typical hydraulic pump efficiency made in china

We Jinan Highland Hydraulic Pump Co., Ltd. is a professional manufacture making hydraulic pump, hydraulic motor and hydraulic test bench. Our products mainly include:

By introducing Heavy Series 21-24 static hydraulic transmission from SAUER-SUNDSTRAND of America, we can provide axial hydraulic pump and hydraulic motor assembly and hydraulic system with high quality, high-performance parameters.

Jinan High Land Hydraulic Pump Co., Ltd is a professional and high-tech enterprise. The company boasts solid technical strength, scientific management, advanced production testing equipment.

international equipment, the company has developed high-level hydraulic chechout gauges and comprehensive testing tables among portable hydraulic testing series. The key parts of pump and motor accessories are made of imported raw-material and hydraulic comprehensive testing tables are exported to different countries.

Hydraulic systems are in general members of the fluid power branch of power transmission. Hydraulic pumps are also members of the hydraulic power pack/hydraulic power unit family. Hydraulic units are encased mechanical systems that use liquids for hydraulics.

The hydraulic systems that hydraulic pumps support exist in a range of industries, among them agriculture, automotive manufacturing, defense contracting, excavation, and industrial manufacturing. Within these industries, machines and applications that rely on hydraulic pumps include airplane flaps, elevators, cranes, automotive lifts, shock absorbers, automotive brakes, garage jacks, off-highway equipment, log splitters, offshore equipment, hydraulic motors/hydraulic pump motors, and a wide range of other hydraulic equipment.

When designing hydraulic pumps, manufacturers have many options from which to choose in terms of material composition. Most commonly, they make the body of the pump–the gears, pistons, and hydraulic cylinders–from a durable metal material. This metal is one that that can hold up against the erosive and potentially corrosive properties of hydraulic fluids, as well as the wear that comes along with continual pumping. Metals like this include, among others, steel, stainless steel, and aluminum.

First, what are operating specifications of their customer? They must make sure that the pump they design matches customer requirements in terms of capabilities. These capabilities include maximum fluid flow, minimum and maximum operating pressure, horsepower, and operating speeds. Also, based on application specifications, some suppliers may choose to include discharge sensors or another means of monitoring the wellbeing of their hydraulic system.

Next, what is the nature of the space in which the pump will work? Based on the answer to this question, manufacturers will design the pump with a specific weight, rod extension capability, diameter, length, and power source.

Manufacturers must also find out what type of substance does the customer plan on running through the pumps. If the application calls for it, manufacturers can recommend operators add other substances to them in order to decrease the corrosive nature of certain hydraulic fluids. Examples of such fluids include esters, butanol, pump oils, glycols, water, or corrosive inhibitors. These substances differ in operating temperature, flash point, and viscosity, so they must be chosen with care.

All hydraulic pumps are composed in the same basic way. First, they have a reservoir, which is the section of the pump that houses stationary fluid. Next, they use hydraulic hoses or tubes to transfer this fluid into the hydraulic cylinder, which is the main body of the hydraulic system. Inside the cylinder, or cylinders, are two hydraulic valves and one or more pistons or gear systems. One valve is located at each end; they are called the intake check/inlet valve and the discharge check/outlet valve, respectively.

Hydraulic pumps operate under the principle of Pascal’s Law, which states the increase in pressure at one point of an enclosed liquid in equilibrium is equally transferred to all other points of said liquid.

To start, the check valve is closed, making it a normally closed (NC) valve. When the check is closed, fluid pressure builds. The piston forces the valves open and closes repeatedly at variable speeds, increasing pressure in the cylinder until it builds up enough to force the fluid through the discharge valve. In this way, the pump delivers sufficient force and energy to the attached equipment or machinery to move the target load.

When the fluid becomes pressurized enough, the piston withdraws long enough to allow the open check valve to create a vacuum that pulls in hydraulic fluid from the reservoir. From the reservoir, the pressurized fluid moves into the cylinder through the inlet. Inside the cylinder, the fluid picks up more force, which it carries over into the hydraulic system, where it is released through the outlet.

Piston pumps create positive displacement and build pressure using pistons. Piston pumps may be further divided into radial piston pumps and axial piston pumps.

Radial pumps are mostly used to power relatively small flows and very high-pressure applications. They use pistons arranged around a floating center shaft or ring, which can be moved by a control lever, causing eccentricity and the potential for both inward and outward movement.

Axial pumps, on the other hand, only allow linear motion. Despite this, they are very popular, being easier and less expensive to produce, as well as more compact in design.

Gear pumps, or hydraulic gear pumps, create pressure not with pistons but with the interlocking of gear teeth. When teeth are meshed together, fluid has to travel around the outside of the gears, where pressure builds.

External gear pumps facilitate flow by enlisting two identical gears that rotate against each other. As liquid flows in, it is trapped by the teeth and forced around them. It sits, stuck in the cavities between the teeth and the casing, until it is so pressurized by the meshing of the gears that it is forced to the outlet port.

