A valve is a fluid transportation system with a cut-off, regulation, and infusion, to prevent backflow, pressure stabilization, shunt or overflow pressure relief, and other functions of the accessory. Commonly used valves include globe valves, gate valves, ball valves, non-return valves, safety valves, and regulating valves, etc. Through the various types of valves, the structure of the understanding, according to the requirements of the production process conditions, and the selection of appropriate valves.
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The Role of the Valve
1, opening and closing role - cut off or connect the fluid flow in the pipeline;
2, regulating role - to adjust the flow rate of fluid in the pipeline, flow;
3, throttling - fluid flows through the valve, resulting in a large pressure drop.
Valve Classification
According to different roles in the pipeline, the valve can be divided into globe valves (also known as cut-off valves), throttle valves, check valves, safety valves, and so on;
According to the structure of the form, the valve can be divided into gate valve, plug valve (often referred to as Cocker), ball valves, butterfly valves, diaphragm valves, lined valves, and so on. According to the material used to make the valve, it is divided into stainless steel valves, cast steel valves, cast iron valves, plastic valves, ceramic valves, and so on. Valves commonly used in chemical production are mainly gate valves, globe valves, check valves, ball valves, pressure-reducing valves, plug valves diaphragm valves, and control valves.
Valve Details
1. Gate valve
Gate valve main components for the gate, through the gate, lift to open and close the pipeline. This valve has a small fluid resistance, applicable pressure, temperature range, medium flow direction is not restricted, and good sealing performance. Gate valves are mostly used in large-diameter pipelines, for opening and closing valves, in small-diameter pipelines are also used as control valves. Gate valves should not be used for containing solid particles or materials easy to deposit the fluid, so as not to cause wear and tear on the sealing surface and affect the closure of the gate. Gate valves can be divided into parallel gate valves, wedge gate valves, lift gate valves, rotary rod gate valves, rapid opening and closing gate valves, indented gate valves, flat gate valves, etc.
Manual gate valve structure schematic diagram and outline drawing
2. Globe valve
Globe valve main components for the valve disc and valve seat, the fluid from the bottom up through the valve seat, its structure is more complex, the fluid resistance is larger, but the sealing and regulating performance is better. Globe valves should not be used for viscosity and contain easy-to-precipitate particles of the media. Globe valve opening and closing process between the sealing surface friction is small, more durable, open height is not large, easy to manufacture, and easy to maintain, not only for low-pressure pipelines but also for high-pressure pipelines.
3. Check valve
Check valves are also known as non-return valves or check valves. Check the valve installed in the pipeline so that the fluid can only flow in one direction, and does not allow reverse flow. It is an automatic shut-off valve, there is a valve or rocker plate in the valve body. When the medium is flowing downstream fluid the valve flap automatically opens; when the fluid backflow, the fluid (or spring force) will automatically close the valve flap. According to the different structures of the check valve, the check valve is divided into lift and swing type two categories. The lift check valve flap is perpendicular to the valve channel lifting movement, generally used in horizontal or vertical pipelines; the rotary check valve flap is often called a rocker plate, rocker plate side is connected to the shaft, and the rocker plate can be rotated around the shaft, rotary check valve is generally installed in the horizontal pipeline, small diameter can also be installed in the vertical pipeline, but pay attention to the flow should not be too large. The check valve is generally applicable to a clean media pipeline, containing solid particles and the viscosity of the media pipeline should not be used. Lift type check valve closed performance is better than the rotary open type, but the rotary open type check valve fluid resistance is smaller than the lift type. In general, the swing check valve is suitable for large-diameter pipelines. When installing, pay attention to the direction of fluid flow.
Check Valve Structure Schematic and Outline Drawing
4. Ball valve
The ball valve spool is spherical, in the middle of a tube with a similar diameter to the connecting hole, the structure is simpler than the gate valve and globe valve, opens and closes quickly, is easy to operate, is small in size, lightweight, fewer parts, and components, fluid resistance is small, the full diameter of the ball valve is no fluid resistance. Ball valves are suitable for low temperature and high pressure and viscosity of the medium, but should not be used to regulate the flow.
Ball Valve Structure Schematic and Outline Drawing
5. Plug valve
The plug valve is the earliest use of a valve, with a simple structure, rapid switching, and small fluid resistance. Its main part is a rotatable conical plug, the center has a hole, when the plug rotates to 90 °, the flow channel is all closed, requiring a larger turning torque. Plug valves are easy to jam when the temperature changes, and can not be used for high pressure.
