1、 Press Screw pump Number of inner screws

Although this classification is identified by the surface characteristics of the pump, it has become the most important classification method because its characteristics in the use field directly reflect the important characteristics of the pump. It is generally divided into single screw pump, twin screw pump Three screw pump And five screw pumps. At present, the four screw pumps that are produced and used less generally are not listed as a separate category, but are attached to the three screw pumps with the same screw surface profile according to the type of screw surface profile, as a derivative product of three screw pumps. However, if a four screw pump is formed by a spiral surface profile different from that of a three screw pump, the author believes that under the condition of the same volume, its flow is not as large as that of a five screw pump, and it has no other advantages, so it has no value for existence.

2、 Divided according to the airtight condition of the spiral groove space formed when the screw is engaged in the pump

Generally, it is divided into sealed screw pump and non sealed screw pump.

(1) Sealed screw pump

It is the spiral groove space (this space is called the sealing chamber) formed by the meshing lines of the screw helical segments when they mesh with each other in the hole of the screw bushing. Theoretically, the suction chamber and discharge chamber of the pump can be completely separated. This kind of screw pump is called a sealed screw pump. For example, Allweiler single screw pump, Allweiler triple screw pump and some types of twin-screw pump.

(2) Unsealed screw pump

That is to say, in theory, the above-mentioned sealing chamber cannot completely separate the suction chamber and discharge chamber of the pump. When the pump is running, the medium can partially flow back to the suction chamber from the discharge chamber through the non meshing line of the sealing chamber. For example, most twin screw pumps and five screw pumps.

It should be pointed out that even the theoretically sealed screw pump's sealing chamber is not completely sealed in practice, because if the pump wants to operate normally, it must also consider the existence of reasonable space and the space caused by the processing size error, etc., through which the medium leaks back to the suction chamber from the discharge chamber. As for the sealed screw pump, such leakage is very small, so the volume power η v of the ratio of practical flow to theoretical flow is very high. The classification of Allweiler screw pump is the same as that of KSB screw pump.

At the same time, there are two different views on this classification:

Former Soviet Union Н Г. ∨еновак and others think that: the gear formed by the screw helices of the sealed screw which mesh with each other shall comply with the gear meshing rules; The gears of the helical surfaces of the non sealed screw pumps that mesh with each other do not follow the rules of gear engagement, so the transmission of torque from the driving screw to the driven screw must rely on synchronous gears.

Obviously, this classification criterion does not involve whether the seal chamber can separate the suction chamber and the discharge chamber completely in theory, but is based on whether the constituent gear complies with the gear meshing rules. They admit that most of the screw pumps whose components comply with the gear meshing rules cannot theoretically separate the discharge chamber from the suction chamber by the screw spiral meshing line. Without considering the necessary cooperation space and other conditions, their seal cavities have appropriate areas without engagement lines, that is, the contact lines of the screw helices engaged with each other along the engagement parts are not connected, so that the medium leaks back to the suction cavity from the discharge cavity through the continuous area of the engagement lines. It can be seen that there is an inexplicable contradiction in this classification - the sealed screw pump is a pump with unsealed sealing cavity. The author thinks that Н The classification criteria of Г. женовак, etc. should be more appropriate according to whether the screw pump complies with the gear meshing rules or not.

The author thinks that although some screw pumps with cycloid involute combination screw helical surfaces have a pair of common tooth profiles, which conform to the gear meshing rules, as long as the sealing cavity cannot be completely sealed in theory, they should be classified as unsealed screw pumps together with those screw pumps whose tooth profiles do not conform to the gear meshing rules. This type of screw pump has a larger leakage than the sealed screw pump, and its volume power is relatively low. It is generally suitable for working conditions with lower discharge pressure, not for working conditions with higher pressure.

In addition, the screw pump is also classified into low-pressure pump, medium pressure pump and high-pressure pump according to the outlet pressure; According to bearing orientation, pumps are divided into built-in bearing pumps and external bearing pumps; It can be divided into single suction pump and double suction pump according to the way of suction medium entering the pump; It can be divided into horizontal pump, vertical pump, suspension pump and immersion pump according to the device orientation; It can be divided into lubricating oil pump, fuel pump, hydraulic pump, oil transfer pump, food pump, chemical pump, cargo pump, sewage pump and scavenge pump according to the use; It is even classified by whether the pump is heated or cooled. These are secondary to identifying pump characteristics. There are also Archimedes screw pumps, hyperbola screw pumps and hypocycloid screw pumps, which are seldom produced and used and will not be discussed.

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