BS 7388-1991 Guide for prevention of leaks from hydraulic fluid power systems《液压动力系统防泄漏指南》.pdf

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1、BRITISH STANDARD BS 7388:1991 Guide for Prevention of leaks from hydraulic fluid power systemsBS7388:1991 This British Standard, having been prepared under the directionof the Machinery and Components Standards Policy Committee, was published underthe authority of the BoardofBSI and comes intoeffect

2、on 28 February1991 BSI 09-1999 The following BSI references relate to the work on this standard: Committee reference MCE/18 Draft for comment 89/70465 DC ISBN 0 580 19214 8 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Machinery and Co

3、mponents Standards Policy Committee (MCE/-) to Technical Committee MCE/18, upon which the following bodies were represented: Advanced Manufacturing Technology Research Institute Association of British Mining Equipment Companies Bath University Library British Compressed Air Society British Fluid Pow

4、er Association British Steel Industry Department of Trade and Industry (National Engineering Laboratory) Institution of Mechanical Engineers Ministry of Defence The following body was also represented in the drafting of the standard, through subcommittees and panels: British Hydromechanics Research

5、Association Amendments issued since publication Amd. No. Date CommentsBS7388:1991 BSI 09-1999 i Contents Page Committees responsible Inside front cover Foreword iii 0 Introduction 1 1 Scope 1 2 Specifications 1 2.1 General 1 2.2 Definition of leakage 1 2.3 Operating specification 1 2.4 Conditions ap

6、plying to maintenance 1 2.5 Design specification 2 3 Design considerations 2 3.1 General 2 3.2 Number of pipe joints 2 3.3 Valve mounting methods 2 3.4 Pipe systems 3 3.5 Handling 3 4 Component choice 3 4.1 General 3 4.2 Tubing 3 4.3 Tube fittings 4 4.4 Welded fittings 7 4.5 Hoses and hose fittings

7、8 4.6 Adaptors 11 4.7 Coupling port threads and their sealing methods 11 4.8 Self-sealing couplings 14 4.9 Reservoirs 14 4.10 Cylinders 14 4.11 Pumps and motors 14 4.12 Valves 15 5 Design for maintenance 15 5.1 General 15 5.2 Accessibility 16 5.3 Removal of components for service 16 5.4 Isolating se

8、ctions 16 5.5 Filters 16 5.6 Drip trays and drain tanks 16 5.7 System filling 16 5.8 System draining 16 5.9 System cleaning (flushing) 16 5.10 External cleaning after spillage or as routine 17 5.11 Remaking pipe joints 17 5.12 Self-sealing couplings 17 6 Pipework design 17 6.1 General 17 6.2 Install

9、ation and cleaning 17 6.3 Vibration 17 6.4 Pipe stresses 18 6.5 Location of pipe couplings 19BS7388:1991 ii BSI 09-1999 Page 6.6 Hoses 19 7 Seals 19 7.1 Static seals 19 7.2 Dynamic seals 20 8 Installation 21 8.1 General 21 8.2 Off-site work (preliminary build and test) 22 8.3 On-site installation 22

10、 8.4 Production line installation (where the system is part of product) 22 9 Commissioning and testing 23 9.1 General 23 9.2 Commissioning 23 10 Maintenance 23 10.1 General 23 10.2 System evaluation 23 10.3 Preventive maintenance 23 10.4 Maintenance routines 24 11 Fluid spillage 24 11.1 General 24 1

11、1.2 Prevention of spillage 24 11.3 Precautions should spillage occur 24 12 Responsibilities 24 12.1 Designers responsibilities 24 12.2 Customers responsibilities 25 12.3 Suppliers responsibilities 25 Appendix A Leakage categories 26 Appendix B Cleaning methods and materials 26 Figure 1 Example of a

12、24 bite type compression coupling 5 Figure 2 Example of a 37 flare type compression coupling 6 Figure 3 Example of an “O”-ring type compression coupling 6 Figure 4 Example of welding steel pipe to welding nipple 7 Figure 5 Four-bolt split flange 9 Figure 6 Four-bolt square flange 10 Figure 7 Four-bo

13、lt square welded flange 10 Figure 8 Example of a re-useable hose fitting 11 Figure 9 Example of a swaged hose fitting 11 Figure 10 G thread (BSP) 60 cone fitting (with and without “O”-ring sealing) 12 Figure 11 JIC 74 cone fitting 12 Figure 12 Flat face “O”-ring seal fitting 12 Figure 13 Staple fitt

