Valves are mechanical devices that control the flow, direction, pressure, temperature, etc. of fluid media, and are very important components in pipeline systems. This is the most complete classification of valves, come and have a look!
Below is the classification of valves compiled by the editor, there is no more complete than this, right?
Valves have different requirements according to their types and uses, mainly including sealing, strength, regulation, circulation, opening and closing and other performances. When designing and selecting valves, in addition to considering basic parameters and performance, the performance of the fluid must also be considered, including the phase state of the fluid (gas, liquid or containing solid particles), corrosiveness, viscosity, toxicity, flammability and explosiveness, preciousness and rarity, and radioactivity.
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The valves shown in the video are: 1. Globe valve. 2. Butterfly valve. 3. Ball valve (floating ball). 4. Gate valve (parallel gate valve). 5. Globe valve. 6. Check valve (double plate). Classification by pressure
Vacuum valve: PN is lower than the standard atmospheric pressureLow pressure valve: PN≤1.6 MPa
Medium pressure valve: PN=2.5-6.4 MPaHigh pressure valve: PN=10-80 MPaUltra-high pressure valve: PN≥100 MPa
ps: PN refers to the nominal pressure, that is, the maximum working pressure allowed by the valve at the reference temperature.
Classification by medium working temperature
High temperature valve: t＞450℃Medium temperature valve: 120℃＜t≤450℃Normal temperature valve: -30℃≤t≤120℃Low temperature valve: t＜-30℃
Classification by nominal diameter
Small diameter valve: DN＜40 mmMedium diameter valve: DN=40-300 mmLarge diameter valve: DN=350-1200 mmExtra large diameter valve: DN≥1400 mm
Classification by driving method
Manual valve: driven by hand with the help of handwheel, handle, lever or sprocket, etc., and equipped with gear and other deceleration devices when transmitting large torque. Electric valve: driven by motor, electromagnetic or other electrical devices.
Hydraulic valve: driven by liquid (liquid medium such as water and oil).
Pneumatic valve: driven by compressed air.
Classification by use
1. Gate valve
Refers to the valve whose closing member (gate) moves in the vertical direction along the center line of the channel. It is mainly used for cutting off in pipelines, and also has certain flow regulation performance.
Features
Small fluid resistance. Small opening and closing torque. Unrestricted medium flow direction. Short structural length. Good sealing performance. Sealing surface is easily damaged. Long opening and closing time, large height. Complex structure with many parts, difficult to manufacture and repair.
Classification by valve plate structure
Rising stem gate valve: The valve stem thread and nut are not in contact with the medium, and are not affected by the corrosiveness of the medium temperature. The opening degree is obvious and easy to see, so it is widely used. Non-rising stem gate valve: The screw thread and nut are in contact with the medium, affected by the medium temperature and corrosiveness, but the height of the valve is small. Non-rising stem gate valve is suitable for non-corrosive media and occasions with poor external environmental conditions.
Classification by whether the diameter of the channel in the valve body is consistent
Reduced diameter gate valve: The diameter at the valve seat is smaller than the diameter at the flange connection. Equal diameter gate valve: The diameter at the valve seat is consistent with the diameter at the flange connection. Diameter contraction can reduce the size of valve parts, and the force required for opening and closing is also reduced accordingly, while expanding the general range of parts. However, after the diameter is contracted, the fluid resistance loss will increase.
2. Ball valve
Use a ball with a hole in the middle as the valve core, and control the opening and closing of the valve by rotating the ball. The ball valve can be made into a straight, three-way or four-way. The ball valve is mainly used to cut off, distribute and change the flow direction of the medium on the pipeline.
