Advances in Hydraulic and Pneumatic Drives and Control 2020

Proportional control valves are characterized by smooth opening of flow channels by means of the spool control. At the initial stage of opening, the flow gap is of a small cross-section which then gradually expands. This enables smoother start-up of a device as well as more precise control of the working motion compared to conventional control valves. Among the electromagnetically controlled proportional control valves, some complex solutions equipped with spool displacement transducers, compensating valves, advanced electronics, etc. can be distinguished. This allows compensation for the harmful effects of flow-related forces.The article presents the results of flow tests through the USAB10 proportional control valve, designed and manufactured by PONAR Wadowice. The valve can be both used as a single unit or included in the sectional block which supplies multiple actuators. There are many points of fluid flow direction change as well as cross-sectional area change inside the valve block. This leads to the occurrence of forces associated with the flow which are difficult to determine using standard mathematical formulas. Hence, the research process included building of geometrical models, next preparation of discrete models and then carrying out simulation tests using CFD methods. The tests were conducted in Ansys/Fluent environment which allowed velocity distribution, pressure distribution and values of forces acting on the valve spool to be obtained.

Gerotor pumps are a special type of gear pumps with internal trochoidal gearing. Due to their compact design and simple structure, they are characterized by high reliability and low cost. They are represented in many applications, mostly in the automotive industry. Increasingly stringent environmental regulations require automotive manufacturers to improve vehicle design by increasing the efficiency of their components, including the gerotor pump. This paper presents a procedure for determining the optimal combination of trochoidal gearing design parameters, in order to improve the performance of a gerotor pump. Gerotor performance is affected by sliding velocity, volume efficiency and contact stress. An appropriate mathematical model was developed in order to analyze variation effect of gear design parameters related to value of the pump functional characteristics. In order to reduce the maximum contact stresses, forces and moments’ analysis was performed by analytical and numerical method. Through consideration of the gear tooth profile with technological gaps, their impact on the volume losses and gear ratio of the pump was identified. The verification of the developed models was carried out through the realization of physical gear pairs and performing of a laboratory experiments with simulation of pump operating conditions. These results establish valuable guidelines for constructors to design more efficient construction solutions of the gerotor pumps.

The hydraulic system start-up in low ambient temperature is accompanied by numerous phenomena, which include changes in physical properties of hydraulic fluid, dimensions of cooperating working elements and clearances between these elements, friction and flow resistance. This changes the system efficiency, increases wearing of components and changes other operational features.The volumetric, torque and total efficiency of hydraulic pumps change during start-up in low ambient temperatures, as well as in thermal shock conditions, until they reach the set conditions. The time to reach steady-state conditions depends on many parameters: ambient temperature, flow rate, fluid temperature, design of hydraulic units.The author carried out tests of hydraulic pumps in the Hydraulics Laboratory of the Faculty of Mechanical Engineering of the Gdańsk University of Technology. In the research four types of pumps were investigated: several gear pumps, two axial piston pumps of different designs and one radial piston pump. It was proved, that in thermal shock conditions some malfunctions may occur, especially with large temperature difference between oil and pump.Experimental research of various hydraulic pumps operating in low ambient temperatures, undertaken by the author, allows to answer the question how the volumetric and torque efficiency changes in such conditions and what parameters does it depend on.

Hydraulic systems are widely used in drive and control systems of multiple devices. Various types of control valves are used to determine the appropriate direction of the working fluid movement. This article provides flow analysis of a two-way hydraulic control valve in a cartridge housing. The flow rate through the valve is controlled by a spring and an electromagnet. Design of a poppet ensures tightness in both directions in the cut-off position. Accordingly, there is no need to use additional shut-off valves. However, the fluid stream entering the valve is divided into several jets, due to the cartridge design. This makes the flow complex and difficult to be modelled. Therefore, the advanced ANSYS/Fluent software was used to carry out the analysis. The conducted tests allowed the influence of selected geometrical and physical parameters on the valve characteristics to be examined.

