Valve is used to control the medium in the pipeline, with a movable mechanism of mechanical products. Its basic function is to connect or cut off the flow of pipeline medium, change the flow direction of medium, adjust the pressure and flow of medium, and protect the normal operation of pipeline and equipment.
With the development of modern science and technology, valves are widely used in T industry, construction, agriculture, national defense, scientific research and people’s life. Valves have become indispensable general mechanical products in various fields of human activities.
Industrial valve was born after the invention of steam engine. In recent ten years, due to the needs of petroleum, chemical industry, power station, metallurgy, shipbuilding, nuclear energy, aerospace and other aspects, higher requirements have been put forward for the valve, which urges people to study and produce high parameter valve FJ. The working temperature ranges from – 269 ℃ to 3430 ℃, and the working pressure from 1.33 × l0 ^ – 8 to 1460mpa. The nominal size of the valve ranges from micrometer gauge valve to industrial pipeline valve with nominal size of more than ten meters and weight of dozens of tons. The driving mode has developed from manual operation to electric, pneumatic and hydraulic operators to program control, numerical control and remote control.
It can be seen from the above description that the valve is widely used. However, if the valve is not properly selected, used and maintained, resulting in valve leakage, fire, explosion, poisoning, scald accidents, energy waste, equipment corrosion, material consumption increase, environmental pollution, and even shutdown, the consequences will be unimaginable. How to correctly understand, select, install, use and maintain valves is an urgent problem for users and engineers.
Classification of valves
With the continuous improvement of process flow and performance of various complete sets of equipment, the types of valves are also constantly changing and increasing. There are many kinds of valve classification methods, the classification methods are different, the results are not the same, several commonly used classification methods are as follows.
1.2.1 classification by use and function
The valves can be classified into block valve, check valve, diverter valve, regulating valve, safety valve, other special purpose valve and multi-purpose valve.
Block valve – mainly used to cut off or connect the medium in the pipeline. Such as gate valve, globe valve, ball valve, plug valve, butterfly valve, etc. Check valve type – used to prevent backflow of medium. Such as check valve, etc. Shunt broad class — used to change the flow direction of medium in the pipeline, which plays the role of distributing, dividing or mixing medium. Such as two-way or four-way plug valve T-way or four-way ball valve, distribution valve, etc.
Regulating valve – mainly used to regulate the flow and pressure of medium. Such as regulating valve, pressure reducing valve, flow valve, balance valve, etc. Safety valve – used for overpressure safety protection, discharge excess medium to prevent the pressure from exceeding the rated value of safety valve. When the pressure returns to normal, the valve will be closed to prevent the medium from flowing out. Such as a variety of safety valves, torrent valves, etc.
Other special valves such as steam trap, vent valve, slag discharge valve, blowdown valve, pigging valve, etc.
Multi purpose valves, such as stop check valve, check ball valve, stop check safety valve, etc.
1.2.2 classification by power source
According to the power source, the valve can be divided into automatic valve and drive valve. Automatic valve – a valve that operates by itself depending on the capacity of the medium (liquid, air, steam, etc.). Such as safety valve, check valve, pressure reducing valve, steam trap, emergency shut-off valve, etc.
Actuated valve – a valve operated by manual, electrical, pneumatic, or hydraulic power. Such as gate valve, globe valve, ball valve, butterfly valve, diaphragm valve, etc.
1.2.3 classification by main technical parameters
(1) Classification by nominal size
The valve can be divided into small diameter valve and medium diameter valve according to the nominal size
Door, large diameter valve and extra large diameter valve.
Small diameter valve – valve with nominal size ≤ Dn40.
Medium diameter valve is a valve with nominal size DN, DN50 ≤ DN ≤ DN300.
Large diameter valve – valve with nominal size DN, DN350 ≤ DN ≤ DN1200.
Extra large diameter valve – the valve with nominal size greater than or equal to dn 1400.
(2) Classification by nominal pressure
According to the nominal pressure, the valve can be divided into vacuum valve, low pressure valve, medium pressure valve, high pressure valve and ultra-high pressure valve.
Low vacuum valve – 10 ^ 5 ~ 10 ^ 2PA.
Medium vacuum valve – 10 ^ 2 ~ 10 ^ – 1pA.
High vacuum valve – 10 ^ – 1 ~ 10 ^ – 5pa.
Ultra high vacuum valve – 10 ^ – 5 PA.
Low pressure valve – valve with nominal pressure ≤ PN16.
Medium pressure valves – PN16 & lt; valves with nominal pressure ≤ PN100.
High pressure valves – PN100 & lt; valves with nominal pressure ≤ pn1000.
Ultra high pressure valve – nominal pressure & gt; pn1000 valve
Basic composition of control system (1) Manual control Take the liquid level control shown in Figure 1-1 as an example