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Over the last 30 years, dozens of networks of eddy covariance flux stations have been introduced in different countries and continents around the world. Many of them, such as the ICOS network in Europe or the AmeriFlux network in the US, have a specific focus on greenhouse gas measurement focus, mainly CO2, but in all cases, the latent heat flux is concurrently measured as a required variable, thus actual evapotranspiration can be derived.This important hydrologic parameter is needed both in rainfed and irrigated areas to monitor drought conditions, and soil water balance as well as to determine irrigation water amounts to be applied to crops and the timing of optimal fertilizer applications. Quasi-real-time measurements of actual evapotranspiration can be used by water managers, crop consultants, and producers in both rainfed and irrigated agriculture, reducing water and energy use and associated expenses, ultimately helping increase the efficiency of global food production while reducing its costs. So, the importance of providing freely available, scientific-grade data is imperative.The cutting-edge technologies to assess water use on leaf-level to ecosystem-level scales has been actively developed in academia for past 40 years. One example of such technologies is a next-generation fully-automated evapotranspiration station network, to effectively and efficiently handle the “big data” on water use coming from a grid of measurement stations providing high spatial and temporal coverage of water usage on multiple scales, ranging from a single watershed to a region, state, or a continent.This presentation aims to provide multiple examples, and validations against existing standards, of the latest technology, hardware, and scientific method behind the eddy covariance approach to direct, field-scale, unattended, and automated measurements of evapotranspiration.

Growing food demand and declining water availability are among key global concerns in the modern society. These two opposing trends manifest uniquely at different scales, from the farm field to the global food distribution, and require innovative composite solutions in terms of policy, education, science and technology.To solve the complex interactions of financial, social, and scientific issues, solutions to water use for crops require resource management based upon socioeconomic and scientific understanding. These important goals are achieved through a number of crucial regulatory, social and technical means. The latter include water inventories, water loss and water use measurements, as well as development of the techniques for water use reduction, optimization and prediction, and require direct measurements of water transport in real time, with high temporal resolution.Cutting-edge technologies to assess water use at leaf to ecosystem scales have been actively developed in the academia for the past 40 years. One example of such technologies is a next-generation fully-automated evapotranspiration station network, to effectively and efficiently handle the “big data” on water use coming from a grid of measurement stations providing high spatial and temporal coverage of water usage on multiple scales, ranging from a single watershed to a region, state, or a continent.In this presentation, we will focus on the main features and specifications of the very latest technology and the explanation of the latest scientific assessment methods available for direct, field-scale, unattended, and automated measurements of evapotranspiration.

Background An interlaboratory study was performed to compare the performance of the 3 mL TransFix®/EDTA Vacuum Blood Collection Tube (TVT), with the 5 mL Cyto-Chex® BCT tube (BCT). Both devices are intended for collection and storage of whole blood specimens for immunophenotyping of leukocytes by flow cytometry for up to 14 days. Methods One site in the United States and two in the United Kingdom tested samples from 10 HIV positive patients and four healthy subjects for a total of 42 samples. From each subject, three blood samples were collected: a BD 4 mL K3 EDTA Vacutainer (Vacutainer), a TVT, and a BCT. At all sites, samples were analyzed on a BD FACS Canto II flow cytometer for a full lymphocyte subset count within 6 h of collection (all devices) and on Day 11 and Day 15 (TVT and BCT only). Data obtained from the Vacutainer were used as the control data set with which TVT and BCT data were statistically compared. Results and conclusions Statistical concordance was demonstrated for both devices in relation to cell absolute count recovery. For cell marker signal, both devices exhibited a significant decrease in mean fluorescence intensity (MFI) for the detection of lymphocyte subsets and their target markers. There was a marked increase in autofluorescence observed for BCT stabilized lymphocytes whereas values for the TVTs were comparable to the control. There were eight instances of statistical equivalence between the level of antibody autofluorescence observed in the control tube and the TVT across both patient cohorts, versus two for the BCT. © 2018 International Clinical Cytometry Society.

