Processing plants look for continuous and trouble-free operation from a pump that is capable of transporting even the most delicate whole food products or processed foods, while keeping product damage to a minimum. Pumping food products has an overriding issue—any food product damage can result in degradation to the final product and profit losses at the plant.
While damage is a concern, hydro-transport systems do provide an advantage lacking in other mechanical conveyance. They can be used, with a consistent level of product safety, to convey and clean many foods—carrots, cranberries, pickles, cherries, onions, beans, peppers, leafy vegetables, crawfish, shrimp and hatchery fish. Many food products are hydro-transported. In fact, most packaged salad producers use food handling pumps to process and transport their products, without damage, for the fresh pack industry.
A hydro-transport system involves several components that must function together to safely process and transport food.
In a hydro-transport system, the vortex tank is where the product first comes in contact with the hydraulic conveyance medium. It is traditionally constructed of stainless steel to minimize clean-up time and enhance sanitation levels. The tank is designed to receive product on its return from the reclamation system and mix it with water, reducing air injection and entrapment. Solids are mixed with the liquid at a uniform rate—to minimize loss of prime—and vortexed into the pump suction.
The pump must be located sufficiently below the liquid level in the suction bay to ensure that adequate suction head is maintained. The vortex should draw the product uniformly into the pump’s suction. Product vortexing is especially important with light foods that normally float.
In addition, the vortex—which should be limited to minimize air entrainment—causes long foods, such as string beans, to enter the stream with their length parallel to the flow. The pump must have an adequate and uniform supply of water to minimize loss of prime and prevent surge.
Materials of Construction
Food handling pumps are traditionally constructed of all iron with stainless steel shaft sleeves. Applications associated with abrasive or aggressive pH values often warrant the use of optional construction materials. Optional materials can also be used to resist attack by soaps, detergents and the germicidal agents used to clean the system. Table 1 shows the recommended materials for each pH value range.
Stainless steel should be avoided for salt brine applications. Monel metal can be used for brines. However, monel metal should be avoided when corn, lima beans or peas are pumped since copper may darken the product. Bronze is fairly corrosion resistant but is not recommended for conveying brines in which foods are canned because of possible product discoloration.
Optional materials for applications associated with abrasive material traditionally include hardened ductile iron. The impeller commonly wears 200 percent faster than the back plate or volute. A hardened impeller with a cast iron volute and back plate will normally sustain a similar life cycle.
|pH Range||Reccomended Material|
|0-4||Corrosion resistant alloy steels|
|10-14||Corrosion resistant steels|
In principle, the transport line should be as short as possible and free of sharp bends, protruding edges and rapid increases or decreases in pipe size. The piping coefficient should be strongly considered to avoid abrasion to the product by the pipe wall. The pipe length is traditionally determined by the retention time required for disinfection, hydro cooling, blanching, etc., or the shortest available route. For practical purposes, horizontal and vertical pipe length should be limited to 250 feet and 65 feet respectively. The first part of the evaluation should focus on determining the appropriate line size, which will allow the engineer to design a system with optimum line velocity. Water volume should be determined in gallons per minute. This is accomplished by determining the product to be transported in pounds per minute. Then the recommended volume-to-product ratio is applied, which provides the designer with an equivalent volume of water. The water-to-product ratio should be as great as economically possible and should vary depending on the type of food being transported. Traditionally, highly sensitive products require a greater water-to-product ratio. The piping configuration should be designed to maintain optimum line velocities to prevent the product from falling out of suspension, dragging along the bottom of the pipe or stacking up. High line velocities should also be avoided to reduce product impact. Short radius ells, rough pipe joints or heads inside the welded pipe can cause more damage to the product than the pump.
System Design and Pump Selection
The speed of the pump should be selected to meet the head requirements of the system. The system should be designed to keep the head as low as possible. Excess pump speed produces an excess volume of water used. This results in excess line velocity and increases the possibility of impact damage. Pumping excess water is a needless waste of power.
A pump that is too slow produces insufficient water volume, and as a result, a loss of lift capacity, retention time, etc., which may further damage the product.