The three-screw pump is mainly composed of a bushing (pump cylinder) fixed in the pump body, an active screw rod inserted in the pump cylinder and two driven screws which are engaged with the screw rod pump. Three intermeshing screws, in the pump cylinder by each lead to form a sealed chamber, resulting in suction and discharge between the seal. Pump work, due to the two driven screw symmetrical with the active screw meshing, so the role of the radial force on the active screw completely balanced, the active screw does not bear the bending load. The radial force exerted by the follower screw is supported by the pump cylinder bushing along its entire length. Therefore, it is not necessary to provide a separate bearing on the outer end and substantially not to bear the bending load. In operation, a layer of oil film formed between the outer surface of the screw and the inner wall of the pump cylinder can prevent the direct contact between the metal and greatly reduce the wear of the screw tooth surface. Screw pump work, both ends of the role of the liquid suction pressure, so the screw to produce axial thrust. For small pumps with differential pressure less than 10 kgf / cm2, thrust bearings can be used. In addition, high pressure oil is introduced into the bottom of each screw sleeve through the center bore of the active screw to create a balanced thrust at the lower end of the screw that is counter to axial thrust. Screw Pump Like other positive displacement pumps, when the pump outlet is completely closed, the pressure inside the pump rises to the point of damaging the pump or overloading the motor. Therefore, the suction pump outlet, you must set the safety valve. Screw pump shaft seals, usually mechanical shaft seal, and can work in accordance with the level of pressure to take different forms. Three screw pump features: 1. Three screw pump uniform flow is proportional to the number of teeth, and proportional to the square of the modulus. Small size, light weight, simple structure, easy to manufacture, low price, reliable work, good self-priming performance, insensitive to oil contamination, convenient maintenance and so on. 2.Three screw pump flow is proportional to the tooth width, but the increase of tooth width is limited by the increased hydraulic radial force of the gear, usually taken tooth width B [6-10] meters, high pressure to take a small value. In addition, the volumetric pump, the three screw pump flow pulsation maximum. 3. Progressive speed can improve the pump flow, but limited by the pump inhalation function. Gear pump speed is generally 1000 ~ 1500. Screw pump shaft seals, usually mechanical shaft seal, and can work in accordance with the level of pressure to take different forms. Screw pump has the following advantages: 1, a wide range of pressure and flow. Pressure of about 3.4-340 kgf / cm 2, flow rate of up to 18600cm3 / min; 2) the type and viscosity of a wide range of liquid transport; 3, because the rotary inertia force within the pump is low, it can use high speed ; 4, good inhalation performance, self-priming capability; 5, continuous flow, small vibration, low noise; 6, compared with other rotary pumps, the gas and dirt into the less sensitive; 7, solid structure, installation Easy to maintain. The disadvantage of the screw pump is that the screw machining and assembly requirements are higher; the performance of the pump is sensitive to changes in the viscosity of the liquid.
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