Contemporary gear pumps evolve towards greater internal tightness and consequently, higher working pressures. This trend necessitates the development of novel pump designs with the so-called circumferential compensation. In order to develop a new method of circumferential backlash compensation one needs a computational model for determining stresses and displacements in selected critical point. Thus the adoption of a mathematical model of the compensating element is the starting point for analytical strength calculations. In the considerations presented in this paper the semi-circular shape of the compensating lip is replaced with a model of a curved bar resting in several places on the tooth tips of the gears.The presented material is the result of research work conducted under the project entitled: Development of high-pressure gear pump designs. The project received funding from Applied Research Programme path A, contract no. PBS3/A6/22/2015. The research was carried out in the Hydraulic Drives and Machine Vibroacoustics Laboratory at Wrocław University of Science and Technology in collaboration with the Hydrotor SA company.

The subject of the study is the analysis of the brake-in process of high-pressure external gear pumps. Pumps operating under discharge pressure pt above 30 MPa can be included in the group of highly stressed devices. The durability of such devices is not only influenced by the choice of materials or surface quality after machining, but also by first commissioning and initial working conditions. Hydrostatic drive components, mainly pumps and motors due to their design require break-in but this process is often overlooked, which can have a negative effect on the efficiency and durability. The mathematical model shows that the displacement of gear shafts within the clearance in the bearing depends on the discharge pressure. It was concluded that the brake-in process should be conducted with a variable pressure step. On this basis, an attempt was made to prepare the break-in cycle, which is characterized by a constant displacement step of the gear shaft in the bearings. This newly prepared brake-in process will therefore ensure an optimal, constant volume of material removal from the housing.The material presented in the article is the result of research done under the project “Development of high-pressure external gear pump”.

Axial piston pumps are the core elements of most medium and high-pressure hydraulic systems. High volumetric efficiency and high working pressures are the main advantages of this type of pumps. Therefore it is necessary to accurately calculate the leakage flow through the gaps to design efficient high-pressure pump. The main difficulty of such calculations is the fact, that the gaps change their geometry during pumping process. The change of gaps’ geometry can be caused by the motion of pump’s elements or can be pressure-induced. Both of these factors are included in the article. The paper describes the leakage in: gap between piston and cylinder block, gap in commutation window, gaps in hydrostatic bearings, gap between commutation plate and cylinder block. The article includes methodology and results of FEM and CFD simulation of flow through deformed and undeformed gaps. Basing on the CFD results the mathematical models of such gaps were prepared and added to the article.

A method to generate an asymmetric gerotor gearset based on an elliptical outer gear tooth rotated about its center is presented. While this profile type has been known since the mid $$20^{\text {th}}$$ 20 th century, it has yet to be discussed in scientific literature. A case study is performed to quantify the effects of asymmetry on the size, flow ripple, wear rate, and contact stress of two pumps with the same geometric displacement. The results showed that applying asymmetry can have either a positive or a negative effect on each of the performance goals depending on the values of the other input parameters.

It is a well-known fact that even small deviations from the perfect cylindrical geometry of either the bore or the sealing land of spool valves may cause substantial lateral forces and, in turn, a sticking of the valve. The reason is the pressure distribution in the sealing gap which loses its axisymmetry in such cases. This effect is counteracted by a number of circumferential grooves which even the pressure distribution. That valve sticking effect can be studied by solving the Reynolds equation for such gap geometries and computing the resulting radial force. From a design viewpoint it is valuable to have a compact understanding of the role of design parameters; in the case of non-uniform sealing gaps, of the role of the imperfection parameters. Gaining compact understanding of cause effect relations with numerical solutions is difficult if more than two parameters are involved since a graphical representation by diagrams is impossible. In this paper an approximate but closed form solution is derived for a class of imperfect sealing gap geometries. They provide that immediate insight by a compact formula for the resulting lateral force. The study is based on a Ritz method for a direct solution of the variational formulation of the Reynolds equation and asymptotic expansions concerning the role of the imperfection parameters.

