Spring-loaded PRV

Safety valve (SV) Spring-loaded PRV actuated by the static pressure of the fluid and characterized by rapid opening or pop action. Normally used with compressible fluids (gas, vapours and steam), the SV is also the general denomination in PED. 

Safety relief valve (SRV ) Spring-loaded PRV that may be used as either a safety or a relief valve, depending on the application. The SRV works within well-determined operational limits (per PED it is called safety valve). 

Conventional direct spring-loaded PRV A direct spring-loaded PRV which is held closed by a spring force which can be adjusted within a certain range and whose operational characteristics are direcdy affected by changes in the backpressure which is exercised at the oudet of the valve (see Section 5.2). 

Balanced direct spring-loaded PRV The same as a conventional direct spring-loaded PRV, but which incorporates the means (typically a bellow) of minimizing the effect of backpressure on the operational characteristics (opening pressure, closing pressure and relieving capacity) (see Section 5.2). 

Spring-loaded PRV is further classified into following two types depending on whether it is designed to avoid backpressure influence or not. 

Because the PRV piston has larger area on the pilot valve side than its area on the process side, the PRV piston will be closed even tighter as process pressure approaching its set pressure. This is quite a different feature comparing to the spring-loaded PRV. 

Figure 6 A typical spring-loaded PRV disk lift path versus system pressure during vapor relief. [Courtesy of Tyco Valves and Controls LP]...

The different behavior of vapor and liquid relief for spring-loaded PRV is because of the different nature of vapor and liquid. Vapor is light, will expand, and move fast, but liquid is heavy, will not expand, and move slowly. 

Some spring-loaded PRV may have soft seat (nonmetalHc) at its orifice to prevent disk and nozzle (metallic) damage. This may pose some temperature limttation on the relief service,... 

Unlike spring-loaded PRV, the open or close of pilot-operated PRV is not affected by its backpressure. This means it can be used to protect equipment with higher pressure in relief valve discharge manifolds. 

L Conventional spring-loaded PRV is restricted to be used for PRV has constant or no superimposed backpressure, and very low buildup backpressure service. 

Balanced-bellows spring-loaded PRV can tolerate higher backpressure. Check manufacturer s catalog for the limit. 

For service required large orifice area, spring-loaded PRV may be too heavy to install. Pilot-operated PRV may be a better choice. For medium or small size orifice, an economic comparison may be required to see which type of PRV is a better choice. 

This is a closed-bonnet spring-loaded PRV whose performance characteristics are directly affected by the changes in back pressure on the valve. 

This is a spring-loaded PRV used for liquid service. The valve opens normally in proportion to the pressure increase over tire opening pressure. 

A spring-loaded PRV that may be used as either a safety or a relief valve, depending upon the application. 

Pressure relief device (PRD) is a safety device to protect equipment or piping from damage due to overpressure or vacuum, but in this chapter, we wiU discuss FRD to provcfit overpressure only. Commonly used pressure relief devices are spring-loaded and pilot-operated pressure relief valve (PRV), rupture disk, or pin-actuated pressure relief device. For equipment, it is installed cither directly on the equipment or at its inlet/outlet piping. When the equipment or piping pressure reaches the pressure relief de vice set pressure, it will open to relieve fluid inside the equipment or piping to avoid overpressure. The relief fluid can be vapor, liquid, or two phase mixture. The relieved fluid is either sent to floic system to be disposed or relieved to atmosphere. 

Conventional PRVs are shown in Figure 4.1 and Figure 4.2. This is a self-actuated spring-loaded valve designed to open at a certain set pressure. The basic elements of the valve are ... 

Balanced-bellows PRVs are spring-loaded valves with a bellows or some other means of balancing the valve disk to minimize the effect of back pressme. Typical valve configurations are shown in Figure 4.3 and Figure 4.4. 

Relief valve (RV) Spring- or weight-loaded pressure relief valve (PRV) actuated by the static pressure of the fluid. An RV opens normally in proportion to the pressure increase and is used primarily on incompressible fluids (liquids) (per PED it is called a safety valve). 

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