Which statement is true about the adequate and/or inadequate production of foam when using an in-line proportioner?

The assertion regarding the effect of a partially closed nozzle on the creation of a Venturi effect is accurate. The Venturi effect relies on maintaining a certain flow rate and pressure differential created by the fluid moving through a constricted section of a pipe, such as an eductor. If the nozzle is partially closed, it restricts the flow of water, which in turn can prevent the necessary pressure differential from developing. Without this pressure differential, the eductor cannot effectively draw foam concentrate into the water stream, resulting in inadequate foam production.

Other statements do not accurately reflect best practices or technical understandings surrounding foam application and production. Mixing foam concentrates from different manufacturers, even if classified similarly, can lead to compatibility issues that may affect performance. The positioning of the nozzle also plays a crucial role; if it is too far above the eductor, it can indeed cause excess foaming, but not in the way the statement implies. Lastly, a long attack line may also impact the performance but not always in the straightforward manner suggested. Thus, recognizing the importance of nozzle positioning and flow rate is vital for effective foam production.