What can adversely affect your pumper's handling characteristics, weighs almost five tons, costs $5,000, never sees the light of day, is seldom painted, and influences the efficiency of your engine company? It's your booster tank-something firefighters pay no attention to unless it's empty or it leaks. They should. It carries the wet stuff to put on the red stuff. This article addresses tanks on pumpers only. Tankers (water tenders) are uniquely different and should be addressed separately.
One gallon of water weighs 8.34 pounds and occupies 231 cubic inches of space. A cubic foot weighs more than 62 pounds. One thousand gallons weigh 8,340 pounds. Add the weight of the tank material, substructure, and plumbing, and there are close to five tons occupying 135 cubic feet. How much water and where it is carried on a fire truck influence everything else-including the safety of the crew riding on it.
Booster tanks evolved from the soda-acid tanks of the late 1800s, cylindrical fixtures containing water and sodium bicarbonate-giant fire extinguishers on wheels, although horse-drawn. Injecting sulfuric acid formed carbon dioxide, which forced the mixture through a hard rubber hose. With the introduction of motorized apparatus and engine-driven pumps, the soda acid was replaced with all water-about 100 gallons-and the tank usually sat above the pump or just behind the driver's seat.
The late 1930s saw frame-rail-mounted square and rectangular tanks located ahead of the hosebed seldom exceeding a couple hundred gallons in capacity. T-shaped tanks of various capacities were introduced in the 1950s and remain popular today. Extending upward and outward over the rear inner wheels toward the body-side sheets, some were bustled with the upper "T" extending rearward above the rear-step compartment. Tank designs accommodating rear slide-in storage for ladders and suction hose became popular in the 1980s.
Apparatus builders fabricated their own tanks, usually from the same material as the body. Untreated steel tanks were standard until the 1960s, when galvanized steel became the norm. Stainless steel was introduced in the late 1970s and aluminum the following decade. Molded fiberglass saw limited use; its popularity coincided with the success of mostly regional manufacturers marketing the product. Composite fiberglass, integral with that type body construction, is relatively new.
Today, most apparatus builders outsource tank construction. "Poly Tank" is a registered trademark of United Plastic Fabricating (UPF). Henceforth in this article, "tank" is used generically to describe all thermoplastic tank materials regardless of whether they are called Polyprene, PolyTank III, Polybody, polypropylene, polyethylene, homopolymer, copolymer, and so on. The two prominent tank manufacturers are UPF and Pro-Poly of America. Although their methods of manufacturing are similar, each has a specific product line, detailed specifications, and warranties. Purchasers should evaluate all tank manufacturers when purchasing. Thermoplastic tanks became popular in the early 1990s.
Bill Bruns, vice president of sales and marketing for UPF, and Tim Dean, president and CEO of Pro-Poly, contributed for this article, as did Keith Purdy of Plastisol-America, a composite fiberglass manufacturer. Bruns notes that stainless tanks are still common on the West Coast because of extremely high domestic water pressures, and Donley Frederickson, national sales manager for Rosenbauer, says, "We still build a real small amount of hot dip galvanized tanks."
|(1) Shown is a formed elliptical tank with integral body.
(Photo courtesy of Pro-Poly.)
Methods of Fabrication
Metal tank pieces are bent, formed, and welded together. Although some thermoplastic tank materials can be rolled into elliptical shapes (photo 1), most are fabricated from flat pieces adjoined by extrusion or nitrogen welding. UPF and Pro-Poly both use the welding process, with one also promoting a mechanical lock and the other a sealant. Early technology used molds to form fiberglass tanks. Today, Plastisol-America manufactures composite fiberglass flat stock that is cut and glassed together with resin and fiberglass strands. This article does not recommend a manufacturer, a product, or a process.
Integral Tanks and Bodies
UPF, Pro-Poly, and Plastisol also manufacture bodies with integral tanks (photos 1 and 2). Dean says, "The integration of tank and body is a profound improvement to fire truck design, eliminating duplication of material and resulting in lower center of gravity and lighter weights." Bruns comments that the concept is gaining acceptance. Purdy adds, "An integrated tank design brings additional strength to the apparatus body by making the unit into a single solid product." Dean notes, "With the introduction of thermoplastic tanks, the need for annual maintenance is significantly reduced and even eliminated. Thus, there is really no need to have a removable tank." Up until the 1999 edition, National Fire Protection Association (NFPA) 1901, Standard for Automotive Fire Apparatus, prohibited integral water tanks.
|(2) Shown is an example of an integrated tank and body.
(Photo courtesy of Pro-Poly.)
