The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own. Tomatoes, mandarins. Fergie reveals the secret combination of foods behind her three-stone weight loss The Duchess of York has lost three stone in. It will be the longest journey you have ever taken. It is the journey to find yourself.” This is my personal story. There are many people out there who want to reduce their weight within a few weeks. Most of them will try to do some work out to reduce the weight. Shakeology vs Body By Vi Shake Challenge puts these two top meal replacement shakes head to head. Click to find out the surprising truth. The Benefits of Maximum Efficiency Hydraulic Fluids. Hydraulic systems are widely used in the manufacturing, construction, forestry, mining and transportation industries. Over the years, systems for the transmission and distribution of power have become increasingly sophisticated, their applications more numerous and their operating conditions more demanding. Viscosity variations associated with low starting temperature and high operating temperatures contribute to system efficiency and reliability losses in a variety of ways. Selection of the proper viscosity grade of hydraulic fluid is an important and cost- effective technique that allows equipment to start smoothly at low temperatures, and also deliver adequate oil flow rates needed for efficient operation at high temperatures. This article discusses several techniques that enable the equipment user to identify the practical operating limits of a hydraulic fluid. This information can be used to determine the temperature operating window of a given fluid in a pump. Fluid Selection Viscosity is an important criterion in the selection of a hydraulic fluid. At low temperature, excessive viscosity may result in poor mechanical efficiency, difficulty in starting, and wear. As oil temperature increases, viscosity decreases, resulting in lower volumetric efficiency, overheating and wear. Pump and motor manufacturers often provide hydraulic fluid recommendations in their documentation covering: the maximum startup viscosity under load the range of optimum operating viscosity the maximum and minimum operating viscosity Selection of the optimum fluid viscosity grade will provide the most efficient pump performance at standard operating temperatures, therefore minimizing lost time and energy and fuel costs for the operator. Recent work by the authors has lead to the development of a new performance standard for hydraulic fluids, described as Maximum Efficiency Hydraulic Fluid (MEHF). MEHF fluids are formulated to provide a combination of high viscosity index and good shear stability, which enables all types of hydraulic pumps to deliver increased power at a lower level of energy consumption. Pump Efficiency The performance of hydraulic pumps and motors is a critical factor in overall hydraulic system reliability. There are two elements of hydraulic efficiency: volumetric efficiency and hydromechanical efficiency. The Truth About the Cookie Diet Can you really lose weight by eating junk food? By Adam Campbell October 5, 2010.Hydromechanical efficiency relates to the frictional losses within a hydraulic component and the amount of energy required to generate fluid flow. Volumetric efficiency relates to the flow losses within a hydraulic component and the degree to which internal leakage occurs. Both of these properties are highly dependent on viscosity. Hydromechanical efficiency decreases as fluid viscosity increases due to higher resistance to flow. Conversely, volumetric efficiency increases as fluid viscosity increases because of the reduction of the internal leakage. The overall efficiency of a hydraulic pump is the product of mechanical and volumetric efficiencies . As shown in Figure 1, there is a range of hydraulic fluid viscosity that optimizes the overall efficiency. Relationship of Viscosity to Pump Efficiency. Overall efficiency = Hydromechanical efficiency * Volumetric efficiency . Viscosity influences cavitation because high- viscosity fluids can create excessive pressure drop at the pump inlet. Cavitation causes metal fatigue and spalling which reduce pump life and generate abrasive metal particles in the fluid. Excessive viscosity from low- temperature conditions leads to pump starvation that may result in pump failure. Additionally, loss of the lubricating film creates high contact temperatures, excessive wear and ultimately results in pump seizure. Consequently, pump manufacturers specify a maximum fluid viscosity limit at startup to ensure that cavitation is avoided. Improperly designed or undersized inlets and strainers aggravate the problems associated with high viscosity. One of the essential functions of a hydraulic fluid is to provide a lubricating film that reduces wear on moving pump parts. Film effectiveness depends upon a balance between viscosity, sliding speeds and loads, and fluid stability within a hydraulic pump. As temperatures increase and the film thins, the lubricant film ruptures, allowing metal- to- metal contact, wear within the pump and additional fluid heating. Wear predominantly occurs in locations within a pump that are critical in terms of volumetric efficiency. Loss of volumetric efficiency causes the pump to work harder to produce the required flow. At the same time, high temperatures compromise volumetric efficiency as the result of low- viscosity fluid bypassing critical pump clearances. Thus, inadequate viscosity due to high temperatures creates a destructive