I Screw pump Features of

As a whole, the screw pump has the advantages of stable medium delivery, low turbulence of discharged medium, weak pressure pulsation, low mechanical vibration, low noise, self-priming function, good suction function, high speed operation ability, insensitive to medium viscosity, simple and compact structure, small size, light weight, high efficiency, reliable operation Long life and convenient operation and maintenance. Therefore, the screw pump has a very wide range of applications. Considering all kinds of screw pumps, its ability to transport all kinds of media is better than that of all other pumps. As for different types of screw pumps, their characteristics and scale of use are different.

For the transportation of media that may damage the ecological environment, the magnetic drive seal structure (magnetic pump) can be selected for the pump to improve the reliability of the unit and expand the use scale.

The pressure of the screw pump increases from the pressure in the suction chamber to the pressure in the discharge chamber through the sealing chambers at all levels, which is gradually established. The pressure setting is slow. In addition to the advantages of low pulse, the sound pressure level is also very low, and it has the advantages of ensuring that the transport medium is intact and will not age rapidly. In theory, the screw pump has no pulse, because each rotation angle discharges the same volume of flow. In fact, there are still some pulses because of processing errors, gaps, and operation lengths that are not integral multiples of the seal cavity. But its discharge pressure pulse is far less than other types of pumps. Pressure pulse will cause vibration of the whole equipment, which is a very important reason for noise increase. Therefore, the important characteristic of small pressure pulse also makes it superior to many types of pumps, so it is preferred in hydraulic systems.

Screw pump has little hydraulic loss due to lack of valve, small pulse and other reasons, so it is generally combined with the loss of mechanical friction and is not accounted for separately.

2、 Use scale of screw pump

Because the medium viscosity has a great impact on the useful power, flow, suction height and other functions of the screw pump, our national standard sets the functional parameter of the screw pump as the medium viscosity is 7.5 × 10-5m2/s.

The scale of functional parameters and application occasions in Table 1 and Table 2 only refer to the general situation of a certain type of screw pump, not all kinds of screw pumps. The function parameter value is not certain. As shown in Table 1, the maximum discharge pressure of twin screw pump is 8 (20) MPa, which means О.А.Пыж It is called B-type twin screw pump, while the maximum discharge pressure of A-type twin screw pump is only 1.6MPa.

Table 1: General functional parameter scale of screw pump

Type of pump Single screw pump Twin screw pump Three screw pump Five screw pump

Maximum flow (m2/h) 300 (submersible 570) 3400 450 900

Maximum discharge pressure MPa 2.4 8 25 1.2

Maximum kinematic viscosity of medium mm2/s 4.62 × 106 4.62 × 105 4.62 × 104 1.5 × 104 

The maximum flow rate of 3400m3/h in Table 1 refers to the current situation. It is a symmetrical cycloidal combined helicoid, which we call the omega twin screw pump. In this case, its discharge pressure is low. If necessary, products with larger flow can be developed; The maximum discharge pressure of this type of twin-screw pump is 8MPa or even higher under certain media, certain flow values and certain structures. The gas-liquid mixed transportation in Table 2 is only suitable for omega twin screw pumps, and other types of twin screw pumps cannot be used for gas-liquid mixed transportation. Similarly, non lubricating liquid is only applicable to Ω and "square tooth" twin screw pumps. Although the three screw pump in Table 1 can be in the high-pressure category, because its axial force balance is difficult, it is only applicable to small flow conditions; Although the triple screw pump can choose the double suction structure when the flow is large, the axial force is actively balanced, and the length of the screw is constrained by various factors such as deflection and strength, so it can only be used in low-pressure conditions. Considering the product dimensions and other factors, the large flow three screw pump with a flow rate of more than 200m3/h is rarely used. At a certain speed, the maximum flow of the three screw pump will be constrained, so it is not suitable to be planned as a pump with large flow. As shown in Table 2, the general use of the three screw pump only refers to the clean liquid with lubricity and low lubricity. In fact, after certain measures have been taken in terms of structure and materials, it is also used to transport asphalt containing impurities, but its discharge pressure is very low and its life is short. With the development of science and technology, the successful research of new special raw materials and other factors, the three screw pump that can transport clean water, sea water and other low viscosity non lubrication has also been successfully developed abroad. Although its volumetric efficiency drops rapidly when the discharge pressure increases, it can only be used in the working condition of low discharge pressure, has a short service life, and is rarely used in practice, But this is a breakthrough effect after all. Therefore, the situations listed in Table 1 and Table 2 are only those in general use now.

It should be pointed out that the scope of use of the pump is not consistent with the actual use value. For example, in terms of performance, three screw pump is superior to Gear pump Many professionals have predicted that the three screw pump will replace the gear pump in the 1970s. But today, gear pump is still widely used. Although three screw pumps have been basically used to eliminate gear pumps in China, such as the lubricating oil and fuel system of ships, the tertiary oil recovery technology of oil fields and the lubrication equipment industry, it is only a partial situation after all. The reason is that the price of gear pump is far lower than that of three screw pump, and the overall dimension is smaller. Therefore, gear pumps are still widely used in applications where the requirements for flow, pressure fluctuation and noise are not high. For asphalt transportation, twin screw pump is obviously superior to three screw pump, and its service life is much longer; However, because the price of the three screw pump is lower than that of the twin screw pump, most of the asphalt transportation in China is still using the three screw pump. For another example, the twin-screw pump is more environmentally friendly and has a longer service life than the single screw pump in conveying food and drugs. Because the single screw pump is cheap, the single screw pump is still widely used in these areas in China.

Recommended reading: three screw pump, screw pump, Imo pump