Term Paper: Fire Service Hydraulics

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¶ … fire service hydraulics. This begins with an overview of motorized equipment and pumps that were utilized in the past and the advancements that have been made in today's equipment. A discussion stage pumps vs. multiple-stage pumps will be presented, including the advantages and disadvantages of each. Fire hose advancement will also be presented, from 2 1/2" supply lines to LDH supply lines. This will be followed by a discussion of nozzle improvements, as they've gone from set gallonage to automatic nozzles. Lastly, advancements in the electronics, instruments and construction materials of pumps and pumpers will be presented.

History of Motorized Equipment and Pumps:

Although many would think the bucket brigade as the primary means of fire fighting not so long ago, fire pumps were developed centuries ago. The history of motorized pumps begins in ancient history with the use of hand-held pumps by Greeks and Romans. In fact, "Ctesibius of Alexandria is credited with inventing the first fire pump around the second century B.C. But the idea was lost, ironically, in the burning of Alexandria" (History of Firefighting"). It would then be the Industrial Revolution that would see these pumps advance technologically. Steam pumps were the first motorized pumps, used in the 19th century. By the early 20th century, the internal combustion engine was utilized in fire pumps. Fire engines, during this time, would have a second motor for the fire pump. In 1907, America saw the first fire engine that utilized a single motor to run both the truck and the water pump.

These early pumps quickly replaced the steam-powered pumps that were the predecessor. At first, pistons were used to power the motor. Soon after, however, rotary power was used, and this was quickly followed by the technological improvement using centrifugal force, where compressed air expels water through centrifugal force. "The first centrifugal pump was a single-stage pump, with a single impeller capable of taking suction from only one side of the impeller" ("Single-Stage"). The maximum pump pressure is determined by the speed and size of the engine. This is the model for the modern motorized fire pump, that allowed a higher volume of water and a larger range when fighting fires.

Today, fire pumps have come a long way from the days of hand-pumps used by the Greeks and Romans. Today's motorized fire pumps are high-powered, how volume pieces of machinery that are critical in fighting fires. These fire pumps give a minimum of 750 gallons of water per minute, at 150 pounds per square inch of force ("The History").

Single-Stage vs. Multiple-Stage Pumps:

There is continuing controversy regarding which is better -- single-stage or multiple-stage pumps. Both pumps play important roles in fire fighting; however the choice of which type of pump must depend on the specific pumping requirements. Both single-stage and multiple-stage pumps meet NFPA1901 and NFPA1911 standards, but there are fundamental differences between the two types of pumps ("Single-Stage"). These differences are found in the design of the pumps.

The single-stage pumps of today have "one dual suction impeller designed to take water in both sides of the impeller, providing discharge flows to all discharge gates. The operator has full range pump performance with the operation of the engine throttle. A single-stage pump can reach approximately 350 Psi maximum pressure" ("Single-Stage").

In contrast, a two-stage pump uses two impellers. These operate side-by-side, on a common shaft. This design allows the operator the choice to select either pressure or volume. This allows them to adjust the pump depending on the unique fire event. A transfer valve is incorporated into the design of a two-stage pump to facilitate this choice. The design of the two-stage pump allows it to attain higher pressures than their single-stage counterpart. In fact, many two-stage pumps can reach pressures as high as 600 Psi, this is in contrast to the 350 Psi that the single-stage pump maxes out at ("Single-Stage").

Choosing the best pump for each situation often is based on their advantages. The single-stage pump offers a significant benefit of simplicity. This makes it a highly reliable pump. The two-stage pump is more complex, but it does achieve a higher pump pressure and gives the operator an option of volume or pressure ("Single-Stage").

Fire Hose Advancement:

The use of hoses to fight fires can be traced back to 400 B.C., according to Gilbert. Made from the gut of an oxen, early firefighters filled bags with water and then forced them into the hose. Firefighters would then sit or stomp on the bag and hose to force the water through. The modern fire hose echoes back to 1693, where fifty-foot lengths of leather were sewn together. Developed by Jan Van der Heiden and his son, later Van der Heiden would develop the first suction hose, by including a wire frame inside the hose, to keep it from collapsing.

The next evolution of the fire hose came when James Sellars and Abraham Pennock, both Philadelphia firemen, used metal rivets on the seams of a leather hose, instead of stitching, allowing for higher pressures and fewer breakages. In 1821, the rubbe line, cotton-webbed hose was patented, allowing a 100-foot hose to do the work of 60 men on a bucket brigade. As more and more manufacturers entered the marketplace, the variety of unique sizes became a problem. For this reason, the International Association of Fire Engineers' first convention adopted a standard size for hoses of 71U2 threads per inch. In 1932, the National Fire Hose Standard of 2 1/2 inches -- 7.5 threads per inch hose was made the standard. In 1957, the standard was changed to 1 1/2 inches. More departments were willing to make this change, thanks to the Ely Fire Hose Thread Standardizer that would convert the coupling sizes to the new standard (Gilbert).

Today, Large Diameter Hose (LDH) is the standard hose. This hose is made from reinforced plastic and features rubber lining. it's lighter weight than its predecessors and can even be repacked while it's still wet, without fear of rotting. However, mold is still a potential unpleasant side effect on these lower pressure, high volume hoses (Gilbert).

Nozzle Improvements:

There are a variety of nozzles that are utilized in firefighting. Some provide solid, heavy streams of water. Others produce curtains of spray; while still others create a fire defeating fog. Firefighters typically have a selection of nozzles available to them, and can choose the one that is most appropriate for the amount of heat that needs to be absorbed. Rates of flow vary greatly with these nozzles. Fog-type nozzles may only use 15 gallons of water per minute. In contrast, steady, heavy stream nozzles can use more than 100 gallons per minute. Although straight streams can reach farthest, allowing firefighters the ability to reach and penetrate fires farther away, a fog nozzle can absorb heat more quickly. The water droplets from the fog distributes water in a greater area and can be utilized to "disperse vapors from flammable liquids, although foam is generally used to extinguish fires in flammable liquids" (Gilbert).

In addition to spray pattern, there are five basic nozzle types. The solid bore nozzle is the most basic type, with a simple design and function. it's a solid stream nozzle. The single gallonage nozzle is the simplest combination or fog nozzle. These nozzles provide a predetermined flow rate that cannot be altered. Flow can only be varied by adjusting nozzle pressure. Adjustable gallonage nozzle allows the operator to select the gallonage used. Automatic nozzles, in contrast, provide a relatively constant pressure level, even with a variety of flow rates. There is a mechanism in the nozzle that increases or decreases the flow automatically. Lastly, the multi-purpose nozzle combines solid bore and fog nozzle. This can give bot the reach of a single stream,… [END OF PREVIEW]

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