Patients who have total hip (THR) or knee (TKR) replacement have an elevated risk of venous thromboembolism (VTE). The American College of Chest Physicians guidelines recommend prophylactic anticoagulation. The aim of the study was to examine pharmacologic prophylaxis against VTE among patients with THR or TKR and to assess demographic and clinical correlates related to VTE prophylaxis. Using 15 years of data (1995-2009) from an electronic medical record system for an inner-city public hospital in the United States, we examined pharmacologic prophylaxis against VTE and associated factors in patients after THR (n = 242) and TKR (n = 317). Before the early 2000s, aspirin was the most common prophylaxis agent (THR, 61% and TKR, 65%), and 26% of patients with THR and 19% of patients with TKR did not receive prophylaxis. Enoxaparin use has increased since 2000, and warfarin is now the most common prophylaxis agent (THR, 70% and TKR, 61%). After controlling for time period, factors associated with prophylaxis pattern included obesity, hip fracture, and the surgeon's number of years in practice. VTE prophylaxis medications in patients with total joint replacement have changed over 15 years, in trends generally consistent with the evolution of guidelines. Obesity, history of hip fracture, and physician's experience are associated with the prescription of VTE prophylaxis medications.

© 2017 Elsevier Ltd Background Reoperation rates are high after surgery for hip fractures. We investigated the effect of a sliding hip screw versus cancellous screws on the risk of reoperation and other key outcomes. Methods For this international, multicentre, allocation concealed randomised controlled trial, we enrolled patients aged 50 years or older with a low-energy hip fracture requiring fracture fixation from 81 clinical centres in eight countries. Patients were assigned by minimisation with a centralised computer system to receive a single large-diameter screw with a side-plate (sliding hip screw) or the present standard of care, multiple small-diameter cancellous screws. Surgeons and patients were not blinded but the data analyst, while doing the analyses, remained blinded to treatment groups. The primary outcome was hip reoperation within 24 months after initial surgery to promote fracture healing, relieve pain, treat infection, or improve function. Analyses followed the intention-to-treat principle. This study was registered with ClinicalTrials.gov, number NCT00761813. Findings Between March 3, 2008, and March 31, 2014, we randomly assigned 1108 patients to receive a sliding hip screw (n=557) or cancellous screws (n=551). Reoperations within 24 months did not differ by type of surgical fixation in those included in the primary analysis: 107 (20%) of 542 patients in the sliding hip screw group versus 117 (22%) of 537 patients in the cancellous screws group (hazard ratio [HR] 0·83, 95% CI 0·63–1·09; p=0·18). Avascular necrosis was more common in the sliding hip screw group than in the cancellous screws group (50 patients [9%] vs 28 patients [5%]; HR 1·91, 1·06–3·44; p=0·0319). However, no significant difference was found between the number of medically related adverse events between groups (p=0·82; appendix); these events included pulmonary embolism (two patients [

Item does not contain fulltext BACKGROUND: The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) has been extensively evaluated in groups of patients with osteoarthritis, yet not in patients with a femoral neck fracture. This study aimed to determine the reliability, construct validity, and responsiveness of the WOMAC compared with the Short Form-12 (SF-12) and the EuroQol 5D (EQ-5D) questionnaires for the assessment of elderly patients with a femoral neck fracture. METHODS: Reliability was tested by assessing the Cronbach alpha. Construct validity was determined with the Pearson correlation coefficient. Change scores were calculated from ten weeks to twelve months of follow-up. Standardized response means and floor and ceiling effects were determined. Analyses were performed to compare the results for patients less than eighty years old with those for patients eighty years of age or older. RESULTS: The mean WOMAC total score was 89 points before the fracture in the younger patients and increased from 70 points at ten weeks to 81 points at two years postoperatively. In the older age group, these scores were 86, 75, and 78 points. The mean WOMAC pain scores before the fracture and at ten weeks and two years postoperatively were 92, 76, and 87 points, respectively, in the younger age group and 92, 84, and 93 points in the older age group. Function scores were 89, 68, and 79 points for the younger age group and 84, 71, and 73 points for the older age group. The Cronbach alpha for pain, stiffness, function, and the total scale ranged from 0.83 to 0.98 for the younger age group and from 0.79 to 0.97 for the older age group. Construct validity was good, with 82% and 79% of predefined hypotheses confirmed in the younger and older age groups, respectively. Responsiveness was moderate. No floor effects were found. Moderate to large ceiling effects were found for pain and stiffness scales at ten weeks and twelve months in younger patients (18% to 36%) and in the older age group (38% to 53%). CONCLUSIONS: The WOMAC showed good reliability, construct validity, and responsiveness in both age groups of elderly patients with a femoral neck fracture who had been physically and mentally fit before the fracture. The instrument is suitable for use in future clinical studies in these populations. CLINICAL RELEVANCE: The results are based on two clinical trials. The questionnaires used concern pure, clinically relevant issues (ability to walk, climb stairs, etc.). Moreover, the results can be used for future research comparing clinical outcomes (or treatments) for populations with a femoral neck fracture.

