Which brand of oxygen concentrator is good

Summary: As an indispensable equipment in industrial production such as chemical industry, valves may encounter many problems from selection to use to maintenance. Today, some common problem types are sorted out, hoping to help everyone. I. What are the three main factors to consider when selecting an actuator? 1) The output of the actuator must be greater than the load of the valve and reasonably matched. 2) When checking the standard combination, consider whether the allowable pressure difference specified by the valve meets the process requirements. When the pressure difference is large, calculate the unbalanced force acting on the valve core. 3) Consider whether the response speed of the actuator meets the process operation requirements, especially for electric actuators. II. Compared with pneumatic actuators, what are the characteristics of electric actuators and what are the output forms? Electric drive source is simple and convenient, with large thrust and torque, and large rigidity. However, the structure is complex and the reliability is poor. It is more expensive than pneumatic ones in small and medium specifications. It is often used in occasions without gas source or without strict explosion-proof and fire-proof requirements. Electric actuators have three output forms: angular stroke, linear stroke, and multi-revolution. III. Why is the shut-off pressure difference of angular stroke valves large? The shut-off pressure difference of angular stroke valves is large because the moment generated by the resultant force of the medium on the valve core or valve plate on the rotating shaft is very small, so it can withstand a larger pressure difference. Butterfly valves and ball valves are the most common angular stroke valves. IV. Which valves need flow direction selection? How to choose? Single-seal regulating valves such as single-seat valves, high-pressure valves, and single-seal sleeve valves without balance holes need flow direction selection. Flow open and flow close have their own advantages and disadvantages. Flow-open valves operate more stably, but their self-cleaning performance and sealing performance are poor, and their service life is short; flow-close valves have a long service life, good self-cleaning performance and sealing performance, but when the valve stem diameter is smaller than the valve core diameter, the stability is poor. Single-seat valves, small-flow valves, and single-seal sleeve valves usually choose flow-open, and flow-close can be chosen when scouring is severe or self-cleaning is required. Two-position quick-opening regulating valves choose flow-close type. V. In addition to single-seat, double-seat, and sleeve valves, what other valves have regulating functions? Diaphragm valves, butterfly valves, O-type ball valves (mainly for shut-off), V-type ball valves (large regulating ratio, with shearing action), and eccentric rotary valves all have regulating functions. VI. Why is selection more important than calculation?          Compared with calculation, selection is much more important and complex. Because calculation is just a simple formula calculation, its essence is not in the accuracy of the formula, but in whether the given process parameters are accurate. Selection involves a lot of content. If you are not careful, it will lead to improper selection, not only causing waste of manpower, material resources, and financial resources, but also unsatisfactory use effect, bringing various use problems, such as reliability, service life, and operation quality. VII. Why can't double-seal valves be used as shut-off valves? The advantage of the double-seat valve core is its force balance structure, which allows for a large pressure difference, but its prominent disadvantage is that the two sealing surfaces cannot contact well at the same time, resulting in large leakage. If it is artificially and forcibly used in the shut-off occasion, the effect is obviously not good, even if many improvements are made to it (such as double-seal sleeve valves), it is not advisable. VIII. Why does a double-seat valve oscillate easily when operating at a small opening? For a single core, when the medium is flow-open, the valve is stable; when the medium is flow-close, the valve is unstable. A double-seat valve has two valve cores, the lower valve core is flow-close, and the upper valve core is flow-open. In this way, when working at a small opening, the flow-closed valve core is prone to cause valve vibration, which is the reason why double-seat valves cannot be used for small opening operation. IX. What are the characteristics of a straight-through single-seat regulating valve? Where is it applied? 1) Small allowable pressure difference, due to large unbalanced force thrust. The △P of DN100 valve is only 120kPa. 2) Small flow capacity. The Kv of DN100 is only 120. It is often used in occasions with small leakage and small pressure difference. X. What are the characteristics of a straight-through double-seat regulating valve? Where is it applied? 1) Large allowable pressure difference, because many unbalanced forces can be offset. The △P of DN100 valve is 280KPa. 2) Large flow capacity. The KV of DN100 is 160. 