**By Mark Hatalla**

*I became a member of the fire service in 1977, retired in 2010, and continue to work with the Atlanta (GA) Fire Rescue Department Training Academy. Captain (ret.) Danny Byess and I designed an industrial pumper to replace the existing foam unit that was originally built in 1973 and rebuilt in 2000 for Atlanta.*

As we designed the industrial pumper, we discovered a big training curve. Atlanta, like many fire departments, does not establish high-volume water supplies [greater than 2,000 gallons per minute (gpm)] often or use multiple engines to supply one high-volume pump like the industrial pumper (pump capacity greater than 5,000 gpm).

Establishing a high-volume water supply requires the coordination of pump operators and an understanding of calculating the total gpm being supplied by calculating relay pumping backward or reverse relay pumping. Normally when we relay pump, we get the required gpm from the attack engine, and the supply engine makes the calculations and supplies the water at the correct pressure. There may be more than one engine in a line where each engine is relaying water.

The left column reflects how much water is flowing (gpm). The top row represents how the water is flowing (hose combination). The intersection of the column and row is how far the water is flowing (friction loss per 100 feet). |

## Relay Pumping Calculations

High-volume water supply involves multiple engines relaying water with multiple supply lines [three or four large-diameter hoselines (LDH)] into one apparatus like an industrial pumper for high-volume flows. To determine the total amount of water being supplied, reverse relay pumping calculations must be made for each LDH supply line connected to the intake manifold of the industrial pumper.

To determine the calculations for relay pumping:

- Determine the gpm required (from the attack engine).
- Calculate the friction loss in the hose per 100 feet (by size of the hose).
- Multiply the friction loss per 100 feet by the length of the hose (supply line).
- Add intake pressure for the attack engine [IFSTA 20 pounds per square inch (psi)].
- The result is the pump discharge pressure (PDP).

To determine the calculations for reverse relay pumping:

- Determine the discharge pressure (from the supply engine).
- Subtract the intake pressure for the attack engine (IFSTA 20 psi).
- This is the total friction loss in the supply line (maximum of 10 percent of hose test pressure).
- Divide the total friction loss by the length of the supply line (per 100 feet).
- By using a pump chart (Table 1), determine the gpm by the hose size and the friction loss per 100 feet.
- The result is the amount of water being supplied from the supply engine.

1 The industrial pumper, designated Foam Unit 28, built for the Atlanta (GA) Fire Department. (Photos by author.) |

## Using a Pump Chart

Many fire departments develop a pump chart to help their pump operators determine the proper PDP. It also assists with special applications such as foam, aerials, elevation, and relay pumping. The pump chart precalculates the friction loss for various hoselines at various gpm, usually recorded in 100-foot increments.

- Select gpm flow (column on the left).
- Select hoseline or combination (row on the top).
- Determine the friction loss per 100 feet (where they intersect).

The following examples illustrate using the pump chart to determine friction loss.

- Flowing 450 gpm, with three-inch hose 600 feet long: 16 psi friction loss per 100 feet multiplied by six (length of the hose). The result is 96-psi total friction loss.
- Flowing 1,000 gpm with two three-inch lines 500 feet long: 20 psi friction loss per 100 feet, multiplied by five (length of the hose) results in a total friction loss of 100 psi.

The following examples illustrate using the pump chart to determine PDP for relay pumping.

- Relay pumping 1,500 gpm with a five-inch hose 450 feet long: 18 psi friction loss per 100 feet multiplied by 4.5 (length of the hose) results in total friction loss of 81 psi plus 20 psi for the attack engine’s intake for a PDP of 101 psi.
- Relay pumping 1,200 gpm with three 750-foot-long three-inch lines: 12 psi friction loss per 100 feet multiplied by 7.5 (length of the hose) for a total friction loss of 90 psi plus 20 psi for the attack engine’s intake, resulting in a 110-psi PDP.

These examples illustrate using the pump chart to determine flows when reverse relay pumping.

