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"A commercially available Through-the-Earth (TTE) communications system was evaluated at an active underground longwall mine in West Virginia. This TTE system uses electric field (E-field) sensing to send text based communications using two separate antenna arrays connected in parallel. Each antenna array is composed of interconnected, grounded metallic rods or other such structures. Two-way communication between subsurface locations was investigated in this study using various antenna configurations. This field study was conducted as a part of a larger multi-site evaluation of available TTE systems in an effort to determine their operational sensitivity. INTRODUCTION Wireless, Through-the-Earth (TTE) communication technology is designed to achieve point to point communication through solid strata using very low frequency (VLF) and ultra-low frequency (ULF) electromagnetic waves. This ability allows TTE communication to function without the need for intermediary communications infrastructure, such as repeaters. As a result, such communication systems have the potential to provide reliable, robust communications between surface and underground personnel. Exploration into the use of TTE technology for this purpose dates back to the 1920s (Jakosky and Zellers 1924; Pittman, Church and McLendon 1985), but U.S. permissibility requirements slowed the development of TTE equipment for widespread implementation (Durkin 1980; Pittman, Church and McLendon 1985). One of the primary challenges in producing wireless TTE communications is the counteraction of signal attenuation when propagating through solid strata (Barkand, Damiano and Shumaker 2006; Wadley 1949). The long wavelengths of TTE transmissions make them well-suited for reducing the rate of attenuation. However, even when operating within the VLF to ULF range, the performance of TTE systems is still affected by geologic and anthropogenic factors (Geyer 1973; Geyer and Keller 1976; Geyer, Keller and Ohya 1974; Jakosky and Zellers 1924; Large, Ball and Farstad 1973). Although commercially developed TTE systems have demonstrated the ability to communicate through a variety of conditions, their range and performance have been highly varied (Barkand, Damiano and Shumaker 2006; Geyer and Keller 1976; Geyer, Keller and Ohya 1974; Ilsley, Freeman and Zellers 1928; Jakosky and Zellers 1924; Yenchek et al. 2012)."

Jan 1, 2016

By John Murray, Daniel Ebin, Robert Gould

The Atlanta Plane Train project at Hartsfield-Jackson Atlanta International Airport employed the progressive design-build approach. This provided opportunities for collaboration between the design-builder, design engineer, and owner and the implementation of innovative design and construction approaches. The innovations have reduced risks, allowed for adjustments during design to accommodate new challenges, and provided open-book cost and schedule evaluations. The progressive design-build approach has also allowed for pricing of work to occur in phases—capturing the design/construction challenges as the project evolves and when they are more clearly defined. While this has allowed for pricing to be performed with better project understanding and therefore less contingency, the associated time frame for approvals has required careful consideration to avoid impacts to the schedule. This paper discusses the benefits and challenges of the progressive design-build approach.

Dec 1, 2022

By Nik Sokol, Mike Jaeger, Leo C. Weiman-Benitez

Silicon Valley Clean Water signed a progressive-design-build (PDB) contract with Barnard Bessac Joint Venture (BBJV) to design and construct the Gravity Pipeline tunnel in Redwood City, CA. Owner and Design-Builder teamed with designer Arup to provide a final product: 3.3 miles of 182 in. O.D. precast concrete segmentally lined tunnel with 10 ft. and 11 ft. I.D. Fiberglass Reinforced Polymer Mortar (FRPM) carrier pipe, complete with two FRPM Drop Structures. BBJV and Arup collaborated with SVCW to evaluate alternative design concepts, negotiate an agreeable price and reduce contingencies through a transparent estimating process, and deliver the project ahead of schedule.

Jun 13, 2023

By Herman Gill, Dani Delaloye, Madelyn Rubin

The Foothill Tunnel is a remote 16-mile-long untreated drinking water tunnel in the San Francisco Public Utilities Commission’s (SFPUC) Hetch Hetchy Water and Power (HHWP) system. The 14-foot horseshoe shaped tunnel, constructed in the 1920s, is lined intermittently with concrete over approximately 53% of its length, with the balance being unlined rock. After detailed planning, in January of 2020 Mott MacDonald and HHWP staff completed a visual inspection and documented the condition of the tunnel with electronic data collection, photographs, and video with audio recording. The result was a comprehensive condition assessment that identified key areas of the tunnel to monitor.