14、ing 13 Figure 14 Examples of coupling port thread sealing methods 15 Figure 15 Examples of good and bad pipe runs 18 Table 1 Guide to leakage categories 26 Publications referred to 28BS7388:1991 BSI 09-1999 iii Foreword This British Standard has been prepared under the direction of the Machinery and

15、 Components Standards Policy Committee. For many years users of hydraulic equipment have identified external leakage as a major problem and in certain areas this can constitute a serious hazard to personnel and plant. Two major surveys confirmed this to be the case and further identified pipe coupli

16、ngs as the major source of leakage. External leakage from hydraulic systems is always undesirable and can be prevented. The consequences of such leakage depend upon the situation and can vary from being a mild nuisance to a significant safety hazard. Leakage and its effect on the working environment

17、 are frequently perceived to be a justification for avoiding the use of hydraulics. Oil spills are hazardous both as fire risks and in their potential for creating slippery conditions underfoot. Spilt oil is unsightly in most working situations. The cost of replacing lost fluids can be significant i

18、n large systems, and frequent addition of replacement fluid is a significant cause of contamination. The maintenance costs consequent upon leakage are an unnecessary expense. In many environments, such as food processing plants, such leakage is absolutely inadmissible. The users reaction to leakage

19、is an obstacle to the sales of hydraulic systems and it is in the interests of all concerned in the fluid power industry to prevent it. The major requirements of preventing leakage are acceptance that it can be achieved and the will to ensure that it is done. The techniques are simple and are outlin

20、ed in this British Standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of p

21、ages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 28, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cove

22、r.iv blankBS7388:1991 BSI 09-1999 1 0 Introduction The majority of leaks from hydraulic fluid power systems occur at fittings for the following reasons: a) poor pipework design, which leads to over-stressed fittings; b) poor accessibility, particularly of fittings, which makes maintenance difficult;

23、 this also is a design failure. The designer usually concentrates his efforts on the critical areas of his design brief, principally related to performance and cost. The pipework is then often delegated to juniors, or even left to the fitters. If persons wish to buy or sell leak free systems, they s

24、hould ensure that leakage control is recognized as a significant part of the designers brief which should appear in the specification so that pipework design and design for maintenance are taken seriously. Various clauses in this standard refer to the responsibilities of various persons involved in

25、the purchase, design and maintenance of hydraulic equipment. The accountabilities of these persons are described in greater detail in BS4575-3. 1 Scope This British Standard provides guidance on the design of hydraulic systems and their installations with a view to minimizing external leakage of flu

26、ids and is intended to provide guidance on the way the design specification should define how the customers requirements in respect of leakage are to be met. This standard encompasses system specification, circuit design considerations, component specification, pipework design, installation procedur

27、es and commissioning. This standard is not concerned with aspects of systems other than those which relate to leakage and excludes aerospace application and design of hydraulic components. NOTEThe publications referred to in this standard are listed on page28. 2 Specifications 2.1 General For a fixe

28、d installation, it is usually the customer who writes the performance specification. Therefore, if the customer wants a leak free system, this need should be defined in the performance specification. If leakage is overlooked at this stage, and particularly if the system is ordered from the cheapest

29、quotation, then the customer will have no grounds for complaint if the system is not leak free. Similarly, if the manufacturer specifies the performance, leakage should be included and form part of the inspection requirement. 2.2 Definition of leakage For the purposes of a specification, it is neces

30、sary that the degree of leakage should be defined. A totally leak free system is expensive if only because dynamic seals rely upon a smear of oil for lubrication, so that cylinder piston rods usually run “damp”, and strictly speaking this oil is “leakage”, if it drips off the rod. Recommended catego

31、ries of leakage rates are given inAppendix A. 2.3 Operating specification A leakage specification should be described in terms of what is tolerable. For example, “No oil may be allowed to leak on to the floor either in operation or during maintenance”: this form of words would imply the acceptabilit

32、y of drip trays. “Exposed oily surfaces are not allowed”: this would be more expensive and would require drain cavities on piston rods and probably rod gaiters; drip trays would be excluded. “Oil usage due to leakage during normal operation must not exceed 1L per1000h running time”: this would, in g

33、eneral, be applicable only to large fixed installations, but would have the advantage of being quantified. 2.4 Conditions applying to maintenance 2.4.1 Since maintenance operations commonly create more spillage than normal running, it may be desirable to specify that certain parts of the system are

