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1. In what applications are gate valves, globe valves, and butterfly valves suitable? These three types of valves are arranged in order of ease of operation: globe valve, gate valve, butterfly valve ； Ordered by resistance level: globe valves, butterfly valves, gate valves ； Arranged in order of tight shutoff: globe valve, butterfly valve, gate valve ； Sorted by price from low to high: globe valves, butterfly valves, gate valves ； (Except for special butterfly valves) These three types of valves all fall under the category of actuated valves. Given their 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 for opening and closing main pipelines; they are generally not used for flow regulation. 2. What are the various 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; for applications with higher requirements, it can also be installed on branch pipes or at equipment inlets. 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. The dynamic balance valves introduced in the 1990s are used to maintain a constant flow rate in situations where system pressure fluctuates; that is, the flow rate remains unchanged despite variations in system pressure. Hence, 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. Both of these domestically produced 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 adjusts the flow rate to 50%, the valve can maintain a constant flow rate at that 50% level. Currently, this is the only company in the world that has this product. It is used in place of the electric valve originally installed at the air conditioning terminal; other hydraulic balancing measures for the main and branch pipes (including equal-length piping) can then be eliminated. A brief introduction cannot fully explain the differences between various types of valves. Below, Xiao Qi provides a detailed summary of the origins, characteristics, and categories of different valves. Only by understanding the characteristics of each type of valve can one more clearly distinguish between them. Butterfly valve: The butterfly disc of a butterfly valve is mounted in the diameter direction of the pipeline. 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, are small in size and light in weight, consisting of only a few components. Moreover, it can be quickly opened and closed by just a 90° rotation, making operation simple; at the same time, this valve boasts excellent fluid control properties. When the butterfly valve is in the 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 characteristics. Butterfly valves come in two types of sealing: elastic sealing and metal 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 complete sealing. Metal seals can withstand higher operating temperatures, while elastic seals have the drawback of being limited by temperature. If a butterfly valve is to be used for flow control, the key is to select the correct size and type of 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. A wafer butterfly valve is connected between two pipe flanges using bolts, while a flanged butterfly valve has flanges on it, with the flanges at both ends of the valve being secured to the pipe flanges using bolts. 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 time. Ball valve: The ball valve evolved from the plug valve. It has the same 90-degree rotation lift action, but the difference is that the plug body is spherical, 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 cavity of the valve provides a flow path with very low resistance and a direct route for the medium. It is generally believed that ball valves are most suitable for direct on-off operation, but recent developments have designed them to also serve the purpose of throttling and controlling flow rates. The main advantages of ball valves are their compact structure, ease of operation and maintenance. They are suitable for use with common working media such as water, solvents, acids, and natural gas, as well as for media under harsh working conditions, such as oxygen, hydrogen peroxide, methane, and ethylene. The ball valve body can be integral or modular. Stop valve: The axis of the stem of a stop valve 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 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 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 these sealing surfaces is minimal. Moreover, since the seat and disc of most globe valves can be easily repaired or replaced without having to remove the entire valve from the pipeline, this makes them very suitable for situations where the valve is welded 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 globe valves, the fluid only needs to change direction once, resulting in a lower pressure drop across the valve compared to globe valves with conventional designs. (2) DC 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 variant of the conventional globe valve. In such valves, 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 by two elastic sealing rings fitted over the plunger. The two elastic sealing rings are separated by a collar, and the sealing rings around the plunger are pressed firmly 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. Depending 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. A swing check valve has a hinge mechanism, as well as a valve disc that resembles a door and rests freely on an 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 disc can be made entirely of metal, or leather, rubber, or synthetic covers can be embedded in metal, depending on the requirements of its performance. 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 of the lift-type check valve is seated on the seat sealing surface of the valve body. Apart from the valve disc, which can move up and down freely, this valve operates in a similar manner to a globe valve: fluid pressure lifts the valve disc away from the sealing surface of the valve seat, while backflow causes the valve disc to return to the valve seat, thereby stopping the flow. Depending on the operating conditions, the valve disc can be of a fully metal 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 less restricted. In production processes, in order to ensure that parameters such as pressure and flow rate of the medium meet the requirements of the 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 a 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 workload on operators, and is particularly suitable for high-pressure, large-diameter valves** ； 3) Suitable for installation in locations where manual operation is not possible or where access is difficult; it enables easy remote control, and there are no restrictions on the installation height ； 4) Conducive to 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 disadvantage of valve actuators is their complex structure; they are more difficult to use in humid environments, and explosion-proof measures are required when used with explosive media. 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 electric actuator for Z-type valves 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. According to their protection type, there are ordinary types, flame-retardant types (denoted by B), heat-resistant types (denoted by R), and three-in-one types (i.e., for outdoor use, corrosion resistance, and flame retention, denoted by S). A valve actuator generally consists of a transmission mechanism (reducer), an electric motor, a travel control mechanism, a torque limitation mechanism, a manual-electric switching mechanism, and an opening degree indicator. Pneumatic and 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 valves: Also known as gate cocks, gate valves are characterized by their high level of sealing performance. They are commonly used in water supply pipelines and hot water heating systems. Since it is not feasible to prevent foreign objects from getting in when the gate is opened, they are used as drain valves 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. Globe valves and throttle valves: These two types of valves were formerly 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 globe valves (commonly known as rubber-seated valves), which have a rubber, elastic material, or plastic seat attached to the valve core, are used only in water or low-temperature hot water pipelines; otherwise, the rubber, elastic material, or plastic will deteriorate and lose their sealing properties. 3. Plug valves and ball valves: Plug valves are also known as stop valves; they are commonly referred to as rotary valves. Small plug valves were formerly called cocks. They are types of quick-opening valves, and depending on their flow distribution patterns, they can be of straight-through, three-way, or four-way types. 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 the through-hole in smaller plugs is circular. 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; fluted rings made of fluoroplastic are located on both sides of the sphere and serve as the valve seats – seals. 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 plugs and ball valves are generally 15mm (1/2in) to 50mm (2in). A plug used to open and close the medium in a pipeline can also serve as a throttle valve ； Ball valves are used only for opening and closing pipeline media, and should not be used as throttle valves, to prevent the valve from losing its tightness due to prolonged exposure to the medium. 4. Check valve: Also known as a non-return valve, it is commonly referred to as a one-way valve. It opens automatically based on the pressure difference before and after the valve, and its function is to automatically control the direction of fluid flow, allowing it to move in one direction while preventing backflow. 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 check 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 \"faucet\", etc. 5. Straight valves and right-angled valves: 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 ports of radiators in water heating systems, serving to regulate the amount of steam or water. 6. Pressure reducing valve: The pressure reducing 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.