Wrong Rotation:
When a pump is not delivering liquid, one possible reason could be the wrong rotation of the pump. The impeller of a centrifugal pump must rotate in the correct direction for it to effectively move the liquid. If the pump is rotating in the wrong direction, it will not be able to create the necessary suction to draw the liquid into the pump and discharge it.

Impellers Locked:
If the impellers of the pump are locked or not rotating freely, it can prevent the pump from delivering liquid. This can happen due to issues such as mechanical failures, debris getting caught in the impeller, or lack of lubrication.

Trash in a Casing:
If there is trash or debris present in the pump casing, it can obstruct the flow of liquid and prevent the pump from effectively operating. This can cause a decrease in performance or complete failure of the pump to deliver liquid.

Packing Too Light:
The packing in a pump is responsible for creating a seal to prevent leakage. If the packing is too light or improperly installed, it can result in leakage and loss of suction, leading to the pump not delivering liquid as intended.
In conclusion, while there could be various reasons why a pump is not delivering liquid, one common issue is the wrong rotation of the pump. It is essential to ensure that the pump is rotating in the correct direction, as well as check for other possible causes such as locked impellers, trash in the casing, or light packing to troubleshoot and resolve the problem effectively.