Special lecture on mechanical equipment: “Pumps” – Learn a little every day (17): Canned pumps “Improve yourself””

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To encourage everyone to come and participate in discussions more actively, as well as to study more diligently, the top five participants each time will receive a “Motivation Reward for Active Learning.” Some people might think that it’s terrifying to spend their working days doing nothing useful, performing menial tasks without knowing what to do or what to learn, day after day, year after year, with no vision for their future We must start working hard from now on; even if we learn a little knowledge every day, it will add up over time and help us enrich ourselves. We need to set clear goals – only by filling our minds first can we enrich other aspects of our lives as well. . . . . . It only takes a short ten-odd minutes per day, and you will see the future! ! ! (Anyway, I have learned it; whether you learn it or not is up to you. Besides those experts like Hai Chuan, there are still others who know it.) . . ) Enough talk – let’s start with the basics today~~! I’ve been posting special threads for so many days now; I’m sure everyone has benefited a lot from them. Thank you all for your support!! Welcome everyone to listen. I have started broadcasting, and I hope those who, like me, want to gain knowledge every day will listen. Let’s learn together every day and discuss~~! These past few days, many people have asked questions, and I’ll do my best to answer them all. There might be some I’ve never encountered before, but there are still plenty of people in our community who can help answer them. @AidaiAmu @hcwang12345 @YiHuXiangMing @tjdxz @YouDianDai @NewbiesInHaiChuan @LoveStory @ManTianYun @ZhaoQingsheng Yesterday, a rotary pump was installed; I believe the members of this community now have a better understanding of air rotary pumps!! From now on, I’ll try to break down the knowledge into smaller portions, in manageable amounts, to make it easier for everyone to learn*~~! Someone has been asking me about shielded pumps these past two days! Today, I’ll explain shielded pumps to you all~~! It might not cover everything; if you have any questions, please ask on the floor. Thank you~~! Cage pump 1. Overview of cage pump A cage pump is a leak-free pump that consists of a canned motor and a pump combined together; it is primarily made up of components such as the pump body, impeller, stator, rotor, front and rear bearings, and thrust disk. The stator and rotor are separated by non-magnetic, corrosion-resistant thin-walled sleeves; the rotor is supported by front and rear bearings and immersed in the conveying medium, hence no type of dynamic seal is required to prevent leakage of the conveyed medium. Generally speaking, shielded pumps are centrifugal sealless pumps. Shielded pumps are completely leak-proof; under negative pressure inside the pump, external air cannot be drawn in, making them particularly suitable for use in vacuum systems ； At the same time, it is suitable for high-pressure, high-melting-point, and high/low-temperature media. Shielded pumps are compact in structure, small in size, and light in weight ； It has no cooling fan, generates low noise, has a wide range of applications, operates reliably, and can provide a relatively good working environment. Operating Conditions: Flow rate range: 1~900 m3/h ； Head range: 5～85m ； Rotational speed: 1410 r/min to 2896 r/min. Maximum operating pressure of the system: ≤ 1.6 MPa. Medium temperature: -15°C to +95°C℃ ； Ambient temperature: not higher than +40°C Motor protection rating: IP54 ； Motor insulation class: Class H. Rotation direction: Counterclockwise when viewed from the impeller inlet; clockwise when viewed from the right side of the motor ； Shielded pumps are environmentally friendly and safe, making them highly suitable for transporting flammable, explosive, volatile, toxic, corrosive, and valuable liquids. They are widely used in industries such as chemicals, petrochemicals, and pharmaceuticals. Although the initial cost of shielded pumps is relatively high, their reliability in operation, long service life, and low maintenance requirements make them at least as economical as other types of pumps. 2. Working principle of shielded pumps: In ordinary centrifugal pumps, the drive mechanism involves connecting the impeller shaft of the pump to the motor shaft through a coupling, allowing the impeller to rotate together with the motor in order to function. A shielded pump is a sealless pump; both the pump and the drive motor are enclosed within a pressure vessel filled with the medium to be pumped. This pressure vessel has only static seals, and a set of wires is used to generate a rotating magnetic field that drives the rotor. This design eliminates the rotating shaft sealing mechanism found in conventional centrifugal pumps, thereby achieving complete leaklessness. A shielded pump combines the pump and the motor together; the rotor of the motor and the impeller of the pump are mounted on the same shaft. A shielding sleeve is used to separate the rotor from the stator of the motor. The rotor rotates within the medium being transported, with power being transmitted to it through the magnetic field of the stator. Furthermore, the manufacturing of shielded pumps is not complex; their hydraulic section can be designed and manufactured according to the structural types commonly used in centrifugal pumps as well as relevant standard specifications. A shielded pump combines the pump and the motor together; the rotor of the motor and the impeller of the pump are mounted on the same shaft. A shielding sleeve is used to separate the rotor from the stator of the motor. The rotor rotates within the medium being transported, with power being transmitted to it through the magnetic field of the stator. Furthermore, the manufacturing of shielded pumps is not complex; their hydraulic section can be designed and manufactured according to the structural types commonly used in centrifugal pumps as well as relevant standard specifications. 