Pump Selection Guide

1. Flow rate:

Flow rate is one of the important performance data for pump selection, which is directly related to the production capacity and delivery capacity of the entire device. The normal, minimum and maximum flow rates of the pump can be calculated in the process design. When selecting a pump, the maximum flow rate is used as the basis, while taking the normal flow rate into consideration. When there is no maximum flow rate, 1.1 times the normal flow rate can usually be taken as the maximum flow rate.

2. The head required by the installation system

Generally, the head should be enlarged by 5%~10% to select the model.

3. Liquid properties

Including the name of the liquid medium, physical properties, chemical properties and other properties.

Physical properties include temperature, density, viscosity, solid particle diameter and gas content in the medium, which involve the head of the system, calculation of effective cavitation margin and the type of suitable pump.

Chemical properties mainly refer to the chemical corrosiveness and toxicity of the liquid medium, which is an important basis for selecting pump materials and the type of shaft seal.

We will introduce in detail how to choose the right pump for various corrosive liquids.

Corrosion has always been one of the most troublesome hazards of chemical equipment. If you are not careful, it will damage the equipment at the least, and cause accidents or even disasters at the worst. According to relevant statistics, about 60% of the damage to chemical equipment is caused by corrosion. Therefore, when selecting chemical pumps, you should first pay attention to the scientific nature of material selection. There is usually a misunderstanding that stainless steel is a "universal material". It is very dangerous to use stainless steel regardless of the medium and environmental conditions.

The following is a discussion of the key points of material selection for some commonly used chemical media:

1) Sulfuric acid is one of the strong corrosive media. Sulfuric acid is an important industrial raw material with a wide range of uses. Sulfuric acid of different concentrations and temperatures has a great difference in the corrosion of materials. For concentrated sulfuric acid with a concentration of more than 80% and a temperature of less than 80°C, carbon steel and cast iron have good corrosion resistance, but they are not suitable for high-speed flowing sulfuric acid and are not suitable for use as pump valve materials; ordinary stainless steel such as 304 (0Cr18Ni9) and 316 (0Cr18Ni12Mo2Ti) are also limited in use for sulfuric acid media. Therefore, pumps and valves for conveying sulfuric acid are usually made of high-silicon cast iron (difficult to cast and process) and high-alloy stainless steel (Alloy 20). Fluoroplastics have good resistance to sulfuric acid, and using fluorine-lined pumps (F46) is a more economical choice.

2) Hydrochloric acid Most metal materials are not resistant to hydrochloric acid corrosion (including various stainless steel materials), and molybdenum-containing high-silicon iron can only be used for hydrochloric acid below 50°C and 30%. In contrast to metal materials, most 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 conveying hydrochloric acid.

3) Nitric acid Most general metals are quickly corroded and destroyed in nitric acid. Stainless steel is the most widely used nitric acid-resistant material and has good corrosion resistance to nitric acid of all concentrations at room temperature. It is worth mentioning that stainless steel containing molybdenum (such as 316, 316L) is not only not better than ordinary stainless steel (such as 304, 321) in corrosion resistance to nitric acid, but 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 among organic acids. Ordinary steel will be severely corroded in acetic acid of all concentrations and temperatures. Stainless steel is an excellent acetic acid-resistant material. Molybdenum-containing 316 stainless steel can also be used for high temperature and dilute acetic acid vapor. For high temperature and high concentration acetic acid or other corrosive media, high alloy stainless steel or fluoroplastic pumps can be selected.

5) Alkali (sodium hydroxide) Steel is widely used in sodium hydroxide solutions below 80°C and within 30% concentration. There are also many factories that still use ordinary steel at 100°C and below 75%. Although corrosion increases, it is economical. Ordinary stainless steel has no obvious advantage over cast iron in corrosion resistance to alkali 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 alkali solution, titanium and titanium alloys or high-alloy stainless steel are mostly used. Generally, cast iron pumps can be used for low-concentration alkali solution at room temperature. When special requirements are met, various types of stainless steel pumps or fluoroplastic pumps can be used.

6) Ammonia (ammonia hydroxide) Most metals and non-metals are slightly corroded in liquid ammonia and ammonia water (ammonia hydroxide). Only copper and copper alloys are not suitable for use.

7)Salt water (seawater) Ordinary steel has a low corrosion rate in sodium chloride solution, seawater, and salt water, and generally requires coating protection; various types of stainless steel also have a very low uniform corrosion rate, but may cause local corrosion due to chloride ions. It is usually better to use 316 stainless steel. All types of chemical pumps in the company are equipped with 316 materials.

8) Alcohols, ketones, esters, 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, ethyl ether, butyl ether, etc. They are basically non-corrosive and can be used with commonly used materials. When selecting, reasonable choices should be made based on the properties of the media and related requirements. It is also worth noting that ketones, esters, and ethers are soluble in many types of rubber, so avoid mistakes when selecting sealing materials.

4. Pipeline layout conditions of the device system

Refers to the liquid delivery height, liquid delivery distance, liquid delivery direction, the lowest liquid level on the suction side, the highest liquid level on the discharge side and other data and pipeline specifications and their length, materials, pipe fittings specifications, quantity, etc., in order to calculate the system head and check the cavitation margin.

5. Working conditions

For example, the installation location of the pump (such as ground or underground) will affect the selection of the pump. For example, self-priming pumps are suitable for ground installation, while submersible pumps are suitable for groundwater wells;

Installation environment: the selection of indoor pumps and outdoor pumps is different. Outdoor pumps need to consider rain and dust protection, etc.;

Altitude, ambient temperature, whether the operation is intermittent or continuous, and whether the pump is fixed or movable. There are also some special requirements, such as explosion-proof and corrosion-resistant requirements in some working conditions, and it is necessary to select a pump type that meets the requirements.

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