The resistance coefficient of pneumatic control valve is how to define?

From fluid mechanics point of view, pneumatic control valve is a throttling element of local resistance to change. For incompressible fluids, flow only change with drag coefficient. Pneumatic control valve of the change of drag coefficient is achieved by changing the stroke of valve core. General pneumatic control valve and actuator work together. Such as pneumatic control valve and actuator combined into a whole, is a pneumatic actuator, is the most widely used in modern industrial control system is a kind of actuators. Pneumatic - valve to match the electric actuators, and can be used as a control system of the various actuators ( See pneumatic actuators, electric actuators) 。 There are many kinds of pneumatic control valve in accordance with the USES different structure. Commonly used is direct two-seat valve structure. The valve core to move up and down can change the relative position and valve seat, drag coefficient changed also. Flow through the valve of the relationship between relative flow and relative opening degree of valve, known as the pneumatic control valve flow characteristics, namely type of Q/Q/is relative flow, namely the pneumatic control valve fully open flow under a certain opening and the ratio of the flow; / / L for the relative opening degree, namely, pneumatic control valve fully open under a certain opening schedule and the ratio of the stroke. Pneumatic control valve flow characteristics mainly depends on the shape of the valve core. Common ideal flow characteristic curve has the percentage (such as straight line, Also called logarithmic) And quickly opened several (parabolic See figure shape of valve core and the ideal characteristic curve) , they are under the condition of the constant pressure difference before and after pneumatic control valve. Pneumatic control valve directly into contact with the working medium, working conditions and environmental difference is very big, in order to meet the needs of a variety of different, pneumatic control valve has a variety of forms. In addition to the direct two-seater valve, the commonly used and through single-seat pneumatic - valve pneumatic control valve, tee, Angle type pneumatic control valve, butterfly valve, eccentric rotary pneumatic control valve, etc. Some pneumatic - valve must design according to special requirements, such as food hygiene pneumatic - valve used in the food industry. When choosing pneumatic control valve in addition, according to the requirement of automatic control system, determine the flow characteristics of the type and the types of valves, need according to the flow capacity of the valve C values to determine the structural type and size of the valve.