn into the pump through the suction port. This ‘trapped' product is carried around the body as the impeller continues to rotate (Figure 1, Section 2). As the vanes reach the discharge port area they start to move up a ramp from the large diameter to the small diameter (Figure 1, Section 3). The vanes are now being bent (flexed), and the cell between the two vanes gets squeezed and the product is discharged.
Figure 1. FIP Principle
The performance characteristics of the FIP pump take advantage of both centrifugal pumps and positive displacement pumps. It has the head vs. flow characteristic of a centrifugal pump coupled with the viscosity handling capability of a positive displacement pump. See Figures 2 and 3 below.
|Figure 2. Viscosity vs. efficiency
||Figure 3. Head vs. flow
FIP Offering Food Processors a Unique Combination of Features
An FIP can offer unique features and combinations of features that other pumps cannot. Table 1 below shows how the FIP compares with other pump types.
Table 1. Comparison of FIPs and other common food process pumps
With these features the FIP pump can perform many, but not all, of the duties of most other sanitary pump types, often at a fraction of the cost. In approximate terms FIP pumps cost around the same as a sanitary centrifugal pump, which size for size is around 1/3rd the cost of a rotary lobe pump.
FIPs Follow the “KISS” Principle
We all know that one—Keep It Simple, Stupid. The FIP has one moving part, the impeller, and has no rotors to time, no shims, and no gears. Figure 4 is an example of a pedestal mounted pump.
Figure 4. Typical pedestal mount FIP configuration
Applications in the Food Industry
FIPs are unique pumps that are capable of many different applications. Their applications in the food industry are varied and would be too numerous to list. They range from simple transfer to batching, metering, filling and dosing right through to complex process applications with flows directly linked to process streams. The remainder of this article shows examples of how these pumps are used in the food industry.
Dairy (Milk, Yogurt, Cheese Curd, Cottage Cheese, Cream)
Milk Collection Truck
This truck has a 2-in., sanitary FIP pump, bulkhead mounted in the cabinet on the back of the truck. The pump is used to bring milk from the farm tank to the truck and has flows up to 165 gpm. It is dry self priming to 20 ft – primes almost instantly through 15 to 20 ft of suction hose and has low shear so that it does not damage milk globules or release free fatty acids. It is easy to clean and can be cleaned in place (CIP'd) or easily stripped for manual cleaning.