I. Overview sealless centrifugal pump , also known as leakless centrifugal pump, can be divided into magnetic drive centrifugal pump (hereinafter referred to as magnetic pump) and shielded pump, they are only in the structure of the static seal without the dynamic seal, the liquid can be guaranteed delivery No leak. With the continuous improvement of environmental protection requirements, the application of sealless centrifugal pump is also more and more widely. In order to make everybody choose the sealless centrifugal pump reasonably, this paper summarizes some problems that should be paid attention to when choosing the sealless centrifugal pump by introducing the type, principle and structure of sealless centrifugal pump, comparing the features of the magnetic pump and shielding pump.
Magnetic pump 1. Magnetic pump works Magnetic drive is the use of magnets to attract ferromagnetic material and the magnetic or magnetic field between the magnetic properties of the magnetic properties of non-ferrous material does not affect or seldom affect the size of the magnetic force, it can Non-contact through the non-magnetic conductor (isolation sleeve) for power transmission.
Magnetic drive can be divided into synchronous or asynchronous design. Most magnetic pumps use a synchronous design. Motor through the external coupling and the outer magnet together, the impeller and the inner magnet together. Between the outer magnet and the inner magnet with a fully sealed isolation sleeve, the inner and outer magnet completely separated so that the inner magnet in the medium, the motor shaft through the magnet pole between the suction force directly drives the impeller synchronization Turn.
Asynchronous design magnetic drive, also known as Torque Loop magnetic drive. Replace the inner magnet with a squirrel-cage torque ring, which is attracted at a slightly lower speed by the outer magnet. Because there is no magnet, so the temperature is higher than the synchronous drive magnetic drive.
2. Magnetic pump structure 1) Magnetic Coupler Magnetic drive by the magnetic coupler to complete. Magnetic coupling mainly includes the inner magnet, outer magnet and isolation sleeve and other parts, is the core components of the magnetic pump. Magnetic coupler structure, magnetic circuit design, and its various parts of the material related to the reliability of magnetic pumps, magnetic transmission efficiency and life expectancy. Magnetic coupler should be suitable for outdoor start-up and continuous operation under the specified environmental conditions, and should not appear decoupling and demagnetization.
(1) The inner and outer magnetic steel magnets should be firmly fixed on the guide ring with the adhesive, and the inner magnet should be separated from the medium by the sleeve. The minimum thickness of the sleeve should be 0.4mm, the material should be used non-magnetic materials, and suitable for conveying medium.
The outer magnet is also firmly fixed to the outer magnet ring with adhesive. To prevent damage to the outer magnet assembly, the inner surface of the outer magnet should also be covered with a wrap.
Synchronous magnetic coupling should be used samarium cobalt, neodymium iron boron and other rare earth magnetic materials; Torque ring clutch samarium cobalt, NdFeB and other rare earth magnetic materials, or Alnico magnetic material. NdFeB magnetic energy product is higher than samarium cobalt, the disadvantage is the use of temperature is only 120 ℃, and the magnetic stability is relatively poor. Samarium cobalt magnetic drive efficiency and high energy product, and has a strong anti-demagnetization. There are usually two types of samarium cobalt for magnetic pumps, Samarium Cobalt Grade 1.5 Sm1Co5 and Grade 2.17 Sm2Co17. Samarium cobalt 1.5 contains samarium 35%, cobalt 65%, the highest temperature 250 ℃, Curie temperature 523 ℃; samarium cobalt 2.17 containing samarium 25%, cobalt 50%, titanium, iron, etc. 25%, the highest temperature 350 ° C, Curie temperature 750 ° C.
(2) Isolator Sleeve Isolator Sleeve, also called isolation cover or gland, is located between the inner and outer magnets. The inner and outer magnets are completely separated and the media is enclosed in the isolating sleeve. Isolation sleeve thickness and working pressure and temperature, too thick, then increase the gap size of the inner and outer magnets, thus affecting the magnetic drive efficiency; too thin, it will affect the strength.
There are two types of metal and non-metal insulation cover, metal insulation cover eddy current loss, non-metallic insulation sleeve no eddy loss. Metal isolation sleeve should use high resistivity materials, such as Hastelloy, titanium, etc., but also the choice of austenitic stainless steel, the thickness should generally be greater than or equal to 1.0mm. For low-power magnetic pumps, and the use of low temperature, the isolation sleeve may also consider the use of non-metallic materials, such as plastic or ceramic.
