We all want that “top-of-the-line” engine with its chrome wheels, fancy lights, complete with all the bells and whistles. And for the grand finale, the truck has to have the largest, strongest pump available with the capability to pump more water, faster and farther than any other pump known to mankind.
But is bigger really better?
That depends on a few variables such as water supplies, required fire flows, hose type and most importantly, the department’s needs.
Notice that I said needs and not desires. Let face reality, a 1,500 gpm, or larger fire pump will not provide adequate fire flow unless the remainder of your water delivery system is equally matched.
The volume of water you desire must travel through a pump, hose, appliance and nozzle before it can be used to extinguish a fire.
I am always amazed at the number of fire departments who own the “Cadillac” engine and, upon closer examination, find the remainder of their water delivery system is grossly inadequate. I will bet anyone reading this a steak dinner that a properly matched water delivery system using a 1,250 gpm fire pump can deliver more water than a mismatched water delivery system using a 1,500 gpm fire pump.
We all know it takes water to extinguish the fire. Big fire equals big water. So how do we get it from here to there?
First, let’s examine those previously listed variables. Water supplies come in two forms, static or pressurized.
Fire departments need to examine their water sources and determine whether they can supply the required fire flow. Also, check to see whether the dry hydrants are constructed with adequately sized pipe and the connections are at the proper height to minimize lift.
When thinking about hydrants, keep in mind the size of the water mains that supply them and whether they have steamer connections. Knowing the pressure supplied and whether the system has pressure reducers is also important.
Consider Regionial Use
Look regionally as well and determine whether the water sources in the area compliment or hamper the department’s ability to flow the maximum capacity of your fire pump and for how long.
Now let’s examine the supply hose. Five-inch large diameter hose (LDH) will flow approximately 1,600 gpm, while 4-inch will flow approximately 900 gpm. Trying to push 1,500 gpm through the 4-inch diameter hose is like trying to push a watermelon thru a garden hose.
Let us not forget those discharge pressures. Be aware of the manufacturer’s recommended maximum operating pressure of your supply hose. Think about whether your 1,500 gpm pump can deliver the desired fire flow using 1,000 feet of 5-inch hose at a pressure of 150 psi.
For those pump operators who wish to push the envelope and crank up that throttle, remember a 5-inch hose with 150 psi at failure will produce 2,940 pounds of force. That will certainly cause a memorable event. Usually, the weak link in the water delivery system will be the LDH operating pressures, so plan and train accordingly.
Now comes the complicated part of the equation, which is: how much water will you need? I fully understand we, the members of the fire service, sworn to protect life and property, do not have the time to tour every structure in our region to determine the required fire flow for each one.
Some might say, if we have the “Cadillac” fire truck with a huge 1,500 gpm or better pump, capable of launching men to the moon, why do we have to know how much water would be needed to control the fire?
Be aware, that I’m not advocating visiting every structure, but at least identifying target hazards and calculate accordingly. Enough said.
Let us move on to the fire pump itself. It’s important to plan and have a complete understanding of all the variables in your town and department. Without them, specifying a pump is like trying to order Chinese food in an Italian restaurant.
And what about all those options to consider? Remember that a pump is only as good as its intake and discharge system. Many pump manufacturers offer discharges in 3-, 3.5, and 4-inch diameter. Larger diameter discharges afford you the capability to deliver more water at lower pressures.
However, there will be circumstances when you need to boost those pressures to overcome friction loss and head pressure, especially when supplying an aerial ladder or working a high-rise structure fire.
I have included a picture of a 5-inch discharge casting on a 1,500 gpm pump. As you can see from the picture, the casting does not restrict the water flow and can provide an extremely high volume of water at a low pump discharge pressure.
Using a higher pressure LDH would give you the capability to deliver a large amount of water to a master stream device. The only restriction would be the capacity and adequacy of your water supply.
When speaking of water supply, consider the size of the intakes on your pump. They should be sized and configured appropriately to compliment the pump’s flow. The pump plumbing should have minimal elbows and bends to reduce friction loss and turbulence.
So, is a bigger pump better? My answer is yes, but only if you need it and can supply it adequately.
In all honesty, we seldom need to flow the maximum capacity of any fire pump. Those fires are usually far and few between, but occasionally have a tendency to challenge our competency and skills.
So I leave you with this thought; it is not how big or powerful your pump is, what matters is that you have done your homework, preplanned the structures in your region, calculated your water supplies and, most importantly, equipped and trained your firefighters to safely and effectively manage the fire situation.
So next time you see a “Cadillac” truck, take a closer look and remember, it’s not the pump that puts the fire out, it’s the firefighters.
Editor’s Note: Joe Mercieri is the Fire Chief serving with Littleton Fire Rescue in Littleton, NH. He has served 27 years in the fire service, is an active fire service instructor and holds numerous college degrees and certifications.