Beat the draft

Beat the draft

Byline: Dominic Colletti and Michael Laskaris Hale Products Fire Suppression Division

Major fires rarely occur, but they do happen. When a subdivision, city block or industrial park is involved in a fire of magnitude, the hydrant system (if any) can be an inadequate water source. It’s a real problem.

For an alternative water supply source, many communities tap into a river, lake or pond. However, because of poor access for fire apparatus, pump operators subsequently find that they must draft under less-than-ideal conditions. To succeed in drafting from these hard-to-reach water sources, fire departments must plan to beat the draft.

Now, we’re not suggesting that you perform an act of civil disobedience. We’re asking whether your department has adequately planned for using equipment and procedures to maximize fireground water delivery rates from those hard-to-reach static water sources often found in rural or suburban areas. You’ll need to beat the draft if your district has no pressurized hydrants or if your department may be faced with a major fire that requires a delivery rate greater than the capacity of the hydrant system.

Tough situations

While drafting is a broad topic, there are two major situations that affect our ability to produce needed fire flows from hard-to-reach static water sources: those that require long horizontal suction hoselays and/or those with high vertical lifts.

For example, NFPA 1901 specifies that fire apparatus pumps up to 1500gpm be able to deliver their rated capacities while drafting from a 10-foot lift through one 20-foot suction line and strainer. If we set up a drafting operation with a vertical lift greater than 10 feet or with a suction line longer than 20 feet, we should expect the pump discharge to be less than rated capacity.

To beat the draft, the first consideration has to occur before your apparatus is ever built. Basically, you need to understand the performance characteristics of different fire pumps under draft conditions so you can specify the appropriate type of fire pump. You also should consider adding a drafting eductor such as the TurboDraft to increase flow rates from existing pumpers when operating at draft.

The first step in planning to maximize delivery rates from hard-to-reach static water supplies is to understand the significance of the performance variations of the available fire pumps. A pump then should be specified based on the performance needed to maximize delivery rates under real-world drafting conditions.

While there are a variety of apparatus pumps available today, including transmission, PTO, front-mount and rear-mount, the midship pump is the most widely used. One of subtleties of midship pump design is that most manufacturers offer both small-body and large-body versions. The ratings of small-body pumps usually don’t exceed 1,250gpm, while the ratings of large body pumps can exceed 2,000gpm. The major differences between small- and large-body pumps are the cross-sectional area of the waterway castings and the size of the impeller assemblies.

Fire departments that work with high deep-lift drafting conditions and/or have a static water source with poor apparatus access should consider specifying a large-body midship pump on their next fire apparatus to increase its performance from draft. The technical reason behind this choice is simple. Vacuum at the impeller eye of a pump decreases as the pump reaches its maximum rated capacity. Thus pump performance, the ability to develop vacuum and draw water into the impeller eye, falls off.

Large vs. small

So how do the different types of pumps relate to pre-fire planning a water supply for a drafting operation? To compare the performance of a large-body pump to that of a small-body pump, the Humane Fire Company, Royersford, Pa., conducted a practical test.

Experience tells us that if a 1,000gpm flow is required for a given building and a small-body 1,250gpm pump is to be used, it’s doubtful that the required fire flow is obtainable under real-world drafting conditions. Given the same set of high-challenge drafting conditions and an identical suction hose layout, a large-body pump will significantly out-perform a small-body pump. This is because the large-body pump’s capability to create vacuum remains strong, even at 1,250gpm.

For the water source in their tests, the Humane Fire Company chose a retention pond behind a shopping center. The distance from the pumper to the water line was 44 feet. The lift, or vertical distance, from the surface of the water to the pump inlet was 13H feet.

A 65-foot-long 6-inch Kochek suction hose with Storz couplings was connected to a barrel strainer approximately two feet below the water line. Water was discharged through two 50-foot-long 2H-inch hoselines that supplied a portable master stream device, the tip of which was equipped with a calibrated pitot gauge.

Both pumps were in excellent condition and had passed their annual pump tests. All tests were conducted on the same day with equal barometric pressure and water temperature for an apples to apples comparison.

The first test was conducted using Humane’s Mack pumper equipped with a 1,000gpm small-body midship pump. The maximum pump discharge pressure was 125psi, and the maximum discharge was 618gpm.

Under the same setup, Humane used their KME pumper, equipped with a large-body 2,000gpm midship pump. The large-body pump also had a maximum pump discharge pressure of 125psi, but the maximum discharge was 1,013gpm. This shows a net increase of 395gpm, or 64%, over the small-body pump.

So when the Humane Fire Company is trying to save Mrs. Jones’ barn at 3 in the morning by developing a delivery rate of 1,000gpm from draft, the better choice is to use the engine equipped with the large-body pump.

The winner is …

Unfortunately, some rural departments that routinely draft believe that all they need on a pumper is a small-body 1,250gpm pump. This belief is prevalent where available water supplies are scarce and the department doesn’t have the water delivery system to deliver flows of more than 1,000gpm from the draft site to the fire. Nothing could be further from the truth.

