Hydraulic Pumps PDF

Hydraulic Pumps Hydraulic systems ================= HYDRAULIC systems are essential in various fields such as manufacturing, metallurgy industry, and energy. In light of some advantages such as high stiffness, high precision, fast response, large driving force, and wide speed range, hydraulic syst...

Hydraulic Pumps Hydraulic systems ================= HYDRAULIC systems are essential in various fields such as manufacturing, metallurgy industry, and energy. In light of some advantages such as high stiffness, high precision, fast response, large driving force, and wide speed range, hydraulic systems are widely adopted as the core component of engineering equipment \[1\] Hydraulic systems are fundamental elements in essential mechanical apparatus and are crucial contributors to industrial production and manufacturing operations owing to a multitude of advantages. Hydraulic systems utilize pumps to pressurize fluid, which is then transmitted through tubes to actuators (hydraulic motors and cylinders) for movement or stabilization, before being cycled back through a filter and re-pressurized, offering compactness and efficiency as key advantages \[2\] Hydraulic pumps =============== Figure 1. Hydraulic pump Hydraulic pumps are the power-supplying components within hydraulic circuitry. All pumps used in hydrostatic pressure systems are of the positive displacement type. Nonpositive displacement pumps, usually characterized by the features of low pressure and high flow rate, are incapable of producing sufficient power required by the hydrostatic power systems. Among the positive displacement pumps, fixed displacement gear pumps are often used in circuit applications where customers are sensitive to the initial purchase cost of the system and where the overall operating efficiency does not need to be extremely high. Also, gear pumps can be operated at high speeds and can be used in applications where the operating pressures are low to moderate. Gear pumps use a very simple mechanism to generate flow, and therefore have a minimum number of parts associated with the design. The simplicity of the gear pump design translates into higher reliability as compared to other positive displacement pumps that use a more complex design.\[3\] Classification of pumps ----------------------- Positive-displacement pumps - Reciprocating pumps - Rotary pumps - Gear pumps - External gear pumps - Lobe pumps - Internal gear pumps - Gerotor pumps - Screw pumps - Vane pumps - Piston pumps - Axial piston pumps - Radial piston pumps Non-positive-displacement pumps - Centrifugal pumps - Axial pumps - Radial pumps Positive displacement pumps =========================== In a PDP the transport of fluid is achieved by a periodical displacement of enclosed fluid-containing volumes into the discharge pipe. By changing the volume of a chamber throughout a revolution or contraction of the pump, fluid is forced into or out of a chamber. The generated mechanical and hydraulic forces create a flow against a certain system backpressure or load. The resulting pressure in the discharge pipe is directly proportional to the volume discharge per unit time and the system resistance.\[7\] gear pumps ---------- Though gear pumps enjoy a high level of reliability and offer a low purchase cost to the end customer, they are often accompanied with performance characteristics that tend to create higher noise levels than other types of positive displacement pumps. These noise levels are associated with the substantial flow ripple of the pump, which induces a pressure ripple and oscillating forces within the system. Since the flow ripple is considered to be the first cause of these oscillating forces, it is assumed that a smoother flow delivery of the pump will also attenuate the noise that is generated. This paper is focused on considering the characteristics of the flow ripple from an ideal, or theoretical, point of view.\[3\]  Figure 2. Gear pump configuration Figure 2 shows a cross-sectional view taken through the gears of a typical gear pump. Note: like most actual gear pump designs, this pump is shown with two identical gears that are used for displacing fluid. In the analysis that follows, the numbers of teeth on each gear will be allowed to vary and therefore, in general, the two gears will not be identical. The number of teeth on gear 1 is given by *N*~1~ and the number of teeth on gear 2 is given by *N*~2~. In any case, the addendum radius of each gear will be identified by the dimension *r ~a~*~1,2~, the pitch radius is given by *r ~p~*~1,2~, and the center distance between shafts is given by the dimension *C*. Note: the subscripts 1 and 2 denote the driving and driven gear respectively. The thickness of the gears into the paper is given by the dimension *w*(not shown in Fig. 2). The gears are contained in a close-tolerance housing that separates the discharge port from the intake port. An external shaft is connected to gear 1 while the other gear is supported by an internal shaft and bearing. Note: the shafts connected to the gears are not shown in Fig. 2 as they would protrude out of the paper. The driving gear and shaft rotate at an angular velocity v~1~. The driven gear rotates in the opposite direction at an angular velocity v~2~. When considering the operation of a gear pump, it is a common mistake to assume that the fluid flow occurs through the center of the pump (i.e., through the meshed gear geometry). This is not what happens. To produce flow with a gear pump, fluid is carried around the *outside* of each gear (within each tooth gap) from the intake side of the pump to the discharge side of the pump. As the gear teeth mesh within the gearset, fluid is squeezed out of each tooth gap by a mating tooth and is thereby displaced into the discharge line of the pump. On the intake side, the gear teeth are coming out of the mesh. In this condition, fluid backfills for the volume of the mating teeth that are now evacuating each tooth space. This back filling draws fluid into the pump through the intake port of the pump housing. This process repeats itself for each revolution of the pump and thereby displaces fluid at a rate proportional to the pump speed.\[3\] lobe pump --------- Figure 3. Three-dimensional view of a lobe pump housing and rotors \[12\] The lobe pump receives its name from the rounded shape of the rotor radial surfaces that permits the rotors to be continuously in contact with each other as they rotate. Lobe pumps can be either single- or multiple lobe pumps, and carry fluid between their rotor lobes much in the same way a gear pump does. Lobe pumps have wide range of applications in industry from food, medicine to beverage, biotechnology, *etc*., from very large scale to very small in micron size. Furthermore, the lobe pump is able to work with various materials from low viscosity such as water to very high viscosity such as oil, and even handle with solids. Lobe pumps could be categorized to positive displacement rotary pumps which move fluid using the principles of rotation. Different from other kinds of pump, saying kinetic pumps, the working domain of lobe pump deforms continuously during every revolution of rotors. Thus, to understand the physical phenomena of compressed fluid in such a complex working domain is not an easy work.\[4\] vane pump --------- A balanced vane pump, now widely used in many hydraulic power systems because of its compactness, lightweight, and low cost, is especially suitable for a hydraulic power source in a power steering system of a vehicle, in which low pressure pulsation and low noise are required. When designing a hydraulic pump including the vane pump, the mechanical efficiency as well as the volumetric efficiency constitutes a key factor in evaluating the pump performance. Friction torque characteristics of various pumps and motors have been already studied and mathematical models of the friction torque have been proposed. Authors have also proposed a new mathematical model of the friction torque characteristics for the vane pump because the previously proposed models were not suitable for the vane pump. These mathematical models were constructed conceptually or only to fit measured results in the actual pump torque, but not theoretically. Therefore, the relation between the dimensions of the pump parts and its friction torque in the vane pump has yet to be clarified, and it is generally held that the friction torque in the vane pump has been insufficiently analysed. In this study, the friction torque characteristics, particularly the friction torque caused by the friction between the cam contour and the vane tip are experimentally investigated and theoretically analysed. Further, this investigation tried to clarify the influence of the friction between the cam contour and the vane tip on the mechanical efficiency and to construct the design concept on the relationship between the cam lift and the vane thickness for the vane pump with high mechanical efficiency.  