Internal gear pumps, on the other hand, use bi-rotational gears. To begin the pressurizing process, gear pumps first pull in liquid via a suction port between the teeth of the exterior gear, called the rotor, and the teeth of the interior gear, called the idler. From here, liquid travels between the teeth, where they are divided within them. The teeth continue to rotate and mesh, both creating locked pockets of liquid and forming a seal between the suction port and the discharge port. Liquid is discharged and power is transported once the pump head is flooded. Internal gears are quite versatile, usable with a wide variety of fluids, not only including fuel oils and solvents, but also thick liquids like chocolate, asphalt, and adhesives.

Various other types of hydraulic pumps include rotary vane pumps, centrifugal pumps, electric hydraulic pumps, hydraulic clutch pumps, hydraulic plunger pumps, hydraulic water pumps, hydraulic ram pumps, portable 12V hydraulic pumps, hydraulic hand pumps, and air hydraulic pumps.

Rotary vane pumps are fairly high efficiency pumps, though they are not considered high pressure pumps. Vane pumps, which are a type of positive-displacement pump, apply constant but adjustable pressure.

Centrifugal pumps use hydrodynamic energy to move fluids. They feature a rotating axis, an impeller, and a casing or diffuser. Most often, operators use them for applications such as petroleum pumping, sewage, petrochemical pumping, and water turbine functioning.

Electric hydraulic pumps are hydraulic pumps powered by an electric motor. Usually, the hydraulic pump and motor work by turning mechanisms like impellers in order to create pressure differentials, which in turn generate fluid movement. Nearly any type of hydraulic pump can be run with electricity. Most often, operators use them with industrial machinery.

Hydraulic clutch pumps help users engage and disengage vehicle clutch systems. They do so by applying the right pressure for coupling or decoupling shafts in the clutch system. Coupled shafts allow drivers to accelerate, while decoupled shafts allow drivers to decelerate or shift gears.

Hydraulic ram pumps are a type of hydraulic pump designed to harness hydropower, or the power of water, to elevate it. Featuring only two moving hydraulic parts, hydraulic ram pumps require only the momentum of water to work. Operators use hydraulic ram pumps to move water in industries like manufacturing, waste management and sewage, engineering, plumbing, and agriculture. While hydraulic ram pumps return only about 10% of the water they receive, they are widely used in developing countries because they do not require fuel or electricity.

Hydraulic water pumps are any hydraulic pumps used to transfer water. Usually, hydraulic water pumps only require a little bit of energy in the beginning, as the movement and weight of water generate a large amount of usable pressure.

Air hydraulic pumps are hydraulic pumps powered by air compressors. In essence, these energy efficient pumps work by converting air pressure into hydraulic pressure.

Hydraulic pumps are useful for many reasons. First, they are simple. Simple machines are always an advantage because they are less likely to break and easier to repair if they do. Second, because fluid is easy to compress and so quick to create pressure force, hydraulic pumps are very efficient. Next, hydraulic pumps are compact, which means they are easy to fit into small and oddly shaped spaces. This is especially true in comparison to mechanical pumps and electrical pumps, which manufacturers cannot design so compactly. Speaking of design, another asset of hydraulic pumps is their customizability. Manufacturers can modify them easily. Likewise, hydraulic pumps are very versatile, not only because they are customizable, but also because they can work in places where other types of pump systems can’t, such as in the ocean. Furthermore, hydraulic pumps can produce far more power than similarly sized electrical pumps. Finally, these very durable hydraulic components are much less likely to explode than some other types of components.

To make sure that your hydraulic pumps stay useful for a long time, you need to treat them with care. Care includes checking them on a regular basis for problems like insufficient fluid pressure, leaks, and wear and tear. You can use diagnostic technology like discharge sensors to help you with detect failures and measure discharge pressure. Checking vibration signals alone is often not enough.

To keep yourself and your workers safe, you need to always take the proper precautions when operating or performing maintenance and repairs on your hydraulic pumps. For example, you should never make direct contact with hydraulic fluid. For one, the fluid made be corrosive and dangerous to your skin. For two, even if the pump isn’t active at that moment, the fluid can still be pressurized and may potentially harm you if something goes wrong. For more tips on hydraulic pump care and operation, talk to both your supplier and OSHA (Occupational Safety and Health Administration).

Pumps that meet operating standards are the foundation of safe and effective operations, no matter the application. Find out what operating standards your hydraulic pumps should meet by talking to your industry leaders.

The highest quality hydraulic pumps come from the highest quality hydraulic pump manufacturers. Finding the highest quality hydraulic pump manufacturers can be hard, which is why we have we listed out some of our favorites on this page. All of those whom we have listed come highly recommended with years of experience. Find their information nestled in between these information paragraphs.

Once you have put together you list, get to browsing. Pick out three or four hydraulic pump supply companies to which you’d like to speak, then reach out to each of them. After you’ve spoken with representatives from each company, decide which one will best serve you, and get started on your project.

China hydraulic pump manufacturers, hydraulic pumps and motors, hydraulic pump parts, piston pump parts, hydraulic pump, hydraulic spare parts, hydraulic piston pump, hydraulic vane pump, hydraulic gear pump, Hydraulic Motor,Pilot Pump, Charge Pump for Rexroth,Caterpillar,Vickers,Denison,Sauer,Kawasaki,Commercial,Linde,Parker,Liebherr,Komatsu,Eaton,Daikin,Kubota,Johndeer,Hitachi. T6C,T6D,T6E,45VQ,35VQ,25VQ,20VQ,V10,V20,Hydraulic Motor.

