1、BRITISH STANDARD BS7461:1991 Specification for Electrically operated automatic gas shut-off valves fitted with throughput adjusters, proof of closure switches, closed position indicator switches or gas flow controlBS7461:1991 This British Standard, having been prepared under the directionof the Gas
2、Standards Policy Committee, was published under the authority of the Standards Board and comes intoeffect on 30 September 1991 BSI 02-1999 The following BSI references relate to the work on this standard: Committee reference GSE/22 Draft for comment 91/75437 DC ISBN 0 580 19830 8 Committees responsi
3、ble for this British Standard The preparation of this British Standard was entrusted by the Gas Standards Policy Committee (GSE/-) to Technical Committee GSE/22, upon which the following bodies were represented: Association of Control Manufacturers TACMA (BEAMA Ltd.) British Combustion Equipment Man
4、ufacturers Association British Gas plc Chief and Assistant Chief Fire Officers Association Department of Trade and Industry (Consumer Safety Unit, CA Division) Health and Safety Executive Liquefied Petroleum Gas Industry Technical Association (UK) Society of British Gas Industries Amendments issued
5、since publication Amd. No. Date CommentsBS7461:1991 BSI 02-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 Valves fitted with throughput adjusters 1 4 Valves fitted with proof of closure switches 1 5 Valves fitted with closed position indicator
6、switches 2 6 Valves incorporating start-gas flow control and valves in which the flow rate may be varied electrically 2 Appendix A Test for valves fitted with throughput adjusters 4 Appendix B Test for valves fitted with proof of closure switches 4 Appendix C Test for valves fitted with closed posit
7、ion indicators 4 Appendix D Tests for valves incorporating start-gas flow control and in which the flow rate may be varied 4 Publication(s) referred to Inside back coverBS7461:1991 ii BSI 02-1999 Foreword This British Standard has been prepared under the direction of the Gas Standards Policy Committ
8、ee for publication alongside BSEN161, the European Standard for automatic shut-off valves that replaces BS5963:1982, which is withdrawn. This standard specifies requirements and methods of test for throughput adjusters, proof of closure switches, closed position indicator switches or gas flow contro
9、l which may be fitted to electrically operated automatic gas shut-off valves which were previously within the scope of BS5963:1982 and are outside the scope of BSEN161. The requirements and methods of test for automatic shut-off valves themselves are now covered by BSEN161. This standard retains the
10、 requirements for such additional features, pending publication of European Standards for additional features, and will be withdrawn on the publication of such standards. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are respons
11、ible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to 4, an inside back cover and a back cover. This standard has been
12、updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on theinside front cover.BS7461:1991 BSI 02-1999 1 1 Scope This standard specifies the requirements and test methods for throughput adjusters, proof of closureswitches, closed positio
13、n indicator switches, start-gas flow control and electrical variation of flow rate when fitted to electrically operated automatic gas shut-off valves which themselves fall within the scope of BSEN161. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover
14、. 2 Definitions For the purposes of this British Standard, the definitions given in BSEN161 apply, together with the following. 2.1 closed position indicator switch a switch fitted to a class A, B or C automatic shut-off valve which indicates when the valve is in the nominally closed position 2.2 pr
15、oof of closure switch a switch fitted to a class A, B or C automatic shut-off valve with mechanical overtravel which proves the valve to be in the closed position 2.3 throughput adjuster a device which restricts the throughput of the valve and is set before or during commissioning 2.4 start-gas flow
16、 rate the restricted gas flow rate admitted either to a separate pilot burner or to the main burner during the start-gas flame establishment period 2.5 hazardous condition an abnormal condition involving risk to persons or property 3 Valves fitted with throughput adjusters 3.1 General 3.1.1 Throughp
17、ut adjusters shall be identified and shall be marked to indicate the direction of adjustment. 3.1.2 For adjusters operating over a single turn, means shall be provided for indicating the actual setting and the minimum and maximum positions. 3.1.3 For adjusters operating with a multi-turn screw, the
18、direction of increase and/or decrease shall be indicated. 3.1.4 Adjusters shall retain their set position under normal conditions of use and shall either: a) require the use of tools for their access and setting; or b) require the use of tools for adjustment and be capable of being sealed after sett