In this paper, pressure losses in hydraulic motor supplied with water and mineral oil (two liquids that have significantly different viscosity and lubricating properties) are described and compared. The experimental tests were conducted using an hydraulic satellite motor that is dedicated to working with different liquids, including water. The methodology of measuring the pressure drop in internal channels of this motor is also described. The known mathematical formulas describing the pressure losses in the internal channels are presented also. Experimental studies have shown that a high flow rate in the motor causes the pressure losses in the motor supplied with water to be a several percent greater than the pressure losses in the motor supplied with oil. However, low flow rates cause the pressure losses in the motor supplied with water to be about ten percent lower than the pressure losses in the motor supplied with oil. Furthermore, when the volume of the working chamber nears the minimum, additional pressure increase caused by compression of liquid occurs in this chamber.

In this paper a prototype of a flow control valve is described and numerically simulated. The flow control valve is used in hydraulic systems to maintain constant fluid flow despite changing loads of a receiver. The standard construction of this type of valves is modified mainly by eliminating the spring. The prototype consists the hydrostatically unloaded throttle valve and pressure ratio valve substituting pressure difference valve. The article concentrates on numerical simulation conducted for different positions of pressure ratio valve’s spool and various throttle valve settings. Additionally the rotation of the spool is included in simulation and its influence on valve’s characteristics is evaluated. The article also describes the methodology of determining flow characteristics of control valve. Results from numerical simulation are compared to results of experimental research.

The article describes the influence of displacement of the swash plate rotation axis on the efficiency of axial piston pumps. The dead space volume was defined as the volume of the working chamber in the extreme position of the piston at the end of the pumping phase and its variability was determined as a function of the position of the axis of rotation of the swash plate and the swing angle of swash plate. The influence of swash plate rotation axis displacement on leaks between piston and cylinder was determined. It has been proven that displacement of the swash plate rotation axis reduces the dead space volume and leaks, thus improving the volumetric efficiency visible at small swash plate swing angles. The results of a comparative study of the volumetric and total efficiency of a modified design of a pump that allows the rotation axis to be repositioned are presented. The efficiency curves for the swash plate rotation axis crossing the shaft rotation axis and for the displaced swash plate axis of rotation are compared. The article also presents the author’s construction of an axial piston pump with displaced swash plate rotation axis with a follow-up mechanism of capacity change controlled by a stepper motor. The diagram and view of the test stand are shown, as well as the results of tests of volumetric and hydromechanical pump efficiency.

The study presents the proposed intelligent real-time control system (IRCS) used to the forging process control on the 80 MN hydraulic forging press (HFP). It is a new control system applied to the industrial open-die forging in the process of elongation heavy large steel forgings. An innovative, energy-saving power supply system for the 80 MN HFP was presented. IRCS based on the parameter prediction of the forging process was developed. Compared to the previous work [1], the authors developed an IRCS for the forgings process control, which includes a model predictive control (MPC) of the multiple-input and multiple-output (MIMO) system, a predictive forging force model (PFFM), a recursive polynomial model estimator (RPME) and a discrete-time non-linear state-space model of the hydraulic system (MHS). The main goal of these studies was to develop and implement an innovative industrial process for hot open-die forging heavy, large, and hard-deformable steel forgings on the 80 MN HFP. Expectations that the application of IRCS will improve the quality and durability of forged products as well as increase the energy efficiency of the forging process have been met.

Digital fluid power means a hydraulic plant having one or more discrete valued components actively controlling the system output. In this paper authors present a solution of parallel connected of six fixed pumps. The proposed digital pumping system consists of an electrical single speed motor, fixed displacement pumps, an electromechanically repartition element and an electronic controller. This complex system which can achieve 63 flows was made in our Research Institute and in present is in the Digital hydraulic laboratory for tests.

The paper deals with the control of the test rig for measurement of the stiffness of the spring. The test rig is equipped with the integrated hydraulic actuator which allows to control the piston velocity and position and to produce the force needed for the spring compression and stiffness measurement. The integrated hydraulic actuator was developed at the department, it and has an integrated manifold with four proportional flow control valves connected as the full hydraulic resistance bridge. Each control valve is controlled separately using the input signal. That makes it possible to realize different connections and control strategies of the hydraulic cylinder using the different control algorithms. The hydraulic circuit was modelled and simulated, and the achieved simulation results are presented in the paper. The test rig is controlled using the microprocessor control system and is equipped by different transducers – position transducer, pressure transducers, force transducer to be able to collect data important for the stiffness characteristic evaluation. The experimentally obtained results and evaluated stiffness characteristic of the tested spring are presented in the following chapters.

