Step control valve
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In split-control, the amount of leakage from the valve is a very important issue. In a split-control system where a large valve and a small valve are connected in parallel, if the leakage rate of the large valve is too high, the small valve will be unable to fulfill its control function properly, or even fail to provide any control at all. Therefore, control valves with low leakage or no leakage should be selected. Why is this? Why is there a leak? Why isn’t the small valve working?
In a split-control system where a large valve and a small valve are connected in parallel, if it is specified that the small valve should adjust first, then when the leakage rate of the large valve becomes too high – reaching more than half of the maximum leakage rate of the small valve or even being on par with it – it may be impossible to ensure that the controlled parameter changes as intended, even if the small valve is fully closed. In such cases, the small valve will not be able to fulfill its control function properly, or it may not be able to exert any control effect at all.
Control should have a certain blind zone to reduce leakage.