When fighting a hostile fire, a firefighter needs to know an important piece of equipment on the end of a fire hose at their disposal — the fire nozzle. All firefighters know that the fire nozzle is the business end of their firefighting tools.
The fire zone resembles a battlefield. The better a firefighter knows about the nozzles, the more likely he is going to put out a fire. It makes perfect sense when you think about how a soldier fires his weapons at the enemy.
For every firefighter, controlling a fire nozzle is not just a push/pull of the ball valve
or a left/right twist to adjust the water spray from a fine mist to a powerful stream. As a matter of fact, there are five nozzle basics that all qualified firefighters need to know before fighting a blaze.
Let us now take a quick look at these five things about the nozzle that firefighters should know before using it on the fire ground:
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What is the difference between automatic and conventional nozzles?
On the conventional fog nozzle can always be found a fixed or selectable gpm setting, which is designed to correspond to a specific discharging orifice (or tip size). This ensures that the proper gpm flow is sufficient for the conventional nozzle to work at the desired nozzle pressure of 100 psi with a fixed opening. In other words, only the selectable gallonage nozzle set at 30, 60, 95, and 125 gpm can deliver the flows with nozzle pressure at 100 psi.
Two consequences often occur if the conventional nozzle is not provided with selected flows. Number one, a tickling stream caused by weak flows due to inadequate pressure can not even reach the fire, let alone penetrate it. Number two, higher-than-normal nozzle pressure caused by excessive water flow will make it more difficult for firefighters to handle and hose line, thus putting the nozzle crews’ life in danger.
On the contrary, the automatic nozzle can automatically adjust the discharging orifice based on the nozzle flow, which enables the nozzle pressure and velocity to be set properly and correctly for the best extinguishing efficiency.
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How does the automatic nozzle operate?
The automatic nozzle to some extent resembles the pumper relief valve. Its discharging orifice formed by the baffle, connected to a highly reliable spring, counterbalances the nozzles water pressure, whose variations can be sensed by the spring and further controlled.
The nozzle pressure is maintained at 100 psi because necessary tip size is regulated by that pressure-control spring that moves the baffle in and out. That means the automatic nozzles tip size is changing simultaneously in response to the water being supplied.
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What is the pressure maintained on the automatic nozzle?
Automatic nozzles pressure is set at 100 psi and become a baseline for any operation, thus simplifying its pump operation significantly. The equation that calculates pump discharge pressure is PDP = NP + TPL where PDP represents the pump discharge pressure while NP means the nozzle pressure and TPL is the total pressure loss interpreted as the total sum of hose line friction loss, apparatus friction loss, and elevation pressure.
The nozzle pressure of an automatic nozzle will be a constant represented by the equation revised as: PDP = 100 + TPL.
Where pump discharge pressure is calculated by adding the constant nozzle pressure (100) to total pressure loss. For example, to know the pump pressure required to flow 150 gpm with friction loss at 28 psi per 100 feet of hose, the results will be as follows:
PDP = 100 + (2 x 28) = 100 + 56 = 156
In short, automatic nozzle ensures three key to successful firefighting: variable flow, constant nozzle pressure, and flow control.
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Is an automatic nozzle suitable for foam eductors?
One of the many advantages of automatic nozzles is that they can adjust themselves automatically to the rating of the foam educator if its desired requirements of inlet pressure, maximum hose length, and size can be met. The educator systems nozzle valve is designed to open fully to prevent foam concentrate pickup by reducing back pressure when it is too high.
This can be achieved by adding proper amount of foam concentrate to water to make foam solution which goes through the aeration process by aspirating attachments on the nozzle. Sometimes the stream will pull air to mix with the foam solution in a non-aspirating application.
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Are there trade-offs for low-pressure nozzles?
Nozzle pressure is positively related to nozzle reaction; that is to say, the more the nozzle pressure is reduced, the less the nozzle reaction will be. The question is to what extent the pressure should be reduced to get a desired reaction decrease. Is the use of a low-pressure nozzle delivery system always a good idea to reduce reaction?
The desired nozzle pressure can be reduced from 100 psi to 75 psi when the fog nozzle pressure is reduced. For example, reducing the nozzle pressure of a 200 gpm stream from 100 psi to 75 psi will decrease the reaction from 101 pounds to 88 pounds.
