Valve types and descriptions

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1. Gate valve: Also known as gate plate valve, it is a widely used type of valve. Its principle of closure relies on the highly smooth and even sealing surfaces of the gate and the valve seat, which fit together to prevent the flow of the medium; the sealing effect is enhanced by the use of a top die, springs, or the shape of the gate itself. It mainly serves to cut off flow in the pipeline. Its advantages are: low fluid resistance, easy operation for opening and closing, the ability to be used when the medium flows in both directions without any directionality required; the sealing surface is not prone to erosion when fully open; and it has a short structural length, making it suitable not only for small valves but also for large ones. Gate valves are classified into two types based on the valve stem thread: one is the exposed stem type, and the other is the concealed stem type. Based on the structure of the gate plate, they are also divided into two categories: one is parallel, and the other is modular. 2. Globe Valve: The globe valve, also known as a stop valve, is one of the most widely used types of valves. It is popular because it experiences low friction between its sealing surfaces during operation, is durable, requires little clearance for full opening, is easy to manufacture, and convenient to maintain. It can be used not only in medium and low pressure applications but also in high pressure applications. Its closing principle is to rely on the pressure of the valve stem to bring the sealing surface of the valve disc into close contact with the sealing surface of the valve seat, thereby preventing the flow of the medium. A stop valve allows fluid to flow in only one direction, and it has a specific orientation when installed. Its structural length is greater than that of gate valves, and it also presents high fluid resistance; moreover, its sealing reliability is not strong when in long-term operation. Stop valves are divided into three categories: straight-through, right-angle, and straight-flow inclined stop valves. 3. Butterfly valve: Also known as a butterfly valve, as the name suggests, its key component resembles a butterfly facing the wind and rotating freely. The disc of a butterfly valve is circular in shape, and it rotates around an axis located within the valve seat; the degree of rotation determines the degree to which the valve is open or closed. Butterfly valves are lightweight, use less material compared to other valves, have a simple structure, can be opened and closed quickly, are suitable for both cutting off flow and throttling, present low fluid resistance, and require less effort to operate. Butterfly valves can be made with very large diameters. Where butterfly valves can be used, gate valves should preferably not be employed, as butterfly valves are more economical and offer better control capabilities. Currently, butterfly valves are widely used in hot water pipelines. 4. Ball valve: The working principle of a ball valve is to use the rotation of the valve stem to open or close the valve. Ball valves are easy to operate, compact in size, and can be manufactured in large diameters. They offer reliable sealing, a simple structure, and are easy to maintain. The sealing surface and the ball surface remain in a closed state, making them resistant to erosion by the medium flowing through them; as a result, they are widely used in various industries. Ball valves are divided into two categories: floating ball type and fixed ball type. 5. Plug valve: A plug valve operates by the rotation of the plug around the central axis of the valve body, thereby enabling opening and closing. Its function is to cut off, divide the flow, and change the direction of the medium. It has a simple structure, small external dimensions; only a 90-degree rotation is required for operation, and the fluid resistance is low. Its disadvantages are that the switch is difficult to operate, the sealing surface wears out easily, it tends to get stuck at high temperatures, and it is not suitable for regulating flow. A plug valve, also known as a stopcock, cock, or rotary valve. There are many types of them, including straight-through, three-way, and four-way types. 6. Check valve: A check valve is a valve that opens and closes automatically thanks to the force of the fluid itself; its function is to prevent the medium from flowing in reverse. It has many names, such as check valve, one-way valve, and one-flow gate. They can be divided into two categories based on structure. (1) Lift type: The valve disc moves along the vertical center line of the valve body. There are two types of such check valves: one is horizontal, installed in horizontal pipes, and its shape is similar to that of a globe valve; the other is vertical, installed in vertical pipes. (2) Rotary type: The valve disc rotates around a pin outside the seat. These valves come in single-disc, double-disc, and multi-disc versions, but the principle remains the same. The suction bottom valve on the water pump’s suction pipe is a variant of a check valve; its structure is the same as that of the two types of check valves mentioned above, except that its lower end is open to allow water to enter. 7. Pressure relief valve: A pressure relief valve is an automatic valve that reduces the pressure of a fluid to a certain value; generally, the pressure behind the valve is less than 50% of the pressure before the valve. There are many types of pressure relief valves, mainly piston-type and spring-diaphragm-type. A piston-type pressure reducing valve is a valve that reduces pressure through the action of a piston. A spring-diaphragm type pressure relief valve relies on springs and a diaphragm to achieve pressure balance. 8. Drain valve. A drain 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. There are many types of pressure relief valves, including float-type, ball-type, bell-type float valve, pulse-type, thermodynamic type, and thermal expansion type. The commonly used types are buoy-type, bell float-type, and thermodynamic type. (1) Float-type steam trap: A float-type steam trap is mainly composed of components such as a valve, shaft, conduit, float, and housing. When the condensate in the equipment or pipes enters the steam trap driven by steam pressure, and its amount increases until it approaches filling the float, the weight of the float exceeds its buoyant force causing it to sink, which in turn opens the throttle valve. This allows the condensate water inside the cylinder to be discharged through conduits and valves under the effect of steam pressure. When the condensed water inside the float is nearly exhausted, the float rises due to its reduced weight, which causes the throttle valve to close, and condensed water begins to accumulate again inside the float. By operating in this periodic manner, it can automatically discharge condensed water while preventing steam from escaping. (2) Bell-type float steam trap The bell-type float steam trap is also known as the bucket-type steam trap; it is mainly composed of components such as a control valve, a bucket, a housing, and a filtering device. The bucket inside the steam trap is inverted and starts in a downward position, with the control valve open. When cold air and condensate in the equipment or pipes enter the drain valve driven by steam pressure, they are then discharged through the control valve. On the one hand, as steam along with a small amount of unexpelled air gradually fills the interior volume of the bucket, and condensate water keeps accumulating, the bucket rises due to the buoyancy generated, which causes the control valve to close and stops the discharge of condensate water. On the other hand, a small portion of the steam and air inside the bucket is discharged through the holes at the top of the bucket, while most of it cools down and turns into liquid, thereby gradually reducing the bucket’s buoyancy and causing it to descend. This in turn causes the control valve to open, and the condensed water is discharged. By operating in this periodic manner, it can automatically discharge condensed water while preventing steam from escaping. (3) Thermodynamic steam trap: When condensate from the equipment or pipes flows into the air-venting drain valve, the steam in the pressure reduction chamber condenses, resulting in a decrease in pressure. The force acting on the bottom of the valve disc is greater than that acting on its top, so the valve disc is lifted upward. Since condensed water has a higher viscosity and lower flow velocity than steam, it is difficult for negative pressure to be generated between the valve disc and the valve base. At the same time, condensed water cannot easily flow into the transformer chamber through the gap between the valve disc and the housing, thereby keeping the valve disc in an open position; the condensed water then flows out through the annular groove. When steam from the equipment or pipes flows into the steam trap, since steam has a lower viscosity and higher flow velocity than condensed water, a negative pressure is easily generated between the valve disc and the seat. At the same time, some of the steam enters the pressure-changing chamber, resulting in greater force acting on the upper side of the valve disc than on the lower side, which causes the valve disc to close rapidly. By operating in this periodic manner, it can automatically discharge condensate while preventing steam from escaping.