This is the commonly seen issue in pumps.
When the pump is not able to deliver the required pressure it is considered to be a delivery failure problem.
Steps to tackle the issue:
1. Ensure that the pump is primed properly.
2. Check if the pump is moving with sufficient speed.
3. Check for air leakage.
4. Ensure that the impeller/gear/screw or other liquid driving mechanism is not broken or damaged.
5. The pump shaft should move in the right direction.
6. Check that the suction lift is not more than required.
7. Ensure the temperature of a liquid is not below the “pump-able” limit of the pump.