1. Butterfly valve is a kind of valve whose closure part (disc or butterfly plate) is a disc and rotates around the valve axis to open and close. It is mainly used for cutting off and throttling in the pipeline. The opening and closing part of butterfly valve is a disc-shaped butterfly plate, which rotates around its own axis in the valve body to achieve the purpose of opening and closing or regulating. Butterfly valves are usually less than 90 degrees open to close. Butterfly valves and butterfly rods have no self-locking ability. In order to locate the butterfly plate, worm gear reducer should be installed on the valve stem. The use of worm gear reducer can not only make butterfly plate have self-locking ability, make butterfly plate stop at any position, but also improve the operation performance of the valve. Industrial butterfly valves are characterized by high temperature resistance, high pressure range, large nominal diameter, carbon steel body and metal ring instead of rubber ring. Large high temperature butterfly valve is welded by steel plate, mainly used for flue gas duct and gas pipeline of high temperature medium.
2. The opening and closing parts of stop valve (Globe Valve) are plug-shaped discs. The sealing surface is flat or conical, and the disc moves in a straight line along the center line of the fluid. The movement of the valve stem is in the form of lifting rod (stem lifting, hand wheel not lifting), and lifting rotating rod (hand wheel and stem rotating lifting together, nuts set on the valve body). Globe valves are only suitable for full switching and full switching. Regulation and throttling are not allowed. Globe valve belongs to forced sealing valve, so when the valve closes, pressure must be exerted on the disc to force the sealing surface not to leak. When the medium enters valve 6 from below the disc, the resistance to be overcome by the operating force is the friction between the stem and packing and the thrust generated by the pressure of the medium. The force to close the valve is greater than the force to open the valve, so the diameter of the valve stem is larger, otherwise the failure of the top bending of the valve stem will occur. In recent years, since the emergence of self-sealed valves, the medium flow direction of globe valves has changed from above the disc to enter the valve chamber. Under the action of medium pressure, the force of closing the valve is small, while the force of opening the valve is large, and the diameter of the stem can be reduced accordingly. At the same time, under the action of medium, this form of valve is also tighter. Our country's valve "three-way feed" once stipulated that the flow direction of globe valve should be from top to bottom. When the globe valve is opened, when the opening height of the disc is 25%-30% of the nominal diameter, the flow rate reaches the maximum, indicating that the valve has reached the full open position. Therefore, the full open position of globe valve should be determined by the stroke of the disc.
Globe valves have the following advantages:
1. It is simple in structure and convenient in manufacture and maintenance.
2. Small working journey and short start-up and shut-down time.
3. Good sealing, small friction between sealing surfaces and long service life.
The disadvantages of globe valves are as follows:
1. Fluid resistance is high and the force required for opening and closing is large.
2. It is not suitable for medium with granules, high viscosity and easy coking.
3. The regulation performance is poor.
The types of globe valves can be divided into external threaded and internal threaded according to the position of stem threads. According to the flow direction of the medium, there are direct, direct and angular. Globe valves can be divided into packing sealing globe valves and bellows sealing globe valves.
Structural form of globe valve:
The structure forms of globe valve body are straight through, direct current and right angle. Straight-through structure is the most common structure, but its fluid resistance is the largest. DC fluid has less resistance and is mostly used for fluids with solid particles or high viscosity. The right angle valve body is usually forged, which is suitable for globe valves with smaller pass and higher pressure.
3. Ball valves are evolved from Cock valves. It has the same 90-degree rotation lifting action; the difference is that the cock is a sphere, with a circular through-hole or channel through its axis. The ratio of spherical surface to channel opening should be such that when the sphere rotates 90 degrees, all spherical surfaces should be present at the inlet and outlet to cut off the flow. Ball valves can be closed tightly with only 90 degrees of rotation and a small moment of rotation. Fully equal body chamber provides a direct flow path with little resistance to the medium. It is generally believed that ball valves are most suitable for direct opening and closing, but recent developments have designed ball valves to throttle and control flow. The main characteristics of the ball valve are compact structure, easy operation and maintenance. It is suitable for general working media such as water, solvent, acid and natural gas. It is also suitable for medium with poor working conditions, such as oxygen, hydrogen peroxide, methane and ethylene. Ball valve body can be integral or combined.
Working Principle and Realistic Function of Ball Valve
The working principle of the ball valve is to rely on the love of the rotary valve to make the valve unobstructed or blocked. Ball valve switch is light, small, can be made into a large caliber, reliable seal, simple structure, easy maintenance, sealing surface and sphere are often in closed state, not easy to be eroded by media, widely used in various industries.
Ball valve and cock valve belong to the same type of valve, only its closing part is a sphere, the sphere revolves around the center line of the valve body to open and close a valve.
Ball valves are mainly used in piping to cut off, distribute and change the flow direction of media. Ball valve is a new type of valve widely used in recent years. It has the following advantages:
1. Fluid resistance is small, and its resistance coefficient is equal to that of the same length of pipe.
2. It has simple structure, small volume and light weight.
3. Tight and reliable. At present, the sealing surface material of ball valves is widely used in plastics and has good sealing performance. It has also been widely used in vacuum systems.
4. Easy to operate, quick to open and close, from full to full switching as long as the rotation of 90 degrees, easy to control over long distances.
5. Maintenance is convenient, the ball valve has simple structure, the sealing ring is generally movable, and disassembly and replacement are more convenient.
6. When fully open or fully closed, the sealing surface of the sphere and seat is isolated from the medium. When the medium passes through, it will not cause the erosion of the sealing surface of the valve.
7. It can be used in a wide range of applications, ranging from small to several millimeters in diameter and from high vacuum to high pressure.