- PDP equals 180 psi, one five-inch 800-foot-long hoseline: 180 psi minus 20 psi (attack engine intake) results in 160-psi total friction loss. 160 psi divided by eight (length of the hose) equals the friction loss per 100 feet. The end result is that one five-inch line with 20 psi friction loss per 100 feet is flowing 1,600 gpm.
- PDP equals 200 psi, two 1,000-foot three-inch hoselines: 200 psi minus 20 psi (attack engine intake) equals 180 psi total friction loss. 180 psi divided by 10 (length of the hose) equals the friction loss per 100 feet. The result is that two three-inch lines with 18 psi friction loss per 100 feet are flowing 950 gpm.

2 Foam Unit 28 flowing 4,300 gpm through both the rig’s deck guns. |

## Fire Pump Testing

Class A fire pumps are rated and annually tested to flow:

- 110 percent of their rated capacity at 165 psi (overload test).
- 100 percent of their rated capacity at 150 psi.
- 70 percent of their rated capacity at 200 psi.
- 50 percent of their rated capacity at 250 psi.

Testing is normally conducted at a “draft,” so the pump must do all of the work. On a pressure source such as a hydrant or from a supply engine, these pressures and the volume of water can vary. The pump discharges the highest amount of volume when it develops 150 psi. A centrifugal pump takes advantage of incoming pressure. Therefore, if the pump has an intake pressure of 70 psi and a discharge pressure of 150 psi, the pump is only developing 80 psi. This means that when the pump reaches the 150-psi difference between the intake pressure and the discharge pressure, it is pumping the maximum volume of water.

## Fire Hose Testing

Fire hose is tested annually and should not be operated at more than 90 percent of the test pressure (10 percent safety margin). It is tested at 200 psi to operate at the maximum of 180 psi-for LDH, 185 psi is acceptable-at 300 psi to operate at the maximum of 270 psi and at 400 psi to operate at the maximum of 360 psi.

Figure 1: Engine 1 is flowing 1,300 gpm. Its intake pressure is 50 psi, and its discharge pressure is 160 psi. More water is available. Engine 2 is flowing 1,600 gpm. Its intake pressure is 80 psi, and its discharge pressure is 180 psi, the maximum discharge pressure. Engine 3 is flowing 1,200 gpm. Its intake pressure is 20 psi, and its discharge pressure is 140 psi. It is using the maximum water available. The industrial pumper is flowing 4,100 gpm. More water is available from Engine 1 if needed. |

## Multiple Supply Engines

In the scenario in Figure 1, there are three engines on separate water sources relaying water to the industrial pumper. Depending on the location of the water source(s), inline relay pumping may occur on each supply line. It is possible to have four or five engines inline relay pumping per supply line. This is not a common occurrence for many fire departments. It will require a mutual-aid response, in many cases, and coordination in every case. Departments should identify and note the locations of large water mains and other water sources before an incident occurs. This should also be included as part of the training for high-volume water supply.

Prefire planning for fixed facilities will assist in determining the number of engines required for water supply based on the location of the facility and the water source locations. It will also assist in ensuring that there will be enough hose and adapters to complete the hoselays. Establishing a high-volume water supply will not be a fast operation to set up. It will require a great deal of coordination and planning. Apparatus positioning and placement are critical to achieve the maximum water supply available. It will be difficult to change or correct any problems once the operation begins. “It is only as strong as the weakest link.”

High-volume water supply is not as simple as connecting hoses and flowing water. It requires an understanding of how a Class A pump is rated and operates in addition to the hydraulics involved in making the calculations. Coordination of apparatus positioning and placement is critical to achieve the maximum water flow. Identifying large water mains and continued training, including on hydraulic calculations, are necessary to prepare your crews to successfully establish a high-volume water supply.

Many fire departments relay pump on a regular basis. It is usually one supply engine pumping to an attack engine. Inline relay pumping with several engines supplying an attack engine is not that common. Most residential structure fires require less than 1,000 gpm and do not pose a water supply problem. When the required water flow increases to 4,000 to 5,000 gpm, it creates quite another situation for most fire departments. Fire pumps are designed to work. Proper positioning and water supply to them can produce a high-volume water supply.

**MARK HATALLA **has been in the fire service for almost 30 years and is a captain (ret.) with the Atlanta (GA) Fire Rescue Department. He is an instructor with the Atlanta Fire Rescue Department’s fire academy driver’s section and has an associate’s degree in fire science. He has Officer II, Instructor III, apparatus driver/operator, and evaluator certifications.