There are many local to watch for. So in accordance with the pressure to pick it, so what"s pump selection matters watching it? Today, we look at it together now.

Required pressure (1) hydraulic pressure of the hydraulic pump pressure slightly higher than the executing agency selected the best, China"s machine tool profession hydraulic pump is usually calibrated pressure of 6.3MPa or less. For a detailed working conditions are not the same, the selected pressure pay attention to the following situation: 1) according to a certain output power, under the same pressure and flow condition, the volume of the pump or motor should be as small as 2) With increasing pressure, the oil to heat, oil temperature increases, valves and seals. etc. leak increases. 3) high pressure valve and transmission structure will increase, it is difficult to achieve weight reduction and miniaturization of the pump.

(3) hydraulic pump drive power of resolution, based on the work of the hydraulic pump discharge pressure and useful to determine the oil pump drive power

??1, fuel pump method straight axis swashplate pressure cylinder power plugs from the sucking-two oil types. Pressure for large liquid-type oil pump has a pressure tank are selected, there are also supplemented with hydraulic oil with the body of the cylinder inlet port to supply pressure oil pump liquid type oil absorption since. Strong pressure from the sucking pump ability, without external oil supply. If found to reduce cylinder speed or stuffy that should be made, when the car hydraulic pump repair, check the impeller marginal whether existing injury blow is like, the internal gear pump space is not too large. About suction fluid from the inner, cylindrical plunger pressure oil tank shall not be less than the lower limit of the oil standard sufficient enough to maintain insurance, the number of hydraulic oil. Cleanliness of the hydraulic oil pump pressure fluid, high life expectancy longer apply.

????2, hydraulic piston bearing the heaviest axis is to support member unit, assuming the bearing clearance occurs, you can not pump fluid within the Department of friction normal space permits three pairs, also deputy rub together all bad break The hydrostatic bearing oil film thickness, reduce the number of bearing shaft pump plunger used to make a life. According to data supplied by the pump manufacturer are flat bearing axis, using life expectancy is 10000h, but also to go beyond this need to change the value of the new port. To the axis of the discharge under split bearings, no professional inspection equipment is unable to check the bearing axis gap swim out, can only use visual, such as found in the table change or roller marks marked with pale, it must be replaced. In more should, when bearing axis change note bearing the letters and the type of the original column are large selection of plunger shaft bearing large load bearing capacity, the best gauge of the original acquisition of the former grid, home plant products, assuming that the replacement of another brand, Please bearing axis due to the experience of teaching staff look-up table on the exchange, the intent is to uphold the like of fine grade and load capacity of the bearing axis.

Fixed displacement due to construction constraints, usually only for that gear pumps use the constant flow of hydraulic source. However, the attachment into the threaded connection on the progress of its planned combination valve function, decrease system cost and system reliability of progress is useful, therefore, the gear pump function can come near the price of expensive, messy piston.

Americans like to celebrate successful entrepreneurs who started out with little more than the shirt on their back. But most of us have never heard of Liping Wong. Like a Steve Jobs of the fluid-power world, Mr. Wong started out making pneumatic cylinders in his garage near Shanghai with just two employees. Twenty-five years later his company, Hengli (www.hengli-js.com) is a $2 billion powerhouse in China and reportedly the world’s largest producer of hydraulic cylinders.

In 2009, Hengli built what’s considered the largest hydraulic cylinder production facility in the world, with an annual capacity of 500,000 pieces. More recently it acquired Shanghai Lixin Hydraulic Co., a well-established hydraulics manufacturer capable of turning out 1.5 million valves per year, and it developed a line of piston pumps. That opened the door to complete systems capabilities.

It’s part of Mr. Wong’s vision to make Hengli a worldwide brand, explained Justin Fluegel, general manager of Hengli America. Today, there is no Chinese equivalent of a Rexroth, Parker or Eaton recognized across the globe as a source of high-quality hydraulics. His goal is to change that. With sights on international expansion, three years ago they opened a Chicago office to focus directly on the U.S market.

“There’s a perception of China being a low-quality, high-quantity supplier,” he said. He related that in the 1950s, Japanese products were viewed as mass produced and cheap, but inferior. Thirty years later they became known for quality, delivery and efficiency. China is undergoing that same transition, with companies like Hengli developing and delivering high-quality, highly engineered products.

Being vertically integrated also helps streamline processes and logistics that bring benefits to American customers in terms of cost and delivery, said Fluegel. For instance, while most cylinder manufacturers outsource plating (typically with a three-week turnaround) Hengli controls it in-house. As a result, normal lead times for cylinder delivery are about on par with U.S. suppliers, around 10 to 12 weeks – although rush orders are met in half that.

Calculation of preliminary cooler capacity: Heat dissipation from hydraulic oil tanks, valves, pipes and hydraulic components is less than a few percent in standard mobile equipment and the cooler capacity must include some margins. Minimum cooler capacity, Ecooler = 0.25Ediesel

At least 25% of the input power must be dissipated by the cooler when peak power is utilized for long periods. In normal case however, the peak power is used for only short periods, thus the actual cooler capacity required might be considerably less. The oil volume in the hydraulic tank is also acting as a heat accumulator when peak power is used.

