Safety Relief Valve Selection

WThen the pressure rise in a system is gradual and not explosive in nature, a safety or safety relief valve is the proper detdce, but when it is critical to completely depressure a system or the rate of pressure increase might be expected to be rapid, then a rupture disk is the proper device. Properly designed a pilot operated valve may be selected after checking its performance with the manufacturer. 

Figure 7-20. Recommended API-520 piping for safety relief valve installations. Reprinted by permission, American Petroleum Institute, Sizing, Selection and Installation of Pressure Relieving Devices in Refineries, Part ll-lnstallation, API RP-520, 3rd Ed., Nov. 1988.

Selection Features Safety, Safety-Relief Valves, and Rupture Disks... 

Naturally, we do not want to overpressure the tower, and pop open the safety relief valve. Alternatively, if the tower pressure gets too low, we could not condense the reflux. Then, the liquid level in the reflux drum would fall and the reflux pump would lose suction and cavitate. But assuming that we have plenty of condensing capacity, and are operating well below the relief valve set pressure, why do we attempt to fix the tower pressure Further, how do we know what pressure target to select ... 

Sizing is probably the most important component in selecting the right safety relief valve (SRV) for the job, ensuring optimal safety of the process. Because nowadays sizing is done almost exdusively with software, some available on the market and some supplied by manufacturers, it is important to know what is behind the software and to look into the formulas on which these calculations are based. 

These guidelines will provide some guidance in selecting a safety relief valve (SRV) for use in a specific application or process condition where the use of traditional spring-operated valves could be questionable. 

Selection of Safety Relief Valve Testing Equipment... 

Selection of safety relief valve testing equipment... 

Selected safety/relief valves are associated with the automatic depressurization of the primary system under assumed LOCA conditions. These valves have two independent logic channels powered from different power sources, either of which can initiate depressurization. Valves open automatically and remain open imtil the pressiue falls to a preset closure pressure. These valves open automatically upon signals of high drywell pressure and low reactor water level and confirmation of one LPCI function of the RHR system or LPCS system running. Initiation signals need not be simultaneous. The valves remain open until the primary system pressure is reduced to a point where the LPCI function of the RHR system and/or the LPCS system can adequately cool the core. The initiation of automatic depressurization is delayed from 90 to 120 s to allow the operator to terminate the initiation should the HPCS system initiation and acceptable reactor vessel level have been confirmed. 

In the unlikely event that the RHR shutdown suction line is unavailable during reactor shutdown to cool reactor water and during the period when the LPCI function of the RHR system and/or the LPCS system pumps are injecting water into the reactor vessel, safety/relief valves used for automatic depressurization can be used to pass water from the reactor vessel to the suppression pool via valve discharge lines. For this to occur, the reactor vessel floods to a level above the vessel main steam line nozzles, selected safety/relief valves are opened from the control room to pass reactor water to the suppression pool. 

The ADS consists of redundant logics capable of opening selected safety relief valves, when required, to provide reactor depressurization for events involving small- or intermediate-size LOCAs if the HPCI system is not available or cannot recover reactor vessel water level. 

Pressure-relief valve Pressvue- or temperature-activated device used to prevent buildup of pressure beyond a predetermined maximum that could cause a system to rupture. The design and selection of the device are dictated by codes and standards governing the safe design of the vessel or S3 tem to which it is connected. Also referred to as a relief valve, safety valve, or safety relief valve. 

Sizing, 451, 453, 455, 459, 462 Sonic flow, 461 Types, illustrations, 411-421 Rupture disk, liquids, 462, 466 Rupture disk/pressure-relief valves combination, 463 Safely relief valve, 400 See Relief valve Safety valve, 400, 434 Safety, vacuum, 343 Scale-up, mixing, 312, 314—316 Design procedure, 316-318 Schedules/summaries Equipment, 30, 31 Lines, 23, 24 Screen particle size, 225 Scrubber, spray, 269, 270 Impingement, 269, 272 Separator applications, liquid particles, 235 Liquid particles, 235 Separator selection, 224, 225 Comparison chart, 230 Efficiency, 231... 

A reaction has been characterised as a tempered hybrid system and it has been determined that the system will relieve single-phase gas/, vapour. Relief sizes for both a safety valve and a bursting disc system are required. The reactor contains a charge of 3000 kg. Data for relief sizing have been compiled in Table A6.2. -The type of safety valve selected has a de-rated discharge coefficient under BS 6759131 of 0.87. 

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