Which factor is essential when using an eductor?

Using an eductor effectively requires proper alignment of the fire-main. The eductor relies on a constant and adequate flow of water through the fire-main to create the necessary suction that allows for the drawing of liquid from a lower level or from a source that is not under pressure. If the fire-main is not aligned correctly, it can lead to reduced performance or failures in the suction process, preventing the eductor from functioning as intended.

The other factors, while they may have some importance in specific scenarios or applications, do not have the same critical impact on the immediate operation of the eductor. For instance, while the temperature of the liquid can affect certain physical properties, it is not a primary concern when establishing the eductor's function. Similarly, the water chemistry might influence the corrosiveness or compatibility of materials, but it does not directly impact the fundamental workings of suction and flow in the eductor. The length of the discharge hose can create pressure losses, but alignment of the fire-main is a more crucial aspect necessary for optimal operation of the eductor. Therefore, ensuring that the fire-main is aligned correctly is essential for the eductor to function effectively in damage control operations.