There are so many types of valves – how much do you know about their characteristics and differences?

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This post was last edited by yinkuilin6868 on 2015-11-16 at 22:28. With so many types of valves, how much do you know about their characteristics and differences? Differences between various valves. 1. In what situations are gate valves, globe valves, and butterfly valves suitable for use? These three types of valves, ranked in order of ease of operation: globe valve, gate valve, butterfly valve ； Ranked by resistance level: globe valve, butterfly valve, gate valve ； Arranged in order of tight closure: globe valve, butterfly valve, gate valve ； Sorted by price: globe valve, butterfly valve, gate valve ； (Except for special butterfly valves) These three types of valves all fall under the category of actuated valves. Based on the aforementioned characteristics, it is evident that globe valves are primarily used for opening/closing and flow regulation in small-diameter pipes (branch pipes) or at the ends of pipelines ； Butterfly valves are used for opening and closing main and branch pipes as well as for flow regulation ； Gate valves are used to open and close main pipes, and are generally not used for flow control. 2. What are the different types of balance valves? In what situations are each suitable? There are several types of balancing valves. The first one developed was the static balancing valve, which allows for precise manual adjustment. It can be connected to instruments to measure resistance and convert it into flow rate. This is a valve whose local resistance coefficient can be accurately adjusted. It is usually installed on the main pipe; those with higher requirements can also be installed at branch pipes or at the equipment inlet. The drawback is that it can only balance the system resistance at the rated flow rate; when an electric valve is installed at the end to change the resistance, the hydraulic balance is affected. Dynamic balance valves, which were developed in the 1990s, are used to maintain a constant flow rate even when the system pressure changes; in other words, the flow rate does not change as the system pressure varies, which is why they are called dynamic balance valves. Its application scenarios are clear: it can only be used in systems with a constant water flow rate, and it cannot be used in conjunction with electric valves. These two types of domestic valves were originally developed by the China Air Conditioning Research Institute. The FLOWCON dynamic balance electric control valve produced in Denmark is a next-generation product that combines an electric valve with dynamic balance; when the electric control valve adjusts the flow rate, the dynamic balance system adjusts the preset flow rate accordingly. For example, when the electric control valve regulates the flow rate to 50%, the valve can maintain a constant flow at that 50% level. Currently, there’s only this one company in the world that has this product. It is used in the location where an electric valve was originally installed in the air-conditioning terminal, and other hydraulic balancing measures for the main pipes and branch pipes (including equal-length pipes) can be eliminated. A brief introduction cannot fully explain the differences between various valves; below, Xiao Qi provides a detailed summary of the origins, characteristics, and types of different valves. Only by understanding the characteristics of each type of valve can one more clearly distinguish between them. Butterfly valve: The disc of a butterfly valve is mounted in the diameter direction of the pipe. Within the cylindrical passage of the butterfly valve body, the disc-shaped butterfly plate rotates around its axis, with an angle of rotation ranging from 0° to 90°; when it reaches 90°, the valve is in its fully open position. Butterfly valves have a simple structure, small size, and light weight; they consist of only a few parts. Moreover, it can be quickly opened and closed by just a 90° rotation, making it easy to operate; at the same time, this valve boasts excellent fluid control properties. When the butterfly valve is in its fully open position, the thickness of the butterfly disc is the only resistance to the flow of the medium through the valve body; as a result, the pressure drop across this valve is very small, giving it excellent flow control properties. Butterfly valves come in two types of sealing: elastic sealing and metallic sealing. Elastic-sealing valves, where the sealing ring can be embedded in the valve body or attached around the butterfly disc. Valves with metal seals generally have a longer lifespan than those with elastic seals, but it is difficult to achieve a perfect seal. Metal seals can withstand higher operating temperatures, while elastic seals have the drawback of being limited by temperature. If a butterfly valve is required for flow control, the key is to correctly select the size and type of the valve. The structural principle of butterfly valves makes them particularly suitable for manufacturing large-diameter valves. Butterfly valves are widely used not only in general industries such as petroleum, gas, chemicals, and water treatment, but also in the cooling water systems of thermal power plants. The commonly used butterfly valves are wafer-type butterfly valves and flanged butterfly valves. In a wafer-type butterfly valve, the valve is connected between the flanges of two pipes using double-ended bolts. In a flanged butterfly valve, the valve itself has flanges; these flanges at both ends of the valve are then bolted to the pipe flanges. The strength performance of a valve refers to its ability to withstand the pressure of the medium. Valves are mechanical components that are subjected to internal pressure; therefore, they must possess sufficient strength and stiffness to ensure they do not crack or deform over long periods of use. Ball valve: The