Selecting experiences
The key to select control valve is assess dynamic characteristics
For years people in choosing regulator with considering some traditional factors, such as pressure rated value, pressure drop and flow medium, temperature and cost, etc. However, in the past 10 years much has changed, valve design made a lot of progress, production process cost benefit characteristic is more different than ever before, which makes many traditional factors importance that choose valve must take into account greatly weakened.
dynamic characteristic
Although some traditional factors are still very important, but they are only in laterality to valve "static" performance. Actually They are in the "workbench" to measure valve and obtain results, but the result is difficult to indicate what kind performance under the actual operating conditions. Traditional theory holds that carefully adjust static factors will make valve (thus make the whole circuit) to obtain good performance. However, now we realizes it is not always the case.
Researchers and manufacture for thousands of times performance examination certificate, up to 50% of in-using valve (including many are through considering traditional factors to select) for optimizing control circuit performance failed to produce large effect. Subsequent research shows that the dynamic characteristic of the valve is to reduce head mutabilty played a very important role. In many key processes, different valves reduce head mutabilty amplitude even within 1% can also large amplitude increase production efficiency and reduce the waste, thus, can obtain more than 100 million dollars in economic benefits. Clearly, this economic benefits make us fully deny the traditional way, i.e. according to the initial purchase price to decide whether to buy.
Secondly, the conventional wisdom always thinks, flow optimization improvement is always from controling room control instrument upgrade. But, the test data show that, under using same control instrument conditions, the valve dynamic performance can significantly impact on valve circuit performance. If the regulator precision can only reach 5%, then, spend a lot of money to configure a set of its control precision reaches 0.5% advanced control instrument system does not have much effect.
valve type
When looking for a valve that matching with using situation, first of all, should look four basic types throttling regulator, namely the cage type control valve, rotating float control valve, eccentric valve and butterfly valves.
Cage type control valve adjusting piece forms sort is very broad, so can satisfy most applications requirement, and make it become the first choice of various valves. Cage type control valve adjust piece has a lot of kinds, including balance adjust piece, unbalanced adjustment slice, elastic base seat adjust slice, constrained adjust films and full size adjustment piece. In many cases, one kind of body various adjustment slice configuration are interchangeable.
Cage type control valves also has some shortcomings. First is the valve size restrictions (usually is 16 inches); Second is compare with same dimension sight valve (such as float control valve or butterfly valve), their capacity is low, Third is price is higher, especially large diameter cage type control valve. However, in reducing process mutabilty aspects, cage type control valve has excellent performance, often enough to make these defects.
Eccentric valve friction is smaller than floating control valve, the price is lower. The special structure design makes its process control of the mutabilty more precise. This point from Fisher company's new product BV500 is obvious. In addition, the advantages and disadvantages of eccentric valve is little different with float control valve.
Measure according to the valve performance, butterfly valve belong to low-grade valves. butterfly valve flow is large, and is cheapest, and have a number of different diameters. But butterfly valve characteristic curve only proportion characteristic curve one kind, this greatly limits the butterfly valves reduce process mutabilty performance. For this reason, butterfly valve can only be used for fixed load places. Although butterfly valves have a number of different diameters, and manufactured by most casting alloy, but butterfly valve does not conform to the requirements of ANSI about face-to-face dimensions, also does not apply to easy an empty bubble fluid or noise larger occasions, etc.
