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Posted: Sep 1, 2018

Pump Theory and Engine Purchasing

BY DOUGLAS PIETZ


Apparatus with fire pumps are not unique concepts in the fire service; rather, they are the cornerstone of every department.

Hours are spent on the bells and whistles of new apparatus, whether to purchase an aerial platform rather than a straight stick, and even if a rescue-pumper is the best option for a department. Yet, the biggest part of a pumper is often overlooked, or at least proper attention is not placed on the most important component of the engine—the fire pump.

Pump Theory

In pumper operator class, the hardest lecture to swallow is pump theory. True pump theory has complex formulas and equations to determine maximum capabilities of pumps under various conditions. Unless you are a math geek, most of the fire service is lost at the word formula. We take a complex component of the apparatus and bring everything down to the easiest of ways to interpret complex formulas and develop pump charts. These charts are the backbone to rapid response; they get the operator very close to the actual pressures needed. Soon the formulas are forgotten, and the operator is reliant on a chart and, as a result, the theory of the pump is gone too.

So, what this relates to is sending drivers or officers who are not up on pump capabilities to a prebuild for an engine. As a result, departments are forced to rely on the manufacturer’s build team for advice or recommendations. Thus, larger pumps are put into apparatus, and larger pumps need larger motors to drive them. All of this leads to a larger price tag.

The better choice is to look at the needs of the department and community. What fire loads are present in the district? What are the water demands to meet those needs? What water tower operations or large lines need to be supported? Do you have high-rise buildings? Do you operate a water tower with dual nozzles at the bucket? What flows are your hydrants capable of producing? Do you use a water shuttle operation? Answering these questions will help in the process, which is much like homework. My department operates a 2,250-gallon-per-minute (gpm) pump that is rated at 1,500 gpm. The capability of the pump is a combination of the pump and engine needed to drive the pump. It meets our needs to supply greater than 2,000 gpm from a hydrant to be able to use both nozzles on an aerial platform and also feeds the needs of the downtown high-rise district. The pump is Underwriters Laboratories-derated to ensure that the it will pass pump tests. If we rated our pumps at 2,250, then any decrease in engine or pump performance would yield an apparatus that failed a pump test—and that means being out of service.

None of these questions seem to have anything to do with pump theory. But, I would argue that they have everything to do with it. Do the ratings on your new pumper meet the needs of the community, or are you purchasing the engine that you had because it was adequate? What are the future developments in your area, and are you purchasing an apparatus that is good today but not 15 or 20 years from now when the apparatus is in reserve status?

Pressure or Volume

Generally, with fire pumps, there is a choice of pressure or volume. The lower the pressure on the pump, the more volume can be pushed. The higher the pressure on the pump, the less volume can be pushed. This seems to be a simple concept until an engineer is in a situation where more water is needed. The reaction almost all the time is to throttle up and give more pressure. But, with more pr

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Posted: Sep 1, 2018

Pump Theory and Engine Purchasing

BY DOUGLAS PIETZ


Apparatus with fire pumps are not unique concepts in the fire service; rather, they are the cornerstone of every department.

Hours are spent on the bells and whistles of new apparatus, whether to purchase an aerial platform rather than a straight stick, and even if a rescue-pumper is the best option for a department. Yet, the biggest part of a pumper is often overlooked, or at least proper attention is not placed on the most important component of the engine—the fire pump.

Pump Theory

In pumper operator class, the hardest lecture to swallow is pump theory. True pump theory has complex formulas and equations to determine maximum capabilities of pumps under various conditions. Unless you are a math geek, most of the fire service is lost at the word formula. We take a complex component of the apparatus and bring everything down to the easiest of ways to interpret complex formulas and develop pump charts. These charts are the backbone to rapid response; they get the operator very close to the actual pressures needed. Soon the formulas are forgotten, and the operator is reliant on a chart and, as a result, the theory of the pump is gone too.

So, what this relates to is sending drivers or officers who are not up on pump capabilities to a prebuild for an engine. As a result, departments are forced to rely on the manufacturer’s build team for advice or recommendations. Thus, larger pumps are put into apparatus, and larger pumps need larger motors to drive them. All of this leads to a larger price tag.