Since the ball valve seat uses rubber material, its operating temperature is limited. In order to cope with possible fire situations, many designers use auxiliary metal-to-metal seals. The ball valve is not suitable for use as a throttle valve, but it can be used to reduce the pressure entering or discharging the system in a partially open state. On production equipment, ball valves are often used as general-purpose on/off valves. Floating ball ball valve: Its ball is floating. Under the action of the medium pressure, the ball can produce a certain displacement and press on the sealing ring at the outlet to ensure the sealing of the outlet. This ball valve has a simple structure and good sealing performance, but the pressure at the outlet seal is high and the operating torque is also large. This structure is widely used in medium and low pressure ball valves. Fixed ball ball valve: The ball of this ball valve is fixed and does not move after being pressurized. Usually, rolling or sliding bearings are installed on the upper and lower shafts that are integrated with the ball. The operating torque is small and it is suitable for high-pressure and large-diameter valves.
Three, stop valve
It refers to a valve whose closing part (valve disc) moves along the center line of the valve seat. It is mainly used for cutting off on the pipeline.
The valve stem thread of the upper threaded stem stop valve is outside the medium. The valve stem thread is not corroded by the medium and is also easy to lubricate. This structure is widely used. The valve stem thread of the lower threaded stem stop valve is in direct contact with the medium in the valve body. It is not only unable to be lubricated, but also corroded by the medium. This structure is used for small-diameter valves and mediums with low temperatures.
Four, check valve
The valve disc is automatically opened and closed by the flow of the medium itself. The valve that can only flow in one direction and prevent the backflow of the medium is called a check valve. Lift check valve The valve disc of this valve moves along the center line of the valve seat hole. The valve disc is opened by the thrust of the fluid and falls by gravity. Therefore, it can only be installed on horizontal pipes. The valve body shape of the lift check valve is similar to that of the stop valve, so its flow resistance coefficient is also large. Swing check valve
The valve disc of this valve rotates around the pin at the valve seat. The valve disc is generally an integral structure. Some large-diameter check valves (nominal diameter of 600mm and above) mostly use multi-disc type.
V. Safety valve
Classification by loading structure
Lever weight hammer safety valve: The weight is loaded on the valve disc through the lever, and the load hardly changes with the opening height. Because the size of the lever part of this safety valve is relatively large, the entire valve is relatively heavy, and the return seat pressure is low, it has been seldom used in engineering. Pilot safety valve: It consists of a main valve and an auxiliary valve. The medium pressure and spring pressure are loaded on the main valve disc at the same time. When the pressure is overpressured, the auxiliary valve disc opens first, causing the main valve to open. It is mainly used in large-diameter and high-pressure occasions. Spring-type safety valve: The spring force is loaded on the valve disc, and the load changes with the opening height. The advantages are that it is smaller than the heavy hammer safety valve, lighter, more sensitive, and the installation position is not strictly restricted. It is widely used in oil and gas emergency transmission projects.
Classification by the opening height of the safety valve
Micro-opening safety valve: The opening height is 1/40-1/20 of the valve seat throat diameter, usually made into a gradual opening type (the opening height gradually changes with the pressure change). Mainly used in liquid media with small discharge volume. Full-opening safety valve: The opening height is equal to or greater than 1/4 of the valve throat diameter, usually made into a quick opening type (the valve disc suddenly jumps up at a certain moment of opening and reaches the full opening height). Mainly used in gas, steam media and fluid media with large discharge volume. Gradually opening or quick opening safety valve: The opening height is between the micro-opening type and the full-opening type.
Classification by valve body structure
Fully enclosed type: When discharging, the medium will not leak outward and will be discharged through the discharge pipe. Semi-closed type: When discharging, part of the medium is discharged through the discharge pipe, and the other part leaks outward from the matching point between the valve cover and the valve stem. Open type: When discharging, the medium does not pass through the discharge pipe, but is discharged directly from the top of the valve disc.
Sixth, butterfly valve
The valve disc is a disc. Through the rotation of the valve stem, the valve disc rotates 90 degrees within the range of the valve seat to realize the opening and closing of the valve. It plays a shut-off role in the pipeline. It can also adjust the flow.