2) sliding bearings (1) silicon carbide ceramic magnetic pump generally uses silicon carbide ceramic bearings. In order to prevent free silicon ions from entering the medium, purely sintered α-stage silicon carbide should generally be used on request. Silicon carbide sliding bearing, high carrying capacity, and has strong erosion resistance, chemical resistance, wear resistance and good heat resistance, the use of temperature up to 500 ℃. The service life of silicon carbide sliding bearings is generally up to 3 years.
(2) graphite graphite has good self-lubricating properties, can withstand short-term dry run, the use of temperature up to 450 ℃, the disadvantage is poor wear resistance. The life of graphite plain bearings generally up to 1 year.
3. PUMP PROTECTION SYSTEM (1) Bearing Condition Monitor Some international well-known manufacturers can configure non-contact bearing condition monitor to prevent bearing wear failure, coupling decoupling, rotor stuck, and Power system failure and so on.
(2) Motor Power Monitor The motor power monitor monitors the motor power to avoid low flow or dry operation.
(3) Temperature Probe Use a temperature probe (RTD) to monitor the temperature of the baffle to reflect changes in pump condition during operation. Can prevent the dry pump operation, internal and external bearing wear and tear, severe cavitation, stuffy pump, pump stuck, and the system overheating.
(4) differential pressure switch with differential pressure switch to monitor the pump outlet pressure changes, to prevent the pump dry run, serious cavitation, boring pump, pump stuck. Especially for container emptying / tank truck unloading and so on.
(5) The second layer of protection a. Pressure-tight magnetic coupling box isolation sleeve outside the magnetic coupling box, as shown in Figure 1 dotted line. For high-system pressure delivery of some highly toxic or flammable chemicals, the box should be a pressure-tight container, the design and test pressure value and the hydraulic end of the pump the same; and the pump shaft and the magnetic coupling box Throttle bushing and mechanical seal should be set (commonly known as secondary seal).
b. double isolation sleeve structure (6) liquid leak probe For the use of the second layer of protection of magnetic pumps, liquid leak detectors should be set. For pressure-sealed magnetic coupling box structure of the magnetic pump, when the isolation sleeve ruptures, or for other reasons, the liquid into the magnetic coupling box, the probe will alarm; for double isolation sleeve structure of the magnetic pump, when the isolation sleeve The probe will alarm if it breaks, or for other reasons it has liquid entering the cavity between the inner and outer spacers.
Magnetic pump 1. Magnetic pump works Magnetic drive is the use of magnets to attract ferromagnetic material and the magnetic or magnetic field between the magnetic properties of the magnetic properties of non-ferrous material does not affect or seldom affect the size of the magnetic force, it can Non-contact through the non-magnetic conductor (isolation sleeve) for power transmission.
Magnetic drive can be divided into synchronous or asynchronous design. Most magnetic pumps use a synchronous design. Motor through the external coupling and the outer magnet together, the impeller and the inner magnet together. Between the outer magnet and the inner magnet with a fully sealed isolation sleeve, the inner and outer magnet completely separated so that the inner magnet in the medium, the motor shaft through the magnet pole between the suction force directly drives the impeller synchronization Turn.
Asynchronous design magnetic drive, also known as Torque Loop magnetic drive. Replace the inner magnet with a squirrel-cage torque ring, which is attracted at a slightly lower speed by the outer magnet. Because there is no magnet, so the temperature is higher than the synchronous drive magnetic drive.
2. Magnetic pump structure 1) Magnetic Coupler Magnetic drive by the magnetic coupler to complete. Magnetic coupling mainly includes the inner magnet, outer magnet and isolation sleeve and other parts, is the core components of the magnetic pump. Magnetic coupler structure, magnetic circuit design, and its various parts of the material related to the reliability of magnetic pumps, magnetic transmission efficiency and life expectancy. Magnetic coupler should be suitable for outdoor start-up and continuous operation under the specified environmental conditions, and should not appear decoupling and demagnetization.
(1) The inner and outer magnetic steel magnets should be firmly fixed on the guide ring with the adhesive, and the inner magnet should be separated from the medium by the sleeve. The minimum thickness of the sleeve should be 0.4mm, the material should be used non-magnetic materials, and suitable for conveying medium.
