Let's consider that the acceptance test is one that is conducted onsite prior to the final payment to the pump supplier and that all the pumps are the same model and size and designed for the same service.

The question of how many of a group of 55 screw pumps in fuel-oil service should pass the acceptance test is both a reliability and economical issue.

From the reliability standpoint, it would be ideal if every pump is required to pass an acceptance test.

From the economical view, it would depend on how expensive it's going to be to conduct such a test on every pump and how that compares to the purchase price of the pump. For example if the pumps are fairly small and the test cost is low, then testing them all may be appropriate. However, if the pumps are large and the test cost becomes a significant amount, then it may be more feasible to test a sampling of the pumps only. The numbers of pumps that should be tested with that consideration becomes a very subjective decision.