ball valve evolved from the plug valve. It has the same 90-degree rotational lifting action; the difference is that the plug is a sphere with a circular hole or passage running through its axis. The ratio between the sphere and the opening should be such that when the sphere rotates 90 degrees, the entire area at the inlet and outlet should be covered by the sphere, thereby blocking the flow. A ball valve can be closed tightly with just a 90-degree rotation and a very small torque. The completely equal inner chamber of the valve provides a flow path with very low resistance and a direct route for the medium. Ball valves are generally considered most suitable for direct on/off use; however, recent developments have led to the design of ball valves that can also be used for throttling and flow control. The main characteristics of ball valves are their compact structure, ease of operation and maintenance. They are suitable for general working media such as water, solvents, acids, and natural gas. Additionally, they can also be used with media under harsh operating conditions, such as oxygen, hydrogen peroxide, methane, and ethylene. The body of a ball valve can be integral or assembled. For globe valves, the axis of the valve stem is perpendicular to the sealing surface of the valve seat. The valve stem has a relatively short opening or closing stroke, and it provides a very reliable shut-off action, which makes this type of valve highly suitable for shutting off, regulating, or throttling fluids. Once the valve disc of a globe valve is in the open position, there is no longer any contact between its seat and the sealing surface of the valve disc, resulting in a very reliable shut-off action; this makes such valves highly suitable for shutting off, regulating, or throttling fluids. Once a globe valve is in the open position, there is no longer any contact between its seat and the sealing surface of the disc. As a result, mechanical wear on its sealing surfaces is minimal. Since it’s relatively easy to repair or replace the sealing elements of most globe valves without having to remove the entire valve from the pipeline, this makes them particularly suitable for applications where the valve is welded directly to the pipeline. The flow direction of the medium changes as it passes through such valves; therefore, the flow resistance of globe valves is higher than that of other valves. The commonly used globe valves include the following: (1) Angle-type globe valve ； In angular stop valves, the fluid only needs to change direction once, resulting in a lower pressure drop across the valve compared to stop valves with conventional designs. (2) DC type stop valve ； In straight-through or Y-type globe valves, the flow channel of the valve body forms an angle with the main flow path; as a result, the degree of disruption to the flow pattern is less compared to conventional globe valves, and consequently the pressure loss across the valve is also lower. (3) Plunger-type globe valve: This type of globe valve is a variation of the conventional globe valve. In this valve, the valve disc and seat are typically designed based on the plunger principle. The valve disc is polished to form a plunger that connects with the valve stem, and sealing is achieved through two elastic sealing rings fitted over the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings surrounding the plunger are pressed in place by the load applied to the valve cover by the valve cover nut. The elastic sealing ring can be replaced and is made from a variety of materials. This valve is primarily used for opening or closing, but it also features a special type of plunger or special rings that allow it to be used for regulating flow. Gate valve: A gate valve is used to shut off the flow of a medium; when it is fully open, the flow path is completely unobstructed, resulting in the lowest pressure loss for the medium flowing through it. Gate valves are typically suitable for applications where frequent opening and closing are not required, and where the gate plate needs to remain fully open or fully closed. Not suitable for use as a regulator or throttle. For high-speed flowing media, partial opening of the gate plate can cause vibration in the gate, and this vibration may damage the sealing surfaces of the gate plate and the valve seat; moreover, throttling exposes the gate plate to erosion by the medium. In terms of structural form, the main difference lies in the type of sealing element used. Based on the design of the sealing element, gate valves are often classified into several different types, such as wedge gate valves, parallel gate valves, parallel double-plate gate valves, and wedge double-plate gate valves. The most commonly used types are wedge gate valves and parallel gate valves. The function of this type of valve is to allow the medium to flow in only one direction and to prevent flow in the opposite direction. Typically, such valves operate automatically; the valve disc opens under the pressure of fluid flowing in one direction ； When the fluid flows in the opposite direction, the fluid pressure together with the weight of the valve disc causes the valve disc to act on the valve seat, thereby stopping the flow. Check valves belong to this type of valve; they include swing check valves and lift check valves. The swing check valve has a hinge mechanism, and a door-like disc that freely rests on the inclined valve seat surface. To ensure that the valve disc always reaches the appropriate position on the valve seat surface, it is designed with a hinge mechanism, allowing sufficient rotation space for the valve disc and enabling it to make true, full contact with the valve seat. The valve flap can be made entirely of metal, or leather, rubber can be inlaid on the metal, or a synthetic covering can be used, depending on the required performance characteristics. When a swing check valve is fully open, the fluid pressure encounters little