Outsourcing tank construction relieves apparatus manufacturers from major warranty concerns. Bruns says, "An experienced [tank] manufacturing team working with approved designs will result in an issue-free product." Dean concurs. "Because these tanks have been so reliable and have done an outstanding job reducing the maintenance required in the field, manufacturers have all offered various forms of limited lifetime warranties," he says.
There have been some issues in the field, which, according to Dean, are "related to improper installation, such as not enough support or rubber insulation and improper plumbing." Be fair. Tank manufacturers should not be responsible because an apparatus manufacturer erred. However, both parties should, and do, work together to resolve warranty concerns.
|(3) This internal view of a T-shaped tank shows the numerous baffles, interior walls, and tank overflow piping.
(Photo courtesy of Pro-Poly.)
Dean notes some problems have been attributed to end users. "There are a few operational issues that arise from too fast fill rates," he says. Purdy adds, "Many customers design vehicles to pump massive amounts of water from the tank for rapid knockdowns. Massive water delivery requires larger air systems to avoid tank cavitation." Bruns notes that his company provides pump panel tags indicating maximum tank-fill rates in gallons per minute (gpm) and the maximum fill pressure in pounds per square inch (psi) allowed when filling the tank.
When specifying direct tank fills, especially with large-diameter hose (LDH) connections, purchasers should be aware that they may no longer control their own destinies-or their tanks'. If an inexperienced pump operator decides to fill your tank through five-inch LDH at 1,500 gpm or 185-psi discharge pressure, the manufacturers should not be liable. Regardless of the material used, something somewhere may let loose-perhaps a baffle, a diffuser, a weld-or even launch the fill tower like a Polaris missile (photos 3 and 5). Bruns states, "The majority of the service for a tank can be done at the customer's location. Dean concurs and says, "Even ISO-certified manufacturers with thousands of units in the field may, like with any other manufacturing process, experience an occasional workmanship or installation defect that affects performance. Usually this damage can be easily rectified in the field by certified technicians."
|(4) This Toyne pumper has a 1,000-gallon L-shaped tank. Both rear
discharges are sleeved through the tank. The 2½-inch connection
beneath the right side 2½-inch discharge is a direct tank fill.
Use caution when filling.
(Photo by Dave Fornell.)
The most common tank capacity is 1,000 gallons, usually with an integral foam tank. Next are 750- and 1,500-gallon capacities. Many purchasers specify apparatus with full-depth full-height compartments, eliminating the upper sections of T tanks; hence, the rectangular tank is making a comeback. Noting the trend for more user-friendly hosebeds, Dave Fornell, an apparatus industry insider, says, "There is great acceptance for the L-shaped tank configuration to lower hosebed heights" (photo 4). Manufacturers see an increase in notches, sleeves, tunnels, integral foam cells, and odd-shaped tanks to meet customers' requirements (photo 6 and Figure 1). Bruns notes that apparatus manufacturers will design a body and tank configuration and the tank manufacturer will finalize the technical layout, confirm calculations, build the tank, test it, and certify its capacity.
|Figure 1. This artist's rendering depicts a very customized tank configuration.
(Illustration courtesy of the CustomFIRE Apparatus design department.)
Historically, routing steel piping through an untreated steel tank was a natural invitation for leaks and labor- intensive repairs. "Old-time" specification writers still specify "piping sleeved through the tank is not acceptable." Times have changed. It's time to move on. Bruns says, "Running poly sleeves through tanks is very common" (photo 5). Dean elaborates and states that fabricating a notch is location-sensitive, labor-intensive, and more expensive than a sleeve. Frederickson points out that sleeves allow flexibility in locating discharges for purchasers. Fornell concurs. "A sleeve allows the location of the plumbing to be varied should a purchaser want piping directly under a hosebed for a preconnect," he states. Wayde Kirvida, factory sales with CustomFIRE, says, "Due to a pass-through sleeve being round vs. a square notch, the sleeve is more popular due to more water loss with the notch." Purdy adds, "[In our type of construction], pipes are sleeved through the tank, then 'glassed in,' becoming an important part of the unibody design."
Responsibility, Stability, and Safety
Some pundits extrapolate that, regardless of materials used, poor tank designs are significant factors, if not the direct causes, in many apparatus accidents. That statement may have merit when a tanker has been converted from another use such as a fuel oil truck. The same goes for older apparatus not built to recent editions of NFPA 1901. However, it's not necessarily true in the case of today's custom-designed job-specific tanks for pumpers. Manufacturers build NFPA-compliant apparatus. I believe they are especially compliant when using standard preengineered body styles and tank configurations. They are time-proven, and after one has been built a track record has been established.
