I'm completing a fire flow calibration, and I've noticed some differences depending on how its completed. For our calibration, I've been applying demand to the hydrants. According to the literature, when completing a fire flow the hydrant setting should be changed for "open," however when this is done in addition to applying a demand the flow significantly exceeds the supplied demand. If demand is being applied to the hydrant in this way, is the hydrant supposed to be closed? From what I understand, the hydrant could also just be set to open without a demand and the flows should (hypothetically) match what was seen in the field, but its been a challenge to get this to match with so many additional factors throughout the model.
Additionally, when the demand is applied to the nearest node instead of the hydrant itself the pressure drop is fairly different. Is this difference only due to headloss in the hydrant?
Thanks!