Valve sixteen questions that one difficult to you?

Valve sixteen questions that one difficult to you?

　　1. What are the three main factors that should be considered when selecting an actuator?

　　1)The output of the actuator should be greater than the load of the valve and reasonably matched.

　　2)When checking the standard combination, consider whether the allowable differential pressure specified by the valve meets the process requirements. When the differential pressure is large, the unbalanced force on the valve spool should be calculated.

　　3) Need to consider whether the response speed of the actuator to meet the process operating requirements, especially the electric actuator.

　　Second, compared with the pneumatic actuator, what are the characteristics of electric actuators and what are the output forms?

　　Electric actuator source is simple and convenient, with high thrust and torque and high rigidity. But the structure is complex, poor reliability. Small and medium-sized specifications are more expensive than pneumatic. Commonly used in places where there is no gas source or where strict explosion-proof or explosion-proof is not required.

　　Electric actuators have three output forms: angle stroke, straight stroke and multi-rotary.

　　Third, why the cut-off differential pressure of the angle travel valve is larger?

　　The cut-off differential pressure of the angle valve is large because the combined force of the medium on the spool or valve plate has a small torque on the rotating shaft, so it can withstand a large differential pressure.

　　Butterfly valves and ball valves are the most common angle travel valves.

　　4. Flow direction need to choose which valves? How to choose?

　　Single-seal type regulating valves, such as single-seat valves, high-pressure valves, and single-seal sleeve valves without counterbalance holes, need to be selected for flow direction.

　　There are advantages and disadvantages of opening and closing. Flow type valves are stable in operation, but have poor self-cleaning and sealing performance and a short service life. Closed type valves have long service life, good self-cleaning performance and sealing performance, but are less stable when the stem diameter is smaller than the spool diameter.

　　Single-seat, low-flow, and single-sealed sleeve valves are usually open and can be closed when severe washout or self-cleaning is required. Flow selection and shut-off type two-position quick-open characteristic regulating valves.

　　5. In addition to single-seat, double-seat, and sleeve valves, what other valves have a regulating function?

　　Diaphragm valves, butterfly valves, O-ball valves (mainly globe valves), V-ball valves (with large adjustment ratios and shear functions) and eccentric rotary valves are all valves with regulating functions.

　　6. Why is selection more important than calculation?

　　Compared with calculation and selection, selection is much more important and complex. Because the calculation is just a simple formula calculation, does not depend on the accuracy of the formula, but depends on the accuracy of the given process parameters.

　　Selection involves a lot of content, a little carelessness will lead to improper selection, will not only cause a waste of manpower, material and financial resources, will also bring reliability, service life, quality of operation and other issues.

　　Seven, why can't the double seal valve be used as a cut-off valve?

　　The advantage of double-seated spool is a force-balanced structure, allowing a large differential pressure, and its outstanding disadvantage is that the two sealing surfaces can not be contacted at the same time, resulting in a large amount of leakage.

　　If the cut-off occasions artificially forced to use, the effect is obviously not good, even if it has made a lot of improvements (such as double-sealed sleeve valve), it is not desirable.

　　8. Why is it easy to oscillate when double-seated valves work in small openings?

　　For a single spool, when the medium is open flow, the stability of the valve is better; when the medium flow is closed, the stability of the valve is poor. Double-seated valve has two spools, the lower spool in the flow off state, the upper spool in the flow open state. In this way, in the small opening work, closed flow spool easily caused by the vibration of the valve, which is also a double-seated valve can not be used for small opening work.

　　9. What are the characteristics of straight-through single-seat adjustment valve? What is the occasion?

　　1) Small discharge, because there is only one spool valve is easy to ensure the sealing. Standard discharge rate of 0.01% KV, can be further designed as a shut-off valve.

　　2)Allowable differential pressure is small, the thrust generated by the unbalance force is large. p of DN100 valve is only 120KPa.

　　3)Low cycling capacity.KV of DN100 is only 120.

　　Commonly used in small leakage, small differential pressure occasions.

　　10. What are the characteristics of straight-through double-seat adjustment valve? What are the occasions?

　　1)Allowable differential pressure is large, because it can offset a lot of unbalanced force. p for DN100 valve is 280KPa.

