The rotation by means of a screw pump to suction the liquid, it is most suitable for suction viscous liquid.

1 basic working principle of screw pump

Screw pump is the use of screw rotation to absorb liquid. Figure three shows a cross-sectional view of the 1 screw pump. In the picture, the middle screw is the active screw, which is driven by the prime mover, the screw is driven by the screw, and the screw is rotated in the reverse direction. The main and driven screw threads are stud.

As the mutual engagement of the screw and the close cooperation between the screw and the inner wall of the cylinder liner, the suction port and the discharge port are separated into one or more sealing space. With the rotation of the screw and the engagement, these sealed space in the pump suction side are evolving, the suction chamber in which liquid enclosure, and from the inhalation chamber along the axial direction of the screw continuous passage to the discharge end, will be closed in the space of liquid discharged continuously, like a nut in screw rotation is constantly moving forward the case, this is screw pump of the basic working principle.

The sealing surface between the screw and the shell is a space surface. There are non sealing areas such as AB or de on this surface, and a plurality of triangular gap ABC and def are formed in the groove of the screw. The gap of these triangles constitutes a liquid channel, which makes the active screw groove B is connected with the groove A and C on the driven screw. The groove B, C and along the spiral wound to his back, and D, respectively and the groove on the back of the E connected. Due to the slot D, e and slot f (it belongs to the other end of the spiral) connected to the sealing surface, there are similar to the front of the triangular gap of a 'B' C ', so D, F, e will be connected. In this way, groove ABCDEA also constituted a "robust" shaped seal space (such as the use of single thread, the groove will be along the axial direction disc Rao screw, the suction outlet through, unable to form a tight seal. Is not difficult to imagine, in such a screw, will form many independent "infinity" shaped sealed space, each a sealed space occupied by the axial length of is exactly equal to the tired rod guide t. Therefore, in order to make the screw can suck the oil port, the length of the screw is at least more than one lead.

From the working principle can be seen, the screw pump has the following advantages:

1) pressure and flow range. The pressure of about 3.4-340 in the /cm2, the flow of up to 18600cm3/;

2) the type and viscosity of the liquid are wide;

3) because of the low inertia of the rotary parts of the pump, it can be used very high speed;

4) good suction performance, has the ability of self absorption;

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

6) compared with other rotary pump, the gas and dirt entering is not sensitive to the;

7) a solid structure, easy installation and maintenance.

The disadvantage of the screw pump, screw machining and assembly requirements are higher; pump performance of the liquid viscosity change is more sensitive.

Three 2 screw pump structure

It is mainly composed of a fixed the bushing in the pump body, pump cylinder) and placed in the pump cylinder screw, and with the active engagement of the two driven screw up. The three mutually engaged screw, in the pump cylinder to form as a sealing cavity, resulting in the sealing between the suction line.

When the pump is working, because the two driven screw and the active screw are symmetrical, so the radial force on the active screw is completely balanced, the active screw is not subjected to bending load. Driven by the radial force of the screw along its entire length by the pump cylinder bushing to support, therefore, do not need to set up the outer side of the other side of the bearing, basically do not withstand bending load. In operation, a layer of oil film is formed between the outer surface of the screw and the inner wall of the pump cylinder, which can prevent the direct contact between the metal.

When the screw pump works, the two ends of the suction pressure of the liquid, so the screw to produce axial thrust. For the pressure difference of less than 10 kg of force /cm2 of the small pump, can be used thrust bearing. In addition, but also through the initiative of the central screw hole for oil pressure oil into the bottom of the screw sleeve, and create a and axial thrust direction opposite thrust balance in the lower end of the screw.

The screw pump and the other volume pump, when the pump outlet is completely closed, the pump pressure will rise to the pump damage or the risk of motor overload. So, in the suction line of the pump, it is necessary to set up the safety valve.

The seal of screw pump, mechanical seal generally, and can take different forms according to the level of work stress.

3 screw pump performance

3.1 displacement

The theoretical displacement of the screw pump can be calculated by the following formula:

Qt=60Ftnm3/h

Type: F - pump cylinder effective cross-sectional area, cm2; t - lead screw, m; RPM n active screw.

Internal leakage of screw pump Qs:

Alpha sigma m p/ Qs=

Type: P - pump working pressure;