How is the pump shut-off controlled in a recirculating SF system?

In a recirculating sand filter (SF) system, the pump shut-off is typically controlled using a low-level float switch. This component is essential for the system's operation, as it monitors the wastewater level within the tank. When the wastewater level drops to a predetermined low point, the float switch activates to turn the pump off, preventing it from running dry, which could cause damage to the pump or lead to system inefficiency. This automatic control ensures that the pump operates only when there is sufficient wastewater, thereby protecting the system and maintaining optimal performance.

The other options may reflect different control methods, but they are not applicable to the specific function of shut-off in a recirculating SF system. Manual switches require human intervention, which can lead to inconsistent operation, while timers control the pump based on set intervals rather than the actual wastewater level. Additionally, relying on pressure from the wastewater does not provide the precise control needed for pump operation, as it may not accurately reflect the necessary conditions for safe and effective pump shut-off.