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Pump minimum flow control °ü·Ã ³»¿ëÀä.
A more efficient method of recycle control requires that the discharge flow of the pump itself
is measured, and that a valve in the recycle line is opened when the process does not draw the required minimum flow. The most straightforward way to accomplish this is shown
in Figure 1-9. Note that the recycle line tees off upstream of the control valve. It is precisely
when the control valve is closed that the recycle is needed. There is a small problem with
controlling the minimum flow in this way: The measurement orifice in the discharge consumes energy and also slightly reduces pump capacity. A second problem is that the actual signal being measured is the ∆P across the orifice plate. Since flow varies as the square root of ∆P, a minimum flow of 40% of maximum flow implies a controller whose set point is only 16% of the measurement range. A typical instrument accuracy is 1%. Therefore an error of 7% of the setpoint can be expected. Fortunately the minimum flow need not be held very accurately. Recycle control is sometimes accomplished using a local pneumatic controller mounted directly on the valve.
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1. "an error of 7% of the setpoint can be expected" ¶ó´Â ³»¿ëÀÌ ³ª¿À´Âµ¥, 7%¶ó´Â ¼ýÀÚ´Â ¾îÂî ³ª¿Â °É±î¿ä? ¾Ëµí ¸»µí Çѵ¥, Àß ¶° ¿À¸£Áö ¾Ê³×¿ä.
2. "local pneumatic controller" ¶ó´Â ¸»ÀÌ ³ª¿À´Âµ¥, ÀÌ°Ô ¹»±î¿ä? °æÇè ÀÖÀ¸½Å ºÐ ¼³¸í ºÎŹµå¸³´Ï´Ù.
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