Buyers, take note. Fire trucks and their tanks are built to order. Purchasers directly contribute to a tank's configuration and location by specifying features such as a low hosebed, dual foam cells, short wheelbase, extraordinary storage through or into the tank, large tank capacity, and copious compartments-sometimes in altogether unrealistically small envelopes. Apparatus manufacturers will build to your specifications as long as the unit is NFPA-compliant. And, the tank manufacturer will supply an NFPA-compliant tank for it. The resulting road-handling characteristics of the completed rig are the responsibility of the apparatus manufacturer, not the tank builder. But, be careful-you might not safely get everything you want. We all want safe and compliant fire apparatus. It will be compliant, but just how safe will it be?
|(5) This rectangular tank shows one type of water diffuser, an internal
one-piece machined basket style, in the center tank fill connection.
There is a sleeve above the notch on the right side. The two center
side-by-side openings are for later attachment of foam cell fittings
whose tanks are visible in the upper bulkhead.
(Photo courtesy of UPF.)
The NFPA does not define safe or safety, nor does it set criteria for degrees of safeness. Do you want your new rig to be safe, safer, or the safest? In my opinion, safe is an immeasurable requirement and, without specific thresholds, it can only be measured in the eyes of the beholder. How can it be specified if you can't define it? The NFPA defines stability. And, compliance to stability is measured as pass or fail; there is no in-between. Use caution. Do not write a requirement in your specifications that cannot be defined or measured. Use parameters that can be described, compared, and evaluated.
It is undeniable that the "roadability" of some compliant apparatus is better than others, and a tank's configuration and location can directly affect the same. What's the answer? Carefully evaluate the advice of fire apparatus manufacturers when they recommend that you not incorporate certain design features into your apparatus. If multiple manufacturers take exception to a portion of your tank specifications, recommend changes, or question your general body layout, there is probably a valid reason. If six vendors decline to bid on your new rig, calling for, as an example, a certain tank design or capacity on a single rear axle and one vendor proudly accepts, you might consider asking yourself why. Could safety be a factor? You may not want to be the first one on the block to have a new rig with the most water on a single axle that just marginally meets the safety standards. Use discretion when apparatus manufacturers' engineers warn you that you are pushing the envelope or live with the consequences. Drive carefully.
|(6) This tank is equipped with color-coded fill towers: one for water
and two for foam. A notch is in the upper left-hand corner.
(Photo courtesy of UPF.)
To illustrate tank configurations and their possible impact on apparatus design and weight distribution, apparatus manufacturers provided input. They evaluated common configurations for a 750-gallon tank mounted on a hypothetical rescue-pumper with a custom cab, 180-inch wheelbase, midship-mounted pump, and full-depth and full-height compartments on each side. The theoretical tanks have a common width of about 40 inches and, with water, weigh around 7,000 pounds. The configurations compared (Figures 2 and 3) were as follows:
1. A standard "short rectangular" tank.
2. An L-shaped tank (high in the front and low at the rear).
3. A "long rectangular" tank (running right to the rear body panel).
4. A "bulk" tank located in front of the hosebed.
Both Rosenbauer and CustomFIRE provided detailed computerized analyses of the physical attributes for the hypothetical tank designs. One, illustrating the weight distribution and center of gravity (CG) of just the tank mounted on a bare cab and chassis, is for informational purposes only. It is not intended to promote or denigrate a particular design. Its intrinsic value is only to illustrate how a tank's design and location contribute to the total picture.
The second analysis shows the overall effect tank designs may have on the front-to-rear weight distribution of a completed apparatus. It is imperative to reiterate that this is a hypothetical rescue-pumper, not necessarily reflective of either manufacturer or any particular apparatus.
|Figure 2. Four basic tank styles with
approximate dimensions from ground level
to the bottom of the hosebed.
(Illustration courtesy of CustomFIRE Apparatus.)
The "standard" booster tank in this comparison is shorter in length than the hose body to allow for a rear-step compartment. Sitting on the chassis alone, its center of gravity is 20 inches above the frame rail with five percent of its weight on the front axle and 95 percent on the rear axle, a 5:95 ratio. Don't panic. The projected in-service front-to-rear axle weight ratio of the completed apparatus is 47:53. In my opinion, this is the second best of the four configurations being compared. The hosebed height would be 80 inches from ground level and the rear-step compartment could be about 48 inches high. This is a common firematic configuration acceptable to a broad spectrum of the market.
