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By L. Prosch

"The word 'sustainability' has gotten such a work out lately that the whole concept is in danger of floating away on a sea of inoffensiveness" Michael Pollon. It is estimated that approximately 65% of the roughly 130 million carats of diamonds mined globally per annum originate in Africa and has an annual value of US$ 8.4 billion', Many of these mines are located in remote areas of the continent where the directly affected project community's income is often well below the poverty line. Often associated with these communities are occurrences of localized over exploitation of natural resources, environmental destruction and the abundance of social ills.

Jan 1, 2010

By Gift Makusha, Dave Minney

Anglo Coal South Africa mines coal for both the domestic and export market using open cast and strip mining methods. To establish a mine, a process is set in place to gather ever increasing amounts of geological and metallurgical data to confirm a proven reserve. Increasingly, geotechnical data are also included in this process to confirm that reserve is easily and safely mineable. The mine design process is an iterative one using a combination of numerical modelling and empirical data to arrive at a mining layout that is both, practical, productive and safe. In South Africa it is a legal requirement to compile a code of practice to combat rock fall and slope instability accidents and these have to be revised annually, reinforcing the iterative process of continual improvement. To ensure best practise occurs, all Anglo Coal operations are subjected to annual 2nd party audits and ad hoc 3rd party audit by independent consultants. This paper attempts to explain the process described above in a concise, but understandable manner. 1.0 GEOLOGICAL SETTING The Ecca sediments date from the Permian period and the coal deposits were formed in glaciated valleys on a basement of Dolomite, Ryolite or Granophyre rock types. The sediments overlying the coal deposits are typically flat lying and multiple bedded. The sediments consist of mudstones, shales and sandstones and are generally capable of forming stable highwalls given the time that they must stand up for. Anglo Coal extracts coal from the Witbank, Highveld and Vereeniging coalfields. The Witbank coalfields contain five seams numbered from the base upwards, 1 to 5 Seam; Highveld coalfield the 2 and 4 Seam and the Vereening area the seams are described as Top, Middle and Bottom seams. Coal deposited over the basement Dolomite formation display very erratic dips, as contemporaneous subsidence occurred in some instances over sinkholes that were forming, resulting in local thickening of the coal deposit and resulting in strata that dips toward the centre of the sinkhole.

Jan 1, 2006

By C. Birch

"The purpose of this study was to establish the impact of discount rates on cut-off grades for narrow tabular gold deposits as characterized by the goldfields of the Witwatersrand Basin in South Africa. There are various methods available for determining the cut-off grade, from simple breakeven calculations to sophisticated software packages that consider a variety of inputs to optimize the cut-off grade. For this study a simple financial model was created in Microsoft Excel® that links the ore flow, block listing, and the cash flow. This allows the cut-off grade to be optimized considering how the cost of capital and chosen discount rate affect the cash flow.The discounted cash flow (DCF) and resultant net present value (NPV) are a widely used valuation method for production properties according to the South African Code for the Reporting of Mineral Asset Valuation (SAMVAL Code). The financial model in this study utilizes the Solver function, as well as simple Microsoft Excel spreadsheet formulae to optimize the NPV. Solver was chosen as it is a standard feature in Excel and thus no additional software costs are incurred beyond the basic Microsoft Office suite. For the purpose of this study, just narrow tabular gold deposits of the Witwatersrand Basin were considered. An example of a typical ore block listing, as well as the costing figures, was obtained from an operating gold mine. The results obtained from the study financial model were compared to the current cut-off grades obtained from the mine using their proprietary optimizer program, and were found to be comparable. The methodology utilized for this study thus appears valid.The cut-off grade was optimized considering the cash flow, which includes the variable mineral resource royalty tax, the variable gold income tax, as well as the discount rate. By comparing the resultant NPVs using discount rates of zero, 9%, and 12%, the impact of the discount rate on cut-off grades, resultant life of mine, and average mining grades (AMG) could be compared for the example ore block listing. The South African Code for Reporting of Exploration Results, Mineral Resources and Mineral Reserves (SAMREC Code) does not require operations to state if a discount rate was considered in determining mineable reserves. Mining companies approach the question of applying discount rates in determining their cut-off grades, and thus mine planning strategy, in different ways. Due to the negative impact that optimizing purely on NPV has on the life of mine, some choose to optimize only on profit. Other companies have reverted to utilizing pay limits as their primary grade planning strategy. The calculated cut-off grade is then considered to be another planning indicator rather than a hard determination of mineable reserves."