3) Large leakage, there are two reasons: the two valve cores cannot be sealed at the same time. The standard leakage is 0.1%KV, which is 10 times that of a single-seat valve. Straight-through double-seat regulating valves are mainly used in occasions with high pressure difference and not strict leakage requirements. XI. Why is the anti-clogging performance of straight-stroke regulating valves poor, and the anti-clogging performance of angular stroke valves good? The valve core of a straight-stroke valve is vertical throttling, while the medium flows in and out horizontally. The flow path in the valve cavity must turn and bend, making the flow path of the valve quite complex (shaped like an inverted "S"). In this way, there are many dead zones, providing space for the precipitation of the medium, and over time, causing blockage. The throttling direction of the angular stroke valve is the horizontal direction. The medium flows in horizontally and flows out horizontally. It is easy to take away the unclean medium. At the same time, the flow path is simple, and there is little space for medium precipitation, so the angular stroke valve has good anti-clogging performance. XII. Under what circumstances is a valve positioner needed? 1) Large friction force and occasions requiring precise positioning. For example, high-temperature, low-temperature regulating valves or regulating valves using flexible graphite packing; 2) Occasions where the response speed of the regulating valve needs to be improved for slow processes. For example, temperature, level, and analysis parameter regulation systems. 3) Occasions where the output force and shut-off force of the actuator need to be increased. For example, DN≥25 single-seat valves, DN>100 double-seat valves. Occasions where the pressure drop △P across the valve is >1MPa or the inlet pressure P1 is >10MPa. 4) Occasions where the range regulation system and the operation of the regulating valve sometimes need to change the air-open and air-close forms. 5) Occasions where the flow characteristics of the regulating valve need to be changed. XIII. What are the seven steps to determine the regulating valve diameter? 1) Determine the calculation flow - Qmax, Qmin 2) Determine the calculation pressure difference - select the resistance ratio S value according to the system characteristics, and then determine the calculation (when the valve is fully open) pressure difference; 3) Calculate the flow coefficient - select the appropriate calculation formula chart or software to find the max and min of KV; 4) KV value selection - according to the max value of KV, the closest KV in the selected product series is selected to obtain the initial selection diameter; 5) Opening verification - when Qmax is ≤90% valve opening; when Qmin is ≥10% valve opening; 6) Actual adjustable ratio verification - generally, it should be ≥10; R actual > R required 7) Diameter determination - if it does not meet the requirements, re-select the KV value and verify again. XIV. Why hasn't the sleeve valve replaced the single-seat and double-seat valves as expected? Sleeve valves, which appeared in the 1960s, were widely used at home and abroad in the 1970s. In the 1980s, the proportion of sleeve valves in imported petrochemical devices was relatively large. At that time, many people believed that sleeve valves could replace single-seat and double-seat valves and become the second-generation products. However, this is not the case today. Single-seat valves, double-seat valves, and sleeve valves are all used equally. This is because the sleeve valve only improves the throttling form, and its stability and maintenance are better than the single-seat valve, but its weight, anti-clogging, and leakage indicators are consistent with the single-seat and double-seat valves. How can it replace the single-seat and double-seat valves? Therefore, they can only be used together. XV. Why should shut-off valves preferably use hard seals? Shut-off valves require the lowest possible leakage. The leakage of soft-seal valves is the lowest, and the shut-off effect is naturally good, but they are not wear-resistant and have poor reliability. From the dual standards of low leakage and reliable sealing, soft-seal shut-off is not as good as hard-seal shut-off. For example, a full-function ultra-lightweight regulating valve, sealed with wear-resistant alloy protection, has high reliability and a leakage rate of 10～7, which can already meet the requirements of a shut-off valve. XVI. Why is the valve stem of a straight-stroke regulating valve relatively thin? It involves a simple mechanical principle: sliding friction is large, rolling friction is small. The valve stem of a straight-stroke valve moves up and down. If the packing is slightly tightened, it will wrap the valve stem tightly, producing a relatively large hysteresis. To this end, the valve stem is designed to be very small, and the packing often uses PTFE packing with a small friction coefficient to reduce hysteresis. However, the resulting problem is that the valve stem is thin, which is easy to bend, and the packing life is also short. The best way to solve this problem is to use a rotary valve stem, that is, an angular stroke regulating valve. Its valve stem is 2～3 times thicker than that of a straight-stroke valve, and it uses long-life graphite packing. The valve stem has good rigidity, long packing life, and smaller friction torque and hysteresis.

Key words: Which brand of oxygen concentrator is good