　　2)Strong flow capacity. kV for DN100 is 160.

　　3)Large leakage because both spools cannot be sealed at the same time. The standard emission rate is 0.1% KV, which is twice that of single-seat valve 10.

　　Straight-through double-seated adjustment valves are mainly used for occasions with large differential pressure and less stringent leakage requirements.

　 (4) Why is the anti-blocking performance of straight stroke control valves poor, and the anti-blocking performance of angle stroke valves good?

　　The spool of the straight stroke valve is vertically throttled, and the medium is horizontally in and out, so the flow path in the valve cavity will inevitably be up and down, making the flow path of the valve quite complex (the shape of the inverted 's'). This way there are many dead zones, providing space for the medium to settle, causing blockage in the long run.

　　Angle valve throttle direction is horizontal, the media level in and out, easy to take away the dirty media. At the same time, the flow path is simple, the media precipitation space is small, so the angle valve has good anti-clogging performance.

　　XII. What is the need to use the valve positioner?

　　1) friction, the need for precise positioning of the place. Such as high-temperature, low-temperature control valves or control valves with flexible graphite packing;

　　2) When the slow process needs to improve the response speed of the control valve. For example, temperature, liquid level, analysis and other parameters.

　　3) Where there is a need to increase the actuator output force and cut-off force. For example, single-seated valves of DN 25 and double-seated valves of DN >; 100. pressure drop at both ends of the valve p >; 1mpa or inlet pressure P1 >. 10mpa.

　　4) In the range adjustment system and the operation of the adjustment valve, it is sometimes necessary to change the form of opening and closing of the air.

　　5) Where it is necessary to change the flow characteristics of the control valve.

　　Thirteen, to determine the diameter of the control valve seven steps are?

　　1) Determine - Qmax and Qmin calculated flow rate.

　　2) Determine and calculate the differential pressure - according to the system characteristics of the selected resistance ratio S value, and then determine and calculate the differential pressure (when the valve is fully open);

　　3)Calculate the flow coefficient - select the appropriate calculation formula chart or software to calculate the maximum and minimum values; of kV;

　　4)Selection of KV value -:According to the maximum value of KV, get the KV closest to the first class in the selected product series and get the first class caliber;

　　5) when - the requirement of Qmax, the valve opening 90%; Qmin when the valve opening 10%; 6) the actual adjustable ratio calibration calculations - the general requirements should be 10; actual > r requirements

　　7) caliber determination - if not qualified, re-select the KV value, and then verify.

　　14. Why sleeve valves to replace single-seat and double-seat valves have not been successful?

　　Sleeve valves were introduced in 1960s and widely used at home and abroad in 1970s. Sleeve valves accounted for a large proportion of petrochemical plants introduced in the 1980s. At that time, many people thought that sleeve valves could replace single-seat and double-seat valves and become the second generation products.

　　So far, this has not been the case. Single-seat, double-seat and sleeve valves are all used equally. This is because sleeve valves only improve throttling form, stability and maintenance better than single-seat valves, but have the same weight, blockage prevention and leakage indicators as single- and double-seat valves. How does it replace single and double seated valves? Therefore, they can only be used together.

　　Intelligent electric sleeve adjustment valve

　　XV. Why is the stem of a straight stroke adjustment valve thinner?

　　It involves a simple mechanical principle: large sliding friction and small rolling friction. The stem of a straight stroke valve moves up and down, and if the packing is pressed down slightly, it will compress the stem, causing a large tooth gap.

　　XVI. Why should shut-off valves be hard-sealed whenever possible?

　　The lower the leakage of a shut-off valve, the better. Soft seal valves have the lowest leakage. Cutting is certainly good, but it is not abrasion-resistant and has poor reliability. According to the double standard of low leakage and reliable sealing, soft seal cutting is inferior to hard seal cutting. Such as full-featured ultra-light control valve, the use of wear-resistant alloy to protect the seal stack, high reliability, leakage rate of 10 ~ 7, has been able to meet the requirements of the cut-off valve. Therefore, the valve stem is designed to be very small, usually with a small coefficient of friction of PTFE packing as packing to reduce the tooth gap. However, the resulting problem is that the thin valve stem is easy to bend and the packing life is short.