文献翻译配管工程学概述.docx

1、文献翻译配管工程学概述Back to Basics: An Overview of Plumbing EngineeringBy John SwaffieldAny overview must be personal. In this case, the perspective is based on 25 years of exposure to the whole gamut of plumbing issues from application of mathematical simulations to the efforts necessary to bring water supp

2、ly to the less privileged areas of developing countries; from the investigation of venting problems in underground structures to the political and business issues inherent in the manner in which codes and regulations are specified. This perspective leads to caution in addressing the title “Back to B

3、asics.” In the U.K., and probably other western democracies, this phrase represents the graveyard of many political aspirations. The first step in this overview therefore is to define “basics” and probably more importantly to determine what is not included under this heading. The fundamental require

4、ment of a plumbing system, including both water supply and drainage, is that it does no harm. The public health imperative is supreme. This is often encapsulated within codes through an apparent obsession with such issues as back-siphonage. Drainage systems must carry away waste without posing a haz

5、ard to the user or providing any long term hazard within the areas through which the drainage system passes. Habitable space must be protected from the incursion of foul odor through the provision of venting systems. These requirements are basic and form, in the U.K. at least, the backbone of the Vi

6、ctorian drainage and vent systems installed from the 1880s and which became the precursor of similar systems within the developing Western world at that time. In the U.K. in the mid 19th century Chadwick and other social reformers introduced many of the urban water supply and drainage system techniq

7、ues now taken for grantedeffectively the Industrial Revolution spawned both the problem and the socially aware groups that would provide its solution. To these requirements must now also be added the need to conserve water, not only as an economic and political imperative, but also to meet the deman

8、ds being placed on water supply systems by increases in population, particularly in the cities of the developing world, and the rising expectations of those fortunate to live in developed cities. Whats Not IncludedSo much for the definition of “basics.” The consideration of what should not be includ

9、ed within this title is more controversial. “Back to basics” does not mean a return to some golden age when rule of thumb was supreme, when venting was so excessive that traps never oscillated and flush volumes so great that imperfections in system design and installation went unnoticed, and each co

10、mmunity applied its own codes and standards developed from limited experimentation and observation, unsubstantiated by any degree of engineering analysis or rigor. In the U.S. the design of water supply and drainage systems may be traced back to the fundamental work of Hunter. However, Hunter recogn

11、ized in his definitive 1940 paper that the solutions he proposed were limited by the analysis techniques available to him. Referring to the design of building drainage systems he observed that “.the conventional pipe formulae apply to the irregular and intermittent flows that occur in plumbing syste

12、ms only during that time (usually very short) and that section of pipe in which the variable factors involved (velocity or volume rate of flow or hydraulic gradient and hydraulic radius) are constant.” Hunter recognized that the basic physics underlying water supply and drainage, and, in particular,

13、 drainage, as this arm of the subject offers particular challenges to the analysis due to the free surface nature of the flow, which may also be multi-phase due to the transport of solid material and the possibility of entrained air, is identical in Seattle and Sydney, Hoboken and Helsinki or even A

14、lbuquerque and Auchtermuchty. Yet each of the states or nations represented in this list has its own code or standard. The European Community has struggled for nearly 20 years to generate a common plumbing codeunsuccessfully. Thus, the predominant issue for plumbing engineering at the end of the 20t

15、h century has to do with educationthe need to stress that physics defines operation and mathematical simulations can function without rule of thumb overrides. Water ConservationWater conservation offers an example for the interaction between practitioners and those involved in developing both produc

16、ts and system design simulation processes. A review of the water usage within developed countries indicates surprising similarities in the percentage use of domestic water for a whole range of common requirementsapproximately 30 to 40% of the drinking-quality water is used to flush toilets. Similar

17、figures are found in toilet and urinal usage in commercial buildings. Careful monitoring of usage has provided this data, and to introduce effective water conservation measures it is imperative that water closet flush volumes decrease. This has been a continuing thrust for the whole of this century,

18、 a century which opened with a disagreement between the London Metropolitan Water Board and the ceramic industry over the 10.5 gallons proposed for water closet flushing and closed with arguments in similar arenas as to the acceptability of 1.6 gallons for flushing devices. Similarly, the century op

19、ened in the U.K. with the Institute of Health in London proposing a drain line carry test using half-inch diameter balls and closed with an extremely similar test probably facing demise within the U.S. water closet. Reducing water closet flush volume is imperative. Good design can deliver. The intro

20、duction of dual flush (i.e., a lower flush volume for urine removal, particularly significant in commercial buildings with a high female population), offers further opportunities for conservation. Dual flush was first introduced to the U.K. in the 1980s, where it was unsuccessful due to a lack of cl

21、arity in operation. It will be reintroduced in the 1999 Water Regulations, encouraged to a large extent by the successful use of 1.6 and 0.8 gallon dual flush in Australia. The introduction of non-siphonic flushing devices within the U.K. Water Regulations from January 1, 2001, will allow a simpler

22、and unambiguous two-button mechanism which will ensure that the system in understood by all users. Drainage SystemsHowever, there is a need to recognize that drainage networks are a system. Alteration to one element in isolation may lead to possible problems. There is a need to recognize that reduci

23、ng flush volume should be accompanied by possible reductions in drainage diameters, particularly for isolated water closets or increases in slope. Similarly, the decay of the flush wave needs to be recognized and modeled. Hunter recognized the importance of wave attenuation but was unable to model i

24、t due to the lack of computing power in the 1940s. The modeling method to ensure that these considerations are fully investigated at both the code and design stage exists, developed initially through initiatives at National Bureau of Standards, now NIST, and propagated in the U.S. through ASPE confe

25、rences over the past 10 years. Similarly, water closet design can, and will, benefit from the introduction of modern technology. The application of computational fluid dynamics to the flow regime within water closets has already been demonstrated by such industrial organizations as Toto in Japan. Wh

26、ile there is a need to approach with caution the boundary conditions which must determine the accuracy of any such CFD model, the introduction of such models is a major step forward in the development of water closets. Mathematical simulations can inform the designer when the item is acceptable. Mat

27、hematical models can provide the targets to which design should aspire or confirm the appropriateness of a given set of performance code criteria. This approach would bring the plumbing engineering industry in its broader sense in line with those other industries which depend on a fundamental unders

28、tanding of fluid mechanics. Thus, this overview of plumbing engineering stresses the importance of water conservation and highlights its growing importance in the coming century. There will be a need for the developed world to reduce its usage of water while at the same time being able to provide lo

29、w water use solutions to those countries still developing and whose cities are severely taxed by the overuse of water for purposes that could be achieved at lower cost. In defining the basics of drainage design, the prevention of odor ingress was highlighted. The Victorian concept that smell equalle

30、d disease led to extremely complicated venting systems, known in the U.K. as two-pipe networks where each individual appliance was separately vented to a vent stack and black and grey water were separately taken away from the building through two vertical wet stacks. The development in the 1930s of

31、the one pipe system in the U.S. and, in particular, the introduction of the single stack system in the U.K. from the 1950s on, led to considerable savings in terms of the cost of plumbing installations. In the U.K. in the 1950s such reductions were important in the post-war housing rebuilding proces

32、s. However venting systems are still over-provided. Modern technology allows the analysis of vent system operation and allows the identification of means by which pressure excursions may be limited. The introduction of pressure relief valves or air admittance valves and the opportunity for distribut

33、ed venting up the whole height of a multi-story building offers tremendous advantages and savings for vented system design. In the U.K. the development of waterless trap seals that also act as air admittance valves provide exciting possibilities for system designers in the future. In this context “back to basics” does not mean adhering to comp