The system efficiency is very much dependent on the type of hydraulic work tool equipment, the hydraulic pumps and motors used and power input to the hydraulics may vary considerably. Each circuit must be evaluated and the load cycle estimated. New or modified systems must always be tested in practical work, covering all possible load cycles.

Americans like to celebrate successful entrepreneurs who started out with little more than the shirt on their back. But most of us have never heard of Liping Wong. Like a Steve Jobs of the fluid-power world, Mr. Wong started out making pneumatic cylinders in his garage near Shanghai with just two employees. Twenty-five years later his company, Hengli (www.hengli-js.com) is a $2 billion powerhouse in China and reportedly the world’s largest producer of hydraulic cylinders.

In 2009, Hengli built what’s considered the largest hydraulic cylinder production facility in the world, with an annual capacity of 500,000 pieces. More recently it acquired Shanghai Lixin Hydraulic Co., a well-established hydraulics manufacturer capable of turning out 1.5 million valves per year, and it developed a line of piston pumps. That opened the door to complete systems capabilities.

It’s part of Mr. Wong’s vision to make Hengli a worldwide brand, explained Justin Fluegel, general manager of Hengli America. Today, there is no Chinese equivalent of a Rexroth, Parker or Eaton recognized across the globe as a source of high-quality hydraulics. His goal is to change that. With sights on international expansion, three years ago they opened a Chicago office to focus directly on the U.S market.

“There’s a perception of China being a low-quality, high-quantity supplier,” he said. He related that in the 1950s, Japanese products were viewed as mass produced and cheap, but inferior. Thirty years later they became known for quality, delivery and efficiency. China is undergoing that same transition, with companies like Hengli developing and delivering high-quality, highly engineered products.

Being vertically integrated also helps streamline processes and logistics that bring benefits to American customers in terms of cost and delivery, said Fluegel. For instance, while most cylinder manufacturers outsource plating (typically with a three-week turnaround) Hengli controls it in-house. As a result, normal lead times for cylinder delivery are about on par with U.S. suppliers, around 10 to 12 weeks – although rush orders are met in half that.

The principle of the hydraulic system for an accelerated life test (ALT) is shown in Figure 18. Because of the repeated hydraulic circuit, the entire hydraulic system is simplified into a single pump hydraulic circuit in Figure 18. A direct acting overflow valve is selected as a loading valve to set the pressure of the acceleration circuit and the collection circuit. The two-position four-way electromagnetic valve, cooperating with the direct acting overflow valve, is used for switching between the two circuits [25].

The test-bed is equipped with temperature sensor to monitor the temperature in real time to ensure the single variable. It is also equipped with pressure and flow sensors to collect pressure and flow data. Acceleration sensors are installed in the vertical direction, horizontal direction and axial direction of the gear pump to measure the vibration of the pump casing. A torque sensor is set at the connection of gear pump and motor to monitor the change of torque and speed. In this experiment, pxie-1082 processor is selected and used together with LabVIEW control panel. The processor is efficient and fast, and integrates signal acquisition and control. The measurement and control hardware structure of the gear pump ALT device is shown in Figure 19.

In this experiment, the most widely used gear pump in China is selected, and its model is CBW-F304-CFP. The overflow valve is used as the pressure loading valve to adjust the pressure. According to the structural characteristics of the tested gear pump, the pressure stress is determined as the acceleration stress of this test. On the basis of not changing the failure mechanism, combined with the characteristics of the step-accelerated stress test, three stress levels are selected between the rated pressure of 20 MPa and 30 MPa, they are 23 Mpa, 25 MPa and 27 Mpa respectively. According to the industry standard Hydraulic gear pump JBT7014.2-2018, under the rated working condition, the volume efficiency is less than 82%, which is considered as failure [26,27]. Using a quantitative truncation method, when one of the four pumps reaches the specified amount of degradation for two consecutive measurements, the stress is raised to the next stress stage. According to the principle of single variable, ensure that the pollution degree of hydraulic oil does not exceed NAS 6, the rotation speed is maintained at about 1470 rpm, and the oil temperature is constant at about 50 °C. The test procedure is as follows:Disassemble and survey the four gear pumps under test to ensure no wear inside. After disassembly and observation, clean the parts, restore the pump to its original state and install it on the test stand.

This experiment uses a quantitative truncation method. When the flow of the external gear pump drops to the specified degradation amount, the stress is increased to the next stage. In the final stress stage, when the flow reaches the specified degradation amount, the test is terminated.

As observed in Figure 20, the groove of the oil suction chamber is deeper because of the deflection deformation caused by the high pressure of the pressure oil chamber. At the same time, iron chips generated in wear also contributes to the scratches in the pressure oil chamber, which is consistent with the theoretical analysis results. It can be found from Figure 21 that there are many slight scratches on the surface of the floating bush, which is similar to the results of theoretical analysis. This shows that the wear of the end face has a serious effect on the failure of the gear pump.

In order to judge the degradation state of the gear pump through the method of flow field simulation calculation, the volumetric efficiency data obtained from the simulation and the volumetric efficiency data obtained from the wear degradation test were fitted with cubic functions. The simulation results are analyzed from two aspects of different radial wear conditions and different end wear conditions, and it is considered that the intersection point between the fitting curve and the specified threshold line is the real degradation point [28,29,30]. The fitting curve of the test data and the simulated fitting curve under the radial wear clearance are shown in Figure 22, and the fitting curve of the test data and the simulated fitting curve under the end face wear clearance are shown in Figure 23.