Features
Opening and closing are convenient and quick, labor-saving, and the fluid resistance is small, and it can be operated frequently. The structure is simple, the volume is small, and the weight is light. It can transport mud and accumulate the least liquid at the pipe mouth. Good sealing can be achieved under low pressure. Good adjustment performance. The operating pressure and working temperature range are small. The sealing is poor.
Seventh, pressure reducing valve
The pressure reducing valve is an automatic valve that reduces the medium pressure to a certain value. Generally, the pressure after the valve is less than 50% of the pressure before the valve. There are many types of pressure reducing valves, mainly piston type and spring film type.
The piston pressure reducing valve is a valve that reduces pressure through the action of the piston. The spring diaphragm pressure reducing valve relies on springs and diaphragms to balance pressure. 8. Steam trap
The steam trap is also called steam blocking and drainage valve, steam-water valve, steam trap, return box, return gate, etc. Its function is to automatically discharge the condensate that is constantly generated without letting the steam out. The steam trap must be able to "identify" steam and condensate to play the role of steam blocking and drainage. "Identifying" steam and condensate is based on three principles: density difference, temperature difference and phase change. Therefore, three types of steam traps are manufactured based on the three principles: classified as mechanical type, thermostatic type, and thermodynamic type.
1. Mechanical steam trap: The mechanical type is also called float type. It uses the density difference between condensate and steam. Through the change of condensate level, the float rises and falls to drive the valve disc to open or close, so as to achieve the purpose of steam blocking and drainage. Mechanical steam traps have a small degree of subcooling and are not affected by working pressure and temperature changes. They can drain water as soon as there is water, and there is no water in the heating equipment, which can make the heating equipment achieve the best heat exchange efficiency. The maximum back pressure rate is 80%, and the working quality is high. It is the most ideal steam trap for production process heating equipment. Mechanical steam traps include free float type, free semi-float type, lever float type, inverted bucket type, etc. ① Free float steam trap: The free float steam trap has a simple structure, with only one moving part inside. The finely ground stainless steel hollow float is both a float and an opening and closing part, without wearing parts, and has a long service life. The "YQ brand" steam trap has a Y series automatic air exhaust device inside, which is very sensitive, can automatically exhaust air, and has high working quality. When the equipment is just started, the air in the pipeline is discharged through the Y series automatic air exhaust device, and the low-temperature condensate enters the steam trap. The liquid level of the condensate rises, the float rises, the valve opens, the condensate is quickly discharged, and the steam quickly enters the equipment. The equipment heats up rapidly, the temperature-sensitive liquid of the Y series automatic air exhaust device expands, and the automatic air exhaust device is closed. The steam trap starts to work normally, and the float rises and falls with the condensate level to block steam and drain water. The valve seat of the free float steam trap is always below the liquid level, forming a water seal, no steam leakage, and good energy-saving effect. The minimum working pressure is 0.01Mpa, and it is not affected by temperature and working pressure fluctuations within the range from 0.01Mpa to the maximum operating pressure, and it drains water continuously. It can discharge saturated temperature condensate, the minimum subcooling is 0℃, there is no water in the heating equipment, and the heating equipment can achieve the best heat exchange efficiency. The back pressure rate is greater than 85%, which is one of the most ideal steam traps for production process heating equipment. ②, Free semi-float steam trap: The free semi-float steam trap has only one semi-float ball barrel as a movable part, with the opening facing downward. The ball barrel is both an opening and closing part and a sealing part. The entire spherical surface can be sealed, with a long service life, water hammer resistance, no wearing parts, no faults, durable, and no steam leakage. The back pressure rate is greater than 80%, and saturated temperature condensate can be discharged. The minimum subcooling degree is 0℃, and there is no water in the heating equipment, which can enable the heating equipment to achieve the best heat exchange efficiency. When the device is just started, the air and low-temperature condensate in the pipeline enter the steam trap through the launch tube, and the bimetallic strip emptying element