What is  valve

Valves are pipeline accessories used to open and close pipelines, control flow direction, adjust and control the parameters (temperature, pressure and flow) of the conveying medium. According to its function, it can be divided into shut-off valve, check valve, regulating valve and so on.

The valve is a control component in the fluid delivery system, which has functions such as cut-off, adjustment, flow diversion, reverse flow prevention, pressure stabilization, flow diversion or overflow pressure relief. Valves used in fluid control systems range from the simplest cut-off valves to various valves used in extremely complex automatic control systems, with a wide variety of varieties and specifications.

Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. Valves are also divided into cast iron valves, cast steel valves, stainless steel valves (201, 304, 316, etc.), chrome-molybdenum steel valves, chrome-molybdenum-vanadium steel valves, duplex steel valves, plastic valves, non-standard custom-made valves, etc. according to the material.

Classification and function of valves

(1) Shut-off valve

This type of valve is used for opening and closing. It is permanently installed on the inlet and outlet of cold and heat sources, the inlet and outlet of equipment, and branch lines of pipelines (including standpipes). It can also be used as a water discharge valve and air release valve. Common shut-off valves include gate valves, globe valves, ball valves and butterfly valves.

Gate valves can be divided into bright rods and dark rods, single gates and double gates, wedge gates and parallel gates, etc. The closing tightness of the gate valve is not good, and it is difficult to open the large-diameter gate valve; the size of the valve body is small in the direction of water flow, the flow resistance is small, and the nominal diameter span of the gate valve is large.

Globe valves are divided into three types: straight-through type, right-angle type and straight-through type according to the flow direction of the medium, and there are bright rods and dark rods. The closing tightness of the globe valve is better than that of the gate valve, the valve body is long, the flow resistance is large, and the maximum nominal diameter is DN200.

The spool of the ball valve is a ball with a hole. When the plate moves the valve stem so that the opening of the ball is facing the axis of the pipeline, it is fully open, and when it is turned 90°, it is fully closed. The ball valve has a certain adjustment performance and is more tightly closed.

The valve core of the butterfly valve is a circular valve plate, which can rotate along the vertical shaft perpendicular to the pipeline axis. When the plane of the valve plate is consistent with the axis of the pipe, it is fully open; when the plane of the gate plate is perpendicular to the axis of the pipe, it is fully closed. Butterfly valve body length is small, flow resistance is small, and the price is higher than gate valve and globe valve. [1]

(2) Check valve

This type of valve is used to prevent the medium from flowing backwards. It uses the kinetic energy of the fluid itself to open itself and closes automatically when it flows in the reverse direction. It is always installed at the outlet of the water pump, the outlet of the steam trap and other places where the reverse flow of fluid is not allowed. There are three types of check valves: swing type, lift type and wafer type. For the swing check valve, when fluid can only flow from left to right, it will automatically close when it flows in the opposite direction. For the lift check valve, when the fluid flows from left to right, the valve core is lifted to form a passage, and when the fluid flows in the reverse direction, the valve core is pressed against the valve seat to be closed. For the wafer check valve, when the fluid flows from left to right, the valve core is opened to form a passage, and when the fluid flows in the opposite direction, the valve core is pressed to the valve seat to be closed. Installation, small size, light weight, compact structure. [1]

(3) Control valve

The pressure difference between the front and back of the valve is constant. When the opening of the ordinary valve changes in a wide range, the flow rate changes little, but when it reaches a certain opening degree, the flow rate changes sharply, that is, the regulation performance is not good. The regulating valve can change the stroke of the spool to change the resistance of the valve according to the direction and magnitude of the signal, so as to achieve the purpose of regulating the flow of the valve. Regulating valves are divided into manual regulating valves and automatic regulating valves, and manual or automatic regulating valves are divided into many types, and their regulating performance is also different. Automatic regulating valves include self-operated flow regulating valves and self-operated differential pressure regulating valves. [1]

(4) Vacuum class

Vacuum categories include vacuum ball valves, vacuum flapper valves, vacuum inflation valves, pneumatic vacuum valves, etc. Its function is that in the vacuum system, the components of the vacuum system used to change the direction of the air flow, adjust the size of the air flow, and cut off or connect the pipeline are called vacuum valves.

(5) Special purpose category

Special purpose categories include pigging valves, vent valves, drain valves, exhaust valves, filters, etc.

The exhaust valve is an indispensable auxiliary component in the pipeline system, and is widely used in boilers, air conditioners, oil and gas, water supply and drainage pipelines. It is often installed at commanding heights or elbows to remove excess gas in the pipeline, improve the efficiency of pipeline use and reduce energy consumption.

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