In Figure 22 and Figure 23, the abscissa corresponding to the simulated fitting curve is the wear gap, and the abscissa corresponding to the experimental fitting curve is the experimental time [31,32]. The reasons are as follows: (i) the relationship between flow rate and time cannot be measured in the simulation, but the change of wear gap with flow rate can be obtained; (ii) the flow rate can be monitored in real time during the experiment, but the change in the degree of wear of the gear pump cannot be monitored in real time [33,34].

It can be seen from the simulation fitting curve that the volumetric efficiency of the four sample pumps decreases with the increase of wear clearance. It can be seen from the fitting curve of the experiment that the volumetric efficiency of the four pumps is in the range of 60–70% after working for 1000 h, all of which are in the state of moderate degradation. The specific degradation of the four sample pumps is summarized in Table 2 and Table 3:

Acquired from Table 2 and Table 3, the working time when the volumetric efficiency of the four pumps drops to 70 % is 981.8 h, 960.3 h, 962.2 h and 966.9 h respectively, and the corresponding radial wear clearance and end wear clearance are 98.5 μm and 368.0 μm, respectively. The wear degradation state of the four sample pumps is effectively predicted.

The radial wear of gear pump is uneven, and the wear mainly occurs near the oil suction port. However, it is difficult to get the accurate wear value due to the difficulty in measuring the wear degree. In this paper, the radial wear is determined as uniform annular wear in the simulation, so the simulation results will have certain deviation, but it is still of great significance.

The manufacturer will set a fixed end face clearance for a certain type of pump when producing the gear pump. Due to the existence of floating shaft sleeve, the oil film in the clearance will change constantly, so the end face clearance is always changing in practice. However, in the simulation analysis of end face wear, the end clearance is set as a constant value to deal with, so there will be some errors in the simulation results.

In order to obtain the radial wear and end face wear of the gear pump after wear degradation test, four sample pumps were disassembled, cleaned and dried after ALT of the gear pumps, and the wear was measured by profile measuring instrument. The measuring positions are respectively the inner side of the gear pump housing and the end face of the floating shaft sleeve, corresponding to the radial wear and the end face wear, respectively.

The measurement results of wear show that the radial wear gap is about 70 μm on average, and the end face wear gap is about 20 μm on average. When the radial clearance and the end face clearance are set to 20 μm and 50 μm, the radial and end wear values obtained through simulation are correspondingly 90 μm and 70 μm. This indicates that the radial wear value is closer to the experimental results, and proves that compared with the end face wear, radial wear is the main cause of the volumetric efficiency reduction in the wear degradation test of the gear pumps, which is consistent with the actual situation.

Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in reaction to the load. It means a pump rated for 30 MPa is capable of maintaining flow against a load of about 30 MPa with a low system pressure loss and leakage. Also, pumps have a power density about 10 times greater than an electric motor in terms of volume efficiency. Common types of hydraulic pumps are listed in Table 2. Therefore, pump design techniques, efficiency, reliability, price, and operating conditions are researched by many groups and industries. Modern pump techniques are desirable as the ‘heart’ of the hydraulic machinery.

Effective approaches, or models for studying pump characteristics, are developed by researchers continuously. Some pioneering work on calculating the cylinder pressure during the trapping period between ports was proposed by Yamaguchi (1966). In his work, the efficiencies of pumps and motors were defined with the compressibility of flow, trapping, and relief grooves. The effect of relief groove design on pump power losses and pump noise can be predicted by using this model. This model has been referred to, and successfully applied in lots of further research (Zeiger and Akers, 1985; Schoenau et al., 1990; Manring and Zhang, 2001; Manring, 2003). A comprehensive study of the design and analysis of hydrostatic pumps and motors is described in (Ivantysyn and Ivantysynova, 2003), which provides the understanding of the working principles of pumps and motors and the design of displacement machines in accordance with the state-of-the-art analysis and modern design methods.

In the last 10 years, pump optimization research has been gradually increased in terms of pump efficiency, power loss, and noise level. Many useful tools have been developed for analyzing and optimizing pump performance. A simulation tool CASPAR for the calculation of the non-isothermal gap flow in the connected gaps of swash plate type axial piston machines has been developed (Wieczorek and Ivantysynova, 2002). It is an effective and useful approach to support the development of the pump. CASPAR allows the improvement of the efficiency of swash plate machines by optimization of the gap macro geometry without lengthy testing (Lasaar and Ivantysynova, 2002). However, the software only considers viscous friction, and elasto hydrodynamic effects are not considered. Using CASPAR, for example, the tribological system formed by the piston/cylinder assembly of swash plate axial piston machines, and the influence of a piston macro and micro geometry variation on energy dissipation can be effectively investigated (Ivantysynova and Lasaar, 2004). Besides CASPAR, some particular tools, such as HYGESim (HYdraulic GEar machines Simulator), are being developed for analyzing gear pump performance with high accuracy of simulation (Devendran and Vacca, 2013). It is a multi-domain simulation model for the detailed analysis of external gear machines. HYGESim was successfully utilized to optimize the design of the grooves on the lateral bushes presented in (Vaseena and Vacca, 2010) and an external spur gear pump shown in (Devendran and Vacca, 2013).