Multidetector computed tomography (CT) is an excellent way to supplement the radiographic evaluation of problematic hip prostheses. Multidetector CT is well suited for assessing periprosthetic bone, determining precise acetabular cup position, and evaluating periprosthetic fluid collections or ossified masses. Metal implants pose a number of challenges in the performance and interpretation of CT examinations. However, metal artifacts can be minimized by decreasing the detector collimation and pitch, increasing the kilovolt peak and milliampere-seconds, and using appropriate reconstruction algorithms and section thickness. Image interpretation requires a basic understanding of hip reconstruction and hip implants, as well as use of a systematic method of analysis that incorporates prior radiographic findings and CT findings. Radiologists must be familiar with the normal and abnormal CT appearances of hip prostheses and be able to recognize common complications on CT scans.

The introduction of multichannel CT scanners provides both radiologists and surgeons with a new tool to image patients with orthopedic hardware. The key parameters that have made it possible to image the implants and the surrounding bone with multichannel CT are the higher available technical factors (kVp and mAs) coupled with the ability to acquire thin slices over a large scan region. These properties make it possible to produce high-quality multiplanar reformations that facilitate visualization of the orthopedic device and the surrounding bone. An important consideration for multichannel CT imaging of hardware is the reduction of cone beam artifacts caused by the geometry of multichannel CT scanners. This artifact is reduced by using a narrower x-ray beam collimation and a low pitch setting. This article discusses CT scan parameters and image postprocessing used at our institution and illustrates common clinical problems encountered when imaging implanted orthopedic devices. These include fracture healing, loosening of joint prostheses, evaluation of particle disease, and the use of CT for preoperative planning in revision arthroplasty.

Osseointegrated implants have a large potential for diverse clinical applications, including support for sutural expansion and facial prostheses. The objectives of this study were to evaluate: (1) the histomorphometric response of thin cortical bone to implant placement and (2) whether loading of the bone surrounding these implants affects osseointegration as evaluated by histomorphometry. Eighteen New Zealand White rabbits had two titanium implants placed bilaterally in the anterior surface of their nasal bones. The rabbits were divided into an unloaded control group, one experimental group loaded at 1 Newton (N), and another loaded at 3 N. Fluorescent labels were used to mark areas of active bone formation. All rabbits were euthanized after 12 weeks of loading. Stereological point-hit and line-intercept methods were used to measure bone volume, direct bone-implant contact, new bone volume, and bone turnover rate in the bone surrounding the implants. All the implants remained stable during the loading period. A factorial ANOVA with repeated measures was used to compare the variables. The only significant difference among the three groups was a higher bone volume in the lateral coronal far region in the control group (p < 0. 05). Within all groups, bone volume (p < 0.002), turnover rate (p < 0.001), and percent of new bone (p < 0.05) were higher within 1 mm of the implant compared to 1-3 mm away. This may be due to the increased stress and strain in the bone adjacent to the implant. This study indicates that there are no detrimental effects of loading on osseointegration when implants placed in the thin facial cortices are used as anchors for sutural expansion.

Section thickness has been shown to affect the histomorphometrical measurement of bone-implant contact when analysed under brightfield microscopy. This study investigated whether microradiography of the bone-implant interface eliminated the errors associated with thick section analysis. Seven implant containing sections were utilized. Microadiographs of the thick (approximately 100 microns) sections were taken and the sections were subsequently ground to thicknesses of 50 microns and 25 microns. Photomicrographs were taken of the microradiographs and of the sections at each thickness (100, 50 and 25 microns) under brightfield microscopy. The photomicrographs were analysed for direct bone-implant contact in the cortical passage region and along the total length of the implant. The effect of section thickness on multiple fluorochrome labelling in 10 rabbit femur specimens was also examined. Centre-to-centre interlabel distance was measured for each label pair at a thickness of 100 microns and then again after the sections were ground to 50 microns and 25 microns. The thick (100 microns) sections showed a significantly greater amount of bone-implant contact than either the thin sections or the microradiographs. There was no difference in direct bone-implant contact measured by microradiography or thin sections. However, the microradiographic analysis showed a much lower variability of the bone-implant contact than the sections evaluated under brightfield microscopy. In addition, they have the added benefit of providing information on bone mineral density. Centre-to-centre interlabel distance was not significantly different for any label pair owing to section thickness. Data from this study provides evidence that the use of microradiographs for histomorphometrical analysis of the bone-implant interface is superior to brightfield analysis of thin sections owing to the lower variability of microradiographical data and the ability to obtain bone mineral density measures. Additionally, given that interlabel distance was not significantly affected by section thickness, the use of 100 microns thick sections for analysis of fluorochrome labels in cortical bone is supported.

