What is the optimal condition for pumper capacity at draft?

The optimal condition for pumper capacity at draft is related to the relationship between the lift height and the length of hard suction used. In this context, the situation described in the correct choice provides a balance that allows the fire pump to efficiently move water from a source to the pump.

When the lift is set at 10 feet with 20 feet of hard suction, it indicates an appropriate height that can be effectively managed by the pump while still allowing for proper flow and pressure. This configuration typically falls within the operational capabilities of most fire pumps. It ensures that the negative pressure created by the pump does not exceed the limits that could result in cavitation, which is damaging to the pump and reduces efficiency.

In contrast, other options either exceed this optimal range or do not provide sufficient length of suction. For instance, a greater lift height may create too much strain on the pump, leading to inadequate flow rates or operational failure. Additionally, longer lengths of hard suction can introduce friction losses that negatively impact the pump's ability to move water effectively.

Thus, the 10 feet of lift through 20 feet of hard suction is recognized as the optimal condition, as it strikes the right balance for effective drafting operations without compromising pump performance.