Jan 1, 2016

By A. P. Squelch

The high incidence of accidents and fatalities in the South African mining industry, in particular those associated with falls of ground, is often attributed to ineffective and/or inappropriate training methods and material. Recently introduced mine health and safety legislation in South Africa also requires that all mine workers receive appropriate and effective training to enable them to operate safely in their given mining environment. There can, therefore, be no doubt that methods to provide effective training, in particular safety related training, are urgently required in the South African mining industry. In the search for alternative and improved training approaches, attention has fallen on virtual reality (VR) technology as a possible solution. VR has found acceptance in a number of industries as an effective method of training for a variety of work place activities, including those of a safety related nature. VR has successfully been applied in a number of industries to improve the effectiveness of safety and hazard awareness training. The CSIR: Division of Mining Technology (CSIR Miningtek), in conjunction with the Safety in Mines Research Advisory Committee (SIMRAC), therefore evaluated the potential of VR to be used as a training medium in the South African gold and platinum mining industry. Aspects of the evaluation included an assessment of the technical capability of VR to represent a typical underground mining environment with sufficient realism and the relevance of the VR training concept for a largely illiterate workforce. For these purposes, a prototype PC-based VR hazard awareness training simulator has been developed by CSIR Miningtek, and a series of evaluation sessions conducted at a typical deep level gold mine. The conclusion from this evaluation work is that virtual reality technology has the potential to provide effective training systems that are relevant to the South African mining industry. Keywords: Virtual reality, mine training, safety training.

Jan 1, 2001

By P. Schutte

It is evident from most admired companies, globally, that they drive key priorities such as teamwork, customer focus, fair treatment of employees, initiative and innovation into their organisations. It is clearly proofed in all the research that the role of the human factor, and therefore human behaviour, is pivotal to companies striving to accomplish goals such as competitiveness, customer delight, high quality, growing productivity as well as a safety-committed work force. The challenge of leadership is to change the worker’s poor perception of safety to an excited, empowered, valued employee who is continuously committed to the achievement of high levels of health, safety and conformance – the challenge therefore is to transform from within. Any work force needs a set of behavioural rules which work for it – including safety rules and critical safety behaviours, which are accepted through involvement leadership, encouragement and support.

Jan 1, 2003

Novel flotation reagents were developed to improve the flotation of coarse particles. Laboratory tests conducted on an anthracite coal sample from Kyung-Dong Coal Company, Korea, showed that the reagents can successfully clean 2?3 mm top-size materials. Pilot-scale tests conducted on a 1.41 mm x0 coal gave substantially better results than those obtained using kerosene as collector. The pilot-scale test results were used to develop a flowsheet, in which the 1.41 mm x0 fraction is cleaned by flotation and the 4 x1.41 mm coal is cleaned by single-stage spirals. The performance of this circuit was compared with another flowsheet, in which the 0.5 mm x0coal is floated using the conventional flotation reagent, with the 4 x0.5 mm material being cleaned using two separate spiral circuits. The performance of the two flowsheets was compared by computer simulation. The results showed that the flowsheet consisting of the coarse particle flotation circuit can give substantially higher yield sat a given product grade. Keywords: coal flotation, coarse particle flotation, collector, spirals, computer simulation.

Jan 1, 2002

By G. Humphries, E. Wolmarans

The PPRust North project is an expansion of existing operations on the ?Platreef? orebody in the Limpopo Province of South Africa. Anglo Platinum has been mining and processing the Platreef since 1993 at the adjacent Sandsloot and Zwartfontein South open pits at a current rate of approximately 4.5 million tons per annum. This paper describes the origin of the proposed process flow sheet. A comprehensive test work programme has been conducted evaluating the best process flow sheet for the very hard and variable ore in the proposed mining area. The selection of the comminution circuit is discussed where conventional crushing and SABC options were analysed based on both extensive test work and analyses of current operational data at the existing concentrator. The application of the high pressure grinding roll technology has significant advantages?it replaces the 3rd and 4th stage crushing stages in a conventional circuit. This programme has been conducted over several years and has involved work done at site at pilot scale, internally at the company?s research facilities and externally at various sites. The on-site pilot work was completed over a 7-month period at the existing concentrator facility using a ThyssenKrupp-Polysius, ?Polycom?, 950 mm by 350 mm, high pressure grinding rolls (HPGR) machine. In excess of 185 000 tons of ore was processed through the unit during the trial period. This paper describes the test work programme and particularly the proposed application of high pressure grinding technology and its potential for further application in the platinum industry.

