How many types of valves are there? Have you seen them all?

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How many types of valves are there? Have you seen them all? Valves are mechanical devices used to control the flow rate, direction, pressure, temperature, and other parameters of fluid media, and they are very important components in pipeline systems. Today, Xiao Qi will tell you about the different categories of valves. Come and take a look! Friendly reminder: Click on the image to learn more about valve knowledge~ Below is a classification of valves compiled by Xiao Qi; there’s probably nothing more comprehensive than this Classified by pressure: Vacuum valves: PN below standard atmospheric pressure; Low-pressure valves: PN ≤ 1.6 MPa; Medium-pressure valves: PN = 2.5–6.4 MPa; High-pressure valves: PN = 10–80 MPa; Ultra-high-pressure valves: PN ≥ 100 MPa. PN refers to the nominal pressure, which is the maximum operating pressure allowed for the valve at a standard temperature. Classified by operating temperature of the medium: High-temperature valves: t > 450 ℃; Medium-temperature valves: 120 ℃ < t ≤ 450 ℃; Normal-temperature valves: -30 ℃ ≤ t ≤ 120 ℃; Low-temperature valves: t < -30 ℃. Classified by nominal diameter: Small-diameter valves: DN < 40 mm; Medium-diameter valves: DN = 40 – 300 mm; Large-diameter valves: DN = 350 – 1200 mm; Extra-large-diameter valves: DN ≥ 1400 mm. Classified by actuation method: Manual valves: Operated by human effort using handwheels, handles, levers, or sprockets; gearboxes or other reduction devices are used when a larger torque is required. Electric valves: driven by electric motors, electromagnets, or other electrical devices. Hydraulic valves: Operated by a liquid (such as water, oil, or other liquid media). Pneumatic valves: driven by compressed air. Classified by purpose, gate valves are valves in which the closing element (gate) moves vertically along the center line of the channel. It is mainly used for cutting off flow in pipes, and also has a certain capacity to regulate flow rate. Feature: Low fluid resistance. The opening and closing torque is low. The direction of medium flow is not restricted. The structural length is short. It has good sealing performance. The sealing surface is prone to damage. Long opening and closing time, large height. There are many parts with complex structures, making manufacturing and maintenance difficult. Classified by valve disc structure: Stem gate valves – the valve stem threads and nuts do not come into contact with the medium, so they are not affected by the corrosive effects of the medium’s temperature. The degree of opening is easily visible, which is why they are widely used. Dark rod gate valve: The screw threads and nut are in contact with the medium, and are affected by the temperature and corrosiveness of the medium; however, the height of the valve is relatively small. Dark stem gate valves are suitable for non-corrosive media and applications with harsh external environmental conditions. Classified by whether the diameters of the channels inside the valve body are identical: Reduced-bore gate valves: the diameter at the valve seat is smaller than that at the flange connection. Equal-diameter gate valve: The diameter at the valve seat is the same as that at the flange connection. Path contraction allows the dimensions of valve components to be reduced, thereby decreasing the force required to open and close them; it also expands the versatility of these components. However, after the passage narrows, the fluid resistance loss will increase. Thermostat valve: A thermostat valve is also known as a steam trap, vapor-water valve, desiccant, return box, or return valve. Its function is to automatically discharge the continuously generated condensed water, while preventing steam from escaping. For a steam trap to function as a vapor barrier and water drain, it must be able to “identify” steam from condensed water. “The detection of steam and condensate is based on three principles: density difference, temperature difference, and phase change. A ball valve uses a sphere with an opening in the middle as its valve element, and the rotation of this sphere is used to control the opening and closing of the valve. Ball valves can be straight-through, three-way, or four-way. Ball valves are primarily used on pipelines to shut off flow, distribute it, and change the direction of the fluid flow. Due to the use of rubber material in the ball valve seat, its operating temperature is limited. To deal with potential fire situations, many designers use auxiliary metal-to-metal seals. Ball valves are not suitable as throttle valves, but when partially open, they can be used to reduce the pressure entering or leaving a system. On production equipment, ball valves are commonly used as on/off valves for general purposes. Floating ball valve: Its ball is floating; under the pressure of the medium, the ball can move to a certain extent and press against the sealing ring at the outlet end, thereby ensuring sealing at that outlet. This