Back pressure safety valves
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Catalog excerpts

Back pressure safety valves - 1

Back pressure safety valves 1. Introduction 2. Safety valve in the installation 3. Influence of back pressure on functioning behaviour 4. Limits of admissible back pressure (without metal bellow) 5. Back-pressure compensation using stainless steel bellow 6. Limits of admissible back pressure (with metal bellow) 7. Particularities of construction with stainless steel bellow 8. Summary 9. Bibliography Dipl.-Ing. Erhard Stork, ARI-Armaturen Albert Richter GmbH & Co. KG, D-33756 Schloß Holte-Stukenbrock Tel.: 05207/994-0, Fax: 05207/994-297, E-Mail: info.vertrieb@ari-armaturen.de, Internet:: http://www.ari-armaturen.de t000010301-2.doc

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Back pressure safety valves - 2

2/12 1. Introduction When dimensioning and selecting safety valves for vessels and installations, it is important that this fitting should not be considered as being separate from its supply and blow-off pipes. The pressure and flow situation in neighbouring pipes and installation components may have appreciable adverse influence on the functioning of safety valves. The resulting reduction of the mass flow leads to an inadmissible rise of pressure. In extreme cases, unstable functioning behaviour in the form of flutter and hammering may lead to the valve becoming torn away. An accurate...

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Back pressure safety valves - 3

3/12 blow-off process, the built-up back pressure generated by the pipe resistance, is added. Blow-off vessel Blow-off pipe Safety valve entil Pressure vessel Blow-off in closed vessel systems 3. Influence of back pressure on functioning behaviour Decisive for the functioning of a safety valve is the correct and undisturbed lift movement of the plug, which is also called a disc. Acting as a closure component, it releases the required blow-off quantity of the medium. If the required lift is not reached, or if an uncontrolled vibration occurs (flutter), the valve is unable to divert the...

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Back pressure safety valves - 4

4/12 4. Limits of admissible back pressure (without metal bellow) Test rig measurements were carried out for the determination of the maximum admissible back pressure (see Fig 5). The transient measurement values of “pressure in front of the valve”, "back pressure" and "lift" were stored via rapid computerised measurement data determination and subsequently evaluated. The pressure measuring points for the back pressure was 10 x DN behind the valve. Fig 5: Experimental set-up The generation of the required back pressure took place via a throttle valve, whose setting was found empirically by...

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Back pressure safety valves - 5

Back-pressure experiment, safety valve Medium: Air FigurNr. 25.911 Nennwcitc: DN 50/80 FederNr. 2060 [9,1 - 16 bar] Fig 6: Admissible built-up back pressure (start of spring range) Back-pressure experiment, safety valve Medium: Air FigurNr, 25.911 Ncnnwciic: DN 50/tiO FederNr, 2059 [9,1 - 16 bar] Fig 7: Admissible built-up back pressure (end of spring range) Dipl.-lng. Erhard Stork, ARI-Armaturen Albert Richter GmbH & Co. KG, D-33756 Schloli Holte-Stukenbrock Tel.: 05207/994-0, Fax: 05207/994-297, E-Mail: info.vertrieb@ari-armaturen.de. Internet:: http://www.ari-armaturen.de

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Back pressure safety valves - 6

The maximum admissible back pressure is not only determined by the position of the set pressure in a given spring range, but also by the design of the support on the vessel or the pipe on which the valve is fitted. Here, the additional pressure drop has a negative effect on the maximum possible back pressure. According to AD 2000 A2 [4], an additional pressure drop at the inlet equal to 3% of the pressure difference between the set pressure and the superimposed back pressure is admissible, which must be taken into account when determining the admissible limits. Fig 8 shows an experiment in...

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Back pressure safety valves - 7

Fig 9: Table of admissible back pressures (without stainless steel expansion bellows) 5. Back-pressure compensation by stainless steel expansion bellows If the blow-off pipes of the safety valves are too long or have too many bends, the back pressure limit of 10-15 % is easily reached. In these cases, there is first of all the option of increasing the nominal diameter of this pipe, which often brings about major cost increases, or is not feasible on technical grounds and in such cases there is the option of equipping the safety valve with a balancing bellows. This stainless steel bellows...

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Back pressure safety valves - 8

steel bellows In the case of the introduction of a stainless steel bellows, the maximum admissible back pressures increase. Fig 11 shows the blow-off experiment at a back pressure of Back-pressure experiment, safety valve Medium: Air Figiir Nr. 25.911 FABA Ncnnwcilc: DN 50/80 Fcder Nr. 20*9 [11,6 -16bat] Fig 11: Safety valve functioning with a stainless steel bellow Dipl.-lng. Erhard Stork, ARI-Armaturen Albert Richter GmbH & Co. KG, D-33756 Schloli Holte-Stukenbrock Tel.: 05207/994-0, Fax: 05207/994-297, E-Mail: info.vertrieb@ari-armaturen.de. Internet:: http://www.ari-armaturen.de

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Back pressure safety valves - 9

6. Limits of admissible back pressure (with metal bellow) The higher limits of the version with stainless steel bellows are available in the form of a table. Here too, Fig 12 shows an extract. It should be emphasized at this point, that in contrast with the version without bellows, these limits also apply to superimposed back pressures, since the bellows prevents a change of the set pressure through continuously superimposed back pressure. When sizing the safety valves, it is always necessary to take the back pressure into account, since otherwise the valve can be to small. Here, the...

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Back pressure safety valves - 10

Back pressure experiment, safety valve Ficur Nr. 25.9] ] FABA Nennweite: DN 50/RO FcderNr. 0066 [2.75-3.6 bar, Vollhub] „Not Series !" (Cone version and spring: ..without expansion bellows Fig 13: Inadmissible valve function due to wrong fitted valve with stainless steel Fig 14: Correct valve function with a correctly fitted valve with stainless steel Dipl.-lng. Erhard Stork, ARI-Armaturen Albert Richter GmbH & Co. KG, D-33756 Schloli Holte-Stukenbrock Tel.: 05207/994-0, Fax: 05207/994-297, E-Mail: info.vertrieb@ari-armaturen.de. Internet:: http://www.ari-armaturen.de

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