How to select acid and alkali resistant pumps? Acid and alkali resistant pump selection requirements

　　Acid and alkali resistant pump is a special material pump, widely used in electroplating, PCB, environmental protection equipment and other industries, Schaederbauer acid-resistant pump products are suitable for -20 ℃ ~ +120 ℃ temperature conditions for transporting various types of corrosive media, the overflow part of the entire use of plastic alloys (polytetrafluoroethylene and polyperfluoroethylene propylene and a variety of other materials) after a reasonable formula, molding, processing and become acid-resistant pumps set a variety of plastics of the advantages, with strong corrosion resistance, and has high mechanical strength, no aging, no toxin decomposition and other advantages. With strong corrosion resistance, and high mechanical strength, no aging, no toxin decomposition and other advantages, is the ideal equipment for transporting a variety of strong and weak acids, although it has so many advantages, but the procurement is also a headache, the following Schwab Pump & Valve on how to select the acid and alkali resistant pump.

　　How to select acid and alkali pump

　　First, acid and alkali pump selection principles

　　To select the pump, we must first understand and master the principle of acid and alkali pump selection.

　　1, so that the selected pump type and performance in line with the device flow, head, pressure, temperature, vapor flow, suction range and other process parameters.

　　2, must meet the requirements of the media characteristics.

　　For pumps conveying flammable, explosive toxic or precious media, require reliable shaft seal or leak-free pumps, such as magnetic drive pumps, diaphragm pumps, shielded pumps.

　　For pumps conveying corrosive media, the requirement of convective components using corrosion-resistant materials, such as AFB stainless steel corrosion-resistant pumps, CQF engineering plastic magnetic drive pumps.

　　For pumps conveying media containing solid particles, convective parts are required to use wear-resistant materials, and the shaft seal is flushed with clean liquid if necessary.

　　3, mechanical reliability, low noise, low vibration.

　　4, the economy should be comprehensively considered to the lowest total cost of equipment costs, operating costs, maintenance costs and management fees.

　　5, common occasions of acid and alkali pump selection:

　　(1) centrifugal pump with high speed, small size, light weight, high efficiency, high flow rate, simple structure, no pulsation of infusion, smooth performance, easy to operate and convenient maintenance and so on.

　　(2) Metering pumps are used when there are metering requirements.

　　(3) head requirements are very high, the flow rate is very small and there is no suitable small flow high head centrifugal pump can be selected, you can choose the reciprocating pump, such as cavitation requirements are not high, you can also choose the vortex pump.

　　(4) head is very low, the flow rate is very large, can choose axial flow pumps and mixed flow pumps.

　　(5) medium viscosity (greater than 650 ~ 1000mm2 / s), can be considered to choose rotor pumps or reciprocating pumps (gear pumps, screw pumps)

　　(6) 75% of the media gas content, flow rate is small and viscosity less than 37.4mm2 / s, can choose the vortex pump.

　　(7) for frequent start-up or filling the pump inconvenient occasions, should be used with self-priming performance of the pump, such as self-priming centrifugal pumps, self-priming vortex pumps, pneumatic (electric) special pumps membrane pumps.

　　Second, acid and alkali pump selection basis

　　Pump selection basis, should be based on the process, water supply and drainage requirements, from five aspects to be considered.

　　1. flow is one of the important performance data of the pump selection, which is directly related to the production capacity of the entire device and conveying capacity. Such as the design institute process design can calculate the pump normal, minimum, maximum three kinds of flow. Select the pump, based on the maximum flow, taking into account the normal flow, in the absence of a maximum flow, usually 1.1 times the normal flow as the maximum flow. 2.

　　2. device system required head is another important performance data to select the pump, generally used to amplify the 5% -10% margin after the head to select. 3. the nature of the liquid, including the liquid, the liquid, the liquid, the liquid, the liquid, the liquid, the liquid, the liquid, the liquid, the liquid, the liquid.

　　3. the nature of the liquid, including the name of the liquid medium, physical properties, chemical properties and other properties, which involves the head of the system, the effective cavitation margin calculation and the type of suitable pumps, the choice of pump materials and selection of that a shaft seal type.

