The Nozzle with both Constant Pressure and Variable Gallonage
Have you had enough of the poor fire stream caused by water pressure that is either too high or too low when you are holding the nozzle at the end of a hose line? Have you decided against changing the nozzle tip size or gallonage setting just because you never communicate will with the pump operator about this? Many people have such a bad experience, and frankly it’s not only frustrating but also fatal on the fire ground.
A solution to this problem has been ignored by most firefighters for lack of the least comprehension of a frequently told story they might have heard many times. It describes a catastrophic consequence resulting from an unfortunate firefighter in some fire department involving with this solution known as the automatic nozzle. Simply put, it is exactly a constant-pressure, variable-gallonage combination nozzle, which works far better than the standard constant gallonage or adjustable gallonage nozzles.
The Difference between Two Combination Nozzles
To begin with, we’d like to specify two different types of combination nozzles: the constant-gallonage and adjustable-gallonage nozzles. The constant-gallonage nozzle is the simplest of the same product family, whose nozzle pressure is kept at a predetermined standard value measured as gallons per minute (gpm) by a fixed orifice. In other words, the rated pounds per square inch (psi) produced by the constant-gallonage nozzle will discharge a predetermined volume of water not being able to be adjusted.
In charge of controlling this volume, the pump operator only needs to know the rated nozzle pressure and the pressure loss in the hose-line while properly supplying the nozzle. Controlling the volume of a constant-gallonage nozzle is not much different from that of a fixed orifice smooth bore nozzle by any measure.
Regarded as a modified constant-gallonage nozzle in design, the adjustable-gallonage nozzle has several orifice sizes for the nozzle operator to select manually. This can be done at the operator’s will by rotating a collar on the nozzle to change its orifice size, in the same way how they change a tip on a smooth bore nozzle. Whether the nozzle is adjustable or not should never be a problem because many departments maintain a standard hose length and standard gpm settings for the nozzle. Some even have labeled information right next to the discharge gauges indicating the discharge pressure (DP) for each discharge setting. This is not a bad idea when the hose length or gpm settings can remainunchanged. Most of the time, however, these predetermined settings need to be changed to properly respond to the fireground situation.It is not uncommon that you need to change the standard volume setting to fix the problem of a poor water flow. To do so, you must communicate with the pump operator accurately to make the desired changes. This can be far more difficult and riskier during an offensive interior attack than a defensive attack. A key solution to this problem is the use of automatic nozzles. Below we’d like to provide a deeper insight into how an automatic nozzle work to solve the above-mentioned problem.
Automatic nozzles, also known as constant-pressure nozzles, are functionally identical to pressure relief valves, which release the pressure that exceeds what has been selected by discharging certain amount of water through the valve. The higher the water pressure, the wider the discharge opening. That’s why a constant pressure can be maintained.
It’s something as simple as a springpushing a ball against a pipe opening. When the constant pressure produced by the spring is greater than that of the water pressure in the pipe, the ball will be firmly fitted into the pipe opening, so there is no discharge of water. If the water pressure continues to increase and exceeds 100 psi, it will compress the spring to push the ball away from the pipe to discharge certain amount of water so that 100 psi can be maintained in the pipe. Reversely, when the water pressure in the pipe drops below 100 psi, the ball resumes its position against the pipe opening and once again prevents the water from discharging.
In the same token, an automatic nozzle operates almost the same way and is more than just that.It can discharge any volume of water in many different shapes within its volume rating in response to the rapidly changing situation at fire scenes. That’s why it is called a “constant-pressure, variable-gallonage combination nozzle” and has a critical role to play in all the fire departments.