19、ing. 3.2 Adjusters forming part of the valve body 3.2.1 Adjusters forming part of the valve body shall be tested in accordance with Appendix A, after which they shall comply with 3.1.4. A single sample shall be tested for each size of adjuster. 3.2.2 Where the adjuster limits the travel of the valve
20、 disc, an endurance test, as specified in 4.11.3 of BSEN161:1991, shall be carried out on three samples with the adjuster set to give either minimum flow or10% of maximum flow, whichever is the greater. Following this endurance test, any variation in the set flow shall not exceed 10%. 3.3 Adjusters
21、forming part of the valve actuating mechanism Adjusters forming part of the valve actuating mechanism shall comply with 3.2.2. 4 Valves fitted with proof of closure switches 4.1 General Valves fitted with proof of closure switches shall be designated as type0or type50 according to the following. The
22、 switch shall be fitted to the valve in such a manner that the switch will not indicate closure until: a) for valves designated type0, the valve is fully closed and leak-tight when tested in accordance with 4.7.3 of BSEN161:1991; or b) for valves designated type50, the valve is closed and does not p
23、ass in excess of50dm 3 /h when tested in accordance with 4.7.3 of BSEN161:1991. Valves with a mechanical overtravel characteristic and fitted with proof of closure switches shall comply with 4.2 to 4.5 and in addition shall comply with BSEN161. 4.2 Drift from design/setting position The switch assem
24、bly and actuating mechanism shall be such that any drift from its design/setting position shall not impair its correct operation. Setting adjusters shall be sealed to prevent interference.BS7461:1991 2 BSI 02-1999 4.3 Indication of proof of closure A single modified valve shall be tested to determin
25、e leakage in accordance with B.1. The leakage measured shall not exceed the maximum permitted value for the type of switch as specified in 4.1. 4.4 Endurance Three unmodified valves fitted with proof of closure switches shall be tested in accordance with B.2, after which no failure which could cause
26、 a hazardous condition shall have occurred. 4.5 Indication of proof of closure after endurance test The valves used for the test in 4.4 shall be modified and tested in accordance with B.1. All three shall not exceed the maximum permitted leakage for the type of swich as specified in 4.1. 5 Valves fi
27、tted with closed position indicator switches 5.1 General Whilst closed position indicator switches may indicate closure before the valve is fully closed, they shall not indicate closure until the flow through the valve is equal to or less than10% of the equivalent fully open flow at the same pressur
28、e differential or until the valve is within 1mm of its closed position. Valves fitted with closed position indicator switches shall comply with 5.2 to 5.5 and in addition shall comply with BSEN161. 5.2 Drift from design/setting position The switch assembly and actuating mechanism shall be such that
29、any drift from its design/setting position shall not impair its correct operation. Any setting adjuster shall be sealed to prevent interference. 5.3 Indication of closure A single modified valve shall be tested in accordance with C.1 for flow or distance open. Flow or distance open shall not exceed
30、the maximum value specified in 5.1. 5.4 Endurance Three unmodified valves fitted with closed position indicator switches shall be tested in accordance withC.2, after which no failure which could cause a hazardous condition shall have occurred. 5.5 Indication of closure after endurance test The valve
31、s used for the test in 5.4 shall be modified and tested in accordance with C.1. Flow or distance open for all three valves shall not exceed the maximum permitted value specified in 5.1. 6 Valves incorporating start-gas flow control and valves in which the flow rate may be varied electrically 6.1 Gen
32、eral Valves of the following type shall comply with 6.2 and BSEN161: a) valves where the burner start-gas flow rate can be electrically controlled by the burner management system after having been manually pre-set; b) valves where the levels of flow can be achieved by the valves responding to extern
33、al electrical signals, either in discrete steps (e.g. high/low) or in proportion to the applied signal. 6.2 Requirements and tests 6.2.1 Adjustment and mechanical inspection The method of adjustment of each flow level shall allow adjustment over the full range claimed by the manufacturer. When setti
34、ng up in accordance with the manufacturers instructions, the adjustment of one level of flow shall not alter or disturb the setting of any other by more than5%. If the adjustment of one flow level is capable of disturbing the setting of any other flow level, this shall be clearly indicated in the ma