　　4. device system piping arrangement conditions refers to the delivery of liquid height delivery distance delivery of liquid towards, suction such as the side of the lowest liquid level, discharge side of the highest liquid level and some other data and pipeline specifications and its length, materials, fittings, specifications, quantity, etc., in order to carry out the Department of the comb head calculations and the calibration of the cavitation margin.

　　5. Determination of operating conditions, such as liquid operation T saturated vapor force, suction side pressure (absolute), discharge side container pressure, altitude, ambient temperature operation is intermittent or continuous, the pump position is fixed or removable. Are the important basis for selection.

　　Third, a variety of conditions under the factors of acid and alkali pump selection requirements

　　Acid and alkali pump piping arrangement

　　When designing and arranging the pipeline, the following matters should be noted:

　　A. Reasonable selection of pipe diameter, pipe diameter, in the same flow rate, liquid flow velocity is small, resistance loss is small, but the price is high, pipe diameter is small, it will lead to a sharp increase in resistance loss, so that the head of the selected pump increase, with power increase, cost and operating costs are increased. Therefore, it should be considered from the technical and economic point of view.

　　B. Discharge pipe and its fittings should be considered to withstand the maximum pressure.

　　C. The pipeline arrangement should be arranged as straight as possible, minimize the accessories in the pipeline and reduce the length of the pipeline as much as possible, must be turned, the bend radius of the elbow should be 3 to 5 times the diameter of the pipe, the angle is greater than 90 ℃ as far as possible.

　　D. Valves (ball valves or globe valves, etc.) and check valves must be installed on the discharge side of the pump. Valves are used to regulate the operating point of the pump, and the backstop valve prevents the pump from reversing when liquid flows backwards and allows the pump to avoid water hammer strikes. (When the liquid flows backwards, a huge reverse pressure is generated, damaging the pump.)

　　Selection of sealing for acid and alkali resistant pumps

　　No leakage is the everlasting pursuit of chemical equipment, and it is this requirement that contributes to the ever-expanding application of magnetic pumps and shielded pumps.

　　1. Seal form

　　For static sealing, usually only two forms of gaskets and seals, and seals and O-rings are most widely used.

　　For dynamic seals, acid and alkali pumps rarely use packing seals, mainly mechanical seals, mechanical seals and single-end and double-end, balanced and unbalanced type, balanced for high-pressure media sealing (usually refers to the pressure is greater than 1.0MPa), double-end machine seals are mainly used for high temperature, easy to crystallize, viscosity, containing particles, and toxic volatile media, double-end machine seals should be injected into the sealing cavity of the isolation fluid, the pressure is generally higher than the medium pressure. Its pressure is generally higher than the medium pressure 0.07~0.1MPa.

　　2.Seal material

　　Acid and alkali pump static seal material is generally used fluoroelastomer, special circumstances before the use of PTFE material; mechanical seal dynamic and static ring material configuration is more critical, not carbide to carbide is the best, the price is high on the one hand, there is no hardness difference between the two is not reasonable, so it is best to differentiate according to the characteristics of the medium.

　　Acid and alkali pumps special media selection

　　Sulfuric acid

　　Different concentrations and temperatures of sulfuric acid on the material corrosion difference is large, for the concentration of more than 80%, the temperature is less than 80 ℃ concentrated sulfuric acid, carbon steel and cast iron have better corrosion resistance, but it is not suitable for high-speed flow of sulfuric acid.

　　Not suitable for use as a material for pumps and valves:

　　Ordinary stainless steel such as 304 (0Cr18Ni9), 316 (0Cr18Ni12Mo2Ti)

　　Pumps and valves for conveying sulfuric acid are usually made of high-silicon cast iron (casting and machining difficulties), high-alloy stainless steel (alloy 20). Fluorine plastic has better resistance to sulfuric acid, the use of fluorine lined pumps (F46) is a more economical choice.