Jun 13, 2021

By G. Frey, D. Scott, C. Pritchard

Controlled recirculation has been used in the metal/nonmetal mining industry for energy savings when heating and cooling air, in undersea mining and for increasing airflow to mining areas. For safe and effective use of controlled district recirculation, adequate airflow to dilute contaminants must exist prior to implementation, ventilation circuit parameters must be accurately quantified, ventilation network modeling must be up to date, emergency planning scenarios must be performed and effective monitoring and control systems must be installed and used. Safety and health issues that must be considered and may be improved through the use of controlled district recirculation include blasting fumes, dust, diesel emissions, radon and contaminants from mine fires. Controlled recirculation methods are expected to become more widely used as mines reach greater working depths, requiring that these health and safety issues be well understood. The U.S. National Institute for Occupational Safety and Health (NIOSH) conducted two controlled recirculation tests over three days at a Wyoming trona mine, utilizing an inline booster fan to improve airflow to a remote and difficult-to-ventilate development section. Test results were used to determine the effect that recirculation had on air qualities and quantities measured in that section and in other adjacent areas. Pre-test conditions, including ventilation quantities and pressures, were modeled using VnetPC. During each test, ventilation quantities and pressures were measured, as well as levels of total dust. Sulfur hexafluoride (SF6) tracer gas was used to simulate a mine contaminant to monitor recirculation wave cycles. Results showed good correlation between the model results and measured values for airflows, pressure differentials, tracer gas arrival times, mine gasses and dust levels.

Jan 1, 2013

By Roy A. Grancher

HAPPY BIRTHDAY Not only is 1971 the Centennial Year of the AIME, but it also marks the One Hundredth Anniversary of the United States Portland Cement Industry. On September 26th in 1871 David O. Saylor of Allentown, Pennsylvania, received his patent Numbered 119,413 for the manufacture of portland cement. "Cement" had been used in the United States before that. This was, however, natural cement - a direct product of rocks as found in nature, usually burned at low temperatures in open kilns. During the early 1800s this natural cement played an important role in such projects as the building of the Erie Canal. It was only after the Civil War that small amounts of high priced portland cement was imported from Europe. The successful use of this material in construction led to Saylor's experiments and subsequent patent for the manufacture of a scientifically controlled product in this country. These one hundred years have witnessed four major "ages" of cement . . . three of them occurring in the last quarter century since World War Two. The first age was the "Age of Development", a seventy-year period which saw the growth of cement and its concrete end uses as major construction materials. Next followed a period called the "Age of Demand" when, after the war, cement became in short supply relative to large building requirements. In effect a cement shortage existed. The decade of the Sixties proved to be the "Age of Reaction", with its courses of action coming in response to the problems that arose when the industry's expansion programs provided too much capacity. Today cement, and the concrete industries, find themselves entering the "Age of Reason". Overcapacity, low price, rising costs, and poor returns are several of the reasons behind that name, As these industries face the construction challenge of the Seventies, and beyond, the application of basic management principles (otherwise known

Jan 1, 1971

By C. R. DeGennaro, M. R. Girman, J. Bickson, J. P. Homer, C. C. Jobes

Between 2005 and 2021, a NIOSH internal review showed that haul trucks were involved in 54 incidents at surface mines in the United States. Haul truck collision warning and avoidance systems (CXS) can assist in preventing accidents at surface mines. CXS use technologies to detect people or objects and alarm to alert haul truck operators. Robust testing can help ensure that they detect objects without excessive false positive alarms. Testing and validation would increase confidence in and encourage implementation of a CXS. Researchers from the National Institute for Occupational Safety and Health (NIOSH) reviewed documents related to the evaluation and validation of CXS with two objectives: (1) to identify methods and parameters used to evaluate detection performance and (2) to identify gaps in CXS test methods and in detection performance. Stakeholders can use the findings from this research to guide implementation of CXS to improve safety at surface mines.

