What is a pneumatic diaphragm regulating valves, principle of work is what, have what effect?

Commonly used in valve equipment, manual control valve and pneumatic control valve, the valve is to control the flow velocity and the closed switch gear, what are the role for pneumatic diaphragm regulating valves, first of all to understand what the pneumatic control valve, what are the working principle? Pneumatic control valve is compressed gas ( Purified compressed air) is often used to As the power source, the cylinder as actuator, and according to the actual demand optional electricity/gas valve positioner, electric/gas converter, solenoid valve, valve, gas storage, gas filter/pressure/such as attachments to drive the valve, oil mist separator to achieve adjustment, industrial automation control system receives the control signal to complete adjustment of pipeline medium, such as flow, pressure, temperature, liquid level and other process parameters. 1, the working principle of the pneumatic control valve of the industrial control system such as DCS, PLC system sent out 4 - 20 ma current signal and sent to the pneumatic - valve locator. The locator, according to the current value received by automatically adjust the volume of compressed air ( Pressure) Size, and compressed air film room on/to the inferior vena. When the membrane indoor air pressure is greater than the spring pressure within the elastic range and the body and other resistance, can drive the valve core, valve stem, push rod components such as freedom of movement. 2, pneumatic control valve FO and FC pneumatic control valve action type is divided into two kinds: open type gas ( 空气打开) The gas type ( 空气关闭) 。 一个。 Gas open type: when the film head air pressure increases, the valve to increase the opening direction of the movement, when to input pressure limit, the valve is in the fully open position. On the other hand, when the air pressure is reduced, the valve moves in the direction of closing, when no input air, the valve full close. So sometimes gas type valve is also called fault closed type ( 失败关闭FC) 。 b。 Gas closed type: movement direction is just the reverse of gas type, when the air pressure increases, the valve to close the direction of movement, air pressure decrease or not, open valve to the direction of movement, until it is fully open, sometimes referred to as the failure to open type ( 无法打开FO) 。 Pneumatic control valve of gas or gas close, usually by the body internal structure and the actuator assembly. 3, pneumatic control valve FO the two forms of A: air cavity into the film chamber, spring is located in the membrane room inferior vena, valve core is installed, after intake valve shut off. B: air into the film chamber inferior vena, spring on the membrane chamber cavity, the valve core, after the intake valve is closed. 4, pneumatic control valve of FC in two forms: A room inferior vena air into the membrane, the spring on the film chamber cavity, the valve core is installed, after intake valve to open. B: air into the film chamber on the cavity, the spring is located in the inferior vena membrane room, the valve core, after the intake valve to open. It is worth mentioning that the internal structure of the body by the vast majority of occasions valve core. 5, pneumatic control valve spring range spring range: refers to a valve in the static startup film chamber pressure to go completely trip film chamber pressure. 20 ~ 100 kpa, said the static startup membrane valve chamber pressure is 20 kpa, closing film chamber pressure is 100 kpa. Commonly used spring range of 20 ~ 100 kpa, 20 ~ 60 kpa, 60 ~ 100 kpa, 60 ~ 180 kpa, 40 ~ 200 kpa. 6, the summary of pneumatic - valve positioner valve locator: after different periods of development, has a mechanical, intelligent, early have other type, valve positioner is the main control valve accessories, usually with pneumatic control valve, it receives the output signal of control system, and then to its output signal to control the pneumatic control valve, when the control valve, the valve stem of the displacement feedback through mechanical device to valve locator. Valve position condition can through the electrical signal, or additional valve position switch to digital signal to the industrial control system, also can not transfer. Normally locator input signal increases, the positioner output signal increases the positive role of gas, on the other hand, The locator gas output signal decreases) As the reaction, the locator monomer of positive and negative effect has nothing to do with the actuator and the valve body. Valve positioner is: input current signal, the output to the end of the film pressure increase, The adverse effect of the valve positioner: input current signal, the output to the end of the film pressure decreased;