The long-term maintenance of a rigid bone-implant interface (osseointegration) is the clinical goal of most dental implant systems, although the biological mechanism for retaining a foreign object in living bone is unclear. Little data are available on the physiological turnover (remodeling) of the supporting osseous tissue. The objective of this study was to histomorphometrically assess bone remodeling surrounding rigidly integrated titanium implants in multiple species. Implants, in place from 6 months to 5 years, were recovered from human, monkey, dog, and rabbit subjects. With the use of stereological point-hit and linear-intercept methods, indices of bone formation and resorption were determined. Remarkably similar patterns emerged among all investigated species. Repeated-measures ANOVA showed a 3 to 9 fold increase in remodeling within 1 mm of the bone-implant interface (P0.001; data expressed as percent turnover / month, mean +/- SEM for n = 3-11). All morphometric indices (percent new bone, percent fluorochrome-labeled bone, percent resorption space) showed similar trends. These data suggest that the physiological mechanism for maintaining rigid osseous integration (osseointegration) is a sustained elevation of remodeling adjacent to the bone-implant interface.

Publisher Summary Many industrial processes such as packaging lines consist of pneumatic actuators, which follow a predetermined sequence of operations. These sequences can be considered as a series of steps, each step resulting in the operation of pneumatic solenoids. Progression between steps is controlled by sensors on the controlled plant, like photo-cells, stroke limit switches, and timers. Sequence systems are built around two-position pneumatic shuttle valves. Sequences are driven by limit switches which pass, or block or vent pneumatic pressure. Many simple applications can be controlled without limit switches by using the pressure rise when a cylinder reaches end of stroke to operate a shuttle valve. Most sequences can be considered to be a series of states. There are many standards for distributed systems. Many manufacturers of pneumatic and hydraulic equipment now offer valve manifolds complete with built-in distributed system interfaces, which greatly simplify both piping and cabling.

Publisher Summary Hydraulic or pneumatic system is concerned with moving, gripping, or applying force to an object. Devices that actually achieve this objective are called actuators, and can be split into three basic types. This chapter discusses linear and rotary actuators. Linear actuators are used to move an object or apply a force in a straight line. Rotary actuators are the hydraulic and pneumatic equivalent of an electric motor. The third type of actuator is used to operate flow control valves for process control of gases, liquids or steam. These actuators are generally pneumatically operated and are described with process control pneumatics. The operational speed of an actuator is determined by the fluid flow rate and the actuator area (for a cylinder) or the displacement (for a motor).

Publisher Summary Most industrial processes require objects or substances to be moved from one location to another or a force to be applied to hold, shape, or compress a product. Such activities are performed by prime movers, the workhorses of manufacturing industries. In many locations all prime movers are electrical. Rotary motions can be provided by simple motors, and linear motion can be obtained from rotary motion by devices such as screw jacks or rack and pinions. Where a pure force or a short linear stroke is required, a solenoid may be used. Electrical devices are not however the only means of providing prime movers. Enclosed fluids (both liquids and gases) can also be used to convey energy from one location to another and, consequently, to produce rotary or linear motion or apply a force. Fluid-based systems using liquids as transmission media are called hydraulic systems. Gas-based systems are called Pneumatic. The most common gas is simply compressed air although nitrogen is occasionally used. The main advantages and disadvantages of pneumatic or hydraulic systems both arise out of the different characteristics of low density compressible gases and (relatively) high density incompressible liquids.

Pneumatic process control has by no means been superseded by electronic and microprocessor technology, so it is worth looking at the reasons for its popularity. First and foremost is safety. Much process control is done in chemical or petrochemical plants, where explosive atmospheres are common. If electrical signals are used, great care must be taken to ensure no possible fault can cause a spark, which could ignite an explosive atmosphere. While this can be achieved, the result is complex and maintenance may be difficult. A pneumatic system contains only air, so it presents no hazard under these conditions. No particular care needs to be taken with installation, and maintenance work can be carried out “live” with simple nonelectrical test instruments. A great deal of design and application experience has evolved over the years, and this base of knowledge is another major reason for the continuing popularity of pneumatic control. Companies with a significant investment in pneumatic control and a high level of staff competency are unlikely to change. Many devices in the loop are, in any case, best provided by pneumatic techniques. Although electrical actuators are available, most valves are driven by pneumatic signals—even when transducer and controller are electronic.