Jan 1, 2006

"Chairman: Professor J. C. Griffiths Rapporteur: Mr J. P. G. PRETORIUSPapers:Mine-mill production scheduling by dynamic programming by R. J. Roman Optimization of a large mining venture by J. C. Paynter, B. K. Loveday and C. G. Robinson Economic surface mining of multiple seams by T. V. Falkie and W. E. PorterIn introducing his paper, Mr Roman said that whereas in manufacturing plants the yearly production levels were usually chosen to produce the largest annual cash flow, in a mining operation, the raw materials (ore) were exhaustible so that the production had to be scheduled to maximize the total net present worth of the operation. This optimum production schedule could be determined by using dynamic programming. The required information was readily available to management at most mines. The 'possible operating range' of production rates lay between the rate with the highest profit per ton. and that with the highest profit per year. The optimum production rate started typically at the top of this range and decreased slowly as the deposit was depleted.Dynamic programming was used to determine several production schedules for a hypothetical mine-mill complex. The effects of changes in the ore grade estimates, size of deposit and acceptable rate of interest on the production schedule were taken into account. Apart from the fact that the net present worth of the overall profits was larger than that obtained by conventional methods, it appeared from the cases studied that the amount of metal recovered was also greater.Dr it P. King commented that this was a very interesting application of dynamic programming. He pointed out, however, that the market price of the metal was likely to vary significantly and randomly during the life of the mine, and he suggested that the problem should, therefore, be reformulated as a stochastic dynamic programming problem.If the price of the metal rose to abnormally high levels, a much higher than normal production rate could be expected. The results of analyses given in Table 5 showed that the production rate was a function of market price. In his view the stochastic problem could be solved just as easily as the deterministic problem.In reply to a question by Dr King as to whether the function relating recovery to production rate (Table I) was based on real data, the author replied that it was based on the results of an analysis conducted at the Union Carbide Corporation's Pine Creek tungsten mine in California.Dr D. M. Hawkins stated that costs were incurred when the production rate was altered, for example, in appointing or laying off staff, and that in practice it may be necessary to take these costs into account in finding the optimum production rate. Mr Roman replied that, while normal administrative costs were accounted for, the additional costs incurred in appointing and laying off staff were not taken into account."

Jan 1, 2014

By J. K. Williams, M. P. Wells

"As part of the planning system at each division of Nchanga Consolidated Copper Mines, Limited, the Mine Planning Department is required to produce a detailed production schedule for each shaft.Because of the difficulties in producing a schedule which satisfies all the mining constraints, and because of the large clerical effort involved, the full range of possible schedules can never be considered.It has been found possible to produce a schedule using linear programming which satisfies the majority of the many varied mining constraints. Computer programs have been written to enable the mine planning department to use this mathematical system without assistance.The system has a large degree of flexibility to enable the planner to include conditions which cannot be incorporated readily in the linear program. This system permits the more efficient production and evaluation of schedules and reduces the amount of clerical effort."

Jan 1, 2014

By T. J. Otto, G. C. Lindeque

Productivity is improved by increasing the ratio of output to input. In an operating open-pit mine, improving the productivity of heavy mining equipment (HME) enables the unit cost of production to be reduced. To optimize HME productivity, the Kolomela open-pit iron ore mine transitioned to an enhanced short-term mine planning (STMP) process that supports the application of a manufacturing-type operating model. At the core of the enhanced STMP process is a focus on integration across the open-pit mining value chain. The interdependencies between mining activities are highlighted and emphasized, thus ensuring that mining activities are synchronized. The improvements related to HME productivity were monitored from 2019 to 2020. The utilization of mining area in the Leeuwfontein pit improved from 71% to 90%, and the blasting frequency reduced by 14% while the average blast size increased by 17%. The distance travelled during shovel relocations between mining phases reduced by 16%, and the lost time associated with drills relocating reduced by 53%. These productivity improvements resulted in an 11% increase in the loading rate of the main waste shovel at Kolomela from 0.9 Mt/month in 2019 to 1.0 Mt/month in 2020. The enhanced STMP process can be adapted to other open-pit mining operations.

