Spring-operated reliefs

For a conventional spring-operated relief, the valve opens based on the pressure drop across the valve seat that is, the set pressure is proportional to the pressure drop across the seat. Thus, if the backpressure downstream of the valve increases, the set pressure will increase and the valve may not open at the correct pressure. In addition, the flow through the conventional relief is proportional to the difference in pressure across the seat. The flow through the relief, therefore, is reduced as the backpressure increases. 

Rupture discs are available in much larger sizes than spring-operated relief valves, with commercial sizes available up to several feet in diameter. Rupture discs typically cost less than equivalently sized spring-operated relief valves. 

Give four examples of situations requiring a combination of spring-operated reliefs in series with rupture discs. 

Describe the advantages and disadvantages of a rupture disc followed by a spring-operated relief valve. See Grossel and Louvar (2000). 

Conventional Spring-Operated Reliefs in Liquid Service... 

Figure 9-3 Overpressure correction Kp for spring-operated reliefs in liquid service. Source API RP 520, Recommended Practice for the Sizing, Selection, and Installation of Pressure-Relieving Systems in Refineries,...

A horizontal vessel, 10 ft long and 3 ft in diameter, contains water. What relief size is required to protect the vessel from fire exposure Assume the following vapor relief only, M AWP of 200 psig, conventional spring-operated relief. 

A 1-in (internal diameter) pipe is used to supply water to a low-pressure tank with an MAWP of 20 psig. The water is supplied through a regulator from a source with a maximum pressure of 100 psig. Determine the diameter of a conventional spring-operated relief required to protect the vessel from a regulator failure. Be sure to state clearly any assumptions and your justifications for them. 

Disc (disc insert) A metal disc with (in the case of a metal-to-metal, spring-operated relief valve) a smoothly lapped surface which ensures tightness in... 

Raising air is admitted by a norm ally-closed (closed when de-energized) solenoid valve located at the bottom of the cylinder, along with a solenoid operated,normally-open bleed valve and orifice and a spring operated relief valve. A large, normally open solenoid exhaust valve with an orifice is... 

Pilot-operated relief valves use the pressure in the vessel rather than a spring to seal the valve and a pilot to activate the mechanism. Figure 13-6 is a schematic of a typical pilot-operated valve. A piece of tubing communicates pressure between the relief valve inlet and pilot. When this pressure is below the set pressure of the pilot, the pilot valve is in the position... 

There are two general categories of relief devices (spring-operated and rupture discs) and two major types of spring-operated valves (conventional and balanced-bellows), as illustrated in Figure 8-7. 

On spring-operated valves the adjustable spring tension offsets the inlet pressure. The relief set pressure is usually specified at 10% above the normal operating pressure. To avoid the possibility of an unauthorized person changing this setting, the adjustable screw is covered with a threaded cap. 

First open-ended spring-operated Safety Relief Valve... 

Power actuated/assisted safety valves (CSPRS - controlled safety pressure relief system) A spring-operated safety valve actuated or assisted by an externally powered control device which can be hydraulic, pneumatic or electric (Figure 3.15). 

API Standard 526, Flanged Steel Pressure Relief Valves This is a purchase specification for flanged steel PRVs. Basic requirements, such as orifice designations and area, materials, pressure-temperature limits and centre-to-face dimensions, inlet and outlet, are given for both spring-operated and pilot-operated PRVs (Figure 4.13). 

Types of spring-operated SRVs 5.2.6.1 Thermal relief valves... 

Direct spring operated PRV I Relief cycle (pop action)... 

Extreme fast-acting pressure relief is required Rupture discs can be considered as process pressure protection when there is a potential risk for chemical runaway reactions. Depending on the choice of the SRV (for instance, a non-coded spring-operated valve), there could be a risk that they would... 

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. 

Operating pressures between 90% and 95% of set Here the use of pilot-operated safety relief valves (POSRVs) or soft-seated, spring-operated SRVs should be considered. Metal-seated spring valves will not stay tight for long and usually get damaged after a couple of operations. On the other hand, soft-seated valves are limited in temperature and sometimes also in pressure (see Section 5.2.6.5). 

Pressure-relief devices include direct spring-loaded and pilot-operated relief valves that close or reseat if the vessel pressure is brought back into a safe condition, as well as non-reclosing devices such as rupture disks and breaking-pin devices. 

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