Figure 1 shows a cross-sectional view of a balanced vane pump, composed of a cam ring with an elliptic inner bore, a rotor with a series of radially disposed vanes, and two-side plates located at both sides of the rotor. The pump is so designed that both suction and delivery ports in the pump are diametrically opposed to provide complete balance of all internal radial forces. In this pump, the side plates have vane backpressure grooves at the sides facing the rotor to introduce the delivery pump pressure to all the bottoms of the vane slot of the rotor. During the pump operation, the vane is always pushed from the bottom by the delivery pressure and rotates with the loads imposed by the vane tip on the cam contour. The rotor is driven by a shaft through a very loose-fitting spline and the rotor and vanes rotate between two-side plates with running clearance. \[6\] hydraulic piston pumps ---------------------- ince the inauguration of "Industry 4.0" in Germany, "Made in China 2025", "Industrial Internet" in America, and "Society 5.0" in Japan, the world has focused on the development of intelligent factories, production, electronic information and logistics, including human--computer interactions, high-end CNC machine tools and robotics, new energy vehicles, biomedicine, etc. These measures continue to strengthen the innovative applications of key digital technologies \[1,2\]. This is promoting digitization, networking, and intelligence in the manufacturing industry and an innovation-driven development path. Hydraulic transmission systems are widely used in the aforementioned engineering fields due to their advantages of stepless speed regulation, large speed regulation ranges, high load tolerance, and easy automation. As the "power heart" of hydraulic transmission systems, hydraulic piston pumps have consistently attracted the attention of engineers and academia. Scholars and research institutions have achieved compelling research results in the study of fault diagnosis methods for various pumps. HPPs have occupied an important place and are widely used in high-tech fields, including aerospace, navigation, national defense, and industry, such as marine power drives, offshore wind power, oil-gas exploration, deep sea exploration, industrial machine tools, construction machinery, etc. \[3\]. However, a piston pump has numerous components, and its internal structure is rather complicated and often faces complex working conditions, such as high temperature, high pressure, and variable load. Thus, some typical failures of piston pumps often occur in extreme operating conditions. Once a fault occurs, it is difficult to quickly determine the cause and accurately locate and identify its location. This may lead to damage to the internal structure of the pump and eventually causes the pump and equipment to stop operation, resulting in economic losses and major accidents, such as system paralysis and production shutdown, even threatening the safety of the staff \[4\]. Therefore, fault diagnosis technology for HPPs is particularly important to guarantee the safety of the entire equipment and reduce the incidence of accidents. In modern industry, HPPs are continuously evolving in higher precision, and their structures are becoming increasingly sophisticated and complex. This means that an efficient, accurate, and intelligent fault diagnosis technology has broad application prospects in both scientific research and engineering practice. With the rapid advancement of the big data era, the data presented by piston pumps have become important information sources that reflect the working statuses and fault manifestation processes, if any, of the pumps. The scale and interpretability of these data have also become an important part of current fault diagnosis technology \[5\]. However, due to the influence and interference of multiple factors in working environments, and the complexity and variability of work tasks, HPPs present many challenges in the process of fault identification. The fault diagnosis approaches for HPPs mainly focus on collecting different types of signals to analyze and reflect their operating status. These signals mainly include vibration signals, sound signals, pressure signals, flow signals, etc. When an HPP runs at complex conditions, it generates a large number of complex signals, which reduces the purity of the original signal, increases the difficulty of signal feature extraction, and also increases the complexity of signal processing. Therefore, traditional fault recognition methods are difficult to achieve precise identification. Meanwhile, various intelligent fault identification or combined fault diagnosis approaches utilize intelligent algorithms for data mining and establishing fault identification models, and then complete the identification of different states. These methods have high accuracy and are more intelligent, and have become the mainstream of fault identification methods. In recent years, numerous experts and scholars have researched fault identification methods for HPPs, and several articles have provided an overview of the fault recognition methods for piston pumps \[6,7\]. They have summarized current fault identification methods from the view of different types of signals, but there are relatively few detailed classifications and comparative