Selecting the right materials
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Centrifugal pumps manufactured in thermoplastic materials are engineered for safe operations with aggressive media. They are mainly made in four different materials: PP, PVC, PVDF e PE-HD with components in PTFE, PE-HD, PFA, FPM, EPDM, CERAMIC (AL2O3), SIC, PRFV. These materials solve the problems concerning the pumping of hazardous fluids, because no metal part comes in contact with the fluid: all structural, sealing and wearable parts are chosen in relation to the type of system and fluids conveyed.
In these pumps, the construction materials are carefully selected according to technical documentations, experience and direct tests. Each pump component is chosen to satisfy the required performance, according to chemical resistance and specific engineering considerations.
Our Data Sheet will help you analyze the liquid properties necessary for the correct selection of the material; amongst other details, the following are taken into consideration
Dry working: it is always advised to keep the pump from dry working conditions. One of the more used methods is to set the vat to a minimum level that stops the pump as soon as it reaches a dangerous working level.
Working temperatures: because of the above mentioned reasons, it is important to be aware of the maximum and minimum temperatures (besides the standard working temperature). The temperature of the pumping fluid has considerable consequences on the materials: very low temperatures might weaken a certain plastic while high temperatures might induce softening and deformation of structural parts
Suspended solids: in this case too, is paramount to be aware of the nature of such matter: in facts, there are materials that - although with similar resistance towards chemical aggressivity - have different resistance to abrasion. The nature of such solids can also influence the choice of the type of pump: in certain cases a vertical pump without guide bushings might be recommended while in other cases it might be unwise to use magnetic coupling pumps.
Pump installation: it is necessary to ensure that the pump can suck in from an area of the vat or reservoir where the fluid has good properties.
For example, if the liquid tends to deposit slush on the vat bottom, the liquid must be kept in constant motion to avoid sucking this deposit in or, alternatively, the pump must be set at a higher level, thus avoiding bringing in too much slush that could clog the inlet.
CONSTRUCTION MATERIALSOn the basis of our experience, we suggest the following materials for different aggressive liquids:
Caustic Soda, Acetic Acid, diluted Sulfuric Acid, waste waters.
Thermoplastic belonging to the polyolefin group; the polypropylene exhibits a high resistance against attacks by chemicals. Hallmarked by first-rate mechanical properties, special thermal forming resistance and resistance to a wide range of chemical agents. Its density is lower than the one of known thermoplastics. PP is resistant against acids, alkaline solutions, solvents, alcohol and water. Unsuitable for highly halogen/oxidative, concentrated acids (fluorine, chlorine, bromine and iodine). Maximum working temperature: 90°C.
PVC (Polyvinyl chloride)
Cold Chromic Acid solution and Hydrochloric Acid (- 40°C), cold solution of concentrated Sulfuric Acid, Sodium hypochlorite.
It is a widely used material in plant engineering. Polyvinylchloride is one of the most important, mass-produced plastics. It is resistant to most mineral acids, bases, saline solutions, organic composites, aliphatic hydrocarbons and elemental chlorine, while it is unsuitable for chlorinated and aromatic hydrocarbons. PVC-U is highly weather-resistant. Maximum working temperature: 45°C.
PVDF (Polyvinylidene fluoride)
Concentrated Nitric Acid, warm solution of concentrated Hydrochloric Acid and Sulfuric Acid (+ 40°C), Chlorine.
Polyvinylidene fluoride belongs to the class of fluorine polymers and is a partially crystalline thermoplastic having outstanding mechanical, physical and chemical characteristics. It has an exceptional resistance to acids, saline solutions, aliphatic hydrocarbons, chlorinates and aromatics, alcohol and halogens, while it is unsuitable for organic bases, alkaline solutions, chetons, esters and ethers. Suitable for the semiconductors industry and with liquids to be safeguarded from contamination. PVDF shows its advantages especially at higher temperatures: maximum working temperature: 100°C, which enables this material to be employed in a wide range of industrial applications.
PE-HD (Polyethylene - High Density)
It has the polypropylene same chemical resistance and it is valued for its resistance to chemical attack. Maximum working temperature: 60°C.EPDM (Ethylene-propylene terpolymer)
A highly elastic elastomer with an optimum resistance to acids, bases, alcohol and chetons. Unsuitable for hydrocarbons, oils and greases. Maximum working temperature: 90°C.
High thermal stability, low permanent deformation and high chemical resistance to acids, solvents, lubricants and fuels.
Sintered ceramic (Al203 99%)
Base material for sealing rings and wear elements. Elevated hardness, resistant to wear and to chemical agents attack. Not recommended at high temperatures in the presence of highly concentrated hydrofluoric acid, soda and sodium hypochlorite.
Sintered silicon carbide (SiC, without free silicon)
Material with greater characteristics as compared to aluminium oxide: greater heat shock resistance and chemically inert at the plastic pumps working temperature.
PTFE (Polytetrafluoro ethylene)
PTFE is characterized by extreme temperature resistance and the best chemical resistance of all plastics. Chemically inert up to 250°C in presence of any chemical agent. Not advisable for alkaline welded metals, chlorine trifluoride and gaseous fluorine at high temperatures. Can be filled with materials such as glass or ceramic or with graphite and carbon. Ideal for sealing elements and wear sleeves
FEP and PFA
Fluoroplastics having the same characteristics of the PTFE but with less permeability. Used for welding, for example when coating mechanical seal and O-ring springs
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