The paper presents research of the hydraulic cylinder drive system equipped with gear pump driven by asynchronous motor fed by the frequency inverter using a developed method of pump leakage compensation (LPC) to control the flow. The pump parameters at various pressures and various angular speeds of the asynchronous motor, including in the speed range below the minimum recommended by the pump manufacturer, have been tested. The obtained pump characteristics showed the presence of two components of internal pump leakage - independent and dependent of pressure. The linear internal leakage model was developed for the pump. This model has been implemented to the verified model of the drive system of the variable ratio mechanism driven by a hydraulic cylinder - scissor lift. The pump flow correction algorithm has been added to the previously developed hydraulic cylinder speed control system. This correction was aimed at improving the mapping of the assumed speed of the hydraulic cylinder. The compensation block has been added to the hydrostatic drive of the scissor lift equipped with an open control system - developed in the LabView environment. Experimental tests confirmed the improvement in mapping of the hydraulic cylinder assumed speed regardless of its variable load resulting from the scissor system geometry and the weight of the load on the scissor lift platform. The developed leakage compensation system on the pump can be used in hydrostatic systems with fixed or variable ratio, regardless of the load on the hydraulic cylinder.

Position control is particularly important in systems with pneumatic drives. Many centres around the world are looking for an optimal and effective method especially for rod and rodless pneumatic cylinders. Position control of pneumatic drives is a difficult process due to the compressibility of the working medium, friction occurring in the drive system, stick-slip phenomenon, clearances in the cylinder, sticking of the piston to the cylinder in final positions. The problem is to set and maintain a constant speed of motion, especially in the low speed range, and to precisely stop the piston of the cylinder in intermediate positions between the end positions of the cylinder.The article presents the theoretical foundations of fuzzy logic controllers and the principles of their design for pneumatic drive systems. A fuzzy control system for an electro-pneumatic servo-drive made of a rodless cylinder controlled by a proportional flow valve has been analysed. An experimental stand for testing designed fuzzy logic controllers and assessing the quality of control has been presented. Experimental tests have been conducted for the implementation of changeover control, tracking control and following up the curvilinear trajectory.

This paper presents the modelling and simulation of transient flow in micro-hydraulic pipe systems. Liquid stream energy dissipation occurs mainly as a result of friction losses. Theoretical considerations of water hammer resulting from rapid valve closing, supported by experimental verification, were undertaken. The experimental system incorporated a straight two-meters long section of a steel pipe with an internal diameter of 4·10−3 m. An attempt was made to determine the degree of conformity of the transient flow model (previously verified in conventional pipes) to the experimental results obtained for small-internal-diameter pipes. Shear stress on the pipe wall was modelled using first a simplified quasi-steady approach and then an effective modified unsteady friction model. The pressure waveforms at the valve (at the downstream end of the pipe) were obtained for initial flow velocity, v01 = 2.39 m/s and v02 = 1.14 m/s, respectively. Experimental studies were carried out in the region of laminar flows with Reynolds numbers below 100.

The leveling process for the hydraulic lifting mechanism of the bricklaying robot is complicated. The article presents the designing process and method of controlling a four-cylinder electro-hydraulic (EH) servo drives system. As a part of the research, a mathematical model was established and the process of leveling a mobile support platform of the bricklaying robot was optimized. A kinematic analysis of the lifting mechanism was carried out. The mathematical model of the hydraulic system was presented. The work scheme was designed on the base of the strategy of leveling and planning the displacement trajectory of individual EH servo drive. The designed control system takes into account not only position errors for individual drive axis, but also synchronization errors with neighboring axes. The synchronization function for the control system, which takes into account the positioning errors of individual drive axis, was specified.

