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A vane pump is a widely used and extensively produced fluid machinery device; it is a pump in which the vanes within the rotor grooves come into contact with the pump casing (stator ring), pushing the liquid drawn in from the inlet side to the outlet side. It propels liquids by the high-speed rotation of an impeller equipped with blades. Vane pumps have a simple structure and are easy to maintain, making them the most widely used in practical applications. Classification of vane pump models: Vane pumps come in two types depending on their classification: 1) Refers specifically to slide vane pumps, which are a type of positive displacement pump. II) Refers to the three types of dynamic pumps (centrifugal pumps, mixed-flow pumps, axial-flow pumps) or other special pumps. Pump products of this type are generally not called vane pumps. However, as a specialized subject, vane pumps come in a wide variety of types and specifications due to differences in performance parameters, the medium being transported, and application requirements; their structures also take on various forms. Vane pumps can be classified according to their working principle into centrifugal pumps, mixed-flow pumps, and axial-flow pumps. Based on the position of the pump shaft, they can be divided into horizontal pumps, vertical pumps, and inclined pumps. According to the type of discharge chamber, they are categorized as volute pumps and diffuser pumps. Based on the way in which air is drawn in by the impeller, they can be classified as single-stage pumps and double-stage pumps. Lastly, depending on the number of impellers (stages), they are divided into single-stage pumps and multi-stage pumps. Vane pumps almost always refer to centrifugal pumps, mixed-flow pumps, axial flow pumps, etc. Based on whether their theoretical displacement per revolution is fixed or variable, they can be divided into vane variable pumps and vane fixed-displacement pumps. 1. The characteristics of centrifugal pumps are low flow rate and high head. 2. The characteristics of axial flow pumps are high flow rate and low head. 3. The characteristics of mixed-flow pumps lie between those of centrifugal pumps and axial-flow pumps. In practical applications, vane pumps are further divided into double-acting vane pumps and single-acting vane pumps. Double-acting vane pumps can only be used as fixed-displacement pumps, while single-acting vane pumps can be used as variable-displacement pumps. The double-acting vane pump gets its name from the fact that, as the rotor rotates one full circle, the vanes slide twice within the rotor’s vane grooves, thereby completing two cycles of oil suction and oil discharge. In a single-acting vane pump, the rotor completes one rotation, which results in oil being drawn in and pushed out once each, hence the name single-acting. Working principle of vane pump: As the rotor of the vane pump rotates, the vanes, under the action of centrifugal force and pressure oil, press their tips tightly against the inner surface of the stator. In this way, the working volume formed by the two blades together with the inner surfaces of the rotor and stator draws in oil from a small volume to a larger one, and then discharges the oil from a large volume back to a smaller one; one full rotation of the blades completes one cycle of oil intake and discharge. I. Working principle of the single-acting vane pump: 1-rotor, 2-stator, 3-vanes. The working principle of the single-acting vane pump is as shown in the figure; it consists of a rotor 1, a stator 2, vanes 3, and end caps. Stator 2 has a cylindrical inner surface; there is an eccentricity e between stator 2 and rotor 1. Blades 3 are mounted in the rotor slots and can slide within them. As rotor 1 rotates, the centrifugal force causes the blades 3 to press against the inner wall of the stator. In this way, several sealed working spaces are formed between the stator 2, rotor 1, blades 3, and the oil distribution plates on both sides. When the rotor 1 rotates counterclockwise, in the right part of the diagram, the blades 3 gradually extend outward, and the volume of the sealing chamber between the blades increases gradually; oil is drawn in from the oil inlet, and this is the oil suction chamber. On the left side of the diagram, blade 3 is gradually pressed into the groove by the inner wall of the stator, causing the working space to shrink; this pushes the oil out through the oil pressure port – this is the oil pressure chamber. There is an oil-sealing area between the oil suction chamber and the oil compression chamber, which separates the two. With each rotation of this vane pump, each working chamber completes one cycle of oil suction and oil discharge; hence it is called a single-acting vane pump. As the rotor 1 keeps rotating, the pump continuously draws in oil and discharges it. By changing the eccentricity of the rotor 1 and the stator 2, the flow rate of the pump can be adjusted. The greater the eccentricity, the higher the flow rate. If rotor 1 and stator 2 are adjusted to be almost concentric, the flow rate approaches zero. Therefore, most single-acting vane pumps are variable pumps. There is also a pressure-limited variable pump. When the load is low, the pump delivers a high flow rate, allowing the actuator to move quickly ； As the load increases, the pump’s output flow decreases, the output pressure rises, and the speed of the actuator slows down. This can reduce