Engine Company, Firefighter Training, Firefighting, Tech Zone

Dual Pumping: The Convenience Evolution

Article and photos by Paul Shapiro 

We have all seen it on the fireground: a fire requiring more than one pumper to extinguish. There are several methods firefighters use to supply these pumpers. The use of multiple supply lines is one method; this is almost a must when each pumper is moving large amounts of water. But what about the fires that for whatever reason require more than one pumper, but the flows are kept reasonably low? Sure, each pumper could bring in it’s own supply line, but is this the most efficient way to operate? More hose will be needed and depending on where the hydrants are located, and this could require a large amount of hose.

An alternative to this is having one pumper bring in the supply and pumping smaller supply lines to additional units. This operation will in most cases eliminate the excess hose on the ground that might otherwise be needed if additional hydrants were used. However, the management of this type of operation can be difficult. Picture the evolution. The first pumper is supplying a couple of handlines on an interior attack. It is also supplying an additional pumper on the other side of the building with a 2-1/2-inch supply from its discharge at 50 psi discharge pressure. The second pumper is pumping a handline to the roof to support ventilation operations. Initially, the operation is working well but all of a sudden the handline on the second pumper becomes extremely overpressurized to the tune of 300 psi. What happened? It’s simple. A handline on the first pumper was shut down and the pump operator did not adjust for it. The pressure was passed on unexpectedly to the second pumper, which in turn shot up the pressure on the handline to the roof. The bottom line for this type of operation is that the operators involved need to pay close attention to the operation at all times.

The best way to share water between pumpers on the fireground is with a dual pump operation. With dual pumping, one hydrant, especially a strong one, can be used to supply two or more pumpers. In this operation water is shared between the pumpers by connecting a supply line from the unused intake of the pumper connected to the supply line from the hydrant to the intake of the next pumper. Because of the design of the centrifugal pump, any water not used by the first pump will be passed through the impeller and directed out the opposite intake under hydrant pressure. It is this same hydrant pressure that will than move the water through the supply line between the pumpers, thus allowing the water to be shared.

Again, because of the design of the centrifugal pump, the pump that receives the water first from the original supply line from the hydrant will never be robbed of water from the next pump. It will always have first priority. Initially, the discharge pressure may drop on the first pumper when the second pumper starts flowing water because of the additional water being drawn from the hydrant. Don’t let this confuse you into thinking that the first pumper is losing water. The pump operator on the first pumper simply has to throttle back up to the required engine pressure.
Now let,’s change the scenario and use dual pumping in a large scale fireground operation. We have a fire that is requiring big water. Let’s say this fire is a big commercial surround-and-drown type with multiple engines pumping each with their own supply line. As long as it is feasible based on location of units , why not connect as many of these pumpers together with a dual pump operation as possible> This will form what I like to call an above-the-ground looped supply line evoluton. Each pumper will receive their own water supply from the supply line they are connected to and have the potential of being supplemented with additional water through the dual pump line. The lowest residual pressures within the looped system will receive any left over water from the higher residual pressures in the system. This evolution can be set up even before the potential need for extra water. Set the system up and forget about it. The pressures will direct the water as needed. Again, remember, the initial pump from the supply line will never be robbed from water.                                 

Paul Shapiro is Director of Fire Flow Technology. He is a nationally recognized instructor on large flow water delivery. He is also a retired engineer from the City of Las Vegas (NV) Fire Department. Paul has authored numerous articles for fire trade magazines. He has been in the fire service since 1981 and is author of the popular book Layin’ the Big Lines and produced the first in a series of videos on large flow water delivery.  Paul can be reached at 702-293-5150 or Layinline @aol.com to answer any questions.