The paper presents problems related to the lubrication of moving machine nodes that are operating in an aggressive environment occurring in copper mines. The analysis was based on the exploitation of self-propelled wheeled machines, such as transport vehicles, loaders, drilling and anchoring cars. In self-propelled machines there are from 15 to 40 moving parts exposed to high impact loads and stresses. These are mainly bolted joints performing swinging motion as well as rotary motion at low rotational speeds up to 10 rpm. Observations and operational tests of several dozen manifolds and pumps operating in the environment occurring in KGHM Polska Miedź copper mines were carried out during two years. It was stated that elements made of aluminum or its alloys should not be used, and should be replaced with bronze (the proposal results in the increase of weight and costs of the system, but observational studies have shown that the durability and reliability of pumps increased more than three times, and the durability of the manifolds with the bronze body has increased more than five times). It was recommended to avoid the use of electronic systems on actuators in central lubrication systems (control systems should be encapsulated) and to use pumps with a hydraulic drive, which is commonly used in the working elements of machines used in a copper mine. The proposed lubrication system made of bronze and with hydraulic drive is several times more durable and cheaper to operate compared to the central lubrication systems used so far.

The article presents the results of investigations for reducing noise emissions from a hydraulic power unit. The main sources of noise like electric motor and bellhousing in the power unit were determined. As a measure for the noise reduction the sound-insulating capsulation for the electric motor with mounting bracket (bellhousing) was used. With that measure a significant reduction in sound power from the power unit has been achieved.

This paper focuses on the noisiness of work machines in the workplace. It assesses the effectiveness of contemporary solutions for lowering the sound level of work machines. Active and passive methods of noise suppression are distinguished. The importance of the two kinds of methods in the process aimed at reducing the noise generated by contemporary equipment and making the latter comply with the current regulations is highlighted. Original solutions designed, made and tested in the Department of Hydraulic Drives and Automation at Wrocław University of Science and Technology are presented.

The possibilities of ultrasonic cleaning of elastic surfaces as exemplified in fabrics are considered. The effect of ultrasonic cavitation processing of fabric for its strength characteristics is analyzed. It has been experimentally proven that cavitation processing of fabric leads to less mechanical destruction compared to traditional drum-type washing. The effect of ultrasonic cavitation processing on the brightness of dyed fabrics faded over time has been experimentally studied. Attention is paid to the inactivation of microorganisms harmful to human health in the ultrasonic cavitation field. Based on the conducted research, the design of an ultrasonic emitter drive and technological equipment for the implementation of technology of ultrasonic cavitation cleaning of elastic surfaces is proposed.

The article is devoted to the study of the possibilities of ultrasonic cavitation inactivation of microorganisms. The possibilities of constructing mobile processing equipment for implementing the technology of ultrasonic cavitation inactivation of harmful and dangerous microorganisms for human health are considered. Two possible ways of increasing the intensity of ultrasonic exposure to biological objects were presented due to the concentration of ultrasonic energy and cavitation treatment in a thin layer on the radiation surface. The results of microbiological analysis as well as recommendations to increase the efficiency of cavitation inactivation of microorganisms had given.

High-intensity ultrasonic vibrations allow to intensify many physical and chemical processes in liquids. In particular, high-intensity ultrasonic vibrations allow efficiently removing the dissolved gases from a liquid. The ultrasonic equipment consists of ultrasonic generator, surfaces for introducing the ultrasonic vibrations into the liquid, cavitation chamber filled with liquid, in which ultrasonic cavitation occurs in the process fluid under the action of intense ultrasound. As higher the intensity of ultrasound, as higher the intensity of the physical processes accompanying ultrasonic cavitation. The intensity of ultrasound is proportional to the value of sound pressure. As a result, an increase in the sound pressure value intensifies the processes occurring in the process fluid.This work is devoted to issues related to equipment efficiency improving for introducing the high-intensity ultrasonic vibrations into a liquid. The cavitation layer which shields ultrasonic vibrations is formed on the surface of the emitter with the introduction of high-intensity ultrasound.The cavitation layer consists of a large number of cavitation bubbles. As a result, a liquid can be considered as a liquid with decreased density. This leads to reduction of the liquid wave resistance.This significantly reduces the value of sound pressure. The use of a liquid pressure transformer makes it possible to increase the sound pressure at the same magnitude of the oscillation amplitude.The liquid pressure transformer is a cavitation chamber with a variable cross-sectional area. The length of such transformer should be a multiple of half the length of the sound wave in the liquid. A liquid pressure transformer can be considered as a resonant system.The paper presents calculations of liquid pressure transformers, modeling of their work and examples of their practical implementation in equipment for biological contaminants removing and degassing.