energy consumption and prevent the oil temperature from rising. II. Working principle of the double-acting vane pump: 1-Rotor; 2-Valve plate; 3-Vanes; 4-Stator; 5-Pump body. The working principle of the double-acting vane pump is similar to that of the single-acting vane pump, with the difference being that the stator surface consists of eight sections: two long-radius arcs, two short-radius arcs, and four transition curves. Moreover, the stator and the rotor are concentric. With the rotor rotating in a clockwise direction as shown, the volume of the sealed working chamber increases gradually at the top left and bottom right corners, which are the oil suction areas, while it decreases gradually at the bottom left and top right corners, which are the oil compression areas ； There is an oil-sealing area between the oil suction area and the oil compression area, separating them. With each rotation of the rotor in this type of pump, each sealing chamber performs suction and compression actions twice, which is why it is called a double-acting vane pump. The two suction areas and the two discharge areas of the pump are radially symmetric, and the hydraulic pressures acting on the rotor are radially balanced; hence it is also known as a balanced vane pump. The instantaneous flow rate of a double-acting vane pump is pulsating, and the pulsation rate is low when the number of vanes is a multiple of 4. For this reason, the number of vanes in double-acting vane pumps is usually 12 or 16. The inner surface of the stator of a double-acting vane pump is approximately elliptical. The rotor 1 and the stator 4 are mounted concentrically, with 2 suction areas and 2 discharge areas arranged symmetrically. For each full rotation of the rotor 1, 2 cycles of oil suction and oil compression are completed. Double-acting vane pumps are mostly positive-displacement pumps. The structure of a vane pump is more complex than that of a gear pump, but it can achieve higher operating pressures, has lower flow fluctuation, operates more smoothly, generates less noise, and has a longer service life. Therefore, it is widely used in medium and low-pressure hydraulic systems such as special machine tools and automated production lines in mechanical manufacturing. However, its structure is complex, its oil absorption properties are not very good, and it is also sensitive to oil contamination. There is also a twin-rotor vane pump, which consists of two sets of single-stage vane pump rotors, stators, vanes, and oil distribution plates assembled within one pump body and driven by the same drive shaft. It has one common suction port and two separate discharge ports. At low pressure, two pumps supply oil in large quantities simultaneously, allowing the system to move rapidly under light load. At high pressure, the large pump releases pressure directly to the oil tank through a unloading valve, thereby reducing power loss; the small pump supplies oil on its own, allowing the system to operate at low speed under heavy load. Structural features of double-acting vane pumps: (1) Since the number of vanes in such pumps is generally an integer multiple of 4, and the two suction areas and the two discharge areas are arranged symmetrically, the hydraulic radial forces acting on the rotor cancel each other out; hence, it is a type of unloading vane pump. (2) The double-acting vane pump is designed such that the angle between the two vanes (i.e., the central angle of 2π/z, where z is the number of vanes) is smaller than the angle s in the oil-sealing area on the distribution plate (i.e., the central angle), thereby preventing the suction and discharge ports from communicating with each other and ensuring proper operation. The central angle of the stator’s arcuate area is greater than or equal to that of the oil-sealing area on the distribution plate, which keeps the volume between the vanes constant within the oil-sealing area; hence, double-acting vane pumps do not experience oil trapping (unlike single-acting vane pumps, which do suffer from oil trapping). (3) To reduce the sealing gap of the pump and improve its sealing performance, the main structural measure taken is to use the fixing bolts of the pump body to press the two oil distribution plates against the stator end face, thereby maintaining an extremely small axial gap between the oil distribution plates and the rotor as well as the side end faces of the blades. The oil groove e on the back of the right oil distribution plate connects to the oil discharge chamber; the oil pressure generated by this discharge presses against the stator from the right side. Since the radial forces on the rotor are in balance, the pump shaft does not bend or deform during operation, allowing the axial clearance to be kept small. Secondly, an annular oil guide groove f is provided on the end face of each oil distribution plate, aligned with space 6 at the bottom of each blade, so as to connect all the blade root spaces together; these spaces are in turn connected to the pump’s discharge chamber through the axial oil guide holes in the right oil distribution plate. In this way, a certain oil pressure is ensured at the root of the blade. When the blade rotates with the rotor into the suction area, the oil pressure at the blade root together with centrifugal force push the blade against the inner surface of the stator, thereby maintaining a small radial gap between the tip of the blade and the inner wall of the stator. In the oil discharge area, both