The future research areas and challenges for pump and motor design will include the accuracy of the pump and motor mathematical model (Eaton et al., 2006), novel design, and optimization techniques (Mauck et al., 2000). Also, high bandwidth pump control techniques will be more and more addressed and investigated in further research (Ivantysynova, 2008). The trend in pump design is gradually moving towards high efficiency, low noise, compactness, and light weight.

Hydraulic control valves are designed to route the fluid to the desired actuator in systems. They usually consist of a spool which can slide to a different position in the housing to control the fluid. The spool position may be actuated by mechanical levers, hydraulic pilot pressure, or solenoids which push the spool left or right. They can be catalogued in different ways in terms of their design techniques, functions, and materials. It is widely recognized that the control valve is one of the most expensive and sensitive parts of a hydraulic circuit.

For example, a high-speed on-off valve is essential for modern digital fluid power systems. Control using high-speed and high flowrate on-off valves has been proposed as a way to significantly improve the efficiency of fluid power systems over a conventional valve control approach in switched inertance hydraulic systems (SIHS) (Pohl et al., 2001; Scheidl et al., 2008a; 2008b; Johnston, 2009; Pan et al., 2014a; 2014b). This will be described in Section 2.2. Cao et al. (2005) suggested that energy can be lost in an on-off valve system as a result of valve transition times, fluid compressibility, pressure drops across the on-off valves, and hysteresis in the accumulator bladder, fluid friction, and leakage. A technology for the smart-design of the high bandwidth on-off valve is desirable. A four-way rotary valve was developed by Brown et al. (1988) with a desired switching frequency of 500 Hz. Winkler (2004) later presented a high flowrate and low resistance poppet valve that used multiple metering edges to provide a flowrate of 45 L/min at a pressure drop of just 0.5 MPa. The valve spool was driven by a solenoid with a rise time of approximately 1 ms. Tu et al. (2007; 2012) described a fluid driven pulse width modulation (PWM) on/off valve based on an unidirectional rotary spool. The valve was expected to give a flowrate of 40 L/min with a low-pressure drop (0.62 MPa), and high speed of 2.8 ms (transition time at 100 Hz PWM frequency). A seat type valve, which switches on and off within 1 ms at a nominal flowrate of 100 L/min at 0.5 MPa pressure drop, was also developed by Winkler and Scheidl (2007). Kudzma et al. (2012) proposed a 3-way linear-acting high-speed valve which enables low flow resistance (65 L/min at 1.0 MPa) and fast switching speed of 0.69 ms, low leakage and very high flow gain. Such high-speed valves give opportunities for improvements in the efficiency of modern digital hydraulic systems (Kogler and Scheidl, 2008).

Poppet type metering valves have many advantages, including low leakage, and an economical design and control design is challenging as the metering element is not hydrostatically balanced (Fales, 2005). It is also found that minor geometric differences in the poppet valve can result in very different valve characteristics. In particular, there is a very strong dependence upon the width of the contact area between the poppet and its seat (Johnston et al., 1991). Numerical simulation of fluid flow in poppet valves was studied in (Vaughan et al., 1992), and nonlinear and linear models for the dynamic analysis and design of the poppet valve were proposed in (Fales, 2006; Muller and Fales, 2008; Opdenbosch et al., 2009). These offer effective tools for investigating the performance of poppet valves. Also, newly developed materials were used in the valve development in order to improve valve performance (Tao et al., 2002; Wang et al., 2011). Moreover, various control schemes for controlling hydraulic poppet valves and compensation have been proposed to achieve high bandwidth, fast response, and robustness (Opdenbosch et al., 2004; 2008; Xiong et al., 2015). As can be seen, the poppet valve is a very typical hydraulic component and is widely used in industry. The research of the poppet valve can help researchers and engineers get a better understanding of the operation and physical phenomena of the valve and offer clever industrial solutions.

High-speed solenoid valves have been widely used for their good performance, fast response, and high energy efficiency. A nonlinear dynamic model of a high-speed direct acting solenoid valve was presented in (Vaughan and Gamble, 1996). The solenoid was modeled as a nonlinear resistor/inductor combination, with inductance parameters that change with displacement and current. The spool assembly was modeled as a spring/mass/damper system. This model can accurately predict the spool displacement of a proportional solenoid valve to a voltage input. It enables the development of a new valve from design to performance evaluation before the manufacture of a prototype. In the meantime, methodologies for nonlinear modeling, parameter determination, and performance evaluation of high performance solenoid valves are studied to speed up the design and optimization (Khoshzaban Zavarehi, 1999; Sohl and Bobrow, 1999; Reuter et al., 2010).

New techniques are also investigated for the development of hydraulic actuators that use hydraulic power to facilitate mechanical operation. For example, piezoelectric material has been used in actuators in terms of the usage of the piezoelectric effect (Sirohi and Chopra, 2003). Also, various adaptive control schemes for manipulating hydraulic actuators have been proposed. Earlier research focused primarily on linear control theory. A robust adaptive controller applied to hydraulic servo systems for noncircular machining was introduced in (Tsao and Tomizuka, 1994), and another robust adaptive control scheme was devised in (Plummer and Vaughan, 1996) for the control of hydraulic servo-systems. For a good performance and a high bandwidth control of a hydraulic actuator, a modern motion controller was required (Bobrow and Lum, 1996).

