Introduction and functions of single-screw pumps　

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Introduction and functions of single-screw pumps: Single-screw pumps belong to the category of rotary positive-displacement pumps. They transport liquids by utilizing the intermeshing of the screw and the sleeve to create volume changes in the suction chamber and the discharge chamber. It is a closed-type internal meshing screw pump, whose main working components consist of a sleeve (stator) with a double-threaded helical cavity and a single-threaded helical screw (rotor) that meshes with it within the stator cavity. When the input shaft drives the rotor to perform planetary motion around the stator center via a universal joint, the stator-rotor pair continuously meshes to form sealed chambers. These chambers move axially at a constant speed with unchanged volume, transporting the medium from the inlet side to the outlet side through the stator-rotor pair; the medium drawn into these sealed chambers flows past the stator without being disturbed or damaged. Boshen single-screw pump classifications: all-steel stainless single-screw pump, shaft-stainless single-screw pump. 　　Single-screw pumps are widely used in developed countries; abroad, they are often referred to as “MONOPUMPS”, while in Germany they are called “eccentric rotor pumps”. Due to its excellent performance, its application scope in China has also been expanding rapidly in recent years. Its greatest advantages are its strong adaptability to different media, stable flow rate, low pressure fluctuations, and high self-priming capacity – features that no other type of pump can match. We have analyzed and studied single-screw pumps produced abroad (such as in Germany, the UK, France, Japan, etc.) as well as products from domestic manufacturers in the same industry, drawing on their strengths to continuously innovate and improve our own products. At present, the products of our company form a complete system, with a pressure range of 0.4–1.2 MPa, which can meet the various needs of customers regarding single-screw pumps. The pumps produced by our company are of reliable quality, come with a three-guarantee service, have relatively low prices, and we also ensure a steady supply of spare parts. Our company is committed to serving our customers, and we accept requests from them for the design and manufacture of single-screw pumps tailored to specific requirements. 　　　The screw has single-start threads; any cross-section of it is a circle with radius R. The center of this cross-section lies on the helical line and is offset from the axis of the screw by an eccentricity e. It rotates around the axis while moving axially. Number of lobes: The number of lobes on the stator of the screw, T1, is one more than the number of lobes on the rotor, T2; that is, T1 = T2 + 1. Their ratio becomes the ratio of numbers. Screw pumps can be divided into single-stage (1:2) and multi-stage (2:3, 3:4), etc. 　　The higher the head ratio, the greater the output torque of the screw pump, and the lower its rotational speed. Conversely, the lower the output torque, the higher the rotational speed. 　　The inner surface of the bushing features double threads; any cross-section of it is an oval, with semi-circles of radius R (equal to the radius of the screw’s cross-section) at both ends, and a straight segment of length 4e in the middle. Any cross-section of the bushing is the same oblong shape, merely offset from one another by an angle. 　　After the screw is inserted into the bushing, closed chambers are formed between the surface of the screw and the internal threaded surface of the bushing; at the same time, any cross-section is divided into two crescent-shaped working chambers, one on top and one below (as shown in Figure 1-3). As the screw rotates, the volume of the first working chamber near the suction chamber gradually increases, creating a negative pressure; under the effect of this pressure difference, the liquid is drawn into the working chamber. As the screw continues to rotate, the volume of the working chamber keeps increasing until it reaches its maximum value; at that point, this working chamber is sealed, and the liquid is pushed axially toward the discharge chamber. At the same time, the upper and lower chambers take turns sucking in and discharging liquid, thereby pushing the liquid continuously from the suction chamber toward the discharge chamber along the axial direction. 　　　　It has a very wide range of applications, mainly in: environmental protection, the shipbuilding industry, the oil industry, pharmaceuticals, the cosmetics industry, the brewing industry, the construction industry, the mining industry, the chemical industry, printing, and the papermaking industry. 　　　　