Analysis of Common Valves

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. Usually, 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, and 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 moves 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 off 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 metallic structure, or it can consist of a frame with rubber gaskets or rings embedded in it. Like gate valves, the flow passage through lift-type check valves is also narrow; as a result, the pressure drop across lift-type check valves is greater than that across swing-type check valves. Moreover, the flow rate of swing-type check valves is subject to few restrictions. During 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 *change the flow area between the valve disc and the valve seat, thereby achieving the adjustment of the aforementioned parameters. Valves that fall into this category are collectively referred to as control valves. Those driven by the energy of the medium itself are known as self-acting control valves, such as pressure reducing valves and pressure stabilizing valves. Those driven by external energy sources such as electricity, compressed air, or hydraulic power are called externally driven control valves, such as electric control valves, pneumatic control valves, and hydraulic control valves. Electrically driven valves are valves that use electric power as their 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 Z-type valve actuator can rotate many full turns, 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., outdoor, corrosion-resistant, and flameproof, 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 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 the pistons of 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. This post was last edited by Yan Dian Qing Tian on 2008-2-14 22:23.]

Manual valves: Manual valves are the most basic type of valve that operates using manual control. 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 transmissions are divided into straight cylindrical gear transmissions and bevel gear transmissions. 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 shut-off valves, these 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 inside 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 flows, while throttle valves are primarily used to regulate flow rates, it is difficult to distinguish them based on their appearance; the only difference lies in the valve core. The end of the valve plug in a stop valve is flat, while that of a throttle valve is conical. Globe valves with copper cores can be used in both steam and water pipelines. Thermal stop valves equipped with a rubber gasket, rubber piece, or plastic element (commonly known as rubber gasket valves) are used only in water or low-temperature hot water pipelines; otherwise, the rubber, rubber piece, or plastic will deteriorate and lose their sealing properties. 3. Plug valves and ball valves: Plug valves are also known as straight-through stop valves; they are commonly referred to as rotary valves. Small plug valves were formerly called cock valves. 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 valve 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; just 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 throttling 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 reverse flow. 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; 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 bottom valve or shower head, 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 lower 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, membrane-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 conveniently regulate and control pressure, which is particularly important to ensure the safe operation of low-pressure systems. This post was last edited by Yan Dian Qing Tian on 2008-2-14 22:24.]

It’s very basic :) stuff! Thank you for sharing, building Stay!

I usually only have a general idea of these things; the original poster’s information is very detailed and useful! :D