The electro-hydraulic actuator (EHA) is a new high-performance actuation system that combines the benefits of conventional hydraulic systems and direct-drive electrical actuators. It originally was developed for the aerospace industry and expanded applications into many other hydraulic industries. This device eliminates the need for separate hydraulic pumps and tubing, simplifying system structures and improving safety and reliability. EHA is a very promising device that has attracted a lot of research interest from its design to control (Alleyne and Liu, 2000; Habibi and Goldenberg, 2000; Liu and Alleyne, 2000; Niksefat and Sepehri, 2000) and the nonlinearities, system identification, model uncertainties, and disturbances (Ling et al., 2011; Lin et al., 2013). According to recent applications of EHA in Airbus A380 aircraft, engineers still face some unique problems with EHA (Van den Bossche, 2006), which include the performance and life of the pump, efficiency of the electric motor, reliability of the power electronics, and heat rejection problem. On Aug. 29, 2005, the A380 n°1 flew for the first time simulating a dual hydraulic system failure, the control surfaces being driven by the EHA and electrical back-up hydraulic actuator. The aircraft operated with no significant difference in the servo control hydraulic system (Van den Bossche, 2006).

The digital hydraulic system has several advantages compared with continuous or analogue technologies, such as higher efficiency, precision, robustness, and reliability. It also offers new functionality that is impossible with existing fluid power systems, such as sensorless incremental actuation and digital control for multiple units’ arrangements. Today, digital fluid power applications have gradually entered into our industries and market. It is certain that they will become much more digital and provide new opportunities for fluid power engineering in the future (Scheidl et al., 2011).

Hydraulic switching control is a sub-domain of digital hydraulics (Scheidl et al., 2013). An SIHS is a typical example of digital fluid power systems. It performs analogously to an electrical ‘switched inductance’ transformer, and is one possible approach to raise efficiency (Brown, 1987; Scheidl et al., 2008b; Johnston, 2009). This technique makes use of the inherent reactive behaviour of hydraulic components. A fluid volume can have a capacitive effect, whilst a small diameter line can have an inductive effect (Johnston, 2009). High-speed switching valves are needed to achieve the sufficient switching frequencies (Pan et al., 2014a; 2014b). It uses a fast switching valve to control flow or pressure, and is potentially very efficient as it does not rely on dissipation of power by throttling.

When the valve is connected to the high-pressure supply port, flow passes from the high pressure supply to the delivery port and the fluid accelerates in the inertance line. When the valve is open to the reservoir, fluid is drawn from the reservoir to the delivery port by the momentum of the fluid in the inertance tube (Pan et al., 2014a; 2014b). As long as the valve is switched quickly, the delivery flow will only reduce slightly due to a small deceleration of fluid velocity when connected to the low-pressure supply, remaining a constant delivery flow. The physical characteristics of the SIHS provide the opportunity for high efficiency.

Digital pump development is another possible future trend in hydraulic systems. As most hydraulic system loads need variable flow for proper operation, it is conventional to control the flow using valves which alter the flow at the expense of energy loss. The digital displacement technique has been proposed for improving hydraulic system energy for transferring energy between mechanical and fluid power (Rampen et al., 1994; Ehsan et al., 2000; Linjama and Huhtala, 2009). Digital pump/motors aim to increase the efficiency and range of operation of fluid power systems by minimizing leakages, friction losses, and compressibility losses. Digital pumps can be implemented similarly to digital valves (Linjama, 2011). The fixed displacement pump is controlled by the high-speed switching on-off valve, which enables the flowrate to continuously switch between the main system and the reservoir. More generally, arranging digital pumps on the same axis and controlling by individual switching on-off valves, the flowrate can be modulated by using different control coding strategies. For the piston pump, the digital control technique is to control each piston of the pump independently by using switching on-off valves. It can be catalogued to the ‘pure pump’ and ‘pump-motor’ modes in terms of piston functions including pump, idle, and motor modes. The motor mode requires continuous switching of the control valves (Linjama, 2011). Artemis Intelligent Power Ltd. started research in the development of piston digital pump/motors in the 1980s and the first publications were in 1990 (Rampen and Salter, 1990). This technique enables innovative solutions for mobile equipment systems (Wadsley, 2011). The piston digital pump/motors research has also been investigated in Purdue University recently (Merrill and Lumkes, 2010; Merrill et al., 2013). The advantages and disadvantages of the different operating strategies and the design trade-offs for digital pump/motors were studied.

The MIT Leg Laboratory is well known for its milestone work of Prof. Marc Raibert, who showed in the 1980s that robotic running could be accomplished using appropriate control strategies and algorithms (Pratt, 2000). His 3D biped is shown in Fig. 4a. Later, Prof. Raibert left MIT to form Boston Dynamics which is an engineering and robotics design company that is best known for the development of BigDog, as shown in Fig. 4b. These two robots are hydraulically driven.

