Pipeline system is closely related to everyone's life, and valve components are closely related to
Pipeline system is closely related to everyone's life, and valve components are closely related to pipeline system. Valves are mainly used to control fluids, including their moving speed, throughput and various functions. They are an indispensable part of modern life. There are many kinds of valves according to their functions, especially according to their materials. The following small series will introduce you to the knowledge of valves.
What occasions are gate valves, globe valves and butterfly valves suitable for?
1. These three valves are arranged according to the difficulty of opening and closing: globe valve, gate valve and butterfly valve.
Arranged by resistance: globe valve, butterfly valve and gate valve;
Strictly according to the closing arrangement: globe valve, butterfly valve and gate valve;
Sort by price: globe valve, butterfly valve and gate valve; (Except for special butterfly valves)
These three valves are all drive valves. According to the above characteristics, it is not difficult to see that the stop valve is mainly used for opening and closing and flow regulation of small-diameter pipelines (branch pipes) or the end of pipelines; Butterfly valve is used to open and close the main branch pipe and adjust the flow; Gate valve is used to open and close the main pipeline, but it is generally not used to adjust the flow.
(1) gate valve
The length of valve body is moderate, and the adjustment performance of rotary adjusting rod is good, which is widely used in large-diameter pipelines;
(2) Stop valve
The valve body is long, and the adjusting performance of the rotary adjusting rod is good, which is suitable for occasions with spacious site and small pipe diameter (generally DN is less than or equal to150 mm);
(3) Butterfly valve
The valve body is short, the adjustment performance of the handle-type adjusting rod is slightly poor, and the price is higher, but the adjustment operation is convenient, and it is suitable for occasions with small site and large pipe diameter (generally DN> 150 mm).
2. Water chillers, heat exchangers and main pipelines can be adjusted by gate valves, globe valves or butterfly valves.
3. In the water distributor and water collector, because its main function is to adjust, generally choose stop valve or gate valve;
4. One valve is installed at the inlet of the water pump and two valves are installed at the outlet. Among them, the valve near the outlet end of the water pump is a check valve, and the other two valves can be gate valves, globe valves or butterfly valves;
5. Small-diameter pipes at the inlet and outlet of heating and air-conditioning terminal equipment can choose stop valves or ball valves;
6. Balancing valves can be installed on the horizontal pipes of each floor of multi-storey and high-rise buildings to balance the flow of each floor;
7. The drain valve is installed at the lowest point of water tank, pipeline and equipment. Since they are not used for adjustment, valves that can be tightly closed, such as gate valves and globe valves, should be selected.
8. In steam-condensate pipeline systems, such as steam heating system, boiler water system, steam lithium bromide refrigerator and steam-water heat exchanger system, a pressure reducing valve is generally installed at the steam inlet; Install safety valves where high pressure may occur; Install a trap at the condensate drain.
What kinds of balance valves are there? What occasion are they suitable for?
There are several kinds of balance valves. The first type is static balance valve, which can be adjusted manually and accurately, and can be connected to an instrument to measure resistance and convert it into flow. This is a valve that can accurately adjust the local resistance coefficient. Generally located on the main pipe, it can also be located at the entrance of branch pipes or demanding equipment. The disadvantage is that the system resistance can only be balanced under the rated flow, and the hydraulic balance will be affected by setting an electric valve at the end to change the resistance.
The dynamic balance valve, which came out in 1990s, is used to keep the flow constant when the system pressure changes, that is, the flow does not change with the system pressure, so it is called dynamic balance valve. Its application is obvious, it can only be used in the system with constant water flow, and it can't be used with electric valves.
These two kinds of domestic valves were initiated by China Air Conditioning Research Institute.
FLOWCON dynamic balance electric regulating valve produced in Denmark is a new generation product. It combines electric valve with dynamic balance, and when the electric regulating valve is adjusted, the preset flow of dynamic balance is also adjusted. For example, when the electric regulating valve regulates the flow to 50%, the valve can maintain a constant flow at the 50% flow point. At present, this is the only company in the world that owns this product. It is used at the position where the electric valve was originally set at the end of the air conditioner, and other hydraulic balance measures of the main pipe and the branch pipe (including the same direction pipe) can be cancelled.
ball valve
Ball valve is evolved from plug valve. There is also a lifting action of rotating 90 degrees, but the difference is that the cock body is a sphere with a circular through hole or channel passing through its axis. The ratio of spherical surface to channel opening should be such that when the ball rotates 90 degrees, all spherical surfaces should appear at the inlet and outlet, thus cutting off the flow.