The flow in the throttle channel of the hydrodynamic cavitator was visualized. Previous studies have shown that luminous radiation - luminescence can be observed in the area at the output of the throttle under certain conditions of cavitation. This phenomenon is not acceptable in some hydraulic systems, so it is necessary to study the patterns and conditions of its occurrence. As today there is no solid theory of its origin, this study aims to study the effect of material from which the elements of the throttle are made on the intensity of luminescence. A model of a hydrodynamic cavitator and a series of screws of heterogeneous materials, which are at opposite parts of the triboelectric series, were developed. The model’s hydraulic tests showed that the material the throttle elements are made of has some influence on the radiation intensity.

As a result of development works, which were carried out by Wrocław University of Science and Technology and by HYDROMAR company and which focused on a new design of hydraulic cylinders characterized by, among others, an increased degree of reliability, it was possible to develop and test a prototype of the new solution. During the implementation of the project, a new hydraulic cylinder testing stand was designed, which allows the identification of dynamic phenomena occurring in the hydraulic power system. Tests of the new solution were carried out in the area of both dynamic and thermal phenomena associated with the exchange of liquid in the cylinder chambers. In terms of dynamics, the research allowed identifying the responses of the cylinder system with supply lines and flow control valves to a variable, external dynamic excitations. The tests also allowed determining the response of the hydraulic cylinders with supply lines and control valves to rapid overloading. The dynamic load was simulated by switching the control valves in a cut-off position during the movement of a working system arm with specific mass parameters. Comparative tests of dynamic response systems were carried out using a classic cylinder and a new design of a hydraulic power supply system. The article presents the results of tests and of the preliminary analysis of the impact that the type of hydraulic power supply system has on the dynamic response of the system. It should be emphasized that the presented results are part of a broad research and implementation project carried out in cooperation between the research and scientific unit and the industrial partner.

The paper indicates some sources of external forces acting on microhydraulic valves. Mechanical vibrations characterized by a wide frequency spectrum were considered as an example of these excitations, with high-frequency vibrations being the most dangerous in microhydraulic components. The impact of external mechanical vibrations on the microhydraulic relief valve results in falling into the vibrations of the valve control element and causes changes in the amplitude-frequency spectrum of pressure pulsation of the system in which the valve works. The resulting pressure pulsation causes further propagation of mechanical vibrations, among others through vibrating microhydraulic pipes. The paper attempts to use the interval classification of induction trees to determine the impact of selected valve design and operating parameters on valve sensitivity to external mechanical vibrations. In the generation of inductive decision trees, a series of tests are carried out in a specific order. The criterion for choosing the attribute used to expand the tree is entropy as a measure of information. For hierarchically ordered classes of measuring intervals in the whole frequency range, induction trees defining the range of the most important measuring points were generated. Then, in order to acquire knowledge from data, it is possible to select the most important individual points and rules determining the relationships between construction parameters.

Reciprocating compressors operated in gas transmission systems are equipped with passive pressure pulsation dampers protecting the system against the negative effects of excessive pulsation and the related dynamic phenomena. The transmission loss characteristics are determined by means of numerical simulations or measurements at test stands. Most often, however, both the simulations and the bench tests cover either only some assumed simplified operating conditions, e.g. experimental tests of acoustic characteristics, without taking into account the flow of medium, or numerical simulations without taking into account the geometry of the entire installation (the anechoic boundary condition). The article presents a proposed methodology for determining the transmission loss characteristics of pulsation dampers with allowance for variable operating parameters and with the use of a specially designed test stand equipped with a piston compressor and a variable volume damper. In addition, the influence of operational parameters (flow rate and pressure) on pressure pulsation attenuation was tested. The research results presented in the article may form the basis for the development of new improved mathematical models simulating the characteristics of pulsation dampers with allowance for the operational parameters of a system.

