Over the years people have been considered in the select control valves several traditional factors, for example, pressure rating, pressure drop, flow medium, temperature and cost. Over the past 10 years, however, happens, great changes have made a lot of progress in valve design, the characteristics of the cost-effectiveness of the production process is very different than before, which makes many formerly traditional factors must be considered in the choice of the valve importance has been greatly weakened.
Dynamic characteristic
While some traditional factors are still important, but they only emphasis on the "static" performance of the valve. In fact, they are on the "table" the valve to the results obtained by the measurement, but this results in the actual operating conditions, the valve is difficult to explain what kind of performance will be exhibited. The traditional theory is that, carefully adjust the static factors will make the valve (and hence the entire loop) to obtain good performance. However, we recognize that the situation is not always the case.
Performance checks of thousands of researchers and manufacturers proved unable to produce much effect, up to 50% with valve (many of which are selected by taking into account traditional factors) for optimizing the control loop performance. Subsequent studies have shown that play an important role in reducing the process variability of the dynamic characteristics of the valve. In many of the key processes in the different electric control valve to reduce the magnitude of process variability, even a difference of 1% can greatly improve production efficiency and reduce waste, thereby to obtain more than $ 1 million in economic benefits. Obviously, the economic benefits we can negate the traditional approach, that is based only on the initial purchase price of the valve to decide whether to buy. Pursuing a dream content management system
Secondly, the conventional wisdom is always that the process optimization improvements are always from the control room instrumentation upgrade. However, the test data indicate that a significant effect of the dynamic characteristics of the valve can be generated on the loop performance under the conditions of using the same control instrumentation. If the accuracy of the control valve is only 5%, then spend a lot of money to configure a set of its control precision can reach 0.5% of control instrumentation system does not play much role.
Valve type
Find one and use the occasion to match valve should first look at the four basic types of throttle control valve, cage ball rotation float valve eccentric valve with butterfly valve.
The cage ball trim tab form the kind of very extensive and therefore be able to meet the needs of most applications, thus making it the first choice for a variety of valves. Cage ball trim tab balance adjustment piece, unbalanced trim tab, flexible seat trim tab by constraint adjustment piece and full-size adjustment piece. In many cases, a valve body of various adjustments sheet configuration is interchangeable.
The cage ball has several disadvantages. First, the size of the valve is limited (usually 16 inches); valve (line of sight with the same specifications as the ball valve or butterfly valve) compared to its relatively low capacity; Third, higher selling prices, especially diameter cage ball of. However, in reducing the process variability, the cage ball having excellent performance, is often sufficient to compensate for these defects.
Flow ratio of the rotation of the float valve cage ball of equal caliber. Although the the rotating float valve control range greater than cage ball, but still better than most other types of valves. Allowable pressure drop and temperature range allows rotational float valve cage ball. They are usually of pressure drop ceiling of 7.0x105kg/m2, suitable for at a temperature below 398 ℃ occasions. The float valve is not used for easy liquid from the vacuoles, and for the higher pressure drop in the gas, often may issue a large noise.
Eccentric valve is smaller than the friction of the float valve, lower prices. The unique design of the structure to make it more precise control of process variability. This is evident from the Fisher's new products BV500. In addition, the advantages and disadvantages of eccentric valve float valve less.
The valve performance measure, butterfly valve is a low-end valve. Butterfly valve flow, the cheapest price, but also a variety of different caliber. Butterfly valve characteristic curve, however, could only wait for the proportion of characteristic curves a, which greatly limits the butterfly valve to reduce process variability performance. For this reason, the butterfly valve can only be used for the occasion of the load constant. Although a variety of different caliber, and with most of the cast alloy manufacturing butterfly valve, butterfly valve does not meet the ANSI requirements for face-to-face dimensions, easy to play does not apply to the vacuolar fluid or noisy and other occasions .
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