Water, Hose, Fire Weight Inline Pumping Decision
departments
The Volunteers Corner
Inline pumping is an effective way for the first-in engine company to get fast water on a fire. It is an option that should be available to engine company officers in areas with adequate water systems, but it is an option that should be used judiciously.
In the inline pumping evolution, the engine company drops parallel 2 1/2 or 3-inch lines (it can be one of each or a single 3 1/2,4,5 or even 6-inch line) at the hydrant and lays to the fire. At the fire, a preconnected hand line is stretched into the building and this line is first charged with booster tank water. A man left at the hydrant opens the hydrant and when the water reaches the pumper, the operator opens first one and then the second inlet valve as he shuts the booster tank drop valve. Without any noticeable effect on the nozzle, the pump’s water supply is thereby shifted from booster tank to hydrant.
Sounds great? Sure, but there are some drawbacks to inline pumping that must be considered to avoid some pitfalls, such as:
- The supply hose may be too small and allow only an inadequate water flow.
- The maximum flow from the hydrant may be too little.
- The volume of fire may be far too great for the maximum capabilities of inline pumping.
Hose size: Let’s first take a look at hose sizes. The maximum amount of water that can flow through a hose at a specific pressure is determined by the diameter of the hose and the length of the lay. The diameter of the hose determines the cross-section area through which water flows and the larger the area, the larger the potential flow at the same pressure.
The accompanying table of hose sizes and cross-section areas increase in square inches far more rapidly than the increase in hose diameter. Add only an inch to the diameter of 2 1/2-inch hose and you have a cross section that is almost twice as great—4.9 inches for 2 1/2-inch hose and 9.6 inches for 3 1/2-inch hose. Use 4-inch hose—a common size in large diameter supply lines—and you have a cross section that is 12.6 square inches, or better than 2 1/2 times the cross section of 2 1/2-inch hose.
For practical purposes, we are limited to stretching two lines from a hydrant for inline pumping. From the table, it is obvious that with 2 1/2 and 3-inch lines, parallel lines are a must. At the same time, the table shows the advantage of using a single 4 or 5-inch supply line.
Potential Flow: What you get out of any hose line is what goes into it. With inline pumping supply lines, the volume of water that goes into the lines depends on the potential flow of the hydrant.
You should flow-test hydrants so that you know the potential flow of hydrants throughout your area. Each company officer should be familiar with the flows of hydrants in his first-due area. You have to concede that there is no supply line layout that will carry more water than the hydrant provides.
Large diameter hose minimizes friction losses, but these losses rise rapidly in 2 1/2-inch hose. A useful drill is to measure the water obtained in inline pumping from a single 2 1/2-inch supply line that is 200 feet long. Then measure the flow with the 2 1/2-inch line 400 feet long. Try this with other sizes and stretches.
Don’t be fooled by the static pressure of the hydrant. A 1/4-inch copper tube can have a pressure of 150 psi, but you won’t get much of a flow from it. Look at the size of the main serving the hydrant. The larger the main, the more water you can expect from the hydrant.
Volume of fire: Become familiar with the flows you can expect in different areas with the inline pumping supply line layout in your department. Keep this in mind when, as the first-in engine company officer, you get your first sight of the fire. The vital question you have to answer—still at least one hydrant away from the fire—is whether inline pumping will provide enough water.
Understandably, you don’t see from a distance all you will when you arrive at the fire building. Nevertheless, the inline pumping decision must be made before you pass the last hydrant. There are fires of such extent that the need for large volumes of water and a direct hydrant hookup of the pumper are obvious. The difficult decisions come out of the gray area where the fire “looks” as though it is within the extinguishing capability of inline pumping flows.
The inexcusable decision is for a second engine company to do inline pumping. If pumping by a second engine is needed, then that engine should hook up big to a hydrant so that it can pump the full flow of that hydrant. For the second engine company, the ability to provide the maximum flow of water is more important than a reduction in time in getting a second or third line on the fire.
Try to establish inline pumping procedures that use the most efficient hose sizes your department can provide and know what your hydrants will supply through these layouts so you can relate inline pumping potential to the volume of the fire.