resistance; therefore, the pressure drop across the valve is relatively small. The disc seat of the lift check valve rests on the valve body’s seat sealing surface. Apart from the fact that the valve disc can move up and down freely, all other aspects of this valve are similar to those of a globe valve. Fluid pressure causes the valve disc to lift off from the seat sealing surface; conversely, backflow of the medium causes the disc to return to the seat, thereby stopping the flow. Depending on the operating conditions, the valve disc can be of a fully metallic structure, or it can consist of a frame with rubber gaskets or rings embedded in it. Like globe valves, the flow passage through lift check valves is also narrow; as a result, the pressure drop across lift check valves is greater than that across swing check valves. Moreover, the flow rate of swing check valves is hardly restricted. In the production process, in order to ensure that parameters such as the pressure and flow rate of the medium meet the requirements of the manufacturing process, regulating mechanisms must be installed to adjust these parameters. The main working principle of the regulating mechanism is to adjust the aforementioned parameters by changing the flow area between the valve disc and the valve seat. Valves of this type are collectively referred to as control valves. Those that are driven by the power of the medium itself are known as self-acting control valves, such as pressure reducing valves and pressure stabilizing valves. Those that are driven by external power sources (such as electricity, compressed air, or hydraulic power) are called externally acting control valves, such as electric control valves, pneumatic control valves, and hydraulic control valves. Electrically driven valves are valves that use electric power as the driving mechanism; this type of driving device is commonly referred to as a valve actuator. The characteristics of valve actuators are as follows: 1) They can open and close quickly, thereby **reducing the time required to operate the valve ； 2) It can **reduce the labor intensity of operators; it is particularly suitable for high-pressure, large-diameter valves** ； 3) Suitable for installation in locations where manual operation is not possible or difficult; it facilitates remote control, and there are no restrictions on the installation height ； 4) Facilitates the automation of the entire system ； 5) Power sources are easier to obtain than gas and liquid sources, and the installation and maintenance of their wires are also much simpler than those of compressed air and hydraulic pipelines. The disadvantages of electric valve actuators are their complex structure; they are even more difficult to use in humid environments. When used with explosive media, explosion-proof measures must be taken. Valve actuators can be divided into two main categories, Z-type and Q-type, depending on the type of valve they drive. The output shaft of the Z-type valve actuator can rotate many times, making it suitable for driving gate valves, globe valves, diaphragm valves, etc ； The output shaft of the electric actuator for Q-type valves can only rotate 90 degrees. It is suitable for driving plug valves, ball valves, butterfly valves, etc. Based on their protection type, they include standard type, flameproof type (denoted by B), heat-resistant type (denoted by R), and three-in-one type (i.e., for outdoor use, corrosion resistance, and flameproofing, denoted by S). A valve actuator generally consists of a transmission mechanism (reducer), an electric motor, a travel control mechanism, a torque limiting mechanism, a manual-electric switching mechanism, and an opening degree indicator. Pneumatic and hydraulic valves: Pneumatic butterfly valves, hydraulic valves. Pneumatic and hydraulic valves use air, water, or oil under certain pressure as a power source, with the movement of cylinders (or hydraulic cylinders) and pistons being used to operate the valves. Generally, the air pressure in pneumatic systems is less than 0.8 MPa, while the water or oil pressure in hydraulic systems ranges from 2.5 MPa to 25 MPa. or diaphragm valve ； Rotary gas and liquid actuation devices are used to drive ball valves, butterfly valves, or plug valves. Hydraulic actuators have high driving force and are suitable for driving large-diameter valves. When used to drive plug valves, ball valves, and butterfly valves, the reciprocating motion of the piston must be converted into rotational motion. In addition to being driven by pistons in cylinders or hydraulic cylinders, there are also those driven by pneumatic diaphragms; due to their limited stroke and driving force, they are mainly used in control valves. Manual valve: A manual valve is a valve that uses the most basic type of actuation. It includes two types: direct drive using a handwheel, handle, or wrench, and drive through a transmission mechanism. When the starting torque of the valve is high, it can be driven via gear or worm gear transmission in order to eliminate this requirement. Gear transmission is divided into straight cylindrical gear transmission and bevel gear transmission. Gear drives offer a low reduction ratio and are suitable for gate valves and globe valves, while worm gear drives provide a higher reduction ratio and are suitable for plug valves, ball valves, and butterfly valves. 1 Gate valve: A gate valve is also known as a gate cock. It is characterized by its high level of sealing performance and is commonly used in water supply pipes and hot water heating systems. Since the gate does not effectively prevent foreign objects from passing through once it is opened, it is used as a drain valve in heating systems as well as in small boilers (such as vertical tube boilers). This type of valve is generally not used in steam pipelines, as at high pressures, gate valves find it difficult to open due to the pressure acting on one side only. Gate valves are suitable for operating in the fully open or fully closed position, and are appropriate for regulating flow. If the gate plate operates for an extended period in a semi-open state, its sealing surface will become less tight due to erosion by the medium. 