Vibrational behaviour of hydraulic power system elements is crucial in aspects of noise problems. Hydraulic lines used in engineering systems to transfer hydraulic energy are also a structural and fluid coupling between vibrating elements of the entire system. Excitation generated in different places of the hydraulic systems due to external loads, control elements or flow pulsation are all transferred through hydraulic lines on which resonances may occur. Experimental investigations were undertaken in order to identify the influence of hydraulic pressure on the natural frequencies and mode shapes of a basic hydraulic line model. Modal analysis was conducted on a hydraulic line at several pressure increments to identify the change in natural frequencies and mode shapes.

The article considers the problems of ensuring the durability of technological equipment for ultrasonic cavitation. The results of planning and conducting an experimental investigation of the structural materials erosive destruction from which ultrasonic emitters and parts of cavitation chambers are presented. The study allowed us to determine the most preferred materials in terms of cavitational strength in the presence of fatigue stresses.

Water is a natural working fluid, which is increasingly used in hydraulic systems due to environmental requirements. Making plastic parts allows us to enjoy the benefits of this liquid without introducing expensive materials or coatings. In the hydraulic pump, gears are a key component, therefore the type of material used to make them and the process of their production affect the operating parameters of the pump. The article presents the results of tests of volumetric efficiency of a water-supplied hydraulic pump with gears from a couple of materials (PPS+GF40 and PEEK) made by two methods: injection moulding and machining. The results were compared with the plots for the pump with gears from POM when working with hydraulic oil. The influence of used materials and manufacturing methods on pump efficiency was discussed.

In the paper results of experimental tests on multi-plate wet clutch torque capacity for various diameters and numbers of friction plates are presented. Construction of an apparatus for laboratory tests of wet clutch engagement, drag torque and maximum torque is shown. Methodology of maximum torque capacity experiment and hydraulic circuit diagram, which supplies a motor and an actuator for the experiment are described. Analytically calculated values of torque capacity are compared to results obtained with laboratory tests. Additionally, the article includes FEM analysis, that was used to obtain pressure distribution on every friction surface in relation to force applied to the assembly and to determine differences in these distributions. The analysis has helped to determine a mean radius of sliding interface on each surface and to compare their values to other plates and to result calculated analytically. A diagram is shown in the article, that demonstrates pressure concentration as a function of number of friction surfaces.

The proposed material presents the results of experimental and theoretical studies of the hydrodynamic mechanism for the development of secondary circulating flows in spherical geometry tanks as applied to the tasks of ensuring flight stability and effective controllability of a spacecraft at near-Earth orbit. It has been established that secondary flows arising in the reservoir meridional planes have the form of circulations (one or several) and are capable to influence the distribution of velocity vector components—azimuthal, radial, and meridional.In turn, the hydrodynamic picture of the three-dimensional flow significantly affects the distribution of force effects from the liquid to the tank walls and the internal guiding baffles, which provides the basis for their more accurate calculation and accounting in the onboard software package of the spacecraft. Noticeable differences between the experimental results and theoretical data obtained by other authors are established.The velocity profiles constructed from the measurement results give a complete three-dimensional picture of the hydrodynamic mechanism for the circulations development and their effect on the circular torque or pressure distribution on the radial damping baffles.

Paper presents the prototype of the gerotor pump with body and gear set made of plastics, its functional tests (checking measurements, run-in process) and experimental research of the efficiency characteristics. The positive results of previous researches of plastics gear sets allowed for the next step in the design of the entire plastic body of the gerotor pump. Experimental research was aimed at checking the proper functioning of the pump with a plastic body and verification of operational factors, impact of speed and pressure on the pump characteristics. Functional tests and experimental studies confirmed the correctness of the structural solution of the pump body. The pump with a plastic body was working correctly as a low pressure unit at low range of rotational speed. Experimental research of the plastic gerotor pump confirm that plastics as a construction material can be used in hydraulics.

