Three screw pump structure and working principle: Screw pump is the use of screw rotation to suction and discharge liquid. The middle of the screw for the active screw, driven by the prime mover rotation, the screw on both sides of the driven screw, with the active screw for reverse rotation. 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. 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.