The outer magnet is also firmly fixed to the outer magnet ring with adhesive. To prevent damage to the outer magnet assembly, the inner surface of the outer magnet should also be covered with a wrap.
Synchronous magnetic coupling should be used samarium cobalt, neodymium iron boron and other rare earth magnetic materials; Torque ring clutch samarium cobalt, NdFeB and other rare earth magnetic materials, or Alnico magnetic material. NdFeB magnetic energy product is higher than samarium cobalt, the disadvantage is the use of temperature is only 120 ℃, and the magnetic stability is relatively poor. Samarium cobalt magnetic drive efficiency and high energy product, and has a strong anti-demagnetization. There are usually two types of samarium cobalt for magnetic pumps, Samarium Cobalt Grade 1.5 Sm1Co5 and Grade 2.17 Sm2Co17. Samarium cobalt 1.5 contains samarium 35%, cobalt 65%, the highest temperature 250 ℃, Curie temperature 523 ℃; samarium cobalt 2.17 containing samarium 25%, cobalt 50%, titanium, iron, etc. 25%, the highest temperature 350 ° C, Curie temperature 750 ° C.
(2) Isolator Sleeve Isolator Sleeve, also called isolation cover or gland, is located between the inner and outer magnets. The inner and outer magnets are completely separated and the media is enclosed in the isolating sleeve. Isolation sleeve thickness and working pressure and temperature, too thick, then increase the gap size of the inner and outer magnets, thus affecting the magnetic drive efficiency; too thin, it will affect the strength.
There are two types of metal and non-metal insulation cover, metal insulation cover eddy current loss, non-metallic insulation sleeve no eddy loss. Metal isolation sleeve should use high resistivity materials, such as Hastelloy, titanium, etc., but also the choice of austenitic stainless steel, the thickness should generally be greater than or equal to 1.0mm. For low-power magnetic pumps, and the use of low temperature, the isolation sleeve may also consider the use of non-metallic materials, such as plastic or ceramic.
2) sliding bearings (1) silicon carbide ceramic magnetic pump generally uses silicon carbide ceramic bearings. In order to prevent free silicon ions from entering the medium, purely sintered α-stage silicon carbide should generally be used on request. Silicon carbide sliding bearing, high carrying capacity, and has strong erosion resistance, chemical resistance, wear resistance and good heat resistance, the use of temperature up to 500 ℃. The service life of silicon carbide sliding bearings is generally up to 3 years.
(2) graphite graphite has good self-lubricating properties, can withstand short-term dry run, the use of temperature up to 450 ℃, the disadvantage is poor wear resistance. The life of graphite plain bearings generally up to 1 year.
3. PUMP PROTECTION SYSTEM (1) Bearing Condition Monitor Some international well-known manufacturers can configure non-contact bearing condition monitor to prevent bearing wear failure, coupling decoupling, rotor stuck, and Power system failure and so on.
(2) Motor Power Monitor The motor power monitor monitors the motor power to avoid low flow or dry operation.
(3) Temperature Probe Use a temperature probe (RTD) to monitor the temperature of the baffle to reflect changes in pump condition during operation. Can prevent the dry pump operation, internal and external bearing wear and tear, severe cavitation, stuffy pump, pump stuck, and the system overheating.
(4) differential pressure switch with differential pressure switch to monitor the pump outlet pressure changes, to prevent the pump dry run, serious cavitation, boring pump, pump stuck. Especially for container emptying / tank truck unloading and so on.
(5) The second layer of protection a. Pressure-tight magnetic coupling box isolation sleeve outside the magnetic coupling box, as shown in Figure 1 dotted line. For high-system pressure delivery of some highly toxic or flammable chemicals, the box should be a pressure-tight container, the design and test pressure value and the hydraulic end of the pump the same; and the pump shaft and the magnetic coupling box Throttle bushing and mechanical seal should be set (commonly known as secondary seal).
b. double isolation sleeve structure (6) liquid leak probe For the use of the second layer of protection of magnetic pumps, liquid leak detectors should be set. For pressure-sealed magnetic coupling box structure of the magnetic pump, when the isolation sleeve ruptures, or for other reasons, the liquid into the magnetic coupling box, the probe will alarm; for double isolation sleeve structure of the magnetic pump, when the isolation sleeve The probe will alarm if it breaks, or for other reasons it has liquid entering the cavity between the inner and outer spacers.
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