Gram Emery (CDNFirefighter0)
The nozzle on the end of a fire hose is probably 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 may not know or have forgotten. In any event, knowing your nozzle offers you an edge 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 advantage over your enemy in a fire attack. (Photo/Tualatin Valley Fire and Rescue)
Conventional fog nozzles have a set or selectable gpm setting. These settings correspond to a specific discharge orifice, or tip size. In order for a conventional nozzle with a set opening to operate at the correct nozzle pressure of 100 psi, the proper gpm flow should be supplied. For instance, a selectable gallonage nozzle with settings of 30, 60, 95 and 125 gpm will only deliver those flows of 100 psi of nozzle pressure.
You can find two possible results when the conventional nozzle is not supplied with the rated or selected flow. First, inadequate flow offers a weak, ineffective stream that does not reach the seat of the fire. Second, too much water flow creates excessive nozzle pressure making the hose line more difficult to take care of and potentially jeopardizing the safety of the nozzle crew.
With an automatic nozzle, the discharge orifice continually adjusts according to the flow to the nozzle. This sets the flow being supplied to the proper nozzle pressure and correct velocity for maximum extinguishing capability.
2. HOW DOES AN AUTOMATIC NOZZLE WORK? The automatic nozzle runs on the principle very similar to 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 reduction in pressure within the nozzle. It then moves the baffle in or out to keep a particular tip size essential to keep the nozzle pressure at 100 psi. In place, the nozzle is continually changing tip size to complement the water being supplied at that time.
3. WHAT PRESSURE OUGHT TO BE PUMPED TO AUTOMATIC NOZZLES? Automatic nozzles greatly simplify pump operation. Since automatic nozzles are created to operate at 100 psi nozzle pressure, this becomes the minimum starting place for any operation.
The essential formula for calculating pump discharge pressure is PDP = NP + TPL ? PDP is the pump discharge pressure, NP is the nozzle pressure and TPL is the total pressure loss (that's hose line friction loss plus apparatus friction loss plus elevation pressure).
Having an automatic, the nozzle pressure will stay constant and the formula can be rewritten as: PDP = 100 + TPL. So, for a 200-foot pre-connected 1 3/4-inch hose, what pump pressure will undoubtedly be required 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 based on the friction loss produced, the number of flow desired, and the space and size of the hose lay.
The advantage of using an automatic nozzle is that any flow could 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