35、nufacturers instructions for setting up. The setting of any gas rate shall require the use of tools and shall be protected by a method which discourages unauthorized adjustments. Compliance with these requirements shall be confirmed by inspection and measurement as necessary. All measurements of flo
36、w shall be performed as specified in 4.10 of BSEN161:1991 and shall be declared as percentages of the fully open flow rate at the pressure differences specified in 4.10 of BSEN161:1991 as appropriate. 6.2.2 Performance It shall not be possible for the start-gas flow rate to exceed50% of the maximum
37、flow. NOTEThis may be achieved either by the incorporation of a physical limit to the start-gas adjustment or by limiting the setting of an electrical interlock. These methods are referred to in other standards, e.g.BS5885-1, as typeP and typeI respectively. Where the start-gas position of the valve
38、 is interlocked, the interlock shall be such that it forms no part of the normal start-gas flow rate control circuitry of the valve. When the valve is opened beyond the set start-gas flow rate position the interlock shall operate before the flow rate through the valve exceeds1.1times the set start-g
39、as flow rate. The setting of the interlock shall require the use of tools and shall be protected by a method which discourages unauthorized adjustment.BS7461:1991 BSI 02-1999 3 For any setting within the manufacturers declared adjustment range, when the valve is tested in accordance with Appendix D
40、the flow rate at the end of the endurance test shall be within 10% of that set prior to the start of the endurance test, when measured under the same conditions. When the flow rate is changed under the effect of external electrical signals, the flow shall not, while attaining the new level of flow,
41、overshoot the new flow level by more than20% of the flow at the particular set point or10% in the case of a start-gas flow rate setting when opening. The manufacturer shall declare the maximum available start-gas flow rate as a percentage of the fully open flow rate. It shall not be possible to adju
42、st the start-gas flow rate to a level in excess of1.1times the declared maximum start-gas flow rate. Tests shall be performed to ensure that all valves subjected to the endurance test (see4.11.3 of BSEN161:1991 and Appendix D) comply with the requirements of this subclause before the endurance test
43、and on completion of the endurance test. In addition, those tests which can be made without adjusting or disturbing the set-point shall be performed to ensure that all valves subjected to the endurance test comply with the requirements of this subclause after completion of the endurance test as deta
44、iled in4.11.3 of BSEN161:1991 and Appendix D.BS7461:1991 4 BSI 02-1999 Appendix A Test for valves fitted with throughput adjusters Operate the adjuster over the full range of adjustment25times and test for external leak-tightness in accordance with 4.7 of BSEN161:1991. Appendix B Test for valves fit
45、ted with proof of closure switches B.1 Indication of proof of closure test Modify a single valve to enable the valve sealing member to be moved and positioned in any partially open position. Slowly close the valve until the switch just indicates valve closure and then test for leakage. B.2 Endurance
46、 test Test three unmodified valves fitted with proof of closure switches in accordance with4.11.3 of BSEN161:1991. Check that the switch indicates valve closure when the valve is de-energized and indicates that the valve is open when the valve is energized. Appendix C Test for valves fitted with clo
47、sed position indicator switches C.1 Indication of closed position test Modify a single valve to enable the valve sealing member to be moved and positioned in any partially open position. Slowly close the valve until the switch just indicates valve closure and then test for flow or distance open, as
48、appropriate. C.2 Endurance test Test three unmodified valves fitted with closed position indicator switches in accordance with4.11.3of BSEN161:1991. Check that the switch indicates valve closure when the valve is de-energized and indicates that the valve is open when the valve is energized. Appendix
49、 D Tests for valves incorporating start-gas flow control and in which the flow rate may be varied D.1 Prepare the valves for the endurance test by adjusting the setting levels of the various flow levels so that, for valves switching in steps, at least one valve is set at each of the upper and lower extremes, but not less than5% of the fully open flow rate, and at least one valve is set at the midpoint of the adjustable range of each switched flow setting. Measure the flows at these settings. For proportional action valves similarly adjust the set proportional ranges. T
