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Tyco butterfly valve in the regulation of the potential benefits of operating conditions
A valve is designed to switch valve can not be used as a regulating valve; and regulating valve can only be used to adjust the condition and can not be used to switch valves. In fact, the two commonly heard at the same time are not irrefutable facts. This article focuses on the butterfly valve can do both the use of regulating valve, but also do the potential advantages of switching valves. In the past, many valve manufacturers and other stakeholders have been trying to convince instrumentation engineers that butterfly valves can be used as a key conditioning unit for process control. Despite their efforts, the prevailing view still holds that butterfly valves have neither good regulation nor precise regulation. Since these points of view are directly related, we can prove that the butterfly valve is actually a good regulator by refuting the second argument. Here, it is necessary to clarify for example: adjust performance, cavitation, Kv value, adjustment range, and other terms. In addition, we also compared six control valves, and by knowing more about the functionality of the control valves in different applications, we can identify more reasonable selection criteria. Looking back at the many advantages of using butterfly valves as control valves, a surprising conclusion may prompt many engineers to rethink their views. Control Valve Design Control valves vary widely depending on the type and have many different forms of valve body. When we compare a variety of different parameters of the control valve, this difference becomes more apparent. There are several types of control valves selected for comparison: 1. Butterfly Valve (Keystone F990 Centerline Butterfly Valve) 2. Butterfly Valve (K-Lok) 3. Butterfly Valve (Vanessa) 4. Eccentric Rotary Valve (Manufacturer A) 5. Type V Ball Valve (Manufacturer B) 6. Shut-Off Valve (Manufacturer C) 7. Cage Valve (Manufacturer D) Kv Value The Kv value is a key factor when selecting a regulator. In order to give a visual indication of the differences between these regulators selected, the Kv values ​​for the four sizes of valve at full opening are listed in Table 1 below (Kv value refers to the value of the valve that flows through a given opening at a constant pressure drop Of water). Valve Size Butterfly Valve (Centerline) Butterfly Valve (Double Eccentricity) Butterfly Valve (Triple Eccentricity) Rotary Valve V-Ball Valve Cut-off Cage Valve 3 "664248173156293139104 6" 10 "924051982541150231071271924 16" From Table 1 we can see that each Kv values ​​vary greatly for each type of valve and these differences will in part determine the application possibilities of each valve. It can be seen that the butterfly valve Kv value several times higher than the cage-oriented valve. After all, for cage valves, the medium flows in a labyrinthine fashion and therefore has a large resistance to flow, which significantly reduces the flow of medium through the valve. From the Kv value definition can clearly know that for different valve opening Kv value corresponding to different. Draw Kv value corresponding to the valve opening curve that Kv value curve (Figure 2). This curve is usually referred to the valve's inherent characteristic curve. The adjustment range can be determined from this characteristic curve, which shows the area where the valve can function correctly. This area is defined by the minimum Kv value and the maximum Kv value, and the maximum and minimum Kv values ​​are determined by the valve opening where the valve still has sufficient flow to adjust the flow rate. The Kv value is a key factor for the regulator. However, other factors are also important when considering the type of control valve, as discussed below. Adjustment range (range ratio) The adjustment range is the ratio of the minimum Kv value to the maximum Kv value. For example, the minimum Kv value is 12, the maximum Kv value is 100, and the adjustment range is 1: 8. Table 2 shows the various types of valve adjustment range and to reach the regulation range of the valve opening. Butterfly Valve (Centerline) Butterfly Valve (Double Eccentricity) Butterfly Valve (Triple Eccentricity) Eccentric Rotary Valve V-Ball Valve Cut-off Cage Valve Regulating Range 1:15 (25-75) 1:30 (15-80) 1:35 (5 -85) 1:50 (2-50) 1: 3000 (1-80) 1:50 (2-80)> 1: 100 (1-100) F1 Valves 0.250.350.620.700.851.0 Operating Flexibility Properties 322131 or 31 Operating Flexibility Operating flexibility refers to the relationship between the maximum allowable pressure drop and the inlet pressure. Operational flexibility is determined by the internal resistance of the valve. The greater the internal resistance, the greater the pressure drop allowed through the valve, allowing no problems such as noise and cavitation within the pressure drop range. The advantages of butterfly valve As mentioned earlier, the function of the control valve is generally only for adjustment without switching. Normally we know that butterfly valves can be bubble-rated. If you equip it with an actuator, a positioner and give it an adjustment signal transmitted by the controller or PLC, it is able to fine-tune the fluid flow. Assuming that the selection is reasonable, this means that instead of the more expensive shut-off valves that are commonly used, relatively simple and inexpensive butterfly valves can be used. The use of butterfly valves for the user has many advantages: 1. Butterfly valve prices are usually relatively low, especially for large diameter valves. 2. Butterfly valve rarely needs maintenance, even if the maintenance is also relatively simple and low cost. 3. Butterfly valve can shut off the process fluid very well, so the butterfly valve is usually used in the upstream when the valve does not need to install. 4. If an additional shut-off valve is required (for applications where special safety is required), shut-off valves and regulating valves have the flexibility to use butterfly valves at the same time. For example, when the regulator fails, it can be installed on the block valve actuator can be removed and installed on the regulatory function can be implemented without affecting the production. Order a valve to replace the damaged valve. This is the same effect as installing a manual bypass valve in the system. 5. When both butterfly valves are used in the mediation and shut-off valves, the number of spare parts can be greatly reduced. Through the above comparison, we can clearly know that any kind of valve can not be completely suitable for any occasion. In the right place, the application of butterfly valve more advantages. As can be seen from Table 2 butterfly valve range ratio of 1:35 (three eccentric), the operating flexibility of not higher than 45. The following examples of actual process conditions can be used to demonstrate the true superiority of butterfly valves: Example 1: When a turndown ratio of 1:75 is required (maximum Kv = 1500, minimum Kv = 20 Cage valves are usually used. As long as the flow rate is large, requiring more than DN200 diameter valve, the butterfly valve will be a good choice. Such a valve can usually be replaced by two butterfly valves in parallel. When the first valve reaches its maximum adjustment range, the second (usually larger) valve begins to adjust. A DN200 Keystone butterfly valve (Kv from 1500 to 200 - 1: 7.5) can be used to adjust the medium for the main line of the DN300 with DN80 Keystone butterfly valves (Kv values ​​from 200 to 20 - 1: 7.5) for DN100 parallel lines. To adjust the medium. The use of two regulating butterfly valves (including pipe additions) is more economical than using a DN300 cage valve. Example 2: There is a condition, the pressure needs to be reduced from 3.5bara to the actual atmospheric pressure, it is natural to choose cut-off type control valve (operating flexibility of 70). As in the first example, you can choose to use two butterfly valves installed in series for the same purpose. (Note: According to the quantum ratio can use a current limiting orifice instead of the second valve, the cost will be lower.) The use of two butterfly valve in series requires two steps decompression. Valve 1 reduced the pressure from 3.5 bara to 1.8 bara. Valve 2 reduces pressure from 1.8 bara to atmospheric pressure. This arrangement ultimately corresponds to an operational flexibility of 75 and the pressure drop that can be precisely adjusted with triple eccentric butterfly valves. In addition, the use of two butterfly valves in combination with an actuator, positioner and coupling in this case is more economical than the use of a single shut-off valve, which is especially important for shut-off valves above DN200. An additional advantage is the butterfly valve Kv value with other valves