The ball valve can be closed tightly only by rotating 90 degrees and a small rotating torque. The completely equal inner cavities of the valve body provide a direct flow channel with little resistance for the medium. Generally speaking, the ball valve is most suitable for direct opening and closing, but the ball valve has been designed in recent development to make it have the function of throttling and controlling flow. The main features of ball valve are compact structure and convenient operation and maintenance. Suitable for general working media such as water, solvent, acid, natural gas, etc., and also suitable for media with harsh working conditions such as oxygen, hydrogen peroxide, methane and ethylene. Ball valve body can be integrated or combined.
cut-off valve
The stem axis of globe valve is perpendicular to the sealing surface of valve seat. The opening or closing stroke of the valve stem is relatively short, and it has a very reliable cut-off function, which makes this valve very suitable for cutting off or regulating media and throttling.
Once the disc of the cut-off valve is in the open state, its valve seat and the sealing surface of the disc no longer contact, which has a very reliable cutting-off effect, which makes this valve very suitable for cutting off or regulating media and throttling.
Once the globe valve is in the open state, there is no contact between the valve seat and the sealing surface of the disc, so the mechanical wear of the sealing surface is very small. Because the valve seat and disc of most globe valves are easy to maintain or replace seals, it is not necessary to disassemble the whole valve from the pipeline, which is very suitable for the occasion where the valve and the pipeline are welded together. When the medium passes through this valve, its flow direction changes, so the flow resistance of the stop valve is higher than that of other valves.
Commonly used globe valves are as follows:
1, angle cut-off valve; In the angle globe valve, the fluid only needs to change direction once, so the pressure drop through this valve is smaller than that of the conventional globe valve.
2. DC cut-off valve; In the DC or Y-shaped globe valve, the flow passage of the valve body is diagonal to the main flow passage, so the damage degree of the flow state is smaller than that of the conventional globe valve, and the pressure loss through the valve is correspondingly smaller.
3. Plunger globe valve: This type of globe valve is a variant of the traditional globe valve. In this kind of valve, the disc and seat are usually designed according to the plunger principle. The disc is polished into a plunger connected with the valve stem, and the sealing is realized by two elastic sealing rings sleeved on the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings around the plunger are firmly pressed by the load exerted on the bonnet by the bonnet nut. The elastic sealing ring can be replaced and made of various materials. Valves are mainly used for "opening" or "closing", but they are equipped with special plungers or special collars, which can also be used to adjust the flow.
watergate
As the cut-off medium, the gate valve has a straight flow channel when it is fully opened, and the pressure loss of the medium is the smallest at this time. Gate valves are usually suitable for working conditions that do not need to be opened and closed frequently and keep the gate fully open or closed. Not suitable for adjustment or throttling. For high-speed flowing media, the gate will vibrate when it is partially opened, which may damage the sealing surface of the gate and the valve seat, and throttling will make the gate corrode by the media. From the structural form, the main difference is the seal form adopted. According to the form of sealing elements, gate valves are usually divided into several different types, such as wedge gate valves, parallel gate valves, parallel double gate valves and wedge double gate valves. The most commonly used forms are wedge gate valves and parallel gate valves.
The function of this type of valve is to allow the medium to flow only in one direction and prevent it from flowing in the opposite direction. Usually, this valve works automatically. Under the action of unidirectional fluid pressure, the disc opens. When the fluid flows in the opposite direction, the fluid pressure and the self-overlapping disc of the disc act on the valve seat, thus cutting off the flow. Among them, check valves belong to this type of valves, including swing check valves and lifting check valves. Swing check valve has a hinge mechanism, and a disc like a door is freely supported on the inclined seat surface. In order to ensure that the disc can reach the proper position of the valve seat surface every time, the disc is designed in the hinge mechanism, so that the disc has enough swing space to make the disc truly and comprehensively contact with the valve seat. According to the performance requirements, the disc can be completely made of metal or inlaid with leather, rubber or synthetic materials. When the swing check valve is fully opened, the fluid pressure is almost unimpeded, so the pressure drop through the valve is relatively small. The disc of the lifting check valve is located on the sealing surface of the upper valve seat of the valve body. This valve is similar to a globe valve except that the disc can be lifted freely. The fluid pressure makes the disc lift from the sealing surface of the valve seat, and the medium backflow makes the disc fall back to the valve seat, cutting off the flow. Depending on the service conditions, the disc can be all-metal structure, or it can be in the form of embedding rubber pads or rubber rings on the disc frame. Like the globe valve, the passage of fluid through the lifting check valve is narrow, so the pressure drop through the lifting check valve is larger than that of the swing check valve, and the flow rate of the swing check valve is rarely limited in the production process. In order to make the parameters such as medium pressure and flow rate meet the requirements of process flow, it is necessary to install an adjusting mechanism to adjust the above parameters. The main working principle of the adjusting mechanism is to adjust the above parameters by changing the flow area between the valve disc and the valve seat. These valves are collectively called control valves, which are divided into self-driven control valves driven by the power of the medium itself, such as pressure reducing valves and pressure stabilizing valves. , driven by the front power (such as electric power, compressed air, hydraulic power) is called other drive control valve, such as electric control valve, pneumatic control valve, hydraulic control valve, etc.