cycle of rising temperatures, accelerated wear and increased internal leakage. Fluid Viscosity vs. Performance. Multigrade Fluids Offer Improvement Multigrade hydraulic fluids are often recommended for equipment where the operating temperatures can vary widely. High viscosity index (HVI) MEHFs enable efficient equipment operation over a wider temperature range than standard grade mineral oils. MEHF products are also recommended to eliminate seasonal oil changes, since a properly formulated multigrade performs adequately in both winter and summer temperatures. MEHFs provide better low- temperature flow properties than an equivalent grade of single viscosity hydraulic oil at equivalent temperatures. While improved flow characteristics provide smoother operation and improved productivity, the primary performance advantage of an MEHF is its effectiveness in maintaining pumping efficiency at high temperatures. Pump internal leakage increases with increase in temperature and decrease in viscosity. A high VI fluid decreases at a lower rate than a standard single viscosity fluid, which contributes to less leakage and improved pump efficiency. The relationship of viscosity to temperature, and the viscometric advantages of high VI multigrade hydraulic fluids are shown in Figure 3. Viscosity- Temperature. Relationship for Low and High VI Oils. Fluid Selection Techniques A viscosity grade selection system aimed at supporting equipment users has been published by the NFPA, based on the recommendations of leading hydraulic pump manufacturers. Optimum viscosity grades are selected based on the concept of temperature operating window (TOW), which corresponds to the range of temperature where the oil viscosity provides acceptable performance in the pump (typically 1. Details on the use of the ALTOW system are given in NFPA Standard Practice T2. National Fluid Power Web site at www. Performance Advantage of High VI Oils The most commonly used and widely available viscosity grades are ISO 3. The following sections compare the performance of monograde (low- viscosity index) and multigrade (high- viscosity index) versions of these three fluids. It is important to recognize that shear stable fluids must be used in high- pressure hydraulic systems to achieve desirable performance. Fluids with low shear stability are commercially available, and are typically intended for use in low- pressure systems or for other applications such as automatic transmissions (ATF). The multigrade fluids selected for comparison in this work are intended for high- pressure hydraulic system service and have excellent shear stability, meeting the MEHF performance level definition. A description of these fluids can be found in Table 1. Consult your fluid supplier for guidance on the shear stability of its products to verify fluid performance claims. Viscometric Properties of Test Oils. Achieve Fantastic Weight Loss Results & Still Eat The Food You Love! Our Proprietary Blend of All Natural Fiber makes you feel full so you eat less. Arabica Green Coffee Beans, Café Marchand, Café Verde, Café Vert, Coffea arabica, Coffea arnoldiana, Coffea bukobensis, Coffea canephora, Coffea liberica, Coffea. Performance Advantage at Low Temperature Calculations have been made on the additional energy, or hydromechanical losses (in k. W), required to operate a mobile vane pump having a displacement of 1. These data are shown in Figure 4. Hydromechanical Losses as a Function of. Temperature, ISO Grade and VI* Performance gains are based on usedoil viscosity, after shear Table 2. Additional Time Required for a 1. VI Fluidto Deliver the Same Volume as a 2. VI Fluid*at 8. 0. W) than the MEHF to overcome the viscous drag. Additional Time Required for a 1. VI Fluid to. Deliver Same Volume as a 2. VI Fluid* at 1. 00. Energy Savings with High VI Oils* at 8. Additional energy required to overcome the higher viscosity of the 1. VI fluids increases significantly at temperatures below 4. Performance Advantage at High Temperature The authors have computed the actual flow rate and the total power requirement for vane pumps based on a given body, using four different- sized cartridges. Internal cartridge sets (rotors and vanes) are sized to deliver a specific flow rate by controlling the discharge volume per revolution. Calculations were made at a pressure of 2. Flow Rate Advantage – Time Savings Knowing the actual flow rate Qa, one can determine the time needed to fill a given linear motor of volume, V. A linear motor is typically a hydraulic cylinder that fills with fluid, displacing a rod that delivers motion under load. Time = V/Qa . In this work, the authors used the viscosity of the high VI oils after the Sonic 4. Table 1). This represents a good estimate of the used oil viscosity in a 2,0. Time(VI=1. 00)/Time(VI=2. Qa(VI=2. 00)/Qa(VI=1. This is because the larger the cartridge, the lower the internal leakage relative to the pump flow rate. Field studies showed that peak operating temperatures in mobile hydraulic equipment often exceed 1. Therefore, the flow rates in this series of pumps at this higher temperature were also calculated. The data in Table 4 indicate that the high VI fluids at 1. Comparing the data at 8. Efficiency Advantage – Cost Savings Knowing the total power required to deliver the hydraulic power and to overcome the hydromechanical losses, one can determine the energy needed to fill the linear motor of volume V. Energy = Total Power * Time .
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