analyses for fault diagnosis approaches. Hence, a comprehensive summary to provide the latest research progress and application for intelligent fault diagnosis approaches of HPPs is urgently needed. This work takes HPPs as the research object, and the common types and mechanisms of faults in HPPs are analyzed. Then, all kinds of existing fault diagnosis methods are summarized. Novelly, the various fault diagnosis methods are classified into traditional intelligent fault diagnosis methods, modern intelligent fault diagnosis methods, and combined intelligent fault diagnosis methods. Moreover, the achievements and application statuses of the HPP fault diagnosis methods are summarized. Finally, this work analyzes the aforementioned fault diagnosis methods and infers their development trends, and seeks to provide a theoretical reference for scientific research and engineering applications in this field. Figure 4. Schematic diagram of structural composition of piston pump. (**a**) Three-dimensional structural model of hydraulic piston pump. (**b**) Piston ball heads and slippers. (**c**) Slippers and swashplate. (**d**) Pistons and piston holes. (**e**) Cylinder and valve plate. HPPs can be divided into radial piston pumps and axial piston pumps, according to their structural forms, and can be further divided into swashplate types and bent-axis types according to their structural characteristics. This paper uses the example of a swashplate-type HPP (Figure 3a) to introduce the structure of a piston pump. Multiple friction pairs have relative motion inside a piston pump, such as a piston ball head and slipper (Figure 3b), slipper and swashplate (Figure 3c), piston and piston hole (Figure 3d), and cylinder and valve plate (Figure 3e).\[8\] Diaphragm displacement pumps ----------------------------  As shown schematically in Fig. 2a, diaphragm displacement pumps typically are comprised of a pumping chamber connected to inlet and outlet valves necessary for flow rectification. As the diaphragm deflects during the expansion stroke, the pumping chamber expands resulting in a corresponding decrease in chamber pressure. When the inlet pressure is higher than the chamber pressure, the inlet valve opens and liquid fills the expanding chamber (Fig. 2b). During the compression stroke, the volume of the chamber decreases with the moving diaphragm, causing the internal pressure to increase whereby liquid is discharged through the outlet valve (Fig. 2c).\[9\] Non-positive-displacement pumps ------------------------------- ### centrifugal pump Figure 5: Components of single stage centrifugal pump centrifugal pump is a most common pump used in industries, agriculture and domestic applications. The centrifugal pump creates an increase in pressure by imparting mechanical energy from the motor to the fluid through the rotating impeller. The fluid enters from impeller eye and flows along its blades. In this centrifugal force developed due to rotation of impeller. This centrifugal force increases fluid velocity and then kinetic energy is transformed to pressure. Figure 5 shows different components of centrifugal pump.\[11\] Centrifugal pumps account for about 20% of total energy consumption around the world. In this way, production of high performance pumps has an important effect on reducing the energy consumption. Based on the research of the American Hydraulic Institute, 30% of the total electrical energy consumed by pumping systems can be saved by designing more efficient systems and also by selecting appropriate pumps for each application. Furthermore, over 22% of the total energy supplied to electric motors is consumed by the pumping systems. On the other hand, the pumps performance is designed and calculated based on their performance curves and characteristic data. This means that having more precise performance curve results in a better efficiency and more productivity in the designed system.\[12\] a ''centrifugal pump'' is any pump in which the fluid is energized by a rotating impeller, whether the flow is radial, axial, or a combination of both (mixed). Strictly defined (as in European practice), a centrifugal pump is a radial-flow pump only. But colloquial usage is followed here, and thus centrifugal pumps are divided into three groups: - Radial-flow pumps - Mixed-flow pumps - Axial-flow or propeller pumps.  