Screw pump The operating principle of the screw and the medium transported can be regarded as the relative movement of the screw and the nut, if we take a visual analogy. When the screw rolls, if the constraint screw cannot move axially, the nut will move axially along the screw. The screw mentioned here can be regarded as the screw that rotates in the screw pump, and the medium filled with the spiral groove is a liquid nut. However, the simple tissue made according to the above principle cannot actually transport the medium, because the discharge chamber of the pump is connected to the inlet chamber. Taking the Allweiler screw pump as an example, if you want to lift the medium from the input chamber to the discharge chamber, you must block the discharge chamber and the suction chamber, The spiral groove space formed by the engagement of the screw helicoids in the hole of the screw bushing can effectively separate the discharge chamber and the suction chamber of the pump, and the touch line (i.e. the engagement line) between the screw helicoids engaged with each other plays the role of separation. This sealing chamber actually acts like a valve in a reciprocating pump. In this way, when the screw rotates, the liquid nut (the medium in the sealing chamber) can move in a straight line from the suction chamber to the discharge chamber along the axial direction with the sealing chamber, effectively discharging the medium out of the pump.

The reason why the word "useful" should be emphasized here is that, as mentioned above, in fact, the sealing chamber cannot be completely sealed, and there will always be some media leaking back from the discharge chamber to the suction chamber. Obviously, the work done by the pump has meaning only when the leaked medium is relatively small. The less the leaked medium, the higher the pump's volume power η v, so the volume power η v is an extremely important target to measure the function of the screw pump. Each product of Allweiler pump has a corresponding power curve.

In theory, the sealing chamber of certain types of screw pump cannot completely separate the discharge chamber and suction chamber of the pump, but only within a certain speed and discharge pressure range. When transporting a certain medium, the screw pump can work well and still have relatively high volume power, so this kind of screw pump still has the value of existence. This is the theoretical basis of many kinds of unsealed screw pumps. The reason why new types of screw pumps are constantly emerging is that people can develop screw pumps based on this theory, which are composed of different screw numbers, different screw head numbers and various profiles or spiral surfaces combined with various profiles. When the sealing cavities with different spatial shapes formed by meshing in the screw bushing holes, even though the discharge cavity and suction cavity cannot be separated completely in theory, that is, they cannot be completely sealed, as long as they can operate normally when transporting certain media within a certain range of functional parameters and reach a certain volume power, such screw pumps have practical value and can exist. It can be seen that the core technology of the screw pump is to form the profile of the screw helicoid, that is, the tooth profile curve of the helicoid. It is the appearance of various new types of screw pumps that has expanded the use range of screw pumps. Screw pumps have become a new type of industrial pumps widely used.

The operating principle of Allweiler screw pump is the same as that of KSB screw pump

According to the above, the operating principle of the pump can be described as follows: when the screw of the screw pump is driven by an external power source to rotate, the suction end of the screw spiral groove periodically turns over, and the volume V of the suction chamber gradually increases to V+△ V due to the turning over of the spiral groove. According to Boyle Mallett rule, the pressure p of suction chamber will be reduced to:

Ps=P's (V/Va+△ V) where P's - pressure in the suction chamber before the spiral groove is opened.

That is to say, because of the rotation of the screw, a vacuum is formed in the suction chamber, resulting in a pressure difference between the pressure on the surface of the medium and the pressure Ps in the suction chamber. Under the effect of pressure at the inlet end of the pump, the medium flows into the suction chamber that forms vacuum, and then fills the spiral groove formed by the meshing of screw helices in the screw bushing hole, that is, it enters the turned over sealing chamber at one end of the suction chamber. Then, with the rotation of the screw, the turned over sealing chamber is closed by the screw protruding part of the meshing screw, and the medium entering the sealing chamber separating the suction chamber and discharge chamber moves along the screw axis to the discharge chamber and is discharged directly out of the pump.

It should be noted that the structure of some screw pumps does not have a screw bushing, which is integrated with the pump body, and the sealing chamber is composed of a hole in the pump body that contains the screw helical segment.

If the screw pump wants to operate normally, it must make the screws that mesh with each other rotate synchronously. As for the tooth profile formed by a pair of helicoids of automatic screw and driven screw, if the tooth profile of its cross section obeys the meshing rules of gears, the automatic screw can transfer rolling to the driven screw, and it does not need to complete synchronous rotation with the help of special transmission gears and other parts; As for the non sealed screw pump, which is not subject to the gear engagement rules in terms of the formation of the screw surface, the automatic screw must pass through another part, such as the synchronous gear, to transmit torque to the driven screw and complete synchronous rotation.

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