3. Advantages of shielded pumps (1) Fully enclosed. There are no dynamic seals in the structure; only static seals are present at the pump’s casing, which enables complete leak prevention. This makes it particularly suitable for transporting flammable, explosive, valuable liquids, as well as toxic, corrosive, and radioactive liquids. (2) High safety. Both the rotor and the stator are equipped with shielding sleeves to prevent them from coming into contact with the material; even if these shielding sleeves are damaged, there is no risk of external leakage. (3) Compact structure with low land footprint. The pump and motor are integrated; no centering is required for disassembly or assembly. It has low requirements for the base and foundation, requires little routine maintenance, and results in low maintenance costs. (4) It operates smoothly, produces low noise, and requires no lubricant. Since there are no rolling bearings or motor fans, no lubricant is required, and it produces low noise. (5) Wide range of applications: It can meet the requirements in various operating conditions such as high temperature, high pressure, low temperature, and high melting points. 4. Disadvantages of shielded pumps: (1) Since shielded pumps use sliding bearings and are lubricated by the medium being transported, media with poor lubricity are not suitable for transportation using shielded pumps. Generally, the viscosity suitable for the medium in shielded pumps is 0.1 to 20 mPa·s. (2) The efficiency of shielded pumps is usually lower than that of centrifugal pumps with single-face mechanical seals, but it is roughly comparable to that of centrifugal pumps with double-face mechanical seals. (3) Operating for long periods at low flow rates results in lower efficiency of the shielded pump, which leads to heating and evaporation of the liquid, causing the pump to run dry and thus damaging the sliding bearings. 5. Types and application ranges of canned pumps Depending on factors such as the temperature, pressure, viscosity of the liquid being transported, and the presence of particles, canned pumps can be classified into the following types: (1) Basic type: The temperature of the medium being transported does not exceed 120°C, and the head is not more than 150 m. All other types of shielded pumps can be obtained by modifying and improving the basic model. (2) Reverse circulation type: In this type of shielded pump, the flow direction of the liquid used for bearing lubrication, cooling, and motor cooling is exactly the opposite of that in the basic type. Its main feature is that it is less prone to cavitation, making it particularly suitable for transporting liquids that are easy to vaporize, such as liquefied petroleum gas and chloromethane. This imported return pump is a basic (standard) shielded pump (without a cooling water jacket), and its shaft is hollow in design. The main flow direction of the circulating fluid is: the suction inlet of the pump body → the impeller → the small hole in the front bearing end cover → the gap between the stator shield and the rotor shield → the gap between the rear bearing and the rear shaft sleeve → the bolt passage on the rear side → the shaft passage → the impeller. Additionally, a portion of the circulating fluid passing through the small hole in the front bearing end cover flows from the gap between the front bearing and the front shaft sleeve → the gap between the front bearing end cover and the impeller hub → to the inlet of the impeller. (3) High-temperature type: The temperature of the medium being transported is generally up to 350°C, the flow rate can reach up to 300 m3/h, and the head is up to 115 m; it is suitable for high-temperature liquids such as hot oil and hot water. (4) High-melting-point type: The pump and motor are equipped with jackets, which significantly improves the heat resistance of the motor. Suitable for high-melting-point liquids, with a maximum temperature of up to 250°C. Steam or a liquid at a certain temperature can be introduced into the jacket to prevent crystallization of high-melting-point liquids. (5) High-pressure type: The casing of a high-pressure shielded pump is a high-pressure vessel, enabling the pump to withstand very high system pressures. To support the shield casing under internal high pressure, the stator coils can be used to bear the pressure. (6) Self-priming type: When the suction pipe is not filled with liquid, the pump drains the fluid through automatic air extraction, making it suitable for extracting liquid from underground containers. (7) Multi-stage type: Equipped with multiple impellers, suitable for high-head fluid transport, with a maximum head of up to 400 m. (8) Slurry type: Suitable for transporting liquids mixed with a large amount of slurry. 6. Precautions for selecting shielded pumps: Generally, shielded pumps use a portion of the liquid being transported to cool the motor, and since the gap between the components is very small, the liquid to be transported must be clean. When transporting mixtures of various liquids that may produce precipitates, coking, or gels, using a shielded pump (that is not of the slurry type) can lead to blockage of the shielding gap, affecting the pump’s cooling and lubrication and resulting in damage to the graphite bearings and motor. Shielded pumps generally come equipped with circulation cooling pipes; when the ambient temperature is below the freezing point of the liquid being pumped, anti-freezing measures such as insulated pipes should be employed to ensure easy pump startup. Additionally, when starting a shielded pump, it is essential to strictly follow the correct sequence for opening the outlet valve and the inlet valve. When shutting down the pump, first reduce the opening of the outlet valve; once the pump has stopped running, close the inlet valve first and then the outlet valve. In summary, the use of shielded pumps ensures complete leaklessness, effectively preventing environmental pollution and material loss. As long as the right model is selected and the operating conditions remain stable, there is little need for maintenance during normal operation. Shielded pumps