ball valve features a simple structure and good sealing performance, but it experiences high pressure at the sealing area at the outlet end, as well as a relatively large operating torque. This structure is widely used in medium and low pressure ball valves. Fixed ball valve: In this type of ball valve, the ball is fixed and does not move under pressure. Rolling or sliding bearings are installed on the shafts that are integral to the ball, resulting in low operating torque; it is suitable for high-pressure and large-diameter valves. A globe valve is a type of valve in which the closing element (valve disc) moves along the center line of the valve seat, and it is primarily used for shutting off flow in pipelines. In threaded stem globe valves, the stem threads are located outside the medium; thus they are not exposed to corrosion by the medium and are also easier to lubricate. This design is quite commonly used. In a lower-threaded valve stem globe valve, the valve stem threads are in direct contact with the medium inside the valve body; as a result, they cannot be lubricated and are also subject to erosion by the medium. This design is used for valves with small diameters and for media at moderate temperatures. A check valve is a valve whose valve disc opens and closes automatically based on the flow of the medium itself; it allows the medium to flow in only one direction and prevents backflow of the medium. Lift check valve: The disc of this valve moves along the centerline of the valve seat opening. The disc is opened by the thrust of the fluid and closes due to gravity. Therefore, it can only be installed in horizontal pipelines. The valve body of a lift-type check valve is similar to that of a globe valve, so its flow resistance coefficient is also relatively high. Swing check valve: The disc of this type of valve rotates around a pin at the seat. The valve disc is generally of a monolithic structure; however, some large-diameter check valves (with a nominal diameter of 600 mm and above) use a multi-disc design. Safety valves classified by their loading mechanism: Lever-pendulum type safety valves – in these valves, a pendulum exerts force on the valve disc through a lever, and the load remains almost constant regardless of the opening degree. Due to the relatively large size of the lever part of this safety valve, which makes the entire valve bulky and results in a low reset pressure, it is less commonly used in engineering applications. Pilot-operated safety valve: It consists of a main valve and a pilot valve. Both the medium pressure and the spring pressure act on the main valve disc; when overpressure occurs, the secondary valve disc opens first, causing the main valve to open as well. It is mainly used in applications with large diameters and high pressures. Spring-loaded safety valve: Spring force acts on the valve disc, with the load varying depending on the opening height. Its advantages include a small size, light weight, high sensitivity, and no strict restrictions on the installation location; it is widely used in projects involving rapid oil and gas transportation. Classified by the opening height of the safety valve: Slightly opening safety valves: The opening height is 1/40–1/20 of the seat throat diameter, and they are usually designed to have a gradually changing opening height as pressure varies. It is mainly used in applications involving liquid media with low discharge volumes. Full-open safety valve: The opening height is equal to or greater than 1/4 of the valve throat diameter; it is usually designed to open rapidly (the valve disc suddenly lifts to reach the full-opening height at a certain moment of opening). It is mainly used in applications involving gas and steam media, as well as fluid media with large discharge volumes. Progressive or rapid-opening safety valves: The opening height is between slightly open and fully open. Classified by valve body structure: Fully enclosed type: During discharge, the medium does not leak outside but is entirely discharged through the exhaust pipe. Semi-enclosed type: During discharge, part of the medium is released through the discharge pipe, while the other part leaks out from the junction between the valve cover and the valve stem. Open type: During discharge, the medium is released directly above the valve disc, without passing through a discharge pipe. In a butterfly valve, the valve disc is a disk; by rotating the valve stem, the disc rotates 90 degrees within the valve seat, thereby enabling the opening and closing of the valve. It serves to shut off the flow in the pipeline. The flow rate can also be adjusted. Features: Easy and quick opening and closing, labor-saving, low fluid resistance, and suitable for frequent operation. It has a simple structure, is small in size, and light in weight. It can transport mud, with minimal liquid accumulation at the pipe outlet. A good seal can be achieved at low pressures. It has good adjustment performance. The range of operating pressure and temperature is small. The sealing performance is poor.