In order to understand the formation mechanism of the discs around Be stars, it is imperative to have a good overview of both the differences and similarities between normal B stars and the Be stars. In this paper, we address binarity of the stars. In particular, we investigate a previous report that there may be a large population of subarcsec companions to Be stars. These had hitherto not been detected due to a combination of a limited dynamic range and spatial resolution in previous studies. We present the first systematic, comparative imaging study of the binary properties of matched samples of B and Be stars observed using the same equipment. We obtained high angular resolution (0.07―0.1 arcsec) K-band adaptive optics data of 40 B stars and 39 Be stars. The separations that can be probed range from 0.1 to 8 arcsec (corresponding to 20-1000 au), and magnitude differences up to 10 mag can in principle be covered. After excluding a few visual binaries that are located in regions of high stellar density, we detect 11 binaries out of 37 Be targets (corresponding to a binary fraction of 30 ± 8 per cent) and 10 binaries out of 36 B targets (29 ± 8 per cent). Further tests demonstrate that the B and Be binary systems are not only similar in frequency but also remarkably similar in terms of binary separations, flux differences and mass ratios. The minimum physical separations probed in this study are of order 20 au, which, combined with the similar binary fractions, indicates that any hypotheses invoking binary companions as responsible for the formation of a disc need the companions to be closer than 20 au. Close companions are known to affect the circumstellar discs of Be stars, but as not all Be stars have been found to be close binaries, the data suggest that binarity cannot be responsible for the Be phenomenon in all Be stars. Finally, the similarities of the binary parameters themselves also shed light on the Be formation mechanism. They strongly suggest that the initial conditions that gave rise to B and Be star formation must, to all intents and purposes, be similar. This in turn indicates that the Be phenomenon is not the result of a different star formation mechanism.

The origin of the disks around Be stars is still not known. Further progress requires a proper parametrization of their structure, both spatially and kinematically. This is challenging as the disks are very small. Here we assess whether a novel method is capable of providing these data. We obtained spectro astrometry around the Pa beta line of two bright Be stars, alpha Col and zeta Tau, to search for disk signatures. The data, with a pixel to pixel precision of the centroid position of 0.3..0.4 milliarcsecond is the most accurate such data to date. Artefacts at the 0.85 mas level are present in the data, but these are readily identified as they were non-repeatable in our redundant datasets. This does illustrate the need of taking multiple data to avoid spurious detections. The data are compared with simple model simulations of the spectro astrometric signatures due to rotating disks around Be stars. The upper limits we find for the disk radii correspond to disk sizes of a few dozen stellar radii if they rotate Keplerian. This is very close to observationally measured and theoretically expected disk sizes, and this paper therefore demonstrates that spectro-astrometry, of which we present the first such attempt, has the potential to resolve the disks around Be stars., 6 pages, A&A accepted

Surface replacement (SR) was introduced as a bone-conserving alternative to total hip arthroplasty (THA) 3 decades ago, then was abandoned due to polyethylene wear, stress shielding, and loosening. Improved bearing surfaces have renewed interest in SR. This study examined long-term SR outcome compared to an age- and time-matched THA cohort. Average age was 47 years at index procedure with 16 years follow-up (range, 5-28). Revision rates were 86% and 40% in SR and THA groups, respectively. However, at 20 years, with an end point of either intact SR or primary THA in the SR group, survivorship was 64% +/- 6% versus 39% +/- 7% unrevised in THA cohort. Contemporary and rapidly changing technology may result in longer-term SR success and improved THA longevity in young patients.

Safety legislation differs from country to country, although harmonization is underway in Europe. This chapter describes safety from a British viewpoint, although the general principles apply throughout the European community and are applicable in principle throughout the world. Most safety legislations have a common theme. Employers and employees are deemed to have a duty of care to ensure the Health, Safety, and Welfare of the employees, visitors, and the public. Failure in this duty of care is called negligence. Most industrial plants have the capacity to maim or kill. It is therefore the responsibility of all people, both employers and employees, to ensure that no harm comes to any person as a result of activities on an industrial site. In pneumatic or hydraulic systems, pressure measurement is equivalent to electrical voltage measurement, while flow measurement is equivalent to current measurement. There is no direct simple measurement equivalent to electrical resistance. Pressure tests, and (to a lesser extent), flow tests thus form the bases of fault finding in pneumatic or hydraulic systems. Approved Codes of Practice (ACOPs) are documents written to define safe working methods and procedures by organizations, such as CENELEC and British Standards Institute. They are approved by the Health and Safety Commission. While they are not mandatory, failure to follow ACOPs may be viewed as a contributory factor in investigations of an incident.

