What is a screw pump?

What kind of pump does screw pump belong to? What are the advantages?

What kind of pump does screw pump belong to? Screw pump is a volumetric rotor pump, which relies on the volume change of the sealing chamber formed by screw and bushing to inhale and discharge liquid. Although the family of screw pumps is not so large, according to screw standards, it can also be divided into different types. This paper mainly introduces the most commonly used single screw pump, twin screw pump and three screw pump. Let’s look at it in detail.

Single screw pump is a new type of rotary volume pump with internal engagement. The main working parts are eccentric screw (rotor) and fixed bushing (stator).

Compared with other pumps, single screw pump has its own unique advantages:

Compared with centrifugal pump, single screw pump does not need to install valves, but the flow rate is stable linear flow.
Compared with plunger pump, single screw pump has better self-priming ability.
Compared with diaphragm pump, single screw pump can transport various mixed impurities, media containing gas and solid particles or fibers, as well as corrosive substances.
Compared with gear pump, single screw pump can transport high viscosity material.
Unlike plunger pumps, diaphragm pumps and gear pumps, single screw pumps can be used for filling and measuring agents.

What is a screw pump

twin-screw pump of characteristics

In terms of structure, twin-screw pump is an external meshing screw pump. It uses two screw rods that engage each other and do not touch each other to pump liquid.

Twin-screw pumps are also complete in structure type, including horizontal, vertical, with heating sleeve and other types, which can transport low or high viscosity medium with particles, adjust screw spacing according to particle size, select the right material, and even transport many corrosive media.

Features: As a volumetric pump, the suction chamber in the pump should be tightly separated from the discharge chamber. This requires that the pump body and screw cylindrical surface, screw and screw clearance should be as small as possible. At the same time, the screw and the pump body, screw and screw form a sealing chamber with each other to ensure the sealing, otherwise the liquid may flow back from the gap.

The unique structure of twin-screw pump makes it possible to transport all kinds of media without stirring, pulsation and stability. Because the pump body structure guarantees that there are always pumping liquids as sealing liquids in the working components of the pump, the twin-screw pump has strong self-priming ability and can be mixed with vapor and liquid. The special design of twin-screw pump also ensures that the pump has a high suction performance, i.e. a very small NPSHr value.

Twin-screw pump can be divided into two forms: internal bearing and external bearing.

The bearing is lubricated by the conveyor in the structure of the built-in bearing. The twin-screw pump with external bearing structure is separated from the bearing by the working chamber.

Characteristics of external bearing twin screw pump: There is side clearance between the structure and screw of this pump. Independent lubricated external bearing allows it to transport various non-lubricating media. In addition, the synchronous gear is adjusted so that the screw does not contact, and half of the output torque is transferred to the driven screw.

Like all screw pumps, external bearing twin-screw pumps also have self-priming ability, and most of the pump transport components are double-suction symmetrical layout, which can eliminate the axial force, but also has a large suction.

The advantages of external bearing double screw pump structure greatly broaden the application scope of twin screw pump, that is, besides conveying lubricating medium, it can also convey a large number of non-lubricating medium, medium of various viscosity (maximum viscosity can reach 3*106 mm/s), corrosive (acid, alkali, etc.) and abrasive liquid.

In addition, the twin-screw pump belongs to the non-sealed volume pump because of its constant clearance and the characteristics of the profile. Therefore, besides conveying pure liquid, it can also convey the mixture of gas and liquid, that is, vapor-liquid mixed transportation, which is also one of the unique advantages of the twin-screw pump.

Twin-screw pump can also run dry: because the moving parts do not contact each other when working, so short-term rotation will not destroy the pump components, this feature provides great convenience for the automatic control process, but the dry operation time is limited by many factors, generally very short.
In addition, the twin-screw pump has no shearing and emulsifying effect in the transportation process, so it will not destroy the specific fluid properties formed in the molecular chain structure and working process, and because the transmission depends on synchronous gears, the pump runs with low noise, low vibration and stable operation.

Application: External bearing twin screw pump has been widely used in oil field chemical industry and shipbuilding industry due to its various characteristics. It can also be made of ordinary cast iron, stainless steel and other different materials according to various usage conditions; the conveying temperature can reach 250 C; and it has different heating structures, and the theoretical flow rate can reach 2000 cubic meters per hour.

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