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A peristaltic pump is a type of positive displacement pump used for pumping a variety of fluids. The fluid is contained within a flexible tube fitted inside a circular pump casing (though linear peristaltic pumps have been made). A rotor with a number of "rollers", "shoes" or "wipers" attached to the external circumference compresses the flexible tube. As the rotor turns, the part of tube under compression closes (or "occludes") thus forcing the fluid to be pumped to move through the tube. Additionally, as the tube opens to its natural state after the passing of the cam ("restitution") fluid flow is induced to the pump. This process is called peristalsis and used in many biological systems such as the gastrointestinal tract.
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Applications
Peristaltic pumps are typically used to pump clean/sterile or aggressive fluids, because cross contamination cannot occur. Some common applications include pumping aggressive chemicals, high solids slurries and other materials where isolation of the product from the environment, and the environment from the product, are critical. The peristaltic pump is the standard method for introducing liquids into the nebulizer on an inductively coupled plasma mass spectrometry (ICP-MS) unit.
Variations
Hose pumps
Higher pressure peristaltic hose pumps which can typically operate against up to 16 bar, typically use shoes and have casings filled with lubricant to prevent abrasion of the exterior of the pump tube and to aid in the dissipation of heat, and use reinforced tubes, often called "hoses". This class of pump is often called a "hose pump".
Tube pumps
Lower pressure peristaltic pumps, typically have dry casings and use rollers, use non-reinforced tubing. This class of pump is sometimes called a "tube pump" or "tubing pump".
360 Degree eccentric design
A unique approach to peristaltic hose pump design employs a single oversized roller on an eccentric shaft that compresses an engineered, low friction hose through 360 degrees of rotation. The benefits of this design include more flow per revolution and only one compression and expansion per cycle. At equal performance points this pump runs more slowly, with consequent longer hose lifetime, than pumps with multiple shoes or rollers.
Many older hose pumps use shoes to compress the hose. When the shoe slides over the outside of the hose, it creates friction and heat, and heat is an enemy of long hose life. A single roller pump uses a large diameter lubricated roller on an eccentric shaft that rolls over the hose. This means that it produces less friction, and therefore less heat, than a pump with shoes.
In addition to less heat, an eccentric shaft hose pump functions with only a single compression of the hose per revolution. For every one rotation, the pump has one compression of the hose, while pumps with multiple shoes or rollers have at least two compressions per revolution, and in some cases three or four. Since the hose is the heart of a peristaltic hose pump, and hose life is inversely proportional to the number of squeezes, this design will outperform a pump with shoes at the same speed.
The hose in this type of pump takes up the full 360 degrees of the pump housing. This is important, because at an equal size, this design will produce 55% more flow at the same speed. This means that one can get more flow at the same pump speed, or run the pump more slowly to generate the same flow.
Advantages
Because the only part of the pump in contact with the fluid being pumped is the interior of the tube, it is easy to sterilize and clean the inside surfaces of the pump. Furthermore, since there are no moving parts in contact with the fluid, peristaltic pumps are inexpensive to manufacture. Their lack of valves, seals and glands makes them comparatively inexpensive to maintain, and the use of a hose or tube makes for a relatively low-cost maintenance item compared to other pump types. Peristaltic pumps also minimize shear forces experienced by the fluid, which may help to keep colloids and slurry fluids from separating.
Tubing
It is important to select tubing with appropriate chemical resistance towards the liquid being pumped. Types of tubing commonly used in peristaltic pumps include:
Trade names include Tygon, Viton, Pharmed, Norprene, Marprene, Bioprene, Sta-Pure, Chem-Sure, Neoprene, Fluorel, Pumpsil-D and Pumpsil.
Typical applications
- Dialysis machines
- Open-heart bypass pump machines
- Infusion pump
- AutoAnalyzer
- Sewage sludge
- Aquariums, particularly calcium reactors
- Analytical chemistry experiments
- Carbon monoxide monitors (e.g., at Longannet power station)
- Agriculture
- Food manufacturing
- Beverage dispensing
- Chemical
- Engineering
- Pharmaceutical production
- OEM applications
- Print and packaging
- Paint and pigments
- Pulp and paper
- Science and research
- Water and Waste
Wikipedia content modification information:
- This page was last modified on 28 August 2008, at 14:21.
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