Selection of Valve Electric Actuator Models
Sep 26,2022Read More
An instrument valve is a line accessory. It is a device which is used to change the passage section and the flow direction of the medium and control the flow of the conveying medium. The sealing performance of the instrument valve refers to the ability of each sealing part of the instrument valve to prevent the leakage of the medium, which is the most important technical performance index of the instrument valve.
There are three sealing parts of the instrument valve: the contact between the opening and closing parts and the two sealing surfaces of the valve seat; the matching place between the packing and the valve stem and the stuffing box; the connection between the valve body and the bonnet. The leakage in the former part is called internal leakage. It is commonly referred to as lax closure, which will affect the ability of the instrument valve to cut off the medium. For shut-off valves, internal leakage is not allowed. The leakage in the latter two places is called external leakage, that is, the medium leaks from the inside of the valve to the outside of the valve. External leakage will cause material loss, environment pollution, and even cause serious accidents. For flammable, explosive, toxic or radioactive media, leakage is not allowed, so the instrument valve must have reliable sealing performance.
A regulator that uses an analog signal is also called an analog instrument valve. It determines the deviation between the measured value of the controlled object parameter in the analog form and the given value, and generates an analog output signal according to a certain regulation law to push the actuator to eliminate the deviation, so that the controlled parameter remains near the given value or changes according to a predetermined rule. In automated instruments, instrument valves are often used to synthesize the output signals of the detection instruments to control the production process. The adjusted parameters include temperature, pressure, flow, liquid level, composition, etc.
Instrument valves have the following uses:
(1) Connect or cut off the medium in the pipeline, such as gate valve, globe valve, ball valve, plug valve, diaphragm valve, butterfly valve, etc.
(2) Adjust and control the flow and pressure of the medium in the pipeline, such as throttle valve, regulating valve, pressure reducing valve, safety valve, etc.
(3) Change the direction of medium flow in the pipeline, such as distribution valve, three-way cock, three-way or four-way ball valve, etc.
(4) Prevent the backflow of the medium in the pipeline, such as various structures of check valve, bottom valve and so on.
(5) Separate medium, such as various structures of steam traps, air traps, etc.
(6) Indicate and adjust the liquid level, such as liquid level indicators, liquid level regulators, etc.
(7) Other special purposes, such as temperature control valve, overcurrent protection emergency shut-off valve, etc.
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