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The opening and closing parts of stop valves and Globe Valves are plug shaped valve discs with flat or conical sealing surfaces. The valve discs move in a straight line along the center line of the valve seat. The movement form of the valve stem, (common name: non rising stem), also includes the lifting and rotating stem type. (common name: rising stem) globe valve refers to a valve whose closing member (valve flap) moves along the center line of the valve seat. According to this form of movement of the valve disc, the change in the valve seat opening is in direct proportion to the valve disc stroke. Due to the relatively short opening or closing stroke of the valve stem, as well as the very reliable cutoff function, and because the change in the valve seat opening is proportional to the stroke of the valve disc, this type of valve is very suitable for volume adjustment. Therefore, this type of shut-off valve is very suitable for cutting or regulating and saving.
brief introduction
The shut-off valve, also known as the shut-off valve (12 pieces), is a forced seal type valve. Therefore, when the valve is closed, pressure must be applied to the valve flap to force the sealing surface not to leak. When the medium enters the valve from below the valve flap, the resistance that needs to be overcome by the operating force is the friction between the valve stem and the 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 should be larger. Otherwise, the failure of the top bending of the valve stem will occur in the cast iron screw stop valve and the cast iron screw stop valve. There are three types of connection methods: flange connection, screw connection, and welding connection. After the appearance of a self sealing valve, the medium of the stop valve enters the valve chamber from above the valve disc. At this time, under the action of medium pressure, the force to close the valve is small, while the force to open the valve is large, and the diameter of the valve rod can be reduced accordingly. At the same time, under the action of media, this type of valve is also relatively tight. China's "three chemical" valves have stipulated that the direction of the stop valve should be from top to bottom. This valve should be installed horizontally.
When the stop valve is opened, the opening height of the valve flap is 25% to 30% of the nominal diameter. When the amount has reached a large amount, it indicates that the valve has reached the fully open position. Therefore, the fully open position of the stop valve should be determined by the stroke of the valve flap.
working principle
Stop valve, also known as cut-off valve, is one of the widely used valves. Its popularity is due to the small friction between sealing surfaces during opening and closing, its durability, small opening height, easy manufacturing, and convenient maintenance. It is not only suitable for medium and low pressure, but also suitable for high pressure.
The closing principle of a stop valve is to rely on the pressure of the valve stem to tightly fit the sealing surface of the valve flap and the valve seat, preventing the passage of media.
The stop valve only allows one-way movement of the medium, and has directionality during installation. The structural length of the stop valve is larger than that of the gate valve, and the body resistance is large. During long-term operation, the sealing reliability is not strong.
classification
According to channel direction
1) Straight-through stop valve
2) "Straight stop valve: In a straight or Y-shaped stop valve, the passage of the valve body forms an oblique line with the main passage, so that the degree of damage in the dynamic state is smaller than that of a conventional stop valve, and therefore the pressure loss through the valve is correspondingly smaller.".
3) Angle stop valve: In an angle stop valve, the body only needs to change direction once, so that the pressure drop through this valve is smaller than that of a conventional structure stop valve. American Standard Corrugated Pipe Stop Valve ZDAJ41W Stainless Steel Body
4) Plunger type stop valve: This type of stop valve is a variant of the conventional stop valve. In this valve, the disc and seat are usually designed based on the plunger principle. The valve disc is polished into a plunger and connected to the valve rod. The sealing is achieved by two elastic sealing rings sleeved on the plunger. The two elastic sealing rings are separated by a collar, and the sealing ring around the plunger is pressed firmly by the load applied to the bonnet by the bonnet nut. The elastic sealing ring can be replaced and can be made of various materials. The valve is mainly used for "opening" or "closing", but it is equipped with a special form of plunger or special collar, which can also be used for adjusting the amount.
Location of threads on the valve stem
1) Upper threaded valve stem stop valve: The thread of the stop valve stem is outside the valve body. The point is that the valve rod is not subject to medium erosion and is convenient for lubrication. This structure is more commonly used.
2) Lower thread valve stem globe valve: The thread of the globe valve stem is in the valve body. With this structure, the valve stem threads come into direct contact with the medium, are susceptible to erosion, and cannot be lubricated. This structure is used in places with small diameters and low temperatures.
There are many domestic manufacturers producing globe valves, and most of the connection sizes are not uniform. It is mainly divided into the following categories:
1) General category based on JB/T2203-1999 Structural Length of Stop Valves. Currently, most domestic stop valve manufacturers are designed and produced in accordance with this standard. However, this standard is not perfect and has incomplete specifications. The large nominal diameter of single gate globe valves is DN1200, and the large nominal diameter of double gate globe valves is DN1500. According to the specifications and available information of the stop valve produced by the manufacturer, the nominal diameter of the angle stop valve is currently DN15, while the nominal diameter of the Z-type through stop valve is DN2000. According to research, the connection sizes of various manufacturers are not uniform,. In order to have a unified standard and allow users to interchange the same specification during selection and installation, it is recommended that China General Machinery Research Institute revise JB/T2203-1999 "Structural Length of Stop Valves". It is recommended that the design institute and users select according to standards, and the manufacturer of stop valves design and manufacture according to standards.
