Why use a twin-screw pump to transport lubricating oil in a hydraulic system?

1. The structure of the twin-screw pump determines that it is more energy-saving when transporting hydraulic system lubricating oil and other high-viscosity chemical media.

 

Structurally speaking, the core component of the twin-screw pump, the screw (or sleeve), is formed by a spiral curved surface. When transporting liquid medium, through the rotation of the active and passive screws, the liquid medium undergoes axial translational movement without radial movement, so the medium is transported smoothly without pulsation or stirring. This structural feature of the twin-screw pump has high efficiency when transporting hydraulic system lubricating oil and other high-viscosity chemical media.

 

transport lubricating oil

 

1) Compare with single screw pump

 

Since the single-screw pump has simple mould lines and low requirements for surface processing accuracy, it can adopt efficient processes such as chipless processing, so it is low in price. The viscosity range of the transported medium is as wide as that of the twin-screw pump (up to 2.7×106mm2/s) and can transport various types of non-lubricating media. It has a small vibration, no pulsation, and no stirring of the medium. It is an ideal delivery pump for viscous media and media containing a certain amount of particle impurities. In addition, since the volumes of single-screw pumps and twin-screw pumps per rotation are basically the same, they can generally be used. Quantitative filling and delivery pump for food and beverages.

However, since the internal stator of a single screw pump is made of rubber and rubber-plastic products processed by moulds, it is very easy to be lost and wear (there are also a few parts that use metal materials to make the stator due to the characteristics of the medium). Therefore, the service life is usually very short and wears out. The removed rubber or rubber plastic and special metal powder are easily mixed into the lubricating oil of the hydraulic system, making it difficult to guarantee the quality of the lubricating oil of the hydraulic system.

The twin-screw pump uses a pair of screws that mesh with each other but are not in strict contact (the size of the top gap, side gap, bottom gap and other gaps are determined by the characteristics of the medium) to form a sealed cavity, and the pump body is also not Strict contact, the transmission mode of the active and passive screws is completed by synchronous gears, and the synchronous gearbox has a special lubrication system independent of the flow part. Therefore, there are no accessories that are easily worn, so the service life is much longer than that of a single screw pump in many situations.

 

2) Twin-screw pump vs. gear pump

 

In contrast, since the tooth surface of the gear pump is a straight tooth surface or a tooth surface with a very small angle, this structural feature causes the gear pump to produce radial movement to the lubricating oil when it delivers lubricating oil. This movement This leads to the shearing and stirring of the lubricating oil during the transportation process, and the shearing and stirring intensify the friction heat between the lubricating oil and between the lubricating oil and the gears. This friction heat rises in a straight line as the transportation speed increases. Therefore, when the gear pump transports lubricating oil and other high-viscosity chemical media, it consumes more mechanical energy and has low efficiency, resulting in no energy saving.

In terms of pipeline transportation of lubricating oil and other high-viscosity chemical media, under the same working conditions, compared with gear pumps and screw pumps transporting the same parameters (flow, pressure, etc.), the energy consumption is as high as more than 40%. When transporting high-viscosity media, almost all external gear pumps bear a very large radial force on the two shafts and bearings due to the liquid binding phenomenon caused by the meshing process of the main and driven wheels, and even the shafts may bend to a certain extent. , resulting in contact friction between the top of the gear and the inner wall of the pump body, and rapid damage to the bearings, which in turn causes direct corrosion between the gears, resulting in a rapid decrease in flow and pressure, large pulsation, and loud noise.

The most important thing is that the worn metal powder enters the lubricating oil at the same time, which directly leads to excessive impurity content in the lubricating oil and affects product quality.

When transporting media such as heavy oil, gear pumps generally have a very short continuous service life. Other rotor pumps under the same conditions also have this problem, that is, they are not energy-saving due to radial motion. Compared with twin-screw pumps, these pumps have little difference in energy consumption when conveying low-viscosity liquids, but as the viscosity of the conveyed medium increases, the difference in energy consumption becomes larger and larger.

 

3) Centrifugal pump and plunger pump compared with twin-screw pump

 

For centrifugal pumps or plunger pumps, the situation is even more serious. Since the centrifugal pump achieves the purpose of pumping through the centrifugal force generated by the impeller on the liquid medium, it is recognized that the efficiency of the centrifugal pump drops sharply due to the certain viscosity of the lubricating oil, and the plunger pump cannot achieve normal transportation of lubricating oil.

 

2. The structure of the twin-screw pump determines that it is more suitable for pipeline transportation of lubricating oil and other high-viscosity chemical media, and has a longer service life.

 

Since the twin-screw pump performs axial translation of the lubricating oil when conveying lubricating oil, the conveying process is smooth and pulsation-free, so it has good protection for the conveyed lubricating oil.

