制冷与空调专业英语第2版 林慧珠 主编 3-1新.pptVIP

Unit Three Lesson 9 Control Valves Lesson 10 Liquid Pump Lesson 11 The Reciprocating Compressor Lesson 12 Heat Exchanger Lesson 9 Control Valves New Words Expressions Text Notes to the Text Exercise Lesson 9 Lesson 9 Text Control valves are essential elements in the control of many industrial processes. A valve is a power component whose role is to regulate a flow of liquid in pipes according to the value of what is being measured (a level, a pressure, a temperature, a pH, etc.). 1 This flow often constitutes the control variable of the regulatory loop. Control performance - and particularly its sensitivity and linearity - is, therefore largely dependent upon the type and characteristics of the valve fitted. 2 Text: The choice of valve may affect the dimensioning of the process itself and that is why the choice is important. 3 Emphasis will be placed on determination of the flow evolution curve line with respect to the valve control. The linearity of this curve depends on the process itself and affects control performance. Linearity is difficult to obtain technologically, although the problem can sometimes be overcome by using a microprocessor. Text: Construction of a Valve ACTUATOR The mechanism which converts the controller signal (from the regulator) into the motion which positions the valve plug. BODY Contains one or more seats or parts through which the fluid passes. TRIM Comprises the detachable parts of thevalve which are in contact with the fluid. Text: A control valve is an opening with an adjustable area. A stem driven by an actuator positions a plug which modifies the opening section of the valve.4 This progressive positioning makes possible the control of the flow passing through the valve. Text: The various components of a valve body are given below (for a double port valve)（Fig9-2）. As the body and the trim are the parts of the valve which are exposed