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What are the issues to pay attention to when selecting chemical pumps?

Time of Release:

2023-02-24

The correct selection of chemical pumps should pay attention to: 1. Material selection points. Chemical pump selection should also pay attention to: 2. Medium issues

 What are the issues to pay attention to when selecting chemical pumps?

The correct selection of chemical pumps should pay attention to:

  1、 Key points for material selection: 1. Acetic acid is one of the most corrosive substances in organic acids. Ordinary steel will suffer severe corrosion in all concentrations and temperatures of acetic acid. Stainless steel is an excellent acetic acid resistant material, and stainless steel chemical pumps containing molybdenum can also be suitable for high temperatures and dilute acetic acid vapors. For high temperature and high concentration acetic acid or other corrosive media with strict requirements, high alloy stainless steel chemical pumps or fluoroplastic pumps can be selected. 2. Alkaline (sodium hydroxide) steel is widely used in sodium hydroxide solutions below 80 ℃ and within 30% concentration. Many factories still use ordinary steel at temperatures below 100 ℃ and 75%. Although corrosion increases, it has good economic efficiency. Compared with cast iron, ordinary stainless steel does not have significant advantages in corrosion resistance to alkaline solution. As long as a small amount of iron is allowed to be added to the medium, stainless steel is not recommended. For high-temperature alkaline solutions, titanium and titanium alloys or high alloy stainless steel are often used. The company's general cast iron chemical pumps can be used for low concentration alkaline liquids at room temperature. When special requirements are met, various types of stainless steel pumps or fluoroplastic pumps can be used. 3. Ammonia (hydroxide ammonia) Most metals and non-metals have slight corrosion in liquid ammonia and ammonia water (hydroxide ammonia), and only copper and copper alloys are not suitable for use. 4. Salt water (seawater): The corrosion rate of ordinary steel in sodium chloride solution, seawater, and saline water is not very high, and generally requires coating protection; Various types of stainless steel also have a very low uniform corrosion rate, but may cause localized corrosion due to chloride ions. Generally, 316 stainless steel is preferred. 5. Alcohols, ketones, esters, and ethers. Common alcohol media include methanol, ethanol, ethylene glycol, propanol, etc. Ketone media include acetone, butanone, etc. Ester media include various methyl esters, ethyl esters, etc. Ether media include methyl ether, ether, butyl ether, etc. They are basically non corrosive and can be used with commonly used materials. When selecting, reasonable choices should also be made based on the properties and relevant requirements of the media. Additionally, it is worth noting that ketones, esters, and ethers have solubility in various types of rubber, so errors should be avoided when selecting sealing materials. There are many other media that will not be introduced here. 6. As one of the strong corrosive media, sulfuric acid is an important industrial raw material with a wide range of uses. The corrosion of materials varies greatly with different concentrations and temperatures of sulfuric acid. For concentrated sulfuric acid with concentrations above 80% and temperatures below 80 ℃, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid and are not suitable as materials for pumps and valves. Therefore, chemical pumps and valves for transporting sulfuric acid are usually made of high silicon cast iron (difficult to cast and process) and high alloy stainless steel (No. 20 alloy). Fluoroplastics have good sulfuric acid resistance, and using a fluorine lined pump (F46) is a more economical choice. 7. Most metal materials, including various stainless steel materials, are not resistant to hydrochloric acid corrosion. Molybdenum containing high silicon iron can only be used for hydrochloric acid below 50 ℃ and 30%. Contrary to metal materials, the vast majority of non-metallic materials have good corrosion resistance to hydrochloric acid, so lined rubber pumps and plastic pumps (such as polypropylene, fluoroplastics, etc.) are the best choices for transporting hydrochloric acid. 8. Most metals in nitric acid are rapidly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid resistant material and has good corrosion resistance to all concentrations of nitric acid at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) not only has inferior corrosion resistance to nitric acid compared to ordinary stainless steel (such as 304, 321), but sometimes even worse. For high-temperature nitric acid, titanium and titanium alloy materials are usually used.

  When selecting a chemical pump, attention should also be paid to: 2. Medium problem 1. We all know how important it is to transport the medium during pump selection. Let's start with the temperature of the conveying medium. The transportation of high-temperature media poses higher requirements for the structure, materials, and auxiliary systems of chemical pumps. Below, we will discuss the cooling requirements and applicable pump types for different temperature changes: 1) For media with temperatures below 120 ℃, a dedicated cooling system is usually not set up, and the medium itself is often used for lubrication and cooling. 2) For media above 120 ℃ and below 300 ℃, a cooling chamber should generally be installed on the pump cover of the chemical pump, and the sealing chamber should also be connected to the cooling liquid (equipped with a double end mechanical seal). When the cooling liquid is not allowed to penetrate the media, it should be cooled and connected (which can be achieved through a simple heat exchanger). For high-temperature media above 300 ℃, not only the pump head part needs to be cooled, but the suspension bearing chamber should also be equipped with a cooling system. The structure of chemical pumps is generally in the form of central support, and it is best to use metal corrugated pipe type mechanical seals, but the price is high (more than 10 times that of ordinary mechanical seals). 2. The viscosity of the medium has a significant impact on the performance of chemical pumps. As the viscosity increases, the head curve of the chemical pump decreases, and both the head and flow rate under optimal operating conditions decrease, while the power increases, resulting in a decrease in efficiency. The parameters on the general sample are the performance when transporting clean water, and conversion should be carried out when transporting viscous media. For the transportation of high viscosity slurries, pastes, and viscous liquids, it is recommended to use screw pumps. The biggest characteristics of screw pumps are strong adaptability to media, stable flow rate, small pressure pulsation, and reliable self suction energy, which cannot be replaced by any other pump.
 


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