According to the purpose
The fluorine lined stop valve is applicable to various concentrations of aqua regia, sulfuric acid, hydrochloric acid, hydrofluoric acid, and various organic acids, strong acids, and strong oxidizing agents at temperatures ranging from - 50 to 150 ℃. It is also suitable for use on pipelines with various concentrations of strong alkali organic solvents, and other corrosive gases and liquid media
The national standard stop valve is a commonly used product in the stop valve series. The API American standard stop valve American standard stop valve implements ANSI and API standards. The sealing surfaces of the valve flap and valve seat are made of Stellite cobalt based cemented carbide with different hardness, which is reliable in sealing, high in hardness, abrasion resistance, high temperature resistance, corrosion resistance, good scratch resistance, and long in life.
Needle valve is a small diameter instrument valve that plays a role in opening and closing and precise quantity control in instrument measurement pipeline systems, mainly including power station instrument series, oilfield dedicated series, American standard series, etc.
Low-temperature globe valves generally refer to valves with operating temperatures below - 110 ℃, and are widely used in liquefied natural gas, liquefied petroleum gas, and other low-temperature industries. From 2008, globe valves with temperatures up to - 196 ℃ can be manufactured. All parts are subject to low-temperature pretreatment using liquid nitrogen, completely avoiding seal deformation and leakage during use.
Plunger valve, also known as plunger stop valve, has a radial sealing structure on its sealing surface. The two elastic sealing rings sleeved on the polished plunger compress the elastic sealing rings around the plunger to achieve sealing by applying a load on the valve cover through the connecting bolts between the valve body and the valve cover.
The insulated jacket globe valve adopts an insulated jacket design that utilizes external heat sources to circulate and heat outside the valve, effectively preventing temperature loss when the medium passes through the valve and ensuring the temperature of the medium.
Forged steel globe valves are designed and manufactured in accordance with API 602 standards, and are available in three bonnet design forms: bolted bonnet, welded bonnet, and pressure self-tightening sealing bonnet. Users can choose different forms according to their needs, providing three connection methods: RF flange, NPT thread, and SW welding.
The oxygen dedicated stop valve is made of high-quality silicon brass or stainless steel, with high mechanical strength, wear resistance, and good safety. Used on oxygen pipelines, it has explosion-proof and flame retardant properties, eliminating unsafe factors on oxygen pipelines, and is widely used in pipe networks of oxygen engineering such as steel, metallurgy, petrochemical, and chemical engineering. In addition to the functions of ordinary valves, it also has its own characteristics. Strict oil prohibition measures are adopted during manufacturing, and all parts are strictly degreased before installation.
The corrugated pipe stop valve is designed with a shaped stainless steel corrugated pipe. The corrugated pipe has been subjected to 10000 reciprocating tests without failure, with reliable sealing performance. It is suitable for industries and mines with flammable, explosive, toxic and harmful media, and can effectively prevent valve leakage.
Product Comparison
Comparison between bellows stop valve and ordinary stop valve
1. Dual sealing design (bellows+packing) If the bellows fails, the valve stem packing will also avoid leakage and meet sealing standards.
2. No physical loss, reduced energy loss, and improved plant equipment safety.
3. Long service life, reduced maintenance times, and reduced operating costs.
4. Robust and durable bellows seal design ensures zero leakage of the valve stem, providing maintenance free conditions.
5. The gas medium valve seat adopts PTFE soft sealing material to improve the sealing performance of the valve.
6. The valve seat with high temperature resistance ≤ 425 ℃ adopts a conical hard seal. Achieve airtight performance with zero leakage.
As labor costs continue to rise, reducing labor is the hope of more and more enterprises. With such bellows globe valves, workers can easily switch on and off products with long service life and sealing performance, there is reason to believe that its prospects will become increasingly broad.
Features of electric stop valves
1. The body resistance is small, and its resistance coefficient is equal to that of pipe sections of the same length.
2. Simple structure, small size, and light weight. Electric stop valve
3. Tight and reliable, the sealing surface material of the gate valve is widely used in plastic, with good sealing performance, and has also been widely used in vacuum systems.
4. Convenient operation, quick opening and closing, with only 90 ° rotation from full opening to full closing, facilitating remote control.
5. Convenient maintenance, simple gate valve structure, generally movable sealing rings, and convenient disassembly and replacement.
6. When fully open or fully closed, the sealing surfaces of the ball and valve seat are isolated from the medium, and when the medium passes through, it will not cause erosion of the valve sealing surface.
7. Wide range of applications, ranging from small to a few millimeters in diameter to several meters in diameter, from high vacuum to high pressure applications.
