Screw pump basic working principle and structure

Screw pump is the use of screw rotation to suction and discharge liquid. Figure 1 shows a cross-sectional view of a three-screw pump. In the picture, the middle screw is the active screw which is driven by the prime mover. The screw on both sides is the driven screw, which rotates reversely with the active screw. The main, driven screw thread are double-headed thread. Screw pump due to the mutual engagement of the screw and screw with the inner wall of the liner in close cooperation between the suction and discharge of the pump will be separated into one or more sealed space. As the screw is rotated and engaged, these sealed spaces are constantly formed at the suction side of the pump, the liquid in the suction chamber is enclosed therein and continuously displaced in the axial direction of the screw from the suction chamber to the discharge end, to be enclosed in the spaces Continued discharge of liquid, like a nut in the screw rotation is constantly moving forward, as the case, which is the basic working principle of the screw pump. Screw pump principle The sealing surface between the screw and the housing is a curved surface. There are unsealed areas such as ab or de on this surface and a number of triangular notches abc, def with the groove portion of the screw. The notches of these triangles form a passage for the liquid, allowing the drive screw groove A to communicate with the grooves B, C in the driven screw. The grooves B, C, along with their spiral around the back, respectively, and the back of the grooves D, E communicated. Since there are also triangular notches a'b'c 'similar to the front face on the sealing surfaces where the grooves D, E engage with the groove F (which belongs to the other thread), D, F, E will also communicate. In this way, the groove ABCDEA also form a "∞" -shaped sealing space (such as the use of single-head thread, the groove will be along the axial disk Rao screw, the suction port through, can not form a seal). Not hard to imagine, in such a screw, will form a number of independent "∞" -shaped sealed space, each sealed space occupies the axial length exactly equal to the lead of the tired rod t. Therefore, in order to make the suction and discharge of the screw, the length of the screw thread should be longer than one lead. As can be seen from the above working principle, screw pump has the following advantages: 1) wide pressure and flow range. A pressure of about 3.4-340 kgf / cm 2, a flow rate of up to 18,600 cm 3 / min; 2) a wide range of fluid types and viscosities to be transported; and 3) a high rotational speed ; 4) good suction performance, self-priming capability; 5) uniform flow rate, low 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. 2 three screw pump structure It is mainly composed of a bushing (pump cylinder) fixed in the pump body and an active screw inserted in the pump cylinder and two driven screws engaged therewith. Three intermeshing screws, in the pump cylinder by each lead to form a sealed chamber, resulting in suction and discharge between the seal. Screw pump structure Pump work, due to the two driven screw and the symmetrical symmetry of the active screw, so the role of the active screw on the radial force 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.

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