Pumping grape clusters and juice through different stages of the winemaking process requires gentle, low-shear liquid handling. In the early stages of the process, the pump must avoid causing damage to the grapes, such as cracking skins and crushing seeds. Crushed skins and seeds may release unwanted elements into the juice, affecting the end product. Realistically, 100 percent of the grape clusters will not remain intact after going through any pump. However, certain pump designs are better than others in protecting the grapes during common winery applications.
A rotary lobe pump is a common choice for wineries that produce 1,000 or more cases annually. They are light and compact and can be mounted to a mobile pushcart or permanently installed (see the following images). Rotary lobe pumps also gently handle grape clusters and do not shear the juice.
Inline assembly rotary lobe pumps capable of 1,760 gallons per minute and up to 116 psi
Rotary Lobe Pump Operation
The rotary lobe pump is part of the positive displacement group. It works from the same principle as all positive displacement pumps in that it creates flow by trapping liquid from the suction side, carrying it through the pump and expelling it out the discharge side. What makes the rotary lobe pump special is how it accomplishes this. During operation, two rotors mesh together and rotate in opposite directions (see Figure 1). The rotation forms cavities, and the liquid fills the cavities and is carried through the pump and expelled out the discharge side.
Figure 1. Rotary lobe pump
Rotary Lobe Pump Design
All rotary lobe pumps work from the same operating principle. However, rotary lobe pump design and materials of construction vary between brands. Design details and material options become more or less important based on the specific task performed in the winemaking process. Many wineries choose a cart configuration, which can reduce operating costs by purchasing fewer pumps or one pump for several operations. In this scenario, operators should size and configure the pump for the most difficult operation.
A major design difference between brands of rotary lobe pumps is the design and construction of the rotor. Comparing rotors in wine process applications comes down to two major differences—material and shape. Many manufacturers offer rotors that are coated with an elastomer that is bonded to a solid metal core. Rotors are also commonly machined out of different metals. Elastomer coatings are available in a wide range of materials to be compatible with the liquid being pumped. A nitrile rubber (NBR) elastomer is ideal for most wine processes because it is readily available, economical and robust.
NBR is also a good choice when hard, solid objects are in the liquid stream. When a solid object—such as a staple or wire—enters the pump, it can become jammed between a rotor tip and the pump housing. The NBR elastomer will give enough for the staple to be drawn through the pump and expelled out the discharge side. A metal rotor will not give, which often causes the pump to seize and stop the entire process.
Coatings also offer an advantage in cost savings. Some manufacturers choose to coat the entire rotor while others coat only the tips or only offer solid metal. Fully coated rotors can use a cast iron core, which is inexpensive and readily available. In wine process applications, rotors that are only partially covered or uncovered metal must be machined from 316 stainless steel at a minimum. This can add considerable cost to the initial purchase and spare parts cost. Special consideration needs to be given to elastomer material for processes using high-temperature steam cleaning. Many elastomers will swell when exposed to steam. Ethylene propylene diene monomer (EPDM) elastomer can be used for high-temperature cleaning.
The shape of the rotors can also affect operation. Two basic types are straight and balanced. A straight rotor may have two, three or more lobes. They are straight from front to back and could be elastomer-coated or solid metal.
The second type is the balanced rotor. The balanced rotor may have two, three or six lobes. This design is also available in elastomer-coated, solid metal or flame-spray coated versions. A properly balanced rotor produces a smooth, steady flow of liquid that is free of pulsation. A properly balanced rotor is also much more difficult to design and machine when compared to a straight lobe. Reviewing the performance characteristics of the brand being considered is important if pulsation is a factor in the application.
Common Wine Processes
Pumps perform many tasks. These include must pumping, lees removal, pump over, and pomace movement or disposal.
The first operation in winemaking is turning harvested grape clusters into must. Must is composed of freshly cracked grapes, skins, seeds and stems. Must may also contain hard, solid objects—such as staples and wire (used to attach vines)and small stones.