1. The concept of single screw pump Single screw pump is a new type of internal rotary reciprocating positive displacement pump. The main working parts are eccentric screw (rotor) and fixed bushings (stator). Compared with other pumps, the advantages of single-screw pump Compared with the centrifugal pump, single-screw pump does not require valves installed, and flow is a stable linear flow. Compared with the plunger pump, single screw pump has better self-suction capacity. Compared with the diaphragm pump, single screw pump can convey a variety of mixed impurities, containing gas and solid particles or fibers of the medium, but also convey a variety of corrosive substances. Compared with the gear pump, single screw pump can deliver high viscosity substances. Unlike plunger pumps, diaphragm pumps and gear pumps, single-screw pumps can be used for filling and metering medications. 1 screw pump basic working principle 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. Due to the mutual engagement of the screws and the close cooperation of the screw with the inner wall of the liner, one or more sealed spaces are separated between the suction and discharge of the pump. As the screw is rotated and engaged, these sealed spaces are constantly formed at the suction side of the pump, sealing the liquid in the suction chamber therein and continuously displacing in the axial direction of the screw from the suction chamber to the discharge end to be closed in the respective 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. 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.