Figure 6: Typical flow paths in centrifugal pumps. (a) Radial flow, vertical; (b) mixed flow; (c) radial flow, horizontal; (d) axial flow. These classifications are derived from the manner in which the fluid moves through the pump (see Figure 10-1). Thus, the fluid is displaced radially in a radial-flow pump, axially in an axial-flow pump, and both radially and axially in a mixed-flow pump. ### Capacity The flow rate (capacity, discharge, or Q) of a pump is the volume of liquid pumped per unit of time, usually expressed in SI units in cubic meters per second (m3=s) for large pumps or liters per second (L/s) and cubic meters per hour (m3=h) for small pumps. In U.S. customary units, the capacity of a pump is expressed in gallons per minute (gal/min), million gallons per day (Mgal/d), or cubic feet per second (ft3=s). Equivalent units of measurement are given on the inside back cover and in Appendix A. ### Head The term head (h or H) is the elevation of a free surface of water above (or below) a reference datum (see Figures 10-2 and 10-3). For centrifugal pumps, the reference datum varies with the type of pump, as shown in Figure 10-1. Head is expressed in meters (m) or feet (ft). Pressure can also be expressed as the equivalent head of water. Figure 7: Terminology for a pump with a positive suction head. (\*) The gauge is located to show theoretical pressures at the inlet and outlet flanges; see ''Field Pump Tests'' in Section 16-6 for practical gauge locations. Distances (heads) above the datum are considered positive and distances below the datum are considered negative. Each term, defined graphically in Figures 10-2 and 10-3, is expressed as the height of a water column in meters (feet) of water. H is used for total head, whereas h is used for head from the datum or for headloss. The subscripts s and d denote the pump suction and discharge, respectively. Other subscripts are defined as follows: Total static head (H~stat~): The total static head is the difference in elevation in meters (feet) between the water level in the wet well and the water level at discharge (h~d~ - h~s~). Static suction head (h~s~): The static suction head is the difference in elevation between the wet well liquid level and the datum elevation of the pump impeller. If the wet well liquid level is below the pump datum, as in Figure 10-3, it is a static suction lift, so h~s~ is negative.  Figure 8: Terminology for a pump with a negative suction head. (\*) The gauge location is to show theoretical pressures at the inlet and outlet flanges; see ''Field Pump Tests'' in Section 16--6 for practical gauge locations. ### Power #### Output Power The power output of a pump is the useful energy delivered by the pump to the fluid. In SI units, the power output is defined as \ [\$\$P = \\gamma QH = \\frac{\\text{qH}}{102}\$\$]{.math.display}\ where P is the water power in kilowatts, γ is the specific weight of the fluid in kiloNewtons per cubic meter (kN/m^3^), Q is the flow rate in m^3^/s, H is the total dynamic head in m, q is the flow rate in L/s, and 102 is a conversion factor for water at 15 to 208C.\[10\] \[1\] Huang, K.; Wu, S.; Li, F.; Yang, C.; Gui, W. Fault Diagnosis of Hydraulic Systems Based on Deep Learning Model With Multirate Data Samples. *IEEE Trans. Neural Networks Learn. Syst.* 2021, *33*, 6789--6801. \[[CrossRef](http://doi.org/10.1109/TNNLS.2021.3083401)\] \[2\] Assessing the Remaining Useful Life of Hydraulic Pumps: A Review, Assoc. Prof. PhD. Eng. **Ștefan ŢĂLU1** \[[CrossRef](https://hidraulica.fluidas.ro/2024/nr3/07-18.pdf)\] \[3\] the Theoretical Flow Ripple of an External Gear Pump \[[CrossRef](https://doi.org/10.1115/1.1592193)\] \[4\] FACTORS IMPACTING ON PERFORMANCE OF LOBE PUMPS: A NUMERICAL EVALUATION \[5\] Radial-piston pump for drive of test machines \[[CrossRef](https://iopscience.iop.org/article/10.1088/1757-899X/289/1/012014/meta)\] \[6\] Vane Pump Theory for Mechanical Efficiency \[[CrossRef](https://doi.org/10.1243/095440605X32002)\] \[7\] A review of selected pumping systems in nature and engineering---potential biomimetic concepts for improving displacement pumps and pulsation damping \[[CrossRef](https://iopscience.iop.org/article/10.1088/1748-3190/10/5/051001/meta)\] \[8\] Intelligent Fault Diagnosis Methods for Hydraulic Piston Pumps: A Review \[[CrossRef\]](https://doi.org/10.3390/jmse11081609) \[9\] Recent advances in microscale pumping technologies: a review and evaluation \[[CrossRef](https://doi.org/10.1007/s10404-008-0266-8)\] \[10\] Performance of Centrifugal Pumps \[[CrossRef](https://doi.org/10.1016/B978-185617513-5.50017-2)\] \[11\] Centrifugal pumps performance estimation with non-Newtonian fluids: review and critical analysis \[[CrossRef](https://doi.org/10.29008/ETC2017-248)\] \[12\] Effect of lobe pumping on human albumin: development of a lobe pump simulator using smoothed particle hydrodynamics \[[CrossRef](https://doi.org/10.1042/BA20050188)\] \[13\] Emami, S. A.; Emami, M. H. (2017). Design and Implementation of an Online Precise Monitoring and Performance Analysis System for Centrifugal Pumps. IEEE Transactions on Industrial Electronics, (), 1--1. \[[CrossRef](https://ieeexplore.ieee.org/document/7968412/)\] doi:10.1109/TIE.2017.2723875