The better choice is to look at the needs of the department and community. What fire loads are present in the district? What are the water demands to meet those needs? What water tower operations or large lines need to be supported? Do you have high-rise buildings? Do you operate a water tower with dual nozzles at the bucket? What flows are your hydrants capable of producing? Do you use a water shuttle operation? Answering these questions will help in the process, which is much like homework. My department operates a 2,250-gallon-per-minute (gpm) pump that is rated at 1,500 gpm. The capability of the pump is a combination of the pump and engine needed to drive the pump. It meets our needs to supply greater than 2,000 gpm from a hydrant to be able to use both nozzles on an aerial platform and also feeds the needs of the downtown high-rise district. The pump is Underwriters Laboratories-derated to ensure that the it will pass pump tests. If we rated our pumps at 2,250, then any decrease in engine or pump performance would yield an apparatus that failed a pump test—and that means being out of service.

None of these questions seem to have anything to do with pump theory. But, I would argue that they have everything to do with it. Do the ratings on your new pumper meet the needs of the community, or are you purchasing the engine that you had because it was adequate? What are the future developments in your area, and are you purchasing an apparatus that is good today but not 15 or 20 years from now when the apparatus is in reserve status?

Pressure or Volume

Generally, with fire pumps, there is a choice of pressure or volume. The lower the pressure on the pump, the more volume can be pushed. The higher the pressure on the pump, the less volume can be pushed. This seems to be a simple concept until an engineer is in a situation where more water is needed. The reaction almost all the time is to throttle up and give more pressure. But, with more pr

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Posted: Sep 1, 2018

Firefighting Helicopters Added to Los Angeles County (CA) Fire Department Fleet

BOB VACCARO

The Los Angeles County (CA) Fire Department (LACoFD) has always been a front-runner in air attack superiority for wildfire operations in the Southern California area.

BOB VACCARO

Back in 2001, the county purchased and put in service the first Sikorsky S-70A Firehawks in operation for any fire department in the United States. The S-70A is the civilian version of the Sikorsky UH-60L Blackhawk that Sikorsky has been building for more than 25 years for the U.S. military. Los Angeles County has operated three of the older generation Firehawks that were more military designed.

Fast forward to 2017, and the wildland fire season in California was devastating.

It was the most destructive wildfire season on record, which saw multiple wildfires burning across California. A total of 9,133 fires burned—1,381,405 acres, according to the California Department of Forestry and Fire Protection—including five of the 20 most destructive wildland urban interface fires in the state’s history. Throughout 2017, the fires destroyed or damaged more than 10,000 structures in the state (destroyed 9,470, damaged 810), a higher tally than the previous nine years combined. State data show that the large wildfires killed 43 people—41 civilians and two firefighters—almost higher than the previous 10 years combined.

Current Sikorsky S-70A Fire Hawk with 1,000-gallon belly tank.
An artist’s rendering of a Sikorsky S-70i Firehawk for the San Diego (CA) Fire Department.

1 Current Sikorsky S-70A Fire Hawk with 1,000-gallon belly tank. (Photos courtesy of Sikorsky.) 2 An artist’s rendering of a Sikorsky S-70i Firehawk for the San Diego (CA) Fire Department.

The LACoFD was contemplating the purchase of new helicopters for the future. The workload was increasing, and the department and pilots liked the versatility of the S-70 Firehawk and wanted to improve on the design.

According to Janette Eaton, RVP of North American Commercial Sales for Sikorsky, “When we started with the project on the new variant of the Firehawk, the goal was to carry as much water as possible without interference or reduction to the cabin so it could be multimission, with the tank installed, with the quickest dash speed possible in between water and refueling sources. Thus, having a retractable snorkel hose was a must.”

Effective Fire Attack Tool

The end result was the Firehawk® 70i, which is an effective tool during the initial attack—for the following reasons:

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Posted: Sep 1, 2018

Firefighting Helicopters Added to Los Angeles County (CA) Fire Department Fleet

BOB VACCARO

The Los Angeles County (CA) Fire Department (LACoFD) has always been a front-runner in air attack superiority for wildfire operations in the Southern California area.

BOB VACCARO

Back in 2001, the county purchased and put in service the first Sikorsky S-70A Firehawks in operation for any fire department in the United States. The S-70A is the civilian version of the Sikorsky UH-60L Blackhawk that Sikorsky has been building for more than 25 years for the U.S. military. Los Angeles County has operated three of the older generation Firehawks that were more military designed.

Fast forward to 2017, and the wildland fire season in California was devastating.

