Evolution and Technology Change the Rules for Length of Foam Lines

I was asked, the other day, whats the longest hose lay you can use when operating with a foam injection system.  This question is born from the use of truck mounted bypass eductor systems, where there was a maximum efficient hose lay to allow the eductor to properly pick up the foam concentrate.  The bypass eductor systems required that the correct nozzle be used and that it be open fully, the correct size/length of hose and maximum elevation limitations to properly function.  It could become quite the balancing act. 

The answer to the question of how long of a hose lay you can have with an injected foam system is pretty much unlimited, with the parameters of the system maximum capacities.

Foam Injection Systems

Hale 3.3 System Capacities

Let's use Hale's Foamlogix as an example.  The system uses a foam pump to inject concentrate into a water/foam manifold, where it then provides that foam solution to the discharges that are supplied by that manifold.  The foam capable discharges will be marked as such on the pump panel.  Its also important to remember that the foam system capacity is cumulative for all of the foam capable discharges.  Before we proceed, lets take a look at the maximum capacities of a 3.3 Foamlogix system.

By the data supplied on this plate, we can deduct two important things that relate to total water flow (with foam) capability.  The maximum working pressure of 400 PSI and maximum water flow of 1250 GPM are the two major factors that lead us to the answer of how far we can pump the foam. FoamPro lists similar capacities below.

FoamPro Specs-Courtesy FoamPro

Courtesy of Hale

The other information we need to know is what is the maximum water/foam flow at each percentage.  because the foam pump can only supply 3.3 GPM of concentrate, there are limitations on the total flow it can produce.  For this 3.3 model system, the chart to the right shows the maximum water flow for the chosen foam percentage.  To accomplish this, the system meters water flow and communicates with the foam pump to meter the appropriate amount of concentrate to maintain the foam percentage.  As a sidebar, the best way to take advantage of the capabilities and limitations of a foam injection system when using class B foam is to use lower percentage foam (higher concentration).  1% or 1%/3% foam provides the capability for higher total water flow.  Compare the differences between the 3.3 and 5.0 systems.  The 5.0 system uses a 5 GPM foam pump.

A Bit About Eductors

A simple 125 GPM inline eductor.

 Anyone who's used a truck mounted bypass eductor system will remember the rule of no more than 150ft of hose, or in some cases 200'.  These distances also apply when using portable foam eductors.  Many departments also used red hose on that foam crosslay/preconnect, to make it more apparent that it was the foam line.  Lets take a step back and see where the old distance rules came from.

Most eductors require 200 PSI at the inlet in order to properly create the foam.  The flow of water through a small orafice in the eductor into a larger chamber within it results in a low pressure zone, which draws foam concentrate up the pickup tube and mixes it into the water stream.  The proper pickup of foam concentrate is also influenced by backpressure on the eductor.

Backpressure can be caused by;

• Pressure (friction) loss in the hose.  The distance you can pump beyond the eductor is based largely on the water flow.  This is where basic hydraulics comes back into play.
• The nozzle.  The nozzle creates backpressure by design, this is how we create a useful fire stream.  A nozzle, not opened all the way will create too much backpressure, reducing the efficiency of the foam operation
• Elevation.  Head pressure will create backpressure that will deteriorate the foam operation.

Eductors can use about 65 percent of the inlet pressure on the outlet side.  What this translates to is a maximum discharge pressure of 130 PSI  on the outlet of the eductor before the foam concentrate flow is compromised.  Using an inline gauge on the outlet of the eductor can monitor this, but the information is easy to figure out beforehand.  If you consider the maximum outlet pressure from the eductor is like a maximum pump pressure, then the following chart illustrates the maximum hose lays when using eductors.

Courtesy Akron Brass Corp.

You may note the 150' and 200' hose lays in the first column, when used with 3%/6% concentrate, as it was one of the most common types of ATC/AR foam types used.  Confusing, maybe a little, but planning ahead of time and marking the pump panel can eliminate any confusion.

Tying it Together

Does it seem like we went way off tangent? Perhaps, but it provides the basis from which we got the old rule of thumb for the maximum hose lay with foam systems.  Now that we are seeing more foam injection systems, this hose lay rule doesn't apply the same way, because the required balance of hose length, nozzle, elevation isn't at all similar.  We previously mentioned the maximum capabilities of a Hale system.  Lets see how that translates to real world terms.

If the maximum pressure of the system is 400 PSI, and we are operating a 100 PSI nozzle, we can use the remaining 300 PSI to account for pressure loss in the hose and any elevation loss.  Keep in mind, 400 PSI is an extreme pump pressure, and it might be more realistic to shoot for a maximum pressure lower than this.  Factoring your maximum hose length is probably better done at a maximum of 250 PSI, as any pressure in a hoseline greater than that will be arguably dangerous and difficult to manage (very rigid) when the water is not flowing.  The point here, is to illustrate how to deduct the maximum working length of a hose line when using an injected foam system.  Using the maximum capacity of the system (400 PSI) we can determine the following;

• A 95 GPM foam line can be run about 2100 feet, using a 100 PSI nozzle.  The system capacities will limit the maximum foam percentage to 3% at 110 GPM, so for round numbers (since 95 and 110 are pretty close) your 3% foam can be pumped about 2100 feet in 1 3/4" Hose.  If we switched to 2" hose, the distance increases to 4200 feet.  Using 1 1/2" hose, the maximum distance is 1350 feet.  If your nozzle is a low pressure fog or smooth bore (50 or 75 PSI tip pressure, the distance will be greater).

To arrive at the answer to this question, when using a foam injection system, consider this simple formula;

MD=MSP-NP-FL-EL

MD is Maximum distance

MSP is Maximum System Pressure (Replace with 250 PSI for more realistic flows)

NP is nozzle pressure

FL is fricton loss (for the flow you have chosen)

EL is elevation loss

To truly know the maximum distance, you should consider the maximum flow you will use at each percentage of foam (typically .5, 1, 3 and 6%) and find the friction loss value on a chart to insert that number into the equation.  Because most nozzles are set to predetermined flows (except for automatic nozzles), using predetermined friction loss values for flows such as  95, 125, 150, 180, 200 GPM makes that part of the equation easy to determine.  You will just need to verify your desired flow is within the range of the foam system.

The short and scientific answer here is....

You can go WAY FURTHER than 150 or 200 feet from the rig when using an injected foam system!

Apparatus mounted bypass eductor systems are still an option today, but they limit your foam flow to one discharge and also have top end flow restrictions that are lower than larger injection pump systems.  Understanding the system you have is critical, before you can determine how to best utilize it.

Read the owners manual for your foam system to learn its capabilities.  Links to major manufacturers are below.

Akron: www.akronbrass.com

Hale: www.haleproducts.com

FoamPro: www.foampro.com

Waterous: www.waterousco.com

Pierce: www.pierceparts.com or www.piercemfg.com