We know that the transportation of many liquid media does not allow pulsation, especially stirring. Otherwise, physical or chemical reactions may occur, causing the transported materials to change or even become unusable. For example, in the transportation of liquefied gas, the pulsation or stirring caused by the transportation causes its vaporization; and for some chemical media, the pulsation and stirring caused by the transportation of materials may cause changes in the chemical properties of the materials. The use of twin-screw pumps to transport such materials can solve the problem of smooth transportation. This change is more obvious when transporting media with greater viscosity, and the excellent characteristics of the twin-screw pump are more fully demonstrated.

Twin-screw pumps are known as “semi-permanent pumps” in hydraulic systems. When transporting high-viscosity media, their excellent performance is maximized. The higher the viscosity of the media, the higher its efficiency compared with other pump types. It is also higher, has lower noise and runs more smoothly. Therefore, among various types of pumps, twin-screw pumps have a very long service life when transporting lubricating oil and other high-viscosity chemical media.

 

3. The self-priming property of the twin-screw pump makes it more suitable for transporting lubricating oil.

 

The biggest problem faced by pumps in lubricating oil delivery is overcoming the resistance of the inlet pipeline. Some pumps do not have self-priming capabilities, so lubricating oil cannot enter the pump smoothly. Since the twin-screw pump itself can produce self-priming (theoretically, it has a self-priming force of 8 bar), it is very beneficial to the transportation of lubricating oil under many conditions.

 

4. The twin-screw pump was born to transport lubricating oil and other high-viscosity chemical media.

 

Before the birth of the twin-screw pump, gear pumps and other pumps were used to transport lubricating oil and other high-viscosity chemical media. Screw pumps were first used for ship transportation. At that time, the weather was cold and the viscosity of crude oil and heavy oil was quite high. The transmission efficiency of gear pumps and centrifugal pumps was very low, and they were easily damaged and had a short service life. From this, the screw pump came into being. The emergence of twin-screw pumps further makes the transportation of high-viscosity oil products no longer a problem. Twin-screw pumps not only run smoothly but also have a long service life. Therefore, for decades, whenever it comes to transporting lubricating oil with viscosity, the first thing pump experts consider is: twin-screw pumps.

 

5. In terms of pipeline transportation of lubricating oil and other high-viscosity chemical media, twin-screw pumps are the leader among screw pumps.

We know that screw pumps are divided into single screw pumps, twin screw pumps, three screw pumps and five screw pumps.

Since the rubber stator of the single-screw pump is constantly squeezed during work, its service life is too short, and it is generally not included in the chemical industry pumps;

Due to the influence of “Monkey’s Law”, the use conditions of the three-screw pump are limited to the transportation of “Newtonian fluid” with a certain lubricity and a limited viscosity range. The three-screw pump has good performance when transporting lubricating oil with a certain viscosity. However, when transporting other non-lubricating and high-viscosity media, the three-screw pump will have more problems.

First of all, the front-end positioning of the three screws is achieved by copper or other alloy sliding bearings, which cannot provide a separate lubrication system. Furthermore, the transmission method is also the intermediate driving shaft directly driving the secondary shafts on both sides through the spiral profile for meshing rotation, which is further limited. has limited its scope of application; when the viscosity reaches a certain value or when non-fluid transportation is carried out, due to the essential difference between the spiral groove surface design and the twin-screw pump, there are unfavourable factors of shearing and stirring the medium, resulting in excessive mechanical energy. Consumption causes pumping efficiency to drop sharply,

Another point is that there are fatal flaws in the design of the rear-end support positions of the two countershafts of the three-screw pump, which results in a higher failure rate than that of the twin-screw pump. As the viscosity of the medium increases, the failure rate caused by this flaw is also higher. In most application fields, only twin-screw pumps can be used.

This is not the case with twin-screw pumps. With the development of IT technology, advanced screw pump spiral surfaces have emerged. For a long time, it has become a reality to replace the triangular leakage surface with a spiral surface with high airtightness and high volumetric efficiency. Relying on the foundation of military technology, our company has made major improvements to the most critical part of the screw pump, which is the core technology spiral surface of our company’s core component. Different from other domestic manufacturers, it uses complex involutes and cycloids. , arc lines, with advanced theoretical basis and high volumetric efficiency. The transmission method and sealing method between the main and driven screws have also been significantly improved, such as the special treatment of the journal part of the seal and the packing. The combination of seals and labyrinth seals, the combination of mechanical seals and labyrinth seals, the combination of mechanical seals and packing seals, etc., have achieved exciting and gratifying success, allowing the pump to reduce power loss as much as possible during working conditions. , achieves direct transmission of power, solves the leakage problem that has always troubled practitioners in the pump industry and reduces the operating noise of the pump, ultimately improving the effective working efficiency of the pump.

Screw pumps have undergone substantial improvements through technological innovation in recent years. The liquid medium it transports has an impressively wide viscosity range: the viscosity range of the transport ranges from extremely low viscosity in the liquefied gas state to extremely high viscosity media above 500,000 centistokes, all of which can be safely and reliably transported by the twin-screw pump.

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