What are the trade-offs of low-pressure nozzles?
Reducing nozzle pressure does account for some reduction in nozzle reaction. But how much reduction in pressure is required to get a significant reduction in reaction? And while reduced reaction may be a positive aspect, what are the negative aspects of choosing a low-pressure nozzle delivery system?
Those advocating for reducing the fog nozzle pressure typically would reduce the required nozzle pressure downward from 100 psi to 75 psi. If the flow is kept constant, the reaction reduction from a 25 percent cut in nozzle pressure is 13 percent. It works out this way: a 200 gpm stream at 100 psi has 101 pounds of reaction; cutting the nozzle pressure to 75 psi reduces the reaction to 88 pounds.
Nozzle pressure is directly related to the velocity of the stream. For the given example, instead of a stream speeding through the fire's super-heated gases at 80 mph, it goes through at 60 mph. Which one goes farther? Which splashes more when it hits? Which bores through the wood char to get to deep-seated heat?
Make a comparison to the trend of law enforcement in the United States. As the threat to police officers goes up, are they going to smaller guns with fewer bullets in the clip? Are they taking out the bullets and pouring out half the powder? If they cut out half the powder the gun would kick less, be easier to aim, and it wouldn't hit as hard. Is that what the police want for their weapons?
Fire departments need to ask if this is really what they want for their primary weapon.
Or consider an example that comes closer to home: how many people wish for a shower with less pressure and how many would think that a shower with less pressure does a better job of getting the soap off?
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