When departments are faced with high lifts and/or long suction hoselays, a large-body midship pump is a better choice to maximize drafting performance. Depending on the fire apparatus’ power plant, a large-body midship pump can be UL-rated up to and sometimes even beyond 2,000gpm. The price increase to switch from a small-body pump to a large-body model is a small percentage of a new pumper’s cost.

Many departments specify and pay good money for high-horsepower diesel engines so pumpers can adequately carry required loads, but they then reduce their pumping capability by specifying a small midship pump. If the engine has the horsepower, why not specify a large-body pump that can use the power the department has already paid for to produce higher flows? A large-body pump also will provide superior drafting performance under high-challenge suction conditions. From a cost/benefit standpoint, it just makes good sense.

A large-body midship pump purchased for rural firefighting use can be rated at 1,500- or even 1,750gpm, depending on the engine horsepower available. For those who may be squeamish over the psychological impact to rural fire department members who think that a fire pump rated at 1,500- or 1,750gpm is too big, the large-body pump can be rated at 1,250gpm to keep the troops happy.

Drafting eductors

Specifiying large-body pumps for new apparatus is one thing, but what can be done to enhance the capability of an existing small-body pump under high-challenge drafting conditions? One method is to use an eductor such as the TurboDraft.

The TurboDraft is a combination eductor/suction strainer that provides energy at the base of a hard-suction hose assembly to overcome lift. The unit attaches to the base of a suction hose assembly much like an ordinary suction strainer would.

The big difference is that a 2H-inch hoseline from a pump discharge is connected to the inlet of the eductor to provide water horsepower, which is used by a jet inside the eductor to force water through the 5-inch eductor discharge and 6-inch hard suction hose to the intake of the pumper. According to TurboDraft, the 5-inch unit uses 200gpm when pumped at the recommended 150psi.

What did the Humane Fire Company find when using the eductor in our drafting scenario? At 150psi pump pressure, the Mack engine with the small-body 1,000gpm pump flowed 890gpm, an increase of 272gpm or 44% over the discharge provided through draft.

Using the eductor on the KME engine with the large-body 2,000gpm pump at 150psi pump pressure, the discharge was 1,118gpm, an increase of 105gpm or 10% over the discharge provided through draft.

Of course, eductor performance, like pump performance, can change due to drafting conditions. Using this particular eductor, the percentage increase in performance as shown above isn’t linear across all drafting conditions. In particular, TurboDraft noted that the unit needs a minimum pump discharge pressure of 150psi to work effectively.

The difference in the performance of the eductor when supplied by the small-body and large-body pumps is interesting, as it again demonstrates the reduced performance of small-body pumps during high-challenge drafting operations.

An eductor also can reduce the amount of time and number of people required to set up a drafting operation. When we set up the eductor using a 2H-inch supply and a length of 5-inch supply hose from the eductor to the suction inlet of the large-body pump of the KME engine, we were able to flow a maximum of 442gpm at 150psi pump discharge pressure.

The advantage in using the eductor with 5-inch supply hose is that one person could set up the configuration and establish a water supply to the front or rear pump intake. This is a quick way to supply two 2H-inch attack lines, buying time for other personnel to arrive on scene and set up the conventional drafting operation.

Eductors have proved their usefulness in other fields. For many years, the U.S. Navy has used eductors like the Peri-Jet to deal with high-lift conditions encountered when running portable pumps from the decks of large naval vessels, as well as for dewatering.

High-challenge drafting operations reduce the available flow from any fire pump. As you can see, it was quite easy for us to set up a realistic drafting condition where the capacities of both the large- and small-body pumps were reduced by approximately 50%. Keep this in mind when considering a new pumper and make sure you specify a pump large enough to provide the fire flows you need from your high-challenge drafting sites.

Specifying the appropriate type of fire pump and using drafting eductors can significantly help increase water delivery rates when drafting from high-challenge static sources – both can help you beat the draft. Any increase in delivery rate means a higher gpm application rate onto burning materials to maximize fire-stopping power.

Special thanks to John Major, Chief of Humane Fire Company, and his professional personnel for participating in these tests. Remember, water is where we find it, and it’s our job to deliver it where it needs to go.

Dominic Colletti is the director of sales for the fire suppression division of Hale Products and a firefighter with the Humane Fire Company in Royersford, Pa. Colletti is the author of Class A Foam – Best Practice for Structure Firefighters and co-author of The Rural Firefighting Handbook with Larry Davis. He can be reached at dcolletti@haleproducts.com >.

Michael Laskaris, PE, is a Pennsylvania-licensed engineer and director of engineering for the fire suppression division of Hale Products. Laskaris is a volunteer firefighter and holds U.S. and foreign patents on a wide range of fire service – related products. He can be reached at mlaskaris@haleproducts.com >.

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