in the valve pops the ball barrel open, the valve opens, and the air and low-temperature condensate are quickly discharged. When steam enters the ball barrel, the ball barrel generates upward buoyancy, and at the same time the temperature in the valve rises, the bimetallic strip emptying element shrinks, the ball pokes float to the valve port, and the stop valve, solenoid valve, and valve are closed. When the steam in the ball barrel turns into condensate, the ball barrel loses buoyancy and sinks, the valve opens, and the condensate is quickly discharged. When the steam enters the ball bucket again, the valve closes again, and it works intermittently and continuously. ③. Lever float trap: The basic characteristics of the lever float trap are the same as those of the free float trap. The internal structure is that the float is connected to the lever to drive the valve core, and the valve is opened and closed as the condensate level rises and falls. The lever float trap uses double valve seats to increase the condensate discharge, which can achieve a small volume and large discharge. The maximum drainage volume is 100 tons/hour, which is the most ideal trap for large heating equipment. ④. Inverted bucket trap:
The inverted bucket trap has an inverted bucket as a liquid level sensor inside. The bucket opens downward, and the inverted bucket is connected to the lever to drive the valve core to open and close the valve. The inverted bucket trap can exhaust air, is not afraid of water hammer, and has good anti-fouling performance. The subcooling is small, the steam leakage rate is less than 3%, the maximum back pressure rate is 75%, there are more connectors, and the sensitivity is not as good as the free float trap. Because the inverted bucket steam trap relies on the upward buoyancy of steam to close the valve, it is not suitable for use when the working pressure difference is less than 0.1MPA. When the device is just started, the air and low-temperature condensate in the pipeline enter the steam trap, the inverted bucket falls by its own weight, and the inverted bucket connecting lever drives the valve core to open the valve, and the air and low-temperature condensate are quickly discharged. When steam enters the inverted bucket, the steam in the inverted bucket generates upward buoyancy, and the inverted bucket rises and connects the lever to drive the valve core to close the ball valve and gate valve. There is a small hole on the inverted bucket. When part of the steam is discharged from the small hole, the other part of the steam generates condensate, and the inverted bucket loses buoyancy and sinks by its own weight. The inverted bucket connecting lever drives the valve core to open the valve, working in a cycle, and discontinuous drainage. ⑤. Combined superheated steam trap: 2. The combined superheated steam trap has two isolated valve chambers, which are connected by two stainless steel pipes. It is a combination of float type and inverted bucket type trap. The valve structure is advanced and reasonable. Under the working conditions of overheating, high pressure and small load, it can timely discharge the condensate formed when the superheated steam disappears, effectively prevent the leakage of superheated steam, and has high working quality. The maximum allowable temperature is 600℃, the valve body is all stainless steel, the valve seat is hard alloy steel, and the service life is long. It is a special trap for superheated steam. It has obtained two national patents and filled the domestic gap. When the condensate enters the lower valve chamber, the float of the auxiliary valve rises with the liquid level, and the float closes the steam inlet pipe hole. The condensate rises to the main valve chamber through the water inlet conduit, and the inverted bucket falls by its own weight, driving the valve core to open the main valve and discharge the condensate. When the condensate level in the auxiliary valve chamber drops, the float drops with the liquid level, and the auxiliary valve opens. Steam enters the inverted bucket in the upper main valve chamber from the steam inlet pipe. The inverted bucket generates upward buoyancy, which drives the valve core to close the main valve. When the condensate level in the auxiliary valve chamber rises again, the next cycle begins again, and drainage is intermittent. ①. Thermostatic steam trap: This type of steam trap uses the temperature difference between steam and condensate to cause the temperature sensing element to deform or expand, driving the valve core to open and close the valve. The thermostatic steam trap has a relatively large degree of subcooling, generally 15 to 40 degrees. It can utilize part of the sensible heat in the condensate. There is always high-temperature condensate in front of the valve, there is no steam leakage, and the energy-saving effect is significant. It is used in steam pipelines, heating pipelines, and small heating equipment
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