Hendriksen Blevins (CDNFirefighter1)
The nozzle on the finish of a fire hose is one of the most important pieces of equipment a firefighter has at their disposal when combating a hostile fire. It is the business end of what we do.
Understanding the nozzle involves more than knowing if a push or perhaps a pull opens the bale and if a left or right twist delivers a straight stream. Here are five nozzle questions whose answers you might not know or have forgotten. In any event, knowing your nozzle gives you an advantage over your enemy in a fire attack.
1. HOW ARE AUTOMATIC AND CONVENTIONAL NOZZLES DIFFERENT? Knowing your nozzle offers you an edge over your enemy in a fire attack. Knowing your nozzle gives you an edge over your enemy in a fire attack. (Photo/Tualatin Valley Fire and Rescue)
Conventional fog nozzles have a fixed or selectable gpm setting. These settings match a particular discharge orifice, or tip size. In order for a conventional nozzle with a fixed opening to operate at the right nozzle pressure of 100 psi, the proper gpm flow must be supplied. For example, a selectable gallonage nozzle with settings of 30, 60, 95 and 125 gpm is only going to deliver those flows of 100 psi of nozzle pressure.
You can find two possible results once the conventional nozzle is not given the rated or selected flow. First, inadequate flow provides a weak, ineffective stream that does not reach the seat of the fire. Second, an excessive amount of water flow creates excessive nozzle pressure making the hose line more challenging to take care of and potentially jeopardizing the safety of the nozzle crew.
With an automatic nozzle, the discharge orifice continually adjusts based on the flow to the nozzle. This sets the flow being supplied to the correct nozzle pressure and correct velocity for maximum extinguishing capability.
2. HOW DOES A COMPUTERIZED NOZZLE WORK? The automatic nozzle runs on the principle nearly the same as that of a pumper relief valve. A highly dependable spring, connected to the baffle that forms the discharge orifice, is balanced contrary to the water pressure in the nozzle.
The pressure-control spring senses any increase or decrease in pressure within the nozzle. After that it moves the baffle in or out to maintain a particular tip size necessary to keep carefully the nozzle pressure at 100 psi. In place, the nozzle is constantly changing tip size to complement the water being supplied at that moment.
3. WHAT PRESSURE SHOULD BE PUMPED TO AUTOMATIC NOZZLES? Automatic nozzles greatly simplify pump operation. Since automatic nozzles are made to operate at 100 psi nozzle pressure, this becomes the minimum starting point for any operation.
The basic formula for calculating pump discharge pressure is PDP = NP + TPL ? PDP is the pump discharge pressure, NP is the nozzle pressure and TPL may be the total pressure loss (that's hose line friction loss plus apparatus friction loss plus elevation pressure).
Having an automatic, the nozzle pressure will remain constant and the formula could be rewritten as: PDP = 100 + TPL. So, for a 200-foot pre-connected 1 3/4-inch hose, what pump pressure will be necessary to flow 150 gpm? Friction loss in 1 3/4-inch hose for 150 gpm is approximately 28 psi per 100 feet of hose.
The answer: PDP = 100 + (2 x 28); PDP = 100 + 56; PDP = 156.
To flow 150 gpm in this scenario, a pump discharge pressure of 156 psi is necessary. The required pump pressure will vary depending on friction loss produced, the amount of flow desired, and the distance and size of the hose lay.
The advantage of utilizing an automatic nozzle is that any flow can be delivered by the pump operator and still be controlled by the nozzle operator. Variable flow, constant nozzle pressure, and nozzleman flow control are three essential elements to successful fire streams and fire attack.
4. CAN AN AUTOMATIC NOZZLE BE UTILIZED WITH FOAM AND FOAM EDUCTORS? If the eductor manufacturer's recommendations for inlet pressure,