Nov 1, 2021

By D. Almond

Low-grade, complex mineral deposits have resulted in the need for complicated large-throughput processing plants delivering increased productivity, reliability, and utilization, together with reducing operational costs. Complex mineralogy has resulted in complicated process flow sheets designed to recover minerals as efficiently as possible. In addition, the remote location of many minerals-processing plants, continuously rising energy costs, and fierce competition pose significant challenges to the modern mine, compounded by a global scarcity of qualified and experienced operational personnel. Over the last decade the Internet and automation technologies have undergone major advancements. Automation technologies, solutions, and concepts that existed, but were considered risky or unreliable prior to the year 2000, have now gained acceptance and matured. Furthermore, new technologies and different collaboration schemes have appeared, offering innovative solutions to the mining industry to address many of the challenges described. These advancements in reliable remote systems that access technology through the Internet provide significant opportunity to support mining operations, enhance process performance, provide engineering services, and proactively anticipate and execute maintenance services. This paper references a global survey of automation trends in the mining industry and the potential for an intelligent collaborative environment using automation technologies to exploit opportunities in operating the plant of the future, increasing effectiveness, and reducing operational costs. A variety of possibilities are described, including asset management solutions, remote access capabilities, performance monitoring solutions, advanced process control technologies, and the formation of an intelligent collaborative environment. A real example where this technology is used to support the operation and maintenance at a cement plant in Egypt is given to underpin the concepts described in this paper.

Jan 1, 2012

By K. Kasas, J Kermeci, S. Vujic, S. Secei, P. Kermeci

On the ‘Majdan III’ open pit mine, supplying with brick clays the production plants of the industry of building material ‘Potisje-Kanjiza’ from Kanjiza, a modern ECS (excavator-conveyor-spreader) complex was built, integrating four bucket excavators, six conveyors and one spreader into a whole. This complex connects the mineral-exploitation unit with the final brick-products plant of the company. Monitoring and management of the ECS complex is carried out by modern computer-supported information-management system (IMS) implementing most modern measuring-regulation, computer and GPS equipment. It was concluded that, for safety reasons, the functions of the IMS should be developed by a component of active visual monitoring of the ECS complex. For this purpose, the task of making a project on intelligent system for visual monitoring of the ECS complex was entrusted to the Department of Computer Application at the Faculty of Mining and Geology, University of Belgrade. This paper gives a review of basic project solutions. Keywords: Automation, process management, information management technology, visual system, intelligent systems, TV monitoring, surface exploitation, clay, Majdan III, Potisje-Kanjiza.

Jan 1, 2003

By J J. McEwan

Silver tarnishes readily in common atmospheres and is accelerated in humid atmospheres. Tarnish is the formation of silver sulphide on the surface of silver when it is exposed to a wide range of sulphur-containing atmospheres. Tarnish is unattractive and highly undesirable, and can be removed either with a silver polish or a chemical dip. Dips are generally only recommended when heavy black tarnish cannot be removed with a polish, and care must be taken during cleaning because these can contain aggressive chemicals and give off hazardous and unpleasant smelling fumes. Polishes work best for large areas of plain undecorated silver, and form part of a regular cleaning programme. Some polishes contain chemicals that inhibit tarnishing, but these generally only have a short life. Several methods have been developed to reduce tarnish formation on Silver; these include alloying, surface treatment, and coatings. The authors evaluated a range of self-assembled monolayer (SAM) surface treatments and coatings in earlier research. Four treatments/coatings increased the time to noticeable tarnish by more than ten fold, and the results were reported at the International Corrosion Congress (ICC) in 2005, and at the Mint Directors Conference (MDC) in 2006. SAM treatment using 95% 1-hexadecanethiol (C16H34S) was found to give good anti-tarnish performance and showed potential for the commercial treatment of Sterling silver. Therefore research was performed to optimise the methods of application of this type of coating to provide an easier, faster, and more-user friendly technique to provide an anti-tarnish treatment. Keywords: silver, tarnish resistant coatings.