Mar 2, 2022

By J. D. Miller

"It is now possible to use 3D X-ray tomography analysis for plant-site characterization of coarse particles at a sampling rate of about 3 kg/min for particles which range in size from 150 mm to 1 mm at a voxel resolution of about 150 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant-site coarse particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) with a response time of minutes after receiving the sample. Applications in the mineral industries are discussed including the coal industry, aggregate industry, metal mining and the processing of industrial minerals. INTRODUCTION Plant-site characterization of coarse particles at coal preparation plants, crushed stone/aggregate plants, and mineral processing plants is needed to improve plant capacity, product quality, and/or process efficiency. Not much on-line coarse particle characterization is done at these plants. Some limited information regarding particle size is obtained on-line from reflected light images using systems such as the OPSA, Split, and WipFrag analyzers. Even laboratory analysis of coarse particles has been difficult because of the large amount of sample required to insure statistical significance of the results. During the past decades laboratory 3D characterization of particles from energy and mineral resources by X-ray tomography has been demonstrated and used to good advantage [1, 2]. 3D X-ray tomographic analysis had its origin in the medical services industry; it is used to provide internal images of the human body and now has also been developed for non-medical applications [3]. Figure 1 shows a schematic diagram for the cone-beam geometry micro-CT system. In our case X-rays from a microfocus X-ray generator are partially attenuated by the sample (a packed bed of particles) that is made to rotate in equal steps in a full circle about a single axis of the particle sample. At each rotational position, the surviving X-ray photons are detected by a planar two-dimensional array (image intensifier) large enough to contain the shadow of the specimen. These two dimensional projection images are collected using conventional video technology. The video signal for each projection is then converted to a two-dimensional digital array by an image processing system. Finally, a three-dimensional image is reconstructed from the collected set of projection images. With the availability of automated high speed X-ray tomography [4] it now seems possible to do plant-site particle characterization at a sampling rate of about 3 kg/min for particles which range in size from 150 mm to 1 mm at a voxel resolution of about 150 microns. This is quite a significant advance in X-ray tomography technology and should be useful for plant-site particle characterization (size, shape, composition, density, texture, grain exposure, mineral liberation) with a response time of minutes after receiving the sample. Applications in the mineral industries are discussed including the coal industry, aggregate industry, metal mining, and the processing of industrial minerals"

Jan 1, 2016

By B. W. Lawrence

Shaft alignment requirements are consistently met using conventional shaft sinking methods. Little attention has been given to achieving similar alignment accuracies using rotary drilled shaft methods. Alignment of these shafts is difficult to control and guarantee. Bare shafts and shafts that use drum hoisting systems can accept some deviation. However, combining drilled shafts with Koepe hoist installations presents new accuracy requirements for drilled shafts. This paper describes the importance of verticality with practical examples, and discusses various methods of measuring verticality and their respective limitations.

Jan 1, 1989

By S. A. Saki, J. F. Brune

"INTRODUCTION Longwall coal mining leaves large areas where the coal has been made removed and the roof rock strata collapse, forming a zone of broken rock rubble called the gob. Figure 1 shows a typical longwall gob area along with the gate roads. The ventilation pattern for progressively sealed longwall panels follows a simple “U” pattern where fresh air is coursed inby to the headgate, flows along the face and exhausts through the outby tailgate as shown in figure 1(a). An important variation of this pattern is the back return (BR) arrangement where the exhaust air from the face is drawn inby and around the nearest open cross cut before it turns in the outby direction towards the exhaust fan. Figure 1(b) illustrates the use of back return. This arrangement moves the point of low pressure from the tailgate corner up to 60 m inby and thus maintains fresh air in the tailgate region that could otherwise be contaminated with gob air.The gob area may contain remnants of unmined coal or parts of overlying coal beds that continue to release methane, eventually filling the gob area with methane in concentrations far above the explosive range of about 4.5 to 15%. Many gob areas must be equipped with gob ventilation boreholes (GVBs) to extract methane, and GVBs often exhaust methane at concentrations from 50% to 90% (Saki, 2016). Due to oxidation processes occurring in the gob, the oxygen content is reduced to a low level, with nitrogen and CO2 making up the major remaining components of the gob atmosphere. FORMATION OF EXPLOSIVE GAS ZONES IN GOBS Since the longwall face area is ventilated with fresh air below 1% methane and the face and gob areas are not separated, an explosive fringe will form where the methane content lies within the explosive range and oxygen content remains above 12%. Figure 2 shows a typical development of such an EGZ. This figure is based on a computational fluid dynamics (CFD) model developed by CSM researchers to analyze gas concentrations and flow patterns in longwall mining. Figure 2(a) shows the formation of EGZ in the gob with a U type ventilation scheme, where EGZ lies right behind the shields in the tailgate corner. Figure 2(b) shows the formation of EGZ in the gob combining U type ventilation scheme with BR, where EGZ is pushed away from the face deep into the gob. The CFD modeling parameters and boundary conditions have been verified with field data from two cooperating, active longwall mines (see Worrall 2012, Marts 2015, Gilmore 2015 and Saki 2016). Other mine geometries, methane inflow rates and gob permeability distributions can be modeled to establish representative gob atmospheric conditions. Two GVBs were operating in the model, extracting 0.165 m3/sec each. The methane in the working areas and returns was kept below 1%. Methane flowing into the model from a rider coal bed above the mined seam was at the rate of 0.55 m3/sec."