2 Stop valves and throttle valves – Insulated stop valves. In the past, stop valves and throttle valves were collectively referred to as ball valves. Although stop valves are used to shut off steam and water circuits, while throttle valves are primarily used to regulate flow rate, it is difficult to distinguish them based on their appearance; the only difference lies in the valve core. The end of the valve stem in a globe valve is flat, whereas that of a throttle valve stem is conical. Globe valves with copper cores can be used in both steam and water pipelines. Hot-stop valves (commonly known as diaphragm valves) that have a diaphragm made of rubber or plastic installed on the valve core are used only in water or low-temperature hot water pipelines; otherwise, the rubber or plastic will deteriorate and lose their sealing properties. 3. Plug valves and ball valves: Plug valves, also known as stopcocks, are commonly referred to as rotary valves. Small plug valves were formerly called cocks; they are types of quick-opening valves. Depending on their flow distribution, they come in straight-through, three-way, four-way, and other variants. The stem of the plug is integrated with the valve core, which is in the shape of a frustum; a rectangular through-hole is provided on it, while smaller plugs have circular through-holes. When the groove on the top of the valve stem or the handle is parallel to the inlet and outlet directions of the plug, the valve is fully open; when it is perpendicular, the valve is fully closed. A ball valve is actually a variant of a plug; like a plug, it operates by changing the angle of the valve core to open the valve. The valve element of a ball valve is a sphere, on which there is a cylindrical hole; fluroplastic thermal rings are located on both sides of the sphere and serve as the valve seat – sealing rings. Both plug valves and ball valves are quick-opening valves with low resistance and high flow rates. However, its sealing surface wears easily, it requires significant force to operate, and it tends to get stuck; therefore, it is not suitable for high-temperature and high-pressure conditions. The specifications for cocks and ball valves are generally 15mm (1/2in) to 50mm (2in). A plug used to turn on and off the fluid in a pipeline can also function as a throttle valve ； Ball valves are used only for opening and closing pipeline media, and should not be used as throttling valves, to prevent the valve from losing its tightness due to prolonged exposure to the medium. 4 Check valve (non-return valve) A check valve, also known as a non-return valve or one-way valve, can open automatically based on the pressure difference before and after the valve. Its function is to automatically control the direction of fluid flow, allowing it to move in one direction while preventing it from flowing in the opposite direction. Check valves are commonly used in water supply pipelines, and they have a strict orientation requirement during installation – they must not be installed in the wrong direction. Elevator check valve. The upper part of the valve core of this type of valve is equipped with a guide rod; both the guide rod and the valve core can move up and down freely along the guide sleeve on the valve cover. When fluid flows from left to right, it pushes the valve core open, while when the fluid flows in the opposite direction, the valve core descends onto the valve seat, thereby shutting off the flow path. The swing check valve, also known as the rotary check valve, operates on a principle similar to that of the lift-type valve. The above two types of check valves are only installed on horizontal pipelines. Spring-type check valve, this type of valve is a development of the lift-type valve. Ordinary lift-type check valves can only be installed in horizontal pipes, while spring-lift type check valves are not restricted by direction. It is used in horizontal pipes, vertical pipes, and pipes at an angle. Spring-lift check valve. The sizes of these valves range from 15 mm (1/2 in) to 50 mm (2 in). Bottom valve. A one-way valve specifically installed at the inlet of the water pump’s suction pipe, commonly known as a \"well bottom valve\" or \"shower head\", etc. 5 Straight valves are a type of valve specifically designed for radiators; they can be used at the inlet of steam heating radiators, as well as at the outlets and inlets of water heating appliances. The inlet and outlet of a right-angle valve are at 90 degrees to each other. Right angle. The right-angle valves used in heating systems are commonly known as figure-8 valves. Designed specifically for radiators; it is used at the steam inlet for heat dissipation in steam heating systems, and can be used at the inlet and outlet of radiators in water heating systems to regulate the amount of steam or water. 6 Pressure relief valve: The pressure relief valve is used to reduce the pressure of the medium in the pipeline, so that the pressure meets the requirements of production. Commonly used pressure relief valves include piston-type, diaphragm-type, bellows-type, and spring-type valves. The pressure relief valve should be installed vertically on a horizontal pipe, with its valve cover perpendicular to the horizontal pipe; pay attention to the direction of the arrow on the valve body during installation. Valves should be installed on both sides of the pressure relief valve. Pressure gauges are installed on both the high-pressure and low-pressure pipes, while a safety valve is also required for the low-pressure system. The purpose of these devices is to regulate and control pressure in a convenient and reliable manner, which is particularly important to ensure the safe operation of low-pressure systems.