electrically operated valve
Electric drive valve is a commonly used drive valve. The characteristics of the valve electric device are as follows: 1) The valve can be opened and closed quickly, which can greatly shorten the time required for opening and closing the valve; 2) It can greatly reduce the labor intensity of operators, especially suitable for high-pressure large-caliber valves; 3) It is suitable to be installed in a position that cannot be manually operated or accessed, and it is easy to realize remote control, and the installation height is not limited; 4) it is beneficial to the automation of the whole system; 5) Power supply is easier to obtain than gas source and liquid source, and its wiring and maintenance are much simpler than compressed air and hydraulic pipeline.
The disadvantage of electric valve device is that its structure is complex and it is difficult to use in wet places. When used in explosive media, explosion-proof measures need to be taken.
According to the type of the driven valve, the valve electric device can be divided into Z type and Q type. The output shaft of Z-valve electric device can rotate many times, which is suitable for driving gate valves, globe valves and diaphragm valves. The output shaft of Q valve electric device can only rotate 90? , suitable for driving plug valves, ball valves and butterfly valves. According to their protection types, there are common type, flameproof type (indicated by B), heat-resistant type (indicated by R) and three-in-one type (indicated by S).
Valve electric device is generally composed of transmission mechanism (reducer), motor, stroke control mechanism, torque limiting mechanism, manual-electric conversion mechanism, opening indicator and so on.
Pneumatic and hydraulic valves
Pneumatic and hydraulic valves are driven by air, water or oil with a certain pressure, and valves are driven by the movement of cylinders (or hydraulic cylinders) and pistons. Generally, the pneumatic pressure is less than 0.8MPa, and the hydraulic pressure or oil pressure is 2.5MPa~25MPa.
Rotary gas-liquid driving device is used to drive ball valve, butterfly valve or plug valve. The hydraulic device has large driving force and is suitable for driving large-caliber valves. If it is used to drive plug valves, ball valves and butterfly valves, the reciprocating motion of the piston must be converted into the rotary motion of the surface.
Manual gate
Manual valve is the most basic driving valve. Including direct driving by handwheel, handle or wrench and driving by transmission mechanism. When the opening torque of the valve is large, it can be omitted by gear or worm gear transmission. Gear transmission is divided into spur gear transmission and bevel gear transmission. Gear transmission has a small reduction ratio, which is suitable for gate valves and globe valves, while worm gear transmission has a large reduction ratio, which is suitable for plug valves, ball valves and butterfly valves.
1, gate valve
Gate valves, also known as gate valves, are characterized by good sealing performance and are often used in water supply pipelines and hot water heating pipelines. Because the gate is not suitable for blocking foreign objects after opening, it is used as a drain valve for heating pipe network and small boilers (such as vertical horizontal tube boilers). This valve is not used in steam pipeline, because when the pressure is high, the gate valve will be difficult to open because of the pressure on one side.
Gate valves are suitable for working in full open or full closed state, and are suitable for regulating flow. If the gate works in a semi-open state for a long time, the sealing surface of the gate will become loose due to medium erosion.
2. Stop valve and throttle valve
Globe valves and throttle valves used to be collectively called ball valves. Although the stop valve is used to cut off the steam and water channels, the throttle valve is mainly used to adjust the flow, but it is difficult to distinguish from the appearance, the only difference is the valve core. The end of the stop valve spool is flat, while the throttle valve spool is conical.
Copper spool globe valves can be used for steam and water pipelines. If the valve core is equipped with leather money, rubber or plastic thermal cut-off valve (commonly known as leather money throttle valve), it is only used for water or low-temperature hot water pipeline, otherwise leather money, rubber or plastic will deteriorate and lose sealing performance.
