tailieunhanh - CONTROL VALVE HANDBOOK Episode 2 Part 1

Tham khảo tài liệu 'control valve handbook episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chapter 6 Special Control Valves As discussed in previous chapters standard control valves can handle a wide range of control applications. The range of standard applications can be defined as being encompassed by atmospheric pressure and 6000 psig 414 bar -150 F -101 C and 450 F 232 C flow coefficient Cv values of and 25000 and the limits imposed by common industrial standards. Certainly corrosiveness and viscosity of the fluid leakage rates and many other factors demand consideration even for standard applications. Perhaps the need for careful consideration of valve selection becomes more critical for applications outside the standard limits mentioned above. This chapter discusses some special applications and control valve modifications useful in controlling them designs and materials for severe ser vice and test requirements useful for control valves used in nuclear power plant service. High Capacity Control Valves Generally globe-style valves larger than 12-inch ball valves over 24-inch and high performance butterfly valves larger than 48-inch fall in the special valve category. As valve sizes increase arithmetically static pressure loads at shutoff increase geometrically. Consequently shaft strength bearing loads unbalance forces and available actuator thrust all become more significant with increasing valve size. Normally maximum allowable pressure drop is reduced on large valves to keep design and actuator requirements within reasonable limits. Even with lowered working pressure ratings the flow capacity of some 147 Chapter 6. Special Control Valves Figure 6-1. Large Flow Valve Body for Noise Attenuation Service large-flow valves remains tremendous. Noise levels must be carefully considered in all large-flow installations because sound pressure levels increase in direct proportion to flow magnitude. To keep valve-originated noise within tolerable limits large cast or fabricated valve body designs figure 6-1 have been developed. These bodies normally .