A selection principle, should use high temperature cut-off valve, high pressure tubing, or media devices. Fire power plants, nuclear power plants, petrochemical system of high temperature, high-pressure pipeline. 2, pipeline convection resistance strict requirements of the pipeline. Namely, the pressure loss is not the place to consider. 3, the choice of a small needle valve, instrument valves, sampling valves, pressure gauge valve. 4, flow regulation or pressure regulation, but less precision adjustment, and pipe diameter and relatively small, such as Nominal by ≤50mm the pipeline should be chosen. 5, the industrial production of small synthetic fertilizers and fertilizer should use large nominal PN160 PN320 nominal pressure PN 16MPa or 32MPa high-pressure or high angle globe valve throttle angle. 6. Bayer process alumina production workshop desilication, pipeline easy to coke, easy selection of the divided body, can place the seat, carbide seal pair of DC-DC type valve or throttle. 7, the urban construction of water supply, heating engineering, Nominal by smaller pipeline, the choice of cut-off, balancing valve or piston valve, such as Nominal by less than 150mm in the pipeline. The most obvious advantage is: open and closed process, because the valve body sealing surface on the friction ratio between the gate is small, so wearable. Seat height is generally open only 1/4 channel diameter, so much smaller than the gate. Usually in the valve body and valve sealing surface is only one, and thus the manufacturing process is better, ease of maintenance. Nominal or pressure level: PN1.0-16.0MPa, ANSI CLASS 150-900, JIS10-20K nominal diameter or diameter: DN10 ~ 500, NPS 1/2 ~ 36 "Connection: flange, welding, thread, etc. Temperature: -196 ℃ ~ 700 ℃ driving modes: manual, bevel gear, pneumatic, electric, hydraulic, gas-hydraulic, electro-hydraulic valve body material: WCB, ZG1Cr18Ni9Ti, ZG1Cr18Ni12Mo2Ti, CF8 (304), CF3 (304L ), CF8M (316), CF3M (316L), Ti. choice of different materials, can be separately applied to water, steam, oil, nitric acid, acetic acid, oxidizing medium, urea and other media. cryogenic globe valve works and stem and seat sealing surface perpendicular to the axis of the structure of the low temperature cut-off valve. stem to open or close the relatively short trip, and have very reliable cutting action, making this valve is suitable for medium cut or regulation and throttle use. Once the low temperature cut-off valve is turned on, its valve seat and valve sealing surface is no longer in contact, so it's less sealing surface mechanical wear, due to the valve seat and most of the valve is easier to repair or When the sealing element without replacing the entire valve to be removed from the pipeline, which for the valves and pipes welded into one case where it is applicable. medium flow direction through the valve when such a change, and therefore a higher cut-off valve flow resistance As at other valves used a cut-off valve) straight-off valve 2) angle type valve; the angle globe valve, the fluid simply by changing a direction, so that the valve by the pressure drop is smaller than the cut-off valve of conventional construction 3) DC-type valve; in DC-type or Y-shaped valve, the valve body of the flow channel and the main channel into a slash, the extent of damage to the state of this flow is smaller than the conventional cut-off valve, so the pressure loss through the valve is also corresponding smaller 4) plunger-type valve: This form of cut-off valve is a variant of the conventional cut-off valve in the valve, the valve and seat are usually designed based on the principle of the valve plunger into polished. plunger connected with the stem seal is set on the plunger two elastic seals to achieve. Two elastic rings separated by a collar, and the load applied to the valve cover by the bonnet nut seal around the plunger pressure prison elastic ring can be replaced, you can use a variety of materials, the valve is mainly used for the "on" or "off", but with a special form of plunger or special The collar can also be used to regulate the flow of low temperature cut-off valve is characterized by (1) a simple structure than the gate, manufacturing and maintenance are more convenient. (2) sealing surface easy to wear and abrasion, sealing, and when opening and closing the valve No seal between the valve and the valve sliding surface, and thus wear and scratches are not serious, good sealing performance, long life. (3) open and close the valve a small stroke, which is smaller than the height of the valve shut-off valves, but longer than the gate length of the structure. (4) opening and closing torque, relatively effortless opening and closing, opening and closing time of the principal. (5) fluid resistance, due to the valve body media path more tortuous, large fluid resistance, power consumption. (6) Nominal medium flow direction PN≤16MPa, generally used downstream, upstream from the media under the direction of the valve; when nominal PN≥20MPa, generally countercurrent, media orientation downstream from the valve. To increase the seal performance. When used, the cut-off valve medium can only flow in one direction, you can not change the direction of flow. (7) when fully open valve is often affected by erosion. Cut-off valves are used GB valve, American Standard valve, globe valve German standard, Japanese standard valve, bellows valve, cryogenic valve. The advantages of a low cut-off valve, simple structure, manufacture and maintenance more convenient. 2, the working stroke is small, open and close a short time. 3, sealing, small friction between the sealing surface, longer life expectancy. Disadvantage of a low-temperature cut-off valve, the fluid resistance is large, a large force is required to open and closed. 2, does not apply with particles, viscosity, easy coking medium. 3. Adjust poor performance.