It was the most destructive wildfire season on record, which saw multiple wildfires burning across California. A total of 9,133 fires burned—1,381,405 acres, according to the California Department of Forestry and Fire Protection—including five of the 20 most destructive wildland urban interface fires in the state’s history. Throughout 2017, the fires destroyed or damaged more than 10,000 structures in the state (destroyed 9,470, damaged 810), a higher tally than the previous nine years combined. State data show that the large wildfires killed 43 people—41 civilians and two firefighters—almost higher than the previous 10 years combined.

Current Sikorsky S-70A Fire Hawk with 1,000-gallon belly tank.
An artist’s rendering of a Sikorsky S-70i Firehawk for the San Diego (CA) Fire Department.

1 Current Sikorsky S-70A Fire Hawk with 1,000-gallon belly tank. (Photos courtesy of Sikorsky.) 2 An artist’s rendering of a Sikorsky S-70i Firehawk for the San Diego (CA) Fire Department.

The LACoFD was contemplating the purchase of new helicopters for the future. The workload was increasing, and the department and pilots liked the versatility of the S-70 Firehawk and wanted to improve on the design.

According to Janette Eaton, RVP of North American Commercial Sales for Sikorsky, “When we started with the project on the new variant of the Firehawk, the goal was to carry as much water as possible without interference or reduction to the cabin so it could be multimission, with the tank installed, with the quickest dash speed possible in between water and refueling sources. Thus, having a retractable snorkel hose was a must.”

Effective Fire Attack Tool

The end result was the Firehawk® 70i, which is an effective tool during the initial attack—for the following reasons:

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Posted: Sep 1, 2018

Hose Friction Loss and Flow Testing Importance

BY LAWRENCE P. HAWKINS


Pump operators are responsible for delivering the required water flow [gallons per minute (gpm)] to the nozzle team with a nozzle reaction (NR) that can be safely handled by available firefighters. This can be done if operators can control pressure at the nozzle, since nozzle pressure (NP) largely determines volume flow and NR.

Friction Loss

The fire engine pump creates a mechanical energy force (pressure) measured in pounds per square inch (psi) to pump water. As water courses through the hose, it experiences friction created by rough hose linings, couplings, gravitational forces, and turbulent flow. Friction converts mechanical energy to heat energy, so by the time water reaches the nozzle it has lost a good part of its pressure. It is the operator’s responsibility to know the friction loss (FL) so he may control NP by adjusting pump discharge pressure (PDP). So, you can see the importance of friction loss measurement.

Another reason measurements are so important is that standard industry estimates for FL calculations are outdated and seriously overstated. Consider the equation: FL = c × (gpm/100)2 × L/100.

The “c” term is the so-called friction loss factor and measures the pressure loss per 100 feet. This is multiplied by the square of the volume flow (gpm) and hose length (L) to get total friction loss. The “c” factor is a handy way of comparing results from different tests and flow rates. By measuring friction loss and volume flow, we can determine the “c” factor. For example, 200 feet of 1¾-inch hose with a smooth bore 7⁄8-inch tip and 50-psi NP pumping at 161 gpm has a 49-psi friction loss. This translates to a “c” factor of 9.5 psi per 100 feet.

I have been gathering “c” factors from known fire department tests and research studies.1 Though the analysis is somewhat anecdotal, the results are instructive; “c” factors varied from c=8 to c=13, with a modal point of c= 9.5. The National Fire Protection Association (NFPA) uses an estimate of c=15.5 for 1¾-inch hose, as do many fire departments as well as hose manufacturers in their published FL tables. These “book” operations are not representative of line operations.

Figure 1: Measuring FL

What happens if you use c=15.5 and the actual is c=9.5? At c=15.5, the FL for 200 feet of 1¾-inch hose is calculated to be 80 psi, or 40 psi per 100 feet. To get an NP of 50 psi, discharge pressure would be set at 130 psi. But if the actual “c” was 9.5 or 49 psi, the NP would be 81 psi. You would be pumping 205 gpm with a NR of 97 pounds of force. Clearly, the pump operator needs accurate FL measures to properly do the job.

So, how do you directly measure FL? There are protocols established by the NFPA, but basically they appear as in Figure 1. The test is performed on level ground. Two pitot gauges (calibrated for accuracy) are installed in the hose—one near the discharge gate and one near the nozzle. During testing, the difference between the pitot gauges measures FL in psi.

Static Test

Before conducting the FL test, run the pump to fill the hose and close the nozzle. The readings on the two pitot gauges should be the same; otherwise, there is an elevation d

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