Jan 1, 2006

By D. C. Panigrahi

Extensive field studies have been carried out to investigate the pillar fire problems in one coal mine in India. A Thermal IR gun and a Thermovision camera have been employed for thermal scanning to assess the state of heating in selected pillars. Special sampling set-ups have been designed to collect gas samples from the holes drilled into the selected pillars and the multigas detector is used to analyse the composition of samples in situ. In order to predict the spontaneous heating in coal pillars, different gas ratios have been calculated and it has been observed that some of the established gas ratios, viz. Graham?s ratio, Young?s ratio etc. have resulted in negative values in samples containing high amounts of methane. The modified gas ratios have been proposed which will be useful for predicting the pillar fires. These ratios may also be used for assessing the condition of fires in sealed-off areas.

Jan 1, 2004

By M. Onifade, O. S. Otuogbai, A. F. Mulaba-Bafubiandi, O. D. Eniowo, H. Grobler

Artisanal and small-scale miners in Nigeria struggle to attract formal financing to upgrade their operations to a more sustainable form of small-scale mining operation. Literature shows that for an investment to attract formal sources of financing; the business must be considered creditworthy by potential lenders. This means that the credit risks associated with the investment must be bearable for the potential lender. This study looks at how artisanal and small-scale miners can attract formal funding, which will help them take the leap from artisanal state to a form of sustainable small-scale mining operation. This study evaluates the creditworthiness of artisanal and small-scale mining operators using key credit risk parameters identified in the literature and through primary investigation. A quantitative study is conducted on a sample of 100 artisanal and small-scale miner establishments in Nigeria to evaluate the effect of these identified credit risk parameters on creditworthiness. It is shown in this study that being a member of a mining cooperative society, which is a form of social collateral, best improves the chances of access to formal financing for miners within the sample group. This underpins the role of social collateral, in both the formal and informal economy, and its influence in improving the creditworthiness of a typical artisanal and small-scale miner.

Jul 23, 2025

By M. Z. Naghadehi, F. F. Nasategay, J. Sattarvand, R. Battulwar, E. E. Gohari

After the recent increase in catastrophic failures of tailings dams such as the Burmadinho, Brazil failure in 2019, the mining industry has actively engaged in the stabilisation of tailings dams. Most of the tailings storage facility (TSF) guidelines suggest a laborious action that can be facilitated through imaging by unmanned aerial vehicles (UAVs). Although UAVs are not unknown to most mining operations, automated rill detection through aerial image processing is a new concept. This study utilises images from sites in the U.S. and employs semantic segmentation with a UNet architecture to detect location and size of these rills. The developed model can be used as a tool for monitoring surface erosion of TSFs.

Sep 1, 2021

A decision by joint-venture partners Anglo American, Gencor, and the Industrial Development Corporation to proceed with the expansion of the Columbus Stainless Steel plant in Middelburg will contribute significantly towards the economic growth that South Africa needs so desperately. The expanded facility, expected to come on-line in 1995, will be the largest single-plant producer of stainless steel in the world, and the company will rank sixth overall in world production.

Jan 1, 1993

By N. Gibson

The application of oxygen in a copper smelter by N. GIBSON* (Visitor) This paper describes how the problem of increasing the capacity of the Rokana copper smelter was handled, and how oxygen was found to be technically and economically the best solution. The first phase of its implementation is outlined.

Jan 3, 1974

By A. N. Clay, N. N. Moeketsi, S. Joubert

For many years, mine-impacted water has been regarded as a problem and linked to long-term environmental liabilities. However, this water can be a renewable and a sustainable resource, provided that it is managed in a responsible and sensible manner. South Africa’s National Water Resource Strategy (NWRS, 2013) considers water that can be used to contribute to economic activity to be a water resource. Although all water resources are considered as belonging to the State, government does not appear to have meaningfully explored the use of mineimpacted water to contribute to the country’s economic activity. Africa is blessed with more sunshine than anywhere else, apart from Australia, yet we see no rollout of vast quantities of solar panels to ensure every African family has access to affordable power. This suggests that governments are incapable of managing such a free resource. At the same time, apart from the equatorial areas, water is a seriously constrained resource and yet we expect the same entities to manage a commodity none of us can live without. This paper explores the conversion of mine-impacted water from waste to a resource and how the inclusion of other stakeholders (such as water users, landowners, and ordinary South Africans) could benefit the process.