The L-Shaped Tank
Some purchasers specify an L-shaped tank under the assumption it allows a very low hosebed height. That is not necessarily true. It depends on the height of the lower leg of the L. The L-shaped tank in this comparison has a 15:85 front-to-rear weight ratio for the tank and water, putting 1,000 pounds on the front axle and 5,900 pounds on the rear axle with a CG of 24½ inches above the frame rail. Use caution. Vendors who use tank weight ratios and tank CGs to persuade you to buy their lower-cost "standard" tank may be doing you a disservice. The 15:85 ratio is misleading. Remember, it is for the tank and water only. The in-service weight estimate for the completed apparatus shows a 49:51 front-to-rear ratio (18,862 pounds on the front axle and 19,644 pounds on the rear)-maybe not the best but certainly acceptable to some purchasers. This hypothetical rig has a reasonable 62-inch-high hosebed height from ground level but the rear-step compartment height will be shorter than the standard tank.
The Long Rectangular Tank
The long rectangular tank has the best standalone CG of 17 inches above the chassis frame. By eliminating the rear-step compartment and running the tank the full length of the body, all the tank's weight is on the rear axle-actually offloading weight from the front end. The completed apparatus shows a front-to-rear ratio of 46:54-17,661 pounds on the front and 20,846 pounds on the rear. There is no rear compartment. The hosebed height is 74 inches from ground level.
Kirvida notes that in such scenarios, although a lighter gross axle weight rating (GAWR) can be used on the front, the rear axle rating most likely would have to be increased by almost the same amount. To determine the actual cost of lowering a hosebed, calculate the cost difference in changing the tires, rims, axles, and suspension for both axles along with the cost of the different tank configurations.
|Figure 3. This drawing depicts the center of gravity (CG) and layouts
for various tank configurations: blue for the bulk tank, purple for
the L tank, red for the long rectangular, and green for the short
rectangular. These CGs are for the tank only mounted on a chassis.
(Illustration courtesy of the CustomFIRE Apparatus design department.)
The Bulk Tank
Although the bulk tank puts about 1,700 pounds on the front axle and 5,200 pounds on the rear axle (a 25:75 ratio), the detailed weight analysis of the completed hypothetical apparatus showed an almost equal 50/50 weight balance between front and rear. However, its high center of gravity can become troublesome because it approaches the NFPA's maximum. Lowering the height of the bulk tank and elongating it will help. It may be compliant, but how does one calculate how safe it is? The bulk tank features the lowest hosebed, 44 inches from the ground, and no rear compartment.
Rosenbauer's calculations note that hosebed configurations, which are dictated by a tank's shape, also affect weight distribution. Both bulk and L-shaped tanks have their hose loads favoring the rear of the apparatus-some to the point that all the weight is on the rear axle with some weight being offloaded from the front axle. Concurrently, the size, type, and quantity of hose must also be considered. Eight hundred feet of lightweight poly-lined three-inch supply hose weighs a lot less than 1,200 feet of five-inch LDH.
The synergy of hose loads; materials used in the cab, tank, and body; mounting locations of extraordinarily heavy permanent fixtures such as generators, electric cord, and hydraulic reels; and the weight carried inside each equipment compartment may negate or contribute to the effect a tank's design and location have on the weight distribution of the apparatus and its road handling characteristics. Because of the unlimited possibilities, it is difficult, if not impossible, for salespeople in the field to calculate the actual weights per axle for each tank configuration. It's not fair to ask them to do so; there are too many variables. The apparatus manufacturer's engineering department is your best source for accurate information. However, its answer will be only as accurate as the information you provide.
Kirvida says, "The weight and location of a tank and water on the chassis comprise only one component in determining final weight distribution. The larger the tank, the greater the impact on the overall weight of the vehicle. A 500-gallon tank on a midsized pumper represents approximately 15 percent of the total vehicle weight. A 1,000-gallon tank on that same rig would represent more than 20 percent of the total weight. Similarly, a typical 3,000-gallon tanker might devote 53 percent of its total weight to the tank. This also has implications for the driving behavior of the vehicle, depending on whether the tank is empty or full."
What is more important to you when specifying a booster tank-a particular front-to-rear axle weight distribution ratio, a certain CG, or a low hosebed height? Why? Don't forget Newton's third law of motion: Every action has an equal and opposite reaction. The dynamics of operating a vehicle with five tons of liquid in motion, with particular CG height, and a certain front-to-rear axle ratio are better left to those more versed in the subject.
Common sense and the safe operation of any apparatus are the operator's obligations-an important topic for another discussion.
BILL ADAMS is a former fire apparatus salesman, a past chief, and an active member of the East Rochester (NY) Fire Department. He has more than 45 years of experience in the volunteer fire service.