Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 228

With constant-speed pumps, the well level is controlled over a range to provide for lead–lag operation of the pumps. Start and stop setpoints for each stage (e.g. lead, Lag1, Lag2…Lagx) are typically used to start and stop the pumps, with the lead pump stop setpoint at the lowest well level and the highest lag pump start setpoint at the highest well level. Each stage will have a start level higher than a stop level setpoint and the range will overlap but be at a higher well level than the next lowest stage. The start and stop setpoint for each stage must be far enough apart in well level to ensure that the pump is allowed to run and be off for a sufficient amount of time.

If the pumps are different sizes, it is important to consider pump curves for each pump. If the pump system consists of both small and large pumps, the smaller pumps serve as the lead and lowest lag pumps because they are operating at the lowest flow condition. At higher flow, with large pumps operating, the small pumps may not be able to contribute to the flow because they are at a dead-head condition on the pump curve. In this instance, they may be stopped during operation of the larger pumps if they are not adding to the flow.