Jan 1, 2017

By José Ricardo Lopes, Alaor Coelho, Marco Gomes, Alfredo Dacio Moraes Filho, Akira Koshima

"Very low strength alluvial peat soil was found under two old drainage galleries with just 4.3m cover above a twin tunnel due to be excavated by a 10.6m diameter EPB Shield for São Paulo Metro’s Line 5. Alignment was required to strengthen soil and drive the TBM through safely without damaging the galleries. The design included six levels of self-drilling forepoling with lengths up to 15m, using 100 mm-diameter SCH160 metal tubing and injection bulbs with estimated 0.20m diameter. Two 6m-diameter circular shafts were excavated along the shield-tunnel axis, one each side of the galleries, and forepoling fanned out under gallery foundations. Given the peculiar soil and confined working space, more data were needed for correct drilling geometry. Ground mass treatment was successfully designed and executed and galleries were fitted with instruments to enable the shield’s advance. DESCRIPTION São Paulo Metro’s Line 5 (aka Lilas or purple line) is adding 11 stations along an 11.5km extension and three EPB TBMs are being used simultaneously (three EPBs on the same job for the first time in Brazil) with one of them excavating a large cross- section twin-track tunnel. Currently the largest work-in-progress for São Paulo Metro, this project has been divided into seven lots and 9km are already operational. This study refers to Lot 6 where the 10.6m - diameter EPB shield excavation is only 4.3m below two galleries running through a 10m layer of very soft peat soil in an old alluvial riverside region ringed by major roads. After recent filling, this area (Parque das Bicicletas) was used for recreation, although temporarily it has become a construction site. This paper will describe the original basic design; precautions in relation to the structural condition of the galleries after inspection; the problem of absence of data for their foundations; subsoil bore tests; evolution of the engineering design for the galleries and conditioning and reinforcing the soft soil below the galleries to ensure safe advance of the EPB shield, and finally the successful outcome of the solution used."

Jan 1, 2016

By William Gleason

"With desert temperatures climbing high at Caterpillar’s Tinaja Hills Demonstration and Learning Center near Tucson, AZ in September, a group of editors were given a reprieve from the sun and stepped inside the new Cat Minestar Command Center. The movie theater-like temperatures inside were a welcome relief, and the computer screens stationed around the room were an indication of not just how much things have evolved in the mining equipment sector, but also a peek into the future of where mining is headed.Equipment manufacturers like Caterpillar have always had to deal with peaks and valleys in demand that come with mining, perhaps never more so than in the last five years. Sudhanshu Singh, global product manager for Caterpillar, said that in one month in 2012, at the height of the mining Super Cycle, Caterpillar produced more than 150 large mining trucks (haul trucks that carry 136 t/150 st or more). By contrast, Caterpillar produced about 80 of those trucks in the full year of 2016. Between 2012 and 2016, Caterpillar saw its profits drop by 40 percent.“This shows how cyclical the industry is, and it is a testament to the strength of Caterpillar to be able to tolerate the wide swings,” said Singh. Demand for commodities is once again on the rise as are commodity prices with many signs pointing toward a recovery for the mining sector, and Caterpillar has positioned itself for the recovery. During its 2017 press event in September, company officials emphasized that Caterpillar has added strength in its technology divisions by forming new partnerships and adjusting its operating plan.“At the heart of our enterprise strategy is the operating & execution (O&E) model, a strategic framework to identify areas of the business that either create or consume the most value,” said Caterpillar chief executive officer, Jim Umpleby. “Using the O&E model as a guide, we gain a deeper understanding of where we have a competitive advantage, which is key to generating high returns.”"

