Final answer:
Reverse flow in a flow-meter can be caused by leakage, back-pressure, obstruction, or improper calibration of the flow-meter. These factors disrupt the normal high to low pressure differential that drives flow, potentially causing a reversal.
Step-by-step explanation:
Reverse flow as detected by a flow-meter can be caused by a few different factors. Common causes include leakage, which allows fluid to flow backward through the system; back-pressure, where pressure downstream of the flow-meter exceeds pressure upstream, leading to reverse flow; an obstruction in the flow path that can cause fluid to back up and possibly flow in the reverse direction; and improper calibration of the flow-meter, which may result in incorrect readings including reverse flow. Flow generally moves from an area of high pressure to low pressure, and anything that disrupts this pressure differential can potentially cause reverse flow.