　　Hydrochloric acid

　　The vast majority of metal materials are not resistant to hydrochloric acid corrosion (including a variety of stainless steel materials), molybdenum-containing high-silicon iron can only be used for 50 ℃, 30% of the following hydrochloric acid.

　　Contrary to metallic materials, most non-metallic materials have good corrosion resistance to hydrochloric acid, so rubber lined pumps and plastic pumps (such as polypropylene, fluorine plastic, etc.) are the best choice for conveying hydrochloric acid.

　　Nitric acid

　　Most of the general metal in nitric acid is rapidly corroded and destroyed, stainless steel is the most widely used nitric acid-resistant materials, all concentrations of nitric acid at room temperature have good corrosion resistance, it is worth mentioning that molybdenum-containing stainless steel (e.g., 316, 316L) corrosion resistance to nitric acid is not only not superior to ordinary stainless steel (e.g., 304, 321), and sometimes not even as good as. For high temperature nitric acid, titanium and titanium alloy materials are usually used.

　　Acetic acid

　　It is one of the most corrosive organic acids, ordinary steel in all concentrations and temperatures of acetic acid will be seriously corroded, stainless steel is an excellent acetic acid-resistant materials, molybdenum-containing 316 stainless steel can also be applied to high temperature and dilute acetic acid vapor. For high temperature and high concentration of acetic acid or contain other corrosive media and other demanding requirements, can choose high alloy stainless steel or fluorine plastic pump.

　　Alkali (sodium hydroxide)

　　Ordinary stainless steel on the corrosion resistance of lye compared with cast iron has no obvious advantages, as long as the medium allows a small amount of iron mixed in stainless steel is not recommended.

　　For high temperature lye more titanium and titanium alloy or high alloy stainless steel. The company's general cast iron pumps can be used for low concentration of lye at room temperature, special requirements can be used in various types of stainless steel pumps or fluoroplastic pumps.

　　Ammonia (ammonia hydroxide)

　　Most metals and non-metals in liquid ammonia and ammonia (ammonia hydroxide) in the corrosion are very light, only copper and copper alloy should not be used.

　　Salt water (seawater)

　　Ordinary steel in sodium chloride solution and seawater, salt water corrosion rate is not too high, generally must be protected by paint. Various types of stainless steel also has a very low uniform corrosion rate, but may be caused by chloride ions and localized corrosion, usually using 316 stainless steel is better.

　　Alcohols, ketones, esters, ethers

　　Common alcohol media are methanol, ethanol, ethylene glycol, propanol, etc., ketone media have acetone, butanone, etc., ester media have a variety of methyl ester, ethyl ester, etc., ether media have methyl ether, ethyl ether, butyl ether, etc., which is basically no corrosive, commonly used materials can be applied, the specific selection of the media should also be based on the attributes and related requirements to make a reasonable choice.

　　It is also worth noting that ketone, ester, ether on a variety of rubber solubility, in the selection of sealing materials to avoid mistakes.

　　The effect of viscosity temperature

　　The viscosity of the medium on the performance of the pump is a great influence, when the viscosity increases, the pump head curve decreases, the optimal working conditions of the head and flow rate are followed by a decline in the power is followed by a rise, and thus reduce efficiency. General parameters on the sample are conveying water performance, when conveying viscous media should be converted (different viscosity correction coefficients can consult the relevant conversion chart). For the transportation of slurries, pastes and viscous liquids with high viscosity, it is recommended to use screw pumps.

　　For the temperature below 120 ℃ media, usually do not set up a special cooling system, more use of its own medium to lubricate and cool.

　　For the medium above 120 ℃, 300 ℃ or less, generally in the pump cover shall be equipped with a cooling chamber, the sealing chamber should also be connected to the coolant (shall be equipped with double end mechanical seal), when not allowed to coolant penetration into the medium, should be taken to the medium itself after cooling access (can be realized through a simple heat exchanger).

　　For high-temperature media above 300 ℃, not only the pump head part of the need for cooling, suspension bearing room should also be equipped with a cooling system, the pump structure is generally the center of the support form, the mechanical seal is best to use the metal bellows type, but the price is high (the price is more than 10 times the price of the ordinary machine seal).