API-RP-576

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Reseating (blowdown) Once normal operating conditions have been restored, the valve is required to close again, but since the larger area of the disc is still exposed to the fluid, the valve will not close until the pressure has dropped below the original set pressure. The difference between the set pressure and this reseating pressure is known as the 'blowdown', and it is usually specified as a percentage of the set pressure. For compressible fluids, the blowdown is usually less than 10%, and for liquids, it can be up to 20%. Fig. 9.1.7 Relationship between pressure and lift for a typical safety valve Fion Zhang/ Charlie Chong http://www.spiraxsarco.com/resources/stea m-engineering-tutorials/safetyvalves/introduction-to-safety-valves.asp
The design of the shroud must be such that it offers both rapid opening and relatively small blowdown, so that as soon as a potentially hazardous situation is reached, any overpressure is relieved, but excessive quantities of the fluid are prevented from being discharged. At the same time, it is necessary to ensure that the system pressure is reduced sufficiently to prevent immediate reopening. The blowdown rings found on most ASME type safety valves are used to make fine adjustments to the overpressure and blowdown values of the valves (see Figure 9.1.8). The lower blowdown (nozzle) ring is a common feature on many valves where the tighter overpressure and blowdown requirements require a more sophisticated designed solution. The upper blowdown ring is usually factory set and essentially takes out the manufacturing tolerances which affect the geometry of the huddling chamber. Fion Zhang/ Charlie Chong
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API-RP-576 Inspection of Pressure-r
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Fion Zhang/ Charlie Chong Speaker:
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5 Causes of Improper Performance 5.
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1 Scope Fion Zhang/ Charlie Chong
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The recommendations in this publica
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This publication does not cover tra
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pressure-relief valves Fion Zhang/
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pilot-operated pressure-relief valv
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upture disks Fion Zhang/ Charlie Ch
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2 Normative References Fion Zhang/
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• ASME PTC 25, Pressure Relief De
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3.1 General For the purposes of thi
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galling Fion Zhang/ Charlie Chong
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3.2 Dimensional Characteristics of
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inlet size outlet size Fion Zhang/
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Fion Zhang/ Charlie Chong huddling
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Fion Zhang/ Charlie Chong lift
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Basic Function of a Spring Loaded S
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Valve Closed. In a direct spring lo
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The pressure below the valve must i
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Fion Zhang/ Charlie Chong F p = p*A
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Functional Diagram. The following d
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3.3 Operational Characteristics—S
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3.3.3 maximum allowable working pre
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3.3.4 maximum operating pressure Th
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Fion Zhang/ Charlie Chong Keywords:
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3.4.5 burst-pressure tolerance The
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3.4.10 marked burst pressure or rat
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4 Pressure-relieving Devices Fion Z
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4.2 Pressure-relief Valve Fion Zhna
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4.3 Safety Valve. Fion Zhnag/ Charl
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4.3.1 General. A safety valve is a
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4.3.2 Applications A safety valve i
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4.4.1 General. A relief valve is a
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4.5 Safety-relief Valve. Fion Zhnag
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4.6 Conventional Safety-relief Valv
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4.6 Conventional Safety-relief Valv
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http://www.leser.com/en/products/do
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Conventional safety valves Fig. 9.2
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Types Mediums Limitations Safety-re
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4.7.3 Limitations Balanced safety-r
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Fion Zhnag/ Charlie Chong Fig. 9.2.
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Fion Zhnag/ Charlie Chong http://ww
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4.8 Pilot-operated Pressure-relief
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What is a Pilot operated safety val
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4.8 Pilot-operated Pressure-relief
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Figure 9—High-pressure Pilot-oper
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4.8.2 Applications Pilot-operated s
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4.9 Pressure- and/or Vacuum-vent Va
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4.9.1 General. • A pressure- and/
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Page 111 and 112: Figure 10—Weight-loaded Pallet Ve
Page 113 and 114: Figure 11—Spring and Weight-loade
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Page 121 and 122: Figure 25—Monel Rupture Disks Cor
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Page 129 and 130: 5.1 Corrosion Fion Zhang/ Charlie C
Page 131 and 132: Corrosion is a basic cause of many
Page 133 and 134: http://www.valveworld.net/safetyequ
Page 135 and 136: Because there is metal-to-metal con
Page 137 and 138: Basic interferometry The interferen
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Page 141 and 142: Example: 1 a series of fringes indi
Page 147 and 148: Causes of damaged valve seats; 1. C
Page 149 and 150: Spring failures. 2 modes of failure
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Page 155 and 156: Incorrect calibration of pressure g
Page 157 and 158: How to adjust a PSV The spring dete
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Page 163 and 164: Adjustment pin affect the character
Page 167 and 168: 5.5 Plugging and Sticking Fion Zhan
Page 169 and 170: 5.6 Misapplication of Materials Fio
Page 171 and 172: Typical ball valve material selecti
Page 177 and 178: 5.7 Improper Location, History, or
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Page 183 and 184: Rough handling can occur during;
Page 185 and 186: The following table summarises the
Page 187 and 188: Greater differentials between opera
Page 189 and 190: 5.10 Improper Discharge Piping Test
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Page 195 and 196: 5.11 Improper Handling, Installatio
Page 197 and 198: Rupture disk problems are often ass
Page 209 and 210: 6.1 Reasons for Inspection and Test
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6.2.2 Safety 1. proper authority an
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National Board approved ASME stamps
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The Kdr or aW value can vary accord
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6.2.5 Removal of Device from System
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Exercise; Dismantling of PSV Fion Z
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Highly Reactive Materials Water-Rea
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6.2.7 Inspection of Adjacent Inlet
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Fion Zhang/ Charlie Chong Rupture d
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6.2.10 Visual Inspection This inspe
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6.2.11 Dismantling of Valve. Disman
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Portable Test Separator Internal &
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The pilot assembly and dome area co
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6.2.13 Reconditioning and Replaceme
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Fion Zhang/ Charlie Chong Most test
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After the valve has been adjusted,
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Check for leakage during pressuriza
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6.2.17 Completion of Necessary Reco
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when a valve operates in nonfouling
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ASME BPVC Section I requires; • B
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6.2.20 Inspection, Testing, Mainten
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6.2.21 Inspection, Testing, Mainten
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6.3 Visual On-stream Inspection Vis
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6.4.2 Frequency of Shop Inspection/
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Manufacturer’s Basis • Manufact
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API572, 6.4.3 Frequency of Visual O
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Routine • inspection least interf
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7.1 Objective The primary objective
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7.3 Responsibilities Some companies
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Annex A (informative) Pressure-reli
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API576 Charlie Chong/ Fion Zhang/ H
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A.1 Need and Function of Test Block
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A.2 Testing with Air • Air is com
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A.4 Description of Test Block The s
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Key 1. test station 2. adaptor for
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API-RP-576

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