34、to be isolated and drained before removing pipes or components.BS7388:1991 2 BSI 09-1999 A study of clauses5 and10 may reveal other areas which might be included in the customers operating specification. The circumstances in which maintenance will be performed may be defined, e.g.at sea, in harbour,

35、 in the field, etc.The type of labour available for installation and maintenance should also be a design consideration. 2.4.2 The operating environment should be defined as part of the customers specification. 2.5 Design specification 2.5.1 If the customer writes the operating requirements or functi

36、onal specification to describe what is wanted, the supplier would usually write a design specification to define how the customers requirement is to be met. 2.5.2 Before writing the design specification, it is important that the customers requirement and its implications for design and manufacture a

37、re understood and acceptable. If the customers requirement is not clearly stated, then it should be clarified and a statement included in the proposal about the leakage standard to which the system will be designed. Some caution should be exercised in the use of “dry” as a description. Areas around

38、static seals, such as sub-plate surfaces, tend in time to become damp with oil, even if there is no measurable oil accumulation. In a dusty environment such dampness becomes very evident. The same comment applies to piston rods, as mentioned earlier. Truly “dry” systems can be achieved, but great at

39、tention to detail is necessary. 2.5.3 Having established the customers requirements in respect of leakage, the design specification should define how the requirements are to be met. It should be appreciated that most requirements can be met by the use of good engineering practice and consequently ar

40、e not expensive. However, unnecessarily strict requirements result in expensive solutions. 3 Design considerations 3.1 General 3.1.1 Design System design, as it affects leakage, should be considered in relation to the operating conditions and the environment. The following features will make leakage

41、 control more difficult: a) high pressure levels, e.g. above 200 bar 1) ; b) sudden pressure changes, e.g. pressure ripple or pressure shocks; c) high or low temperatures or wide temperature variations, e.g.above700 C below30 C or more than70 C variation; d) low viscosity fluids, i.e. 10 cSt 2)or le

42、ss; e) systems mounted on vibrating or flexible structures; f) corrosive atmospheres, e.g. marine; g) abrasive environment (the effect on cylinder rods, pump shafts, etc.) 3.1.2 Contamination control It is essential that fluid cleanliness should be maintained in a system to avoid contaminants damagi

43、ng such items as dynamic seals and their sealing surfaces, thereby leading to leakage. 3.2 Number of pipe joints Extensive analysis of working systems has shown that pipe joints account for the majority of leaks. Much can be done to minimize the likelihood of leaks at pipe fitting, but an obvious ap

44、proach to the situation is to reduce the number of such joints. In particular, the reduction or elimination of joints that have to be broken and remade in normal maintenance should be a high priority. Valve mounting methods have a strong influence on the proliferation of pipe joints; the various met

45、hods are described in3.3. 3.3 Valve mounting methods 3.3.1 Pipe mounted (threaded body) valves The pipe connections for such valves have to be disconnected in order to remove them for service; the use of this type of valve normally necessitates the maximum number of pipes and fittings. Such valves s

46、hould be avoided whenever possible. However, the use of breakaway couplings would allow the removal of valves with minimum disturbance of pipework. 3.3.2 Sub-plate mounted valves The use of a sub-plate does not reduce the number of pipes or fittings but it does enable the valve to be removed without

47、 disturbing pipe joints. It does introduce an additional potential leakage path at the interface, but compared with pipe mounting it is much to be preferred. 1) 1 bar = 10 5N/m 2= 100 kPa. 2) 1 cSt = 10 6m 2 /s.BS7388:1991 BSI 09-1999 3 3.3.3 Manifold valve stations A manifold valve station is simil

48、ar in principle to the sub-plate mounting described in3.3.2 except that, instead of individual sub-plates having their own valves, all the valves are mounted on a single manifold block within which fluid interconnections between valves are made through drilled passageways. Manifold blocks range in c

49、omplexity from simple units that accept two or more directional valves, with series or parallel connections, to blocks containing complete circuits. The former can be purchased as stock items, but the latter have to be made to order. Manifold blocks can make a great contribution to reducing the number of joints and are a major aid to maintenance. 3.3.4 Cartridge valves An alternative to the sub-plate valve is the cartridge valve, which fits into a cavity in a housing. The housing is the equivalent of a sub-plate and accepts the