Jan 2, 2022

By M. J. Deats

INTRODUCTION To prepare the reader adequately, reference should be made to the paper 'The Pioneering of Fully Mechanized Longwall Coal Mining in South Africa' by R. T. Naude and M. J. Deats, published in the February, 1967, edition of the Journal. At the time mechanized longwalling had been proved operationally feasible with encouraging results since its inception in South Africa in mid 1965. Subsequently, further top seam panels were successfully extracted with improved productivity and with some modification to equipment. In 1968, after an overseas visit by mine officials, equipment specific to suit local conditions was acquired and lower seam trials commenced. Despite initial obstacles and difficulties the first panel was successfully mined. Modification and improvements to equipment and techniques resulted in the second lower seam panel being extracted economically during 1969-1970 and with productivity exceeding even that of top seam faces. During extraction of the second lower seam panel, gradual and complete surface subsidence occurred over the panel without affecting face operations. Rock mechanics investigations had originally indicated some uncertainty regarding adverse dolerite sill behaviour which could have caused longwall mining to be hazardous. All such doubts have now been removed. RESUMÉ AS AT FEBRUARY, 1967 Mechanized longwalling was introduced in 1965 on an experimental basis in an effort to improve productivity in the newer area of the mine and to increase the quality of the comparatively dirty run of mine feed to the washing plant. In addition advantages could be predicted in the long term by better utilizing reserves of straight coking coal and increasing the life of the mine. The top seam unit was obtained on a rental basis and by the beginning of 1967, two panels, the first having a face length of 215 m, a panel length of 345 m, seam section of 1 219 mm, and the second the same face length, a panel length of 453 m and a seam section of 1 067 mm had been successfully longwalled. At this stage a best month of 24 602 metric tons with an average of 17 364 metric tons per full working month could be reported. Results were sufficiently encouraging for the company to exercise its right to acquire the equipment as its own asset and from 1967 onward, the unit has operated on this basis. From the point of view of rock mechanics, the dolerite sill over the first two panels was known to have 'bridged', only the material below the base of the sill having truly 'goafed'. No adverse pressure effects had significantly affected face operations except for two 'bumps' towards the end of operations in each panel. Gate road maintenance presented no problem. The strong inflows of water experienced on the first face were now known to be associated with an isolated water bearing fault plane and were not experienced on the second face. TOP SEAM EXPERIENCE - MAY, 1966, TO DATE Panel 2 (February, 1966, to November, 1966) The operations in panel 2 (see Fig. 1 for location of panels) continued uneventfully until the final month in this panel. At this stage, the chocks behaved most inconsistently often lowering under the weight of the canopies alone. Roof trouble became so severe that the unit was unable to produce adequately and blasting of chocks became a daily occurrence. Finally 24 m short of the planned limit it was decided that a complete overhaul was the only solution and the extraction operations commenced. At this time, the only fatal accident associated with longwalling occurred when a Non-White inadvertently fell into the panzer conveyor transfer point at the main gate. Some gate road difficulties in this panel were overcome by bolting tapes to the roof as decking and allowing them to pass over the gate chocks and collapse into the goaf. Two cribbed roof falls were also negotiated by the gate chocks at the face ends without undue difficulties. It was decided in the light of maintenance problems encountered on this face that the best solution would be to appoint a foreman solely in charge of face maintenance crews. This step has to a large extent contributed to success achieved subsequently. Panel 2-face length 213 m panel length 456 m cutting height 1 092 mm average monthly output 16 443 t best month 19 130 t Panel 3 (December, 1966, to June, 1967) By the end of 1966 results were sufficiently encouraging for the company to exercise its right to acquire the equipment. This was negotiated and the unit has operated as such to the present date. Prior to installation in panel 3, all face equipment was thoroughly overhauled underground and the chocks boost-tested to yield-load. The costs of overhauling, including almost complete hose replacement, were much higher than anticipated. Advice had been received that complete hose replacement was common practice after +/- 18 months' operation. Shortly after commencement of operations in panel 3 the chocks again failed as they had towards the end of panel 2. At this stage, the suppliers advised that the valve gear should have been repaired during the overhaul as the needle and seat seals could no longer be relied upon. This operation was impossible to carry out on the face and would have been e1ttremely time consuming. Fortunately a new type of valve gear was then available from the suppliers, termed the capsule-type valve, and a complete change over could be made on the face. The encapsulated valve has a delrin pad sealing over a raised