6. Safety valve
In order to ensure the safety of chemical production, in the pressure of the pipeline system, there is a permanent safety device, that is, the selection of a certain thickness of the metal sheet, like the insertion of a blind mounted on the end of the pipeline or tee interface. When the pressure in the pipeline rises, the sheet is broken to achieve the purpose of pressure relief. Rupture plates are generally used in low-pressure, large-diameter pipelines, but in most chemical pipelines with safety valves. There are many types of safety valves, which can be broadly categorized into two main types, namely, spring-loaded and lever-loaded. Spring-loaded safety valves, as shown in the figure, rely mainly on the force of the spring to achieve sealing. When the pressure in the pipe exceeds the spring force, the valve is opened by the medium, and the fluid in the pipe is discharged, so that the pressure is reduced. Once the pressure in the pipe drops below the spring force, the valve is closed again. Lever-type safety valves mainly rely on the force of the weight on the lever to achieve sealing, the principle of action with the spring-type. Safety valve selection is based on the working pressure and working temperature to determine the nominal pressure level, its caliber size can be calculated concerning the relevant provisions to determine. Safety valve structure type and valve material should be selected according to the nature of the medium, and working conditions. Safety valve jumping pressure, test, and acceptance have special provisions, regular calibration by the security department, and seal printing, in use shall not be arbitrarily adjusted to ensure safety, mainly used in steam boilers and equipment under pressure.
Spring Loaded Safety Valve Structure Schematic and Outline Drawing
7. Butterfly valve
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A butterfly valve, also known as a flap valve, is a simple structure of the regulating valve, that can be used for low-pressure piping media. Valves can be used to control the flow of various types of fluids such as air, water, steam, a variety of corrosive media, mud, oil, liquid metals, and radioactive media. The pipeline mainly plays a role in cutting off and throttling. Butterfly valve opening and closing parts is a disc-shaped butterfly plate, in the valve body around its axis rotation, to achieve the purpose of opening and closing or regulation.
Butterfly valve structure schematic and outline drawing
8. pressure-reducing valve
Pressure pressure-reducing valve is to reduce the medium pressure to a certain value of the automatic valve. General pressure after the valve is less than 50% of the pressure before the valve, it mainly relies on the diaphragm, spring, piston, and other parts of the medium to control the pressure difference between the valve flap and the valve seat gap, to achieve the purpose of pressure reduction. There are many types of pressure-reducing valves, the common ones are piston type and diaphragm type.
Pressure Reducing Valve Structure Schematic and Outline Drawing
9. Diaphragm Valve
The structure form of the diaphragm valve is very different from the general valve, is a new type of valve. It is a special form of the cut-off valve, its opening and closing parts are a piece of soft material made of a diaphragm, the diaphragm will be the valve body cavity, and the valve cover cavity and drive parts separated. Diaphragm valves are now widely used in various fields. The opening and closing of the valve shown in the figure is a special rubber diaphragm, the diaphragm is sandwiched between the valve body and the bonnet, and the disc under the valve stem presses the diaphragm tightly against the valve body to achieve sealing. This valve has a simple structure, reliable sealing, easy maintenance, and low fluid resistance. Suitable for conveying acidic media and fluid pipelines with suspended solids, but generally should not be used for higher pressures or temperatures higher than 60 &#; pipeline, should not be used for conveying organic solvents and strong oxidizing media in the pipeline.
Diaphragm valve structure schematic and outline drawing
10. Throttle valve
The throttle valve belongs to a kind of globe valve. The shape of the valve head is conical or streamlined, and can better regulate the flow of fluid or throttling pressure. The valve production requires high precision and good sealing performance. Mainly used for instrumentation control or sampling and other pipelines, but should not be used for viscosity and solid particles in the pipeline.
Throttle valve
11. Lined valves
To prevent corrosion of the medium, some valves need to be lined with corrosion-resistant materials (lead, rubber, enamel, etc.) in the valve body valve head, and other parts. Lining materials should be selected according to the nature of the medium. For the convenience of lining, lined valves are mostly made of right-angle type or direct-flow type.
Lined valve
1-stem; 2-ball (full diameter); 3-body; 4-bonnet; 5-ball seat
12. Traps
Traps, also called automatic drains or condensate drains, can be divided into those used for steam systems and those used for gas systems, and are mainly of the inverted bucket, lever float, and free float types.
Trap Construction Types
As shown in the figure below, traps are switched on and off using the principle of buoyancy to automatically identify steam and water and are commonly used in applications that require continuous drainage, large flow rates, and collection of discharged water for reuse. Lever float traps and inverted bucket traps are complex. Free float traps have a simple structure, do not leak, and are generally used for pipeline or equipment trapping.
Trap Structure Schematic and Outline Drawing
In the process of transporting high-pressure steam, due to heat loss, the steam condenses to form a water-vapor mixture, making the steam transported in the pipeline unsmooth. By installing a water trap in the piping, the condensate can be removed from the piping to ensure the smooth delivery of steam.
Trap Application Examples
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