With the development of the chemical industry and the improvement of people's awareness of the environment and safety, the requirements for chemical pumps are getting higher and higher. In some occasions, absolutely no leakage is required for certain pumps. This demand has promoted the development of shielded pump technology development of. Shielded pumps because there is no shaft seal, you can do absolutely no leakage, and therefore the use of chemical devices has become increasingly common. Principle and structural characteristics of a shielded pump Ordinary centrifugal pump drive is through the coupling of the pump impeller shaft and the electric shaft connected to the impeller and the motor together to rotate and work, and the shield pump is a non-sealed pump, pump and The drive motor is sealed in a plenum filled with a pumped medium. The pressure vessel is only hermetically sealed, and a wire set provides the rotating field and drives the rotor. This kind of structure has canceled the rotary shaft sealing device that the traditional centrifugal pump has, therefore can be completely leakless. Shield pump to pump and motor together, the motor rotor and pump impeller fixed on the same axis, the shield sleeve motor will be separated from the stator and rotor, the rotor is transported medium, the power through the stator field Pass to the rotor. In addition, the shield pump manufacturing is not complicated, the hydraulic end of the centrifugal pump can be used in accordance with the structure type and the relevant standard specifications to design and manufacture. 2 shielded pump advantages and disadvantages 2.1 shielded pump advantages (1) fully enclosed. There is no dynamic seal on the structure, there is a static seal at the pump housing, so it is completely leak-free and is especially suitable for the transport of flammable, explosive, valuable liquids and toxic, corrosive and radioactive liquids. (2) high safety. Rotor and stator each have a shield sleeve so that the motor rotor and stator is not in contact with the material, even if the shield sleeve rupture, it will not produce the risk of external leakage. (3) Compact footprint. Pump and motor system as a whole, disassembly do not need to find the center. Low requirements on the base and the foundation, and the daily maintenance workload, low maintenance costs. (4) smooth operation, low noise, without lubricating oil. Because there is no rolling bearing and motor fan, so no need to add lubricating oil, and low noise. (5) a wide range of use. High temperature, high pressure, low temperature, high melting point and other conditions can meet the requirements. 2.2 The shortcomings of shielded pumps (1) As the shielded pump with sliding bearings, and with the media to be transported lubrication, so poor lubrication of the media should not be shielded pump delivery. Generally suitable for shielding the viscosity of the pump medium is 0.1 ~ 20mPa.s. (2) Shielded pump efficiency is usually lower than the single-end mechanical seal centrifugal pump, and double-sided mechanical seal centrifugal pump roughly the same. (3) For a long period of time, operating at a low flow rate, shielding pump efficiency is low, will lead to heat, liquid evaporation, resulting in dry pump rotation, thus damaging the sliding bearing. 3 shielded pump type and scope of application According to the temperature, pressure, viscosity and particles with or without particles, shielding pump can be divided into the following categories: (1) the basic type of conveying medium temperature does not exceed 120 ℃, lift less than 150m . Various other types of shielding pumps can be based on the basic type, through the modification and improvement. (2) Reverse Circulation In this type of shielded pump, the direction of liquid flow to the bearing lubrication, cooling, and cooling of the motor is exactly opposite to the basic one. Its main feature is not easy to produce cavitation, especially for easy vaporization of liquid transport, such as liquefied petroleum gas, chloroform and so on. (3) High temperature type General conveying medium temperature up to 350 ℃, the maximum flow 300m3 / h, head up to 115m, suitable for hot medium oil and hot water and other high temperature liquid. (4) high melting point pump and motor with a jacket, can greatly improve the motor heat resistance. For high melting point liquid temperature up to 250 ℃. Jacket can pass steam or a certain temperature of the liquid, to prevent the crystallization of high melting point liquid. (5) High-pressure high-pressure shielded pump shell is a high-pressure vessel, the pump can withstand high system pressure. In order to support the shield under internal high pressure, the stator coil can be used to withstand the pressure. (6) When the self-priming suction tube is not filled with liquid, the pump drains liquid by means of automatic suction to adapt to extracting liquid from the underground container. (7) Multi-stage type equipped with multiple impeller, suitable for high-lift fluid delivery, the highest lift up to 400m. (8) Mud type is suitable for transporting liquids mixed with a large amount of mud. 4 shielded pump selection precautions General shielded pump using the transport part of the liquid to cool the motor, and the annular gap is small, so the liquid must be clean. For conveying a variety of liquid mixtures, if they produce precipitation, coking or jelly, then the selection of shielding pump (non-mud type) may block the shielding gap, affecting the pump cooling and lubrication, resulting in burning graphite bearings and motors. Shielded pumps are generally circulating cooling pipe, when the ambient temperature is lower than the freezing point of the liquid pumped, the anti-freezing measures should be used with the accompanying pipe to ensure easy start-up pump. In addition, the shield pump should strictly comply with the opening sequence of the outlet valve and inlet valve at start-up. When the pump is stopped, the outlet valve should be closed first. When the pump operation is stopped, the inlet valve is closed and the outlet valve is closed. In short, the use of shielded pump, completely leak-free, effectively avoiding environmental pollution and material loss, as long as the correct selection, the operating conditions did not abnormal changes in normal operation, almost no maintenance workload. Shielded pump is the ideal pump to transport flammable, explosive, corrosive and valuable liquid.
