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Screw pump is a single screw type transport pump, its main working parts are the screw (called rotor) of eccentric helix and the screw bushing (called stator) with double spiral surface on the inner surface. The principle of the work is that when the motor drives the pump shaft, the screw rotates around its axis on the one hand, and on the other hand it rolls along the inner surface of the bushing, thus forming the seal chamber of the pump. When the screw is rotated for one week, the liquid in the sealed cavity advances a pitch, and with the continuous rotation of the screw, the liquid spiral form is pressed from one sealing cavity to another, and the pump body is squeezed out. Screw pump is a new type of machine for conveying liquid. It has the advantages of simple structure, safe and reliable work, convenient maintenance, continuous and uniform fluid, stable pressure and so on.

A pump that uses the rotation of the screw to suck out the liquid is most suitable for suction and drainage of viscous liquids.

The basic working principle of the 1. screw pump

The screw pump uses the rotation of the screw to suck out the liquid. Figure 1 shows a sectional view of the three screw pump. In the picture, the middle screw is the active screw, driven by the prime mover, the screw on both sides is driven screw, and the screw is rotated with the active screw. The threads of the main and driven screw are both double headed.

Because of the intermeshing of each screw and the close coordination of the screw and the inner wall of the liner, it will be separated into one or more sealing spaces between the suction port and the discharge port of the pump. With the rotation and meshing of the screw, these airtight spaces are constantly formed at the suction end of the pump, sealing the liquid in the suction chamber into it and moving from the suction chamber along the screw axis continuously to the discharge end, and the fluid closed in the space is continuously discharged, as if a nut was continuously pushed forward when the screw was whorled. Like, this is the basic principle of the screw pump.

The sealing surface between the screw and the shell is a spatial surface. There are non sealing areas such as AB or de on the surface, and many triangular notches ABC and def are formed with the groove part of the screw. These triangular gaps form a liquid passage, so that the active screw groove A is connected with the groove B and C on the driven screw. The grooves B and C are connected to their back along their spiral, and are connected with the groove D and E on the back respectively. Since the groove D, E and the slot F (which belong to the other spiral), there are also a triangle gap similar to the front, a 'B' C ', so that D, F, and E will also be interlinked. In this way, the groove ABCDEA also makes up a "infinity" type of sealing space (such as a single head thread, then the groove will screw the axial disc, through the suction hole through, can not form a seal). It is not difficult to imagine that on such a screw, many independent "infinity" sealed spaces will be formed, and the axial length of each sealed space is exactly equal to the guide t of the tired rod. Therefore, in order to separate the screw from the suction and the oil outlet, the thread length of the screw is at least more than one lead.

From the above work principle, we can see that the screw pump has the following advantages:

1) wide range of pressure and flow. The pressure is about 3.4-340 kilogram force /cm2, and the flow rate can reach 18600cm3/.

2) the type and viscosity range of the liquid is wide;

3) because the inertia force of the rotary parts in the pump is low, it can use very high speed.

4) the inhalation performance is good, and it has the ability of self - priming.

5) the flow is uniform and continuous, the vibration is small, and the noise is low.

6) compared with other rotary pumps, it is not very sensitive to gas and dirt.

7) the structure is solid, and the installation and maintenance is easy.

The disadvantage of screw pump is that the screw processing and assembly requirements are high; the performance of the pump is sensitive to the viscosity change of the liquid.

The structure of 2 three screw pump

The utility model is mainly composed of a bushing (pump cylinder) fixed in the pump body, an active screw inserted in the pump cylinder and two driven screws which are engaged with the pump. The three interlocking screws are formed into a sealing cavity in each cylinder according to each lead, resulting in sealing between the suction ports.

When the pump works, the two driven screw and the active screw are symmetrical meshing, so the radial force on the active screw is completely balanced, and the active screw does not bear the bending load. The radial force of the driven screw is supported along the whole length of the pump cylinder liner. Therefore, there is no need to set up the bearing at the outer end, and it does not bear the bending load basically. In operation, a layer of oil film formed between the outer surface of the screw and the inner wall of the pump cylinder prevents direct contact between metals and greatly reduces the wear of the tooth surface of the screw.

When the screw pump works, the two ends act on the suction and discharge pressure of the liquid respectively, so the axial thrust is required for the screw. For small pumps with a pressure difference of less than 10 kg /cm2, thrust bearings can be used. In addition, the high pressure oil is introduced into the bottom of the screw sleeve by the central oil hole of the active screw, so a balance thrust opposite to the axial thrust is produced at the bottom of the screw.

The screw pump, like other volume pumps, when the outlet of the pump is completely closed, the pressure in the pump will rise to the risk of damage to the pump or the overload of the motor. Therefore, at the suction and discharge port of the pump, a safety valve must be installed.

The shaft seal of screw pump usually adopts mechanical shaft seal, and it can take different forms according to the working pressure.

Performance of 3 screw pump

3.1 displacement

The theoretical displacement of the screw pump can be calculated by the next type.

Qt=60Ftnm3/h

Type: F - effective section area of pump cylinder, cm2, T - screw thread lead, m, N - Main