What factors affect the selection of vacuum pump?

Do you know what factors affect the choice of pump?

1, flow is one of the important performance data of pump selection. It is directly related to the production capacity and transmission capacity of the whole plant. If design institute process design can calculate the pump normal, minimum, maximum three kinds of flow. When choosing a pump, take the maximum flow as the basis, take into account the normal flow, in the absence of the maximum flow, usually take 1.1 times the normal flow as the maximum flow.

2. The head required by the device system is another important performance data of the selection pump. Generally, the head should be enlarged by 5%~10%.

3. Liquid properties. Including liquid medium name, physical properties, chemical properties and other properties, physical properties have temperature c density d, viscosity u, solid particle diameter in the medium and gas content, which involves the system head, effective cavitation allowance calculation and the type of appropriate pump. Chemical properties, mainly refers to the chemical corrosiveness and toxicity of liquid medium, is an important basis for the selection of pump materials and the selection of a type of shaft seal.

4. The piping layout condition of the device system refers to the height and distance of liquid delivery. Some data such as the lowest liquid level on the suction side and the highest liquid level on the discharge side, as well as pipe specifications and their length, materials, pipe fitting specifications and quantities, are used to calculate the head of the comb and check the cavitation allowance.

5. There are many operating conditions. Such as liquid operation T saturated steam force P, suction side pressure PS (absolute), discharge side vessel pressure PZ, altitude, ambient temperature operation is clearance or continuous, pump position is fixed or movable.

Influence of corrosion

For a long time, corrosion is one of the most serious hazards of chemical equipment. If you are slightly careless, you may damage the equipment, cause accidents or even cause disasters. According to relevant statistics, about 60% of the destruction of chemical equipment is caused by corrosion, so in the chemical pump selection should pay attention to the scientific material selection. There is a kind of erroneous zone normally, think stainless steel is “omnipotent material”, no matter what medium and environmental condition hold out stainless steel, this is very dangerous.

The following for some common chemical media about the main points of material selection:

1, sulfuric acid,

As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of USES. Sulfuric acid of different concentration and temperature has a great difference in the corrosion of materials, for the concentration of more than 80%, the temperature is less than 80℃ concentrated sulfuric acid, carbon steel and cast iron have a good corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid, not suitable for the material used as a pump valve;

Ordinary stainless steels such as 304(0Cr18Ni9), 316(0Cr18Ni12Mo2Ti) are also of limited use for sulfuric acid media. Therefore, the delivery of sulfuric acid pump valve usually used high silicon cast iron (casting and processing difficulties), high alloy stainless steel (20 alloy) manufacturing. Fluoroplastics have better resistance to sulfuric acid. Fluorine lined pump (F46) is a more economical choice.

2, hydrochloric acid

Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), high ferric silicon containing molybdenum can only be used for hydrochloric acid below 50℃, 30%. Contrary to metal materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pump and plastic pump (such as polypropylene, fluorine plastic) is the best choice for conveying hydrochloric acid.

3, nitric acid

General metal is mostly in nitric acid corrosion damage, stainless steel is the most widely used nitric acid resistant material, at room temperature of all concentrations of nitric acid have a good corrosion resistance, it is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) on nitric acid corrosion resistance is not only not better than ordinary stainless steel (such as 304, 321), sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used.

4, acetic acid,

It is one of the most corrosive substances in organic acid, ordinary iron and steel in all the concentration and temperature of acetic acid will be seriously corroded, stainless steel is an excellent acetic acid resistant material, containing 316 stainless steel can also be applied to high temperature and dilute acetic acid steam. For high temperature high concentrated acetic acid or containing other corrosive media and other harsh requirements, can choose high alloy stainless steel or fluorine plastic pump.

5. Alkali (sodium hydroxide)

Steel is widely used in 80℃ below, 30% concentration of sodium hydroxide solution, there are many factories in 100℃, 75% below the use of ordinary steel, although corrosion increases, but good economy. The corrosion resistance of ordinary stainless steel to alkali liquor has no obvious advantages compared with that of cast iron. Stainless steel is not recommended as long as a small amount of iron is allowed in the medium. For high temperature lye use titanium and titanium alloy or high alloy stainless steel.

6. Ammonia (ammonia hydroxide)

Most metals and nonmetals in liquid ammonia and ammonia (ammonia hydroxide) corrosion is very minor, only copper and copper alloy should not be used.

7. Salt water (seawater)

Ordinary steel in sodium chloride solution and seawater, salt water corrosion rate is not too high, generally must use paint protection; All kinds of stainless steel also have very low uniform corrosion rate, but may cause local corrosion because of chloride ions, usually 316 stainless steel is better.

8. Alcohols, ketones, esters and ethers

Common alcohol medium such as methanol, ethanol, ethylene glycol, propylene glycol, ketone medium such as acetone, butanone, there are all kinds of methyl esters medium, ethyl ester, ethers media such as methyl ether, ethyl ether, butyl ether, their basic no corrosive, commonly used materials are applicable, the specific selection should also according to the requirements of the dielectric properties and related make reasonable choice. It is also worth noting that ketone, ester, ether on a variety of rubber solubility, in the choice of sealing materials to avoid mistakes.

Influence of viscosity

The viscosity of the medium on the performance of the pump is very big.

When the viscosity increases, the lift curve of the pump decreases, and the lift and flow rate of the best working condition decrease accordingly, while the power rises accordingly, thus reducing the efficiency. Generally, the parameters on the sample are the performance of conveying clean water, and conversion should be conducted when conveying viscous medium (correction coefficients of different viscosity can be referred to the relevant conversion chart). For the higher viscosity of pulp, paste and viscous fluid transmission, it is recommended to choose screw pump.