Jan 11, 2017

By Conrad W. Steller

What is the definition of a successful construction or development project? It could be described in many ways: a project that performs as designed; a project completed on time, a project completed within budget. The title of our talk today is, "The Advantages of Applying Design/Build -Construction Management to the Mining Industry." As our talk develops, you will see that rather than tell you how to apply this concept, we will discuss the advantages and details of Design/Build so that you can independently apply the concept. Design/Build is not new, and it cannot be universally applied. It has, however, within the past ten years, carved a specific and substantial place in the overall construction -development market. The reasons for its rather recent rise to considerable prominence as a concept is due, in part, to the increasing urgency of gaining productive access of a production facility and, in part, to the inherent advantages of the concept's economics--and they are considerable. If the Design/Build concept of contracting were fully understood, it would, without exception, be the favored way for private industry to contract for its new construction and development as well as renovation work. The basic advantages are: earliest possible access and completion at the lowest cost. Design/Build is often equated and compared to "fast track" or "turnkey" methods of construction. The Design/Build concept can, in fact, be both of these or neither. "Fast track", in and 6f itself, implies that the project will be phased construction, that is to say, it will be built quickly; whereas I "turnkey" is a measure of the completeness of the project, usually meaning essentially that the

Jan 1, 1977

By Jay F. Colinet

Coal workers’ pneumoconiosis (CWP), commonly known as black lung, is caused by the inhalation of respirable coal mine dust and is a disabling and potentially fatal lung disease with no cure. Historically, CWP has taken a tremendous human and financial toll on the U.S. coal mining industry. Recent health surveillance data indicate that CWP continues to occur at elevated levels. Respirable coal dust exposure must be controlled to prevent the development of CWP. The Pittsburgh Mining Research Division of the U.S. National Institute for Occupational Safety and Health (NIOSH) conducts laboratory and mine-site research to identify control technologies that can be used to successfully reduce respirable dust levels. Various technologies, using multiple methods of control, can be applied to reduce dust levels. An overview of CWP’s impact and a general methodology for controlling respirable dust in underground coal mines are discussed in this paper.

By H. G. Stephenson

Canada and the United states are both developed countries with economies which are extremely dependant on oil. Canada exports 37% of its production (to the United states) and imports 35% of its consumption (mainly into Eastern Canada), making the country self-sufficient in oil. Canada is attempting to increase its oil production so as to simultaneously reduce its dependence on foreign oil while producing more oil for export. The United states -imports no less than 50% of its total consumption of 17 million barrels/day. Canada's exports to the United states form only 7% of the United States total imports. The United States would clearly prefer to achieve self-sufficiency in oil. Consequently both countries are dependent on foreign oil. The united States is however in the sensitive situation of depending, for its imports, on countries which are susceptible to destabilizing political events. It is the author's hypothesis that recent developments in underground oil recovery from the Athabasca oil Sands of Alberta may well, for both countries, form part of the solution to these problems.

Jan 1, 1991

By R. W. Waytulonis

New exhaust control techniques and devices may be necessary to meet future diesel particulate matter emission standards in underground coal mines. This paper reviews conventional work practices and devices used to control diesel exhaust emissions, and new techniques being tested by the Bureau of Mines. Discussions will center on important work practices and on the function and efficiency of exhaust after-treatment devices. An industry/government cooperative research project to develop and test an exhaust after-treatment system for part 36 equipment is also discussed.

Jan 1, 1990

By Shawn T. Sorrell

Phillips Coal Company (PCC) submitted the first surface mine permit application under the Office of Surface &lining approved regulatory program of the State of Louisiana. This application for the Oxbow Lignite Surface Mine which is located approximately 64 kilometers (40 miles) southeast of Shreveport, Louisiana was submitted in March 1981. The State of Louisiana Office of Conservation, Surface Mining Division, assigned this application number LSM-1, indicating it is the first one submitted in Louisiana history. The permit area for the Oxbow Mine encompasses 6,251 hectares (15,627 acres). Of this total permit area, 5,862 hectares (14,656 acres) were classified by soil type as prime farmland by the U.S. Soil Conservation Service (SCS). Prime farmland acreage in the permit area became a major central issue in our early planning stages and throughout the permitting process of the Oxbow Mine, due to the magnitude of acreage involved.

Jan 1, 1982

By V. P. Keran

Design of the Bajo de la Alumbrera Project started in June 1995 and concentrate production commenced early in the Third Quarter of 1997. The project is situated in North-Western Argentina and is being developed by Minera Alumbrera Limited which is owned by MIM Holdings Limited of Australia (50%), North Limited of Australia (25%) and Rio Algom Limited of Canada (25%). This paper outlines the key features that were incorporated in the design from both process and plant layout perspectives. It explains the background of flowsheet and equipment selection for the plant. A feature of the flowsheet is that it incorporates gravity gold circuits in both primary and regrind circuits for recovery of gold to dore as well as in the copper concentrate product.