Transporting high-viscosity media: Depending on the size of the pump, it can transport media with viscosities ranging from 0 to 200,000 centipoise. 　　　　Wear grade 1 and 2: Generally, 0.4 MPa to 0.8 MPa; severely, 0.2 MPa to 0.4 MPa. For media containing particles or fibers: the particle diameter can be up to 30 mm (not exceeding the rotor’s eccentricity). The fiber length can be 350 mm (equivalent to the pitch of 0.4 turns of the rotor). Its content can generally reach 40% of that in a medium-type cellar; when the solids in the medium are in the form of fine powder, the maximum content can reach 60% or even higher, and it can still be transported. When a stable delivery pressure is required and the inherent structure of the medium must not be damaged, it is most ideal to use a single-screw pump for transportation. 　　　　Due to its structure and operating characteristics, the single-screw pump has the following advantages over piston pumps, centrifugal pumps, vane pumps, and gear pumps: 1. It is capable of transporting media with high solid content; 2. It provides a steady flow rate and constant pressure, especially at low speeds; 3. The flow rate is proportional to the pump’s speed, allowing for good variable control; 4. One pump can be used for transporting media of different viscosities; 5. The pump can be installed at any inclination; 6. It is suitable for transporting sensitive materials and those that are prone to damage due to centrifugal forces; 7. It is compact, lightweight, produces low noise, has a simple structure, and is easy to maintain. 　　　The specifications of the pump are determined based on the properties of the liquid to be transported, as well as its flow rate and pressure. The speed of the pump, on the other hand, is chosen considering factors such as the viscosity and corrosiveness of the liquid, in order to ensure the reliable operation of the pump. 　　The designed speed of a pump is the maximum speed allowed when transporting clean water or other non-corrosive liquids similar to clean water. In practical use, due to differences in the properties of the fluid and the requirements regarding lifespan, the operating speed is generally should be lower than the designed speed. For high-viscosity and particulate-containing media, a speed of 1/2 to 1/3 of the designed speed, or even lower, is generally used. A lower speed is beneficial for reducing wear on the pump; however, after use, as flow rate decreases due to stator wear, it is common practice to increase the speed appropriately to compensate for this decrease in flow rate. 　　The temperature of the conveying medium should be between -10 ℃ and 80 ℃; in special cases, it can reach up to 120 ℃. 　　The normal pressure per stage of the pump (one pitch of the stator) is 0.6 Mpa; a pressure of up to 0.8 Mpa is allowed for a short period of time (not exceeding 30 minutes). After wear, the volumetric efficiency decreases gradually at the same output pressure. 　　When pumping clean water, the maximum suction height is 8 meters; it is recommended not to exceed 6.5 meters in practical use. When pumping high-viscosity media, suction should be performed under positive pressure. 　　　　A slurry pump is a single-screw transport pump; its main working components are the eccentric spiral screw (referred to as the rotor) and the screw bushing with a double helical surface on its inner side (referred to as the stator). Its working principle is that when the motor drives the pump shaft to rotate, the screw rotates around its own axis while also rolling along the inner surface of the bushing, thereby creating a sealed chamber in the pump. With each rotation of the screw, the liquid in the sealing chamber is pushed forward by one pitch. As the screw rotates continuously, the liquid is forced in a spiral manner from one sealed chamber to another, and eventually is expelled from the pump body. The thick slurry pump is a new type of machine for transporting liquids, featuring advantages such as a simple structure, safe and reliable operation, ease of use and maintenance, continuous and uniform liquid output, and stable pressure. For the thick slurry pumps produced by our company, all metal components that come into contact with the material are made from high-quality stainless acid-resistant steel. The shaft is made of 2Cr13 material, while the liners are constructed from non-toxic and odorless rubber. The operating temperature can reach 100°C; these pumps can be used for transporting food slurries as well as solutions or suspensions with a viscosity of 10,000 Pascal-seconds, which may contain solid particles or gel-like substances, in corrosive media. Single-screw pumps are widely used in industrial sectors such as food, metallurgy, construction, pharmaceuticals, and chemicals.