ends of the blade are subjected to the oil discharge pressure, resulting in hydraulic equilibrium; at this point, the blade is pressed into the groove by the force exerted by the stator surface. Centrifugal force alone is sufficient to keep the tip of the blade pressed against the inner surface of the stator, thereby meeting the sealing requirements. (4) To prevent uneven wear, jamming, or breaking of the blades and slides, the blades are generally not arranged radially with respect to the rotor, but are tilted forward by a small angle β in the direction of rotation of the rotor; this angle is known as the blade tilt angle, with β typically ranging from 10° to 14°. The purpose of using an inclination angle in vane pumps is to improve the stress conditions on the vanes as they are pressed into the slits in the discharge area. In the oil discharge area, as the tip of the blade slides along the surface of the stator’s transition curve, the inner surface of the stator exerts a normal reaction force N on the blade tip; the angle between the direction of this force and the direction of the blade slot is known as the pressure angle. For single-stage pumps, the blades generally have a backward tilt angle and a backward chamfer; that is, the blade grooves are tilted backward by an angle ranging from 20° to 30°. Since the stator profile of a single-acting vane pump is circular, the distance from each point to the rotor center changes little; as a result, the pressure angle is small. The resistance exerted by the stator surface on the vanes in the discharge area is not significant, so there is no need for an inclination angle. When the vanes move from the suction area to the discharge area, the pressure difference between the suction and discharge sides is large, resulting in considerable frictional resistance as the vanes move outward. If the vanes are inclined backward, this helps to reduce the resistance to their outward movement. Additionally, inclined slots also contribute to maintaining the strength of the rotor. (5) A double-acting vane pump is equipped with two oil distribution plates at both ends of its rotor, which allow the vanes to draw in oil from the suction ports on both sides simultaneously. This reduces the flow velocity at the suction ports (which should generally be between 4–5 m/s, not exceeding 6 m/s), thereby minimizing the suction resistance and helping to prevent cavitation caused by excessively low suction pressure. The upper part of the pump’s casing features an oil passage that ensures the suction ports on both side oil distribution plates are in communication with the suction chamber. In addition, oil drainage windows are provided on both oil distribution plates, but the oil drainage window on the left oil distribution plate is merely a blind hole. Its function is to balance the axial hydraulic pressures acting on the side end faces of the blades. The oil discharge window on the oil distribution plate features triangular relief grooves on the side where the blades enter from the sealed area. These grooves serve to allow the liquid between the blades to gradually connect with the oil discharge window as it moves from the sealed area (low-pressure area) to the oil discharge area (high-pressure area), thereby enabling a gradual change in oil pressure. This helps to reduce fluctuations in the instantaneous flow rate of the pressurized oil and prevents sudden increases in oil pressure that could cause hydraulic shock and noise. Precautions for the maintenance of vane pumps. In addition to preventing dry running and overload, as well as avoiding air ingestion and excessive suction vacuum, the following points should also be taken into account when maintaining vane pumps: 1. If the rotation direction of the pump changes, its suction and discharge directions will also change. Vane pumps have a specified rotation direction, and reverse rotation is not allowed. Because the rotor blade slots are inclined and the blades have chamfers, the bottom of the blades is in communication with the oil discharge chamber; the throttle grooves on the oil distribution plate, as well as the inlet and outlet ports, are designed according to a predetermined orientation. Reversible vane pumps must be designed specifically. 2. Pump assembly: The oil distribution plate and stator should be properly positioned using positioning pins; the vanes, rotor, and oil distribution plate must not be installed in the wrong order. The suction area on the inner surface of the stator is the most prone to wear, and if necessary, it can be installed upside down so that the original suction area becomes a discharge area, allowing continued use. 3. During disassembly and assembly, pay attention to keeping the working surface clean; the oil used should be well filtered. 4. If the gap between the blades in the blade grooves is too large, it will increase leakage; if it is too small, the blades cannot expand and contract freely, resulting in abnormal operation. 5. The axial clearance of the vane pump has a significant impact on ηv. 1) Small pumps – 0.015～0.03 mm2; 2) Medium pumps – 0.02～0.045 mm2. 6. The temperature and viscosity of the oil should generally not exceed 55°C, with the viscosity required to be between 17～37 mm2/s. If the viscosity is too high, it is difficult to absorb oil ； If the viscosity is too low, leakage will be severe. As a pump product, vane pumps more often refer to sliding vane pumps. Vane pumps almost always refer to sliding vane pumps.