Boston Dynamics aims to build unmanned legged robots with rough-terrain mobility superior to existing wheeled and tracked vehicles. The ideal robot would travel anywhere a person or an animal could go using their legs, run for many hours at a time, and carry its own fuel and payload. It would be smart enough to negotiate terrain with a minimum of human guidance and intervention (Raibert et al., 2008). BigDog has onboard systems that pro-vide power, actuation, sensing, controls, and communications. The power supply is a water-cooled two-stroke internal combustion engine that delivers about 15 hp (1 hp=746 W). The engine drives a hydraulic pump which delivers high-pressure hydraulic oil through a system of filters, manifolds, accumulators, and other plumbing to the robot’s leg actuators. It has about 50 sensors which measure the attitude, acceleration of the body, and motion and force of the actuators and also monitor BigDog’s homeostasis. It has successfully performed different locomotion gaits, such as walking, trotting, and bounding, carried up to 154 kg payload and hiked for 2.5 h (Raibert et al., 2008).

Hydraulic Quadruped (HyQ) is a versatile hydraulically powered quadruped robot, which is developed for use as a platform to study the high dynamic motions and the navigation performance of the robot in the Italian Institute of Technology, Italy. Fig. 5 shows the photograph of the HyQ Leg and the CAD model of the robot body with the onboard hydraulic system. The design, component specifications, and experimental validation of the HyQ were described in (Semini et al., 2011).

The researchers of the Korea Institute of Industrial Technology developed the hydraulic actuated quadruped walking robot qRT-2, which is the front drive machine with hydraulic linear actuators and wheeled back legs, as shown in Fig. 7a. The qRT-2 weighs about 60 kg and can carry over 40 kg of payload. It successfully demonstrated the trotting gaits at a speed up to 1.3 m/s on an even surface and walking at 0.7 m/s on an uneven and ramped surface (Kim et al., 2008). They also developed the 4-leg walking robot P2 in 2010 and investigated the hydraulic flow consumption during the robot’s walking behaviour (Kim et al., 2010). A power optimization scheme on the minimization of the hydraulic flow consumption was applied in P2. Simulated and experimental results show very promising performance. All joints of the robotic legs are actuated by small size hydraulic rotary actuators, as shown in Fig. 7b.

In China, a hydraulic quadruped walking robot called ‘Baby Elephant” was developed by Gao’s research team (http://www.china.org.cn/china/2012-11/08/content_27042373.htm) in Shanghai Jiao Tong University. The robot weighs about 130 kg and its length, width, and height are 1.2 m, 0.5 m, and 1 m, respectively. It has 12 degrees of freedom for 4 legs controlled by hydraulic actuators. The lithium battery was applied as the power supply for the 10 kW high-performance motor which was used to drive the hydraulic pump (Chen et al., 2013). It can carry a heavy load and walk through the uneven terrain with a good stability. An energy storing mechanism was introduced in this robot, and the simulated and experimental results show its high efficiency (Chen et al., 2013). More investigation and experiments are continuing for the control strategies and gaits optimization. Another hydraulically actuated quadruped bionic robot was developed by the Robotics Centre of Shandong University. It aims to develop a high dynamic quadruped robot which is able to work in complex terrains with good adaptability. It can walk with an average speed of 1 m/s and a maximum speed of 1.8 m/s without a heavy load and 0.4 m/s with a load of 80 kg (Li et al., 2011). The research team in the Beijing Institute of Technology investigated the energy consumption of the designed quadrupedal robot and the results have been published in (Sha et al., 2013).

ELIKA is the low-noise, high-efficiency, low-pulsation gear pumpdeveloped in close collaboration with the Faculty of Engineering at the University of Bologna through the generation of a dedicated design software.

ELIKA is a solution for all applications requiring low levels of noiseand high-levels of efficiency, particularly at low speeds. ELIKA in fact reduces noise emissions by as much as 15 dBA with respect to traditional external gear pumps. Maximum working pressures are similar to those for the GHP series (cast iron/aluminium), thus reaching 300 bar. The particular tooth profile without encapsulation furthermore allows a considerable reduction in pressure oscillations and vibrations transmitted to other components connected to the pump (hoses, tank and valves), producing numerous advantages in the circuit. The helical gear effectively guarantees continuity of movement despite the low number of teeth. The low number of teeth also significantly reduces the fundamental frequencies of noise output, making the sound particularly pleasant.

The particularly low level of noise produced by the ELIKA pumpmakes it particularly suitable for applications which currently employ much more expensive technologies such as screw pumps, vane pumps, or internal gear pumps. ELIKA, with its characteristics, is the ideal solution regarding a wide range of specifications such as rotation speed, operating pressure and viscosity. The structure of the ELIKApump minimises leaks and maximises volumetric efficiency in all conditions. ELIKA is therefore particularly suited for applications, which use inverters or variable-speed drives to regulate the speed of the actuators.

"Double Elika is a Solution for external gear pumps that allows the same design of gears previously reserved for individual pumps to be used in modular architectures, to reduce vibrations and noise."

600 gpm of water is pumped a head of 110 ft. The efficiency ofthe pump i s 60% (0.6) and the specific gravity of water is 1. The pump shaft power can be calculated as

The shaft power - the power required transferred from the motor to the shaft of the pump - depends on the efficiency of the pump and can be calculated as Ps(kW) = Ph(kW)/ η (3)