Jan 1, 1998

By Terry O. Arney

This paper is a description of the digital Data Acquisition and control System that is installed at Cities Service's Pinto Valley Concentrator. Pinto Valley Concentrator ? The Pinto Valley Concentrator (5, 41 is located approximately seven miles west of the town of Miami, Arizona. The Concentrator is situated south of the open pit mine and was designed to process 40,000 tons of ore per day with an average grade of .45% copper. The comminution process consists of primary, secondary, and tertiary crushing, and single-stage closed-circuit grinding 161. Concentration of the copper sulfides is by means of froth flotation. Concentrates are transferred to the Inspiration Consolidated Copper Company smelter in Miami, Arizona through a slurry pipeline.

Jan 1, 1976

By Robert W. Lawson

INTRODUCTION The two basic types of mine-air compressors are the positive-displacement compressors and the dynamic compressors. Positive-displacement compressors con¬fine successive volumes of air within a closed space and increase the pressure by reducing the volume of that space. Reciprocating and rotary compressors operate on this principle. Dynamic compressors utilize an impeller to acceler¬ate the air, with the increased air velocity converted to pressure through a stationary diffuser. Centrifugal compressors and turbocompressors operate on this principle. Reciprocating Compressors Reciprocating compressors include both single-stage and multistage units. For mine service the most com¬mon is the two-stage intercooled compressor having an atmospheric pressure intake and a discharge pressure of 689 to 861 kPa (100 to 125 psi). The cylinders of a reciprocating compressor may be either single acting or double acting. In the single-acting cylinder, compression occurs on only one side of the piston, while, in double¬acting cylinders, compression occurs on both sides of the piston. Fig. 1 shows a cross-sectional view of a typical two-stage double-acting water-cooled reciprocat¬ing compressor. Fig. 2 illustrates the sequence of opera¬tions occurring in the cylinder of a reciprocating com¬pressor. Most modern mine compressors are double acting and are driven by electric motors. Induction motors are used on low-powered compressors, and synchronous motors are used on larger compressors. Steam-driven compressors once were common and still are applied where a reliable source of low-cost steam is available. For this type of compressor, steam is a desirable power source since a governor that senses the discharge pres¬sure can be used to control the steam inlet. This can be used to regulate the compressor speed to compress only air sufficient to meet the mine's requirements (up to the capacity of the unit). Unlike a constant-speed electric¬driven compressor, no other regulation is required for the cylinders of a steam-driven unit. Rotary Compressors Rotary compressors include sliding-vane, liquid¬piston, two-impeller straight-lobe or cycloidal, and helical-lobe units. Each of these has specific advantages and applications. Of these, the helical-lobe or "screw" compressor has the greatest application for supplying "100-lb air" [689 kPa (100 psi) ] to small- and medium¬size underground mines. Fig. 3 illustrates the operation of a sliding-vane compressor. Fig. 4 illustrates the operation of a helical lobe or screw compressor. Fig. 5 illustrates the operation of a two-impeller straight-lobe compressor. Fig. 6 illustrates the operation of a liquid¬piston compressor. Centrifugal Compressors Centrifugal compressors deliver 0.94 m3/s (2000 cfm) or more of air, and they are best suited to supply¬ing large volumes of compressed air for base loads. The efficiency of a centrifugal compressor declines rapidly when its operation deviates from its design point. If the power cost is not a critical consideration, a centrif¬ugal compressor is attractive as a result of the low initial and installation costs and the high degree of reliability. Fig. 7 illustrates a typical four-stage centrif¬ugal compressor, and Fig. 8 is a cross section of this type of unit. COMPRESSOR SELECTION The process of selecting a compressor requires sev¬eral considerations, including the capacity, the control system, the location, the power supply, and the cooling provisions. Compressor Capacity To determine the required capacity, the total air quantity and pressure requirements must be calculated. The air consumption of various tools, as listed in Table 1, must be included in this calculation. Some of the other considerations include: 1) The correction factor for altitude, as listed in Table 2, must be included in the calculation. While pneumatic tools require additional compressed air as the altitude increases, the compressor produces less. 2) A correction factor must be incorporated for the use of multiple tools. Table 3 lists appropriate correc¬tion factors for rock drills.

Jan 1, 1982