are ideal for transporting flammable, explosive, corrosive, and valuable liquids. The manufacturing cost of shielded pumps is higher than that of ordinary chemical process pumps, but their operating and maintenance costs are much lower than those of chemical pumps with mechanical seals. Firstly, shielded pumps do not have mechanical seals or bearing housings; the pump shaft is completely enclosed within a shielding sleeve. The variable seal is replaced by a static seal, which effectively solves the problems of leakage and lubrication ； Secondly, the shielded pump eliminates the coupling, replacing the rigid connection with a flexible one, which effectively solves the problems of vibration and noise ； Furthermore, the number of vulnerable components in shielded pumps is significantly reduced (only bearings or mouth rings), and the number of faulty components is also reduced (only the shielding sleeve). Finally, the service life of the shielded pump is extended, the frequency and duration of maintenance are **reduced**, and the physical strain associated with maintenance is also **decreased**. According to relevant statistical data, the failure rates due to leakage and malfunctions in conventional pumps are twice those of canned pumps; moreover, the cost of replacing wear parts in mechanically-sealed chemical pumps is twice that of canned pumps with similar specifications. Based on the cumulative total cost, the quantities of the two are roughly equal over a period of one year. Shielded pumps mainly suffer from the following types of damage: (1) Wear of the graphite bearings, shaft sleeves, and thrust plates, or damage caused by dry friction due to a lack of lubricant. (2) Damage to the stator and rotor shielding sleeves. The main cause of damage to these shielding sleeves is bearing failure or wear that exceeds the allowable limits, resulting in friction between the stator and rotor shielding sleeves and subsequent damage ； Secondly, leaks occur in areas such as welds due to chemical corrosion. (3) Stator winding damage: In addition to the causes of stator winding damage that are common to ordinary motors, such as overload, inter-turn short circuits, and ground breakdown, there is also damage to the winding insulation caused by the erosion of the motor windings due to damage to the stator shielding sleeve. The v-bearings and bushings are the only vulnerable components of a shielded pump. During pump operation, the operating conditions of these components must remain stable! Once the bearings exceed their wear limits, it can lead to contact between the rotor shield and the stator shield, resulting in damage to the stator shield; therefore, close attention must be paid to the inspection of the bearings during operation. During operation, if the shielded pump vibrates or makes abnormal noises, or during regular inspections, it is necessary to disassemble the pump to check the bearings. The inner diameter D of the bearings and the outer diameter d of the shaft sleeves for the corresponding model of the shielded pump must be recorded. Wear amount due to bearing replacement: D - d = 0.3～0.5 mm. In other words, if it is found that the wear level of the bearing and the sleeve exceeds this value, one or both of them should be replaced depending on the actual degree of wear. After watching the lecture, have you also gained an understanding of shielded pumps? Come on, learn a little knowledge every day to enrich yourself; little by little, it will add up to something great~~~! Below are the posts in my special series on rotating equipment: “Pumps”. Learn something new every day! (16) Pneumatic diaphragm pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1257985-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (15) Pneumatic diaphragm pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1257433-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (14) Mixed-flow pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1257224-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (13) Axial-flow pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1256970-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (12) Jet vacuum pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1256707-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (11) Automotive pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1256253-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (10) Pump materials – “Enrich yourself” http://bbs.hcbbs.com/thread-1255790-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (9) Self-priming pumps and pump materials – “Enrich yourself” http://bbs.hcbbs.com/thread-1255635-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (8) Oil seals – “Enrich yourself” http://bbs.hcbbs.com/thread-1255340-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (7) Sealing – “Enrich yourself” http://bbs.hcbbs.com/thread-1255132-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (6) O-rings – “Enrich yourself” http://bbs.hcbbs.com/thread-1254912-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (5) Pump structure – “Enrich yourself” http://bbs.hcbbs.com/thread-1254630-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (4) Pump structure – “Enrich yourself” http://bbs.hcbbs.com/thread-1254625-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (3) – “Enrich yourself” http://bbs.hcbbs.com/thread-1253809-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (2) Structural diagram of centrifugal pumps – “Enrich yourself” http://bbs.hcbbs.com/thread-1253590-1-1.html Special lecture on rotating equipment: “Pumps”. Learn something new every day! (1) Selection of pumps – “Enrich yourself” These are the posts in my special series. I will continue to update them daily. Please show your support by reading, listening, and participating in the discussions! ； If there’s any direction that needs to be explained, feel free to contact me. If many people ask for it, I’ll create a separate post to go over it~~! Welcome everyone to listen. I have started broadcasting, and I hope those who, like me, want to gain knowledge every day will listen. Let’s learn together every day and discuss~~!