The paper presents the process of designing a base made of PET that will be used as an element of a hydraulic cylinder made of composite materials. The requirements for the designed element include the possibility of working with mechanical and thermal loads comparable to conventional cylinders. The choice of material based on the set criteria and assigned weights, experimental research of its real properties, numerical calculations of the element as well as experimental verification on the real object were presented. The material’s non-linearity and the change of its parameters as a function of working temperature were taken into account.In order to obtain real values of tensile strength and Young’s modulus, static tensile tests were carried out in accordance with ISO 527–2. The obtained results allowed to include non-linear material properties in the numerical calculations. To know the glass transition temperature and at the same time make sure that the elements made of PET material can be used at temperatures up to 80stC, measurements were carried out using the DMA (Dynamic Mechanical Analysis) method in the temperature range from −120 °C to 250 °C.Numerical calculations were made using Ansys Mechanical 19.0 software. After the design stage was completed, a base prototype was made that was subjected to static tests in the pressure range up to 25 MPa. Element strains were recorded using strain gauges, which allowed validation of the numerical model.

Nowadays the most commonly used brakes are dry ones. However in special situations, harsh and aggressive environments, there was a need for more durable and more powerful brakes. The biggest advantage of wet multidisc brakes is that they can be used in big variety of conditions, from extremely cold to the extremely hot, from very clean to very dusty environment and so on. Because of their very responsible part in heavy machinery design, wet multi-disc brakes presents a very attractive and hard task as for mechanical engineer as for researchers all around the world. This paper presents a practical approach to wet multi-disc brake design improvement. Namely, the most of present wet multi-disc brakes uses a radial placed compression springs for brake activation. This solution leads to lots of difficulties during brakes manufacturing and brakes maintenance. At this paper is presented concept of compression springs replacement with belleville springs. Concept is proven by hand and FEM calculations. At the end of the paper conclusion and further research directions are given.

Performance of the hydrostatic high-pressure drive systems is affected by the changes of working fluid’s volume. Presence of air bubbles in the fluid cause this problem to be even more serious. To study this phenomenon precise measurements of fluid’s bulk modulus are necessary. Different measurement methods are applied, but they are either limited to low pressure range or give inaccurate results.To solve the problem the new measurement device was built. It allows to directly measure volume changes of both pure fluid or fluid-air mixture within the wide pressure and temperature range. Both adiabatic and isothermal module may be determined, the tested fluid may be pure or aerated.Measurements of different fluids were made including vegetable oils (rapeseed, sunflower and linseed), mineral oil and synthetic oil.

The article presents an overview of various materials of which pistons, piston rods and cylinders of hydraulic actuators are currently made. Surface modification issue, aimed at improving both strength and operational properties of the components is also discussed.The materials, of which the basic parts of the actuators are made, will be discussed in detail. In the case of cylinders, it is usually quality steel. Pistons are made of ductile iron or structural steel. Sometimes aluminium alloys are also used for reducing the weight of the element while maintaining adequate mechanical strength. Piston rods are currently one of the most complex in machining parts. They are made of surface-hardened or quenched and tempered steel (possibly stainless steel) and are most often coated with chromium. Recently, many alternatives to chromium have been created due to its harmfulness for people and environment. These are, for example, tungsten carbide coatings and amorphous carbon coatings. Usage of composite materials and plastics is also listed among modern technologies for making components of actuators.

The application of plastics instead of traditional metal materials is a new development trend in the field of fluid power. The Fluid Power Research Group (FPRG) from Wroclaw University of Science and Technology conduct research in this field. In previous works [6, 7, 11, 16–18], which were published on that topic, design solutions where shown, as well as research of models of typical hydraulic elements like gerotors, valves and cylinders, which were made of plastics. on the problem of designing, manufacturing and testing of fluid power elements made of plastics. The aim of this paper is to present the development of the works on hydraulic elements made of plastics. The main novelties are: a gerotor pump with a plastic body, research on global deformation of plastic cylinder, visualization and computer simulations of the valve poppet/seal assembly in plastic hydraulic valves, as well as innovative hydraulic systems.