3, cock and ball valve
Plug valve is also called open water stop valve, commonly known as rotary valve. Small cock used to be called test branch, which is a quick-opening valve. According to its diversion, there are direct, three-way and four-way valves. The valve stem of the cock is connected with the valve core into a whole, the valve core is in the shape of a frustum with a rectangular through hole, and the through hole of the small cock is circular. When the groove or handle at the top of the valve stem is parallel to the direction in which the cock enters and exits, the valve is fully open, and when it is vertical, the valve is fully open.
The ball valve is actually a variant of the cock. Like the cock, it opens the valve by changing the angle of the valve core. The valve core of the ball valve is a sphere with a cylindrical hole, and the two sides of the sphere are lined with fluoroplastic heat rings as sealing rings of the valve seat.
Plug valves and ball valves are quick-opening valves with small resistance and large flow. However, its sealing surface is easy to wear, the switching force is large, and it is easy to jam, which is not suitable for high temperature and high pressure.
The specifications of cocks and ball valves are generally 15 mm (1/2 inches) ~ 50 mm (2 inches). The cock is used to switch the medium in the pipeline and can also be used as a throttle valve; The ball valve is only used to open and close the pipeline medium, and should not be used as a throttle valve to avoid the valve being washed away by the medium for a long time and losing its sealing performance.
4. Check valve (check valve)
Check valve is also called non-return valve, commonly known as single-flow valve, which can automatically open according to the pressure difference before and after the valve, and its function is to automatically control the flow direction of liquid, so that it can flow in one direction and prevent it from flowing backwards. Non-return valves are mostly used in water supply pipelines, and they have strict directionality when installed, and shall not be installed backwards.
Elevator check valve. The upper part of the valve core is provided with a guide rod, and the guide rod and the valve core can freely rise and fall along the guide sleeve on the valve cover. When the fluid flows from left to right, the valve core is pressed open. When the fluid flows in the opposite direction, the valve core descends to the valve seat and the passage is cut off.
Rocker check valve, also known as swing check valve, has the same principle as lift check valve.
The above two check valves are only installed on horizontal pipes.
Spring check valve, which is the development of lifting type.
Ordinary lifting check valves can only be installed on horizontal pipelines, while spring lifting check valves are not limited by direction. Can be used for horizontal pipes, vertical pipes and pipes with a certain angle.
Spring lift check valve. The size of the valve is 15 mm (12 inch) ~ 50 mm (2 inch).
Bottom valve. The one-way valve specially installed at the water inlet of the water pump suction pipe is commonly known as "bottom hole vara" and "shower head".
300X slow-closing check valve is an intelligent valve installed at the outlet of water pump in high-rise building water supply system and other water supply systems, which is used to prevent medium backflow, water hammer and water hammer. The valve has three functions: electric valve, check valve and water hammer eliminator, which can effectively improve the safety and reliability of water supply system. The technical principles of slow start, fast shut-off and slow shut-off to eliminate water hammer are integrated to prevent water hammer from occurring when the pump is started and stopped. Only by operating the on-off button of the water pump motor, the valve can be automatically opened and closed according to the operation law of the water pump, with large flow and small pressure loss. Application and performance specification of silencing check valve for valves below 600 caliber: This valve is used in industrial pipelines as a device to prevent medium from flowing backwards.
5, straight valve and right-angle valve
Straight valve is a special valve for radiator, which can be used at the entrance of steam heating radiator and the entrance and exit of water heating heater. The inlet and outlet of the right-angle valve form a 90-degree right angle. The right-angle valve used in heating system, commonly known as the eight-character valve, is specially used on radiators, the steam inlet for heat dissipation in steam heating, and the inlet and outlet of radiators in water heating to adjust steam or water quantity.
6. Pressure reducing valve
The pressure reducing valve is used to reduce the medium pressure in the pipeline and make the medium pressure meet the production needs. Commonly used pressure reducing valves are piston type, bellows type, tympanic membrane type and spring type.
The pressure reducing valve should be installed vertically on the horizontal pipeline, and the valve cover should be vertical to the horizontal pipeline. Pay attention to the arrow direction of the valve body during installation. Valves should be installed on both sides of the pressure reducing valve. High and low pressure pipelines are equipped with pressure gauges, and low pressure systems are also equipped with safety valves. The purpose of these devices is to adjust and control the pressure conveniently and reliably, which is particularly important to ensure the safe operation of the low-pressure system.
In the above article, Bian Xiao introduced the main uses of valves and the characteristics of some common valves. It is very meaningful to know some common valve types and their characteristics, so that everyone can get more convenience in life. When there is a need to buy valves, they can also replace them and finish things faster. The valve knowledge listed above is basically practical, so you can refer to it more.
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