Publisher Summary A hydraulic system is closed, and the oil used is stored in a tank or reservoir to which it is returned after use. Although, probably the most mundane part of the system, the design and maintenance of the reservoir are of paramount importance for reliable operation. The reliability of a hydraulic system is strongly influenced by the state of fluid. Contamination from dirt or the products of oxidation and deterioration of a fluid's lubrication ability will lead to rapid wear and failure. The various end devices in a pneumatic system are linked to the air receiver by pipes, tubes, or hoses. In many schemes the air supply is installed as a fixed service, similar in principle, to an electrical ring main allowing future devices to be added as required. Generally, distribution is arranged as a manifold or as a ring main. With strategically placed isolation valves, a ring main has the advantage that parts of the ring can be isolated for maintenance, modification, or repair without affecting the rest of the system. Pneumatic systems are vulnerable to moisture and, to provide drainage, the piping should be installed with a slope of about 1% (1 in 100) down from the reservoir. A water trap fitted at the lowest point of the system allows condensation to be run off, and all tap-offs are taken from the top of the pipe to prevent water collecting in branch lines.

Pneumatic systems use a compressible gas, hydraulic systems an incompressible liquid, which leads to some significant differences. The pressure of a liquid may be raised to a high level almost instantaneously, whereas pressure rise in a gas can be distinctly leisurely. The vast majority of pneumatic systems use compressed atmospheric air as the operating medium. Unlike hydraulic systems, a pneumatic system is “open;” the fluid is obtained free, used, and then vented back to atmosphere. Pressure in a hydraulic system can be quickly and easily controlled by devices such as unloading and pressure regulating valves. Fluid is thus stored at atmospheric pressure and compressed to the required pressure as needed. The slow response of an air compressor, however, precludes such an approach in a pneumatic system and necessitates storage of compressed air at the required pressure in a receiver vessel. The volume of this vessel is chosen so there are minimal deviations in pressure arising from flow changes in loads and the compressor is then employed to replace the air used, averaged over an extended period of time. Often, air in the receiver is held at a slightly higher pressure than needed to allow for pressure drops in the pipe lines. A local pressure regulation unit is then employed with the secondary air treatment close to the device using air. Composite devices called service units comprising water separation, lubricator, and pressure regulation are available for direct line monitoring close to the valves and actuators of a pneumatic system.

Publisher Summary There are two types of pump (for fluids) or compressor (for gases) illustrated in this chapter. Typical of the first type is the centrifugal pump. Fluid is drawn into the axis of the pump, and flung out to the periphery by centrifugal force. Flow of fluid into the load maintains pressure at the pump exit. Should the pump stop, there is a direct route from outlet back to inlet and the pressure rapidly decays away. Fluid leakage will also occur past the vanes, so pump delivery will vary according to outlet pressure. These devices are known as hydrodynamic pumps, and are primarily used to shift fluid from one location to another at relatively low pressures. Water pumps are a typical application. A hydraulic pump takes oil from a tank and delivers it to the rest of the hydraulic circuit. In doing so it raises oil pressure to the required level. The operation of such a pump is also illustrated in the chapter. On hydraulic circuit diagrams a pump is represented by a symbol with an arrowhead showing the direction of flow. Hydraulic pumps are generally driven at constant speed by a three phase AC induction motor rotating at 1500 rpm in the UK (with a 50 Hz supply) and at 1200 or 1800 rpm in the USA (with a 60 Hz supply). Often pump and motor are supplied as one combined unit. As an AC motor requires some form of starter, the complete arrangement is also illustrated in the chapter.

Publisher Summary Most control valves are only used to allow or block flow of fluid. Such valves are called finite position valves. An analogy between the two types of valve is the comparison between an electric light dimmer and a simple on/off switch. Connections to a valve are termed “ports.” A simple on/off valve, therefore has two ports. Most control valves, however, have four ports shown in hydraulic and pneumatic forms in this chapter. Pneumatic and hydraulic systems require control valves to direct and regulate the flow of fluid from compressor or pump to the various load devices. Although there are significant practical differences between pneumatic and hydraulic devices, the operating principles and descriptions are very similar. Although valves are used for many purposes, there are essentially only two types of valve. An infinite position valve can take up any position between open and closed and, consequently, can be used to modulate flow or pressure.