Getting “water on the fire” and putting “the wet stuff on the red stuff” are two of the numerous ways to describe the act of stretching a hoseline from an engine and flowing water to extinguish a fire.
Booster lines, 1¾-inch lines, 2½-inch lines, etc. all depend on the pump on the engine to deliver the water either from the rig’s booster tank or a supply line or portable dump tank. The same goes for master stream operations, large-diameter hose relays, or a pumper that takes a hydrant—the water delivery method might change, but the whole operation depends on the pumps working properly to deliver the proper gallons per minute (gpm) to extinguish the fire.
No matter what pump manufacturer a department decides to put into its specs, its apparatus purchasing committee (APC) members must do their homework before adding a pump to their specs. Fire pumps come in many styles to accommodate many applications, so it’s important that the APC take the time to assess the applications a fire pump might be used for and target a product that will meet those requirements. Reach out to fire pump manufacturers with questions so all APC questions can be addressed. A properly specified pump will serve a fire department and its community well for many years. Following are considerations for fire departments specifying a pump for their fire apparatus.
- What’s the Right Size Pump for Your Apparatus
- Fire Pumps: Emerging Trends and New Technologies
- Departments Are Specifying Larger Pumps and Water Tanks on Engines
- Pump Theory and Engine Purchasing
PUMP LOCATION
Generally, today’s fire apparatus have the pumps mounted in one of two places. If the spec calls for a “midship-mounted” pump, this means the fire pump is located in the middle of the apparatus behind the cab. The term “midship” does not designate how a fire pump is driven or the pump’s body style. A rear-mounted pump, regardless of body style, is exactly as it sounds—it is mounted at the rear of the fire apparatus.
Whether midship or rear-mounted, the pumps can have controls located on the side of the rig or on top of the rig. In some cases, pump controls are located on the curb side of the truck. If the pump is controlled via touch screen, these controls can be mounted in several locations.
1 Fire pumps come in many styles to accommodate many applications, so it’s important that the APC take the time to assess the applications a fire pump might be used for and target a product that will meet those requirements. (Photo courtesy of Waterous.)
WHAT STAGE?
It is important to understand the differences between single-stage and two-stage pumps before deciding which to add to your specs.
Single-stage pumps are designed to flow large volumes of water and work best when pumping at or near their rated capacity (e.g. 1,500 gpm). They are not designed to produce high pressures. Many department pumpers do not flow at their rated capacity all the time. A single-stage pump will flow its rated capacity more efficiently (with less engine speed) than a two-stage pump, although both pumps could have the same rated capacity.
Two-stage series/parallel pumps are essentially two pumps in one. When operated in the volume position, they mimic the design of a single-stage pump. In the pressure position, they will flow up to 70% of their rated capacity more efficiently (less engine speed) than a single-stage pump.
Operating efficiency is important when considering things like fuel costs and wear and tear on the pumper’s engine. For example, operating a single-stage pump at less than its rated capacity requires the impeller to spin faster than with a two-stage pump, resulting in additional fuel consumption for the engine. This can also cause wear and tear on engine components.
The faster a diesel engine runs, the more horsepower it develops. A pump only requires a fraction of this horsepower. The excess horsepower is converted into heat energy, which will cause the water in the pump to heat up. If the water gets too hot, a catastrophic pump failure is possible.
Be sure to look at your department’s operations to determine which type of pump works best.
FULL BODY OR END SUCTION
A full body pump has a dual eye impeller. Water enters the pump through the intake manifolding and the water stream is split: Half of the water flows to the impeller eye at the front of the impeller, and the other half flows to the impeller eye at the rear. The water is pressurized by the rotation of the impeller.
Full body pumps typically have larger and heavier pump bodies. The physical size is also larger—the actual footprint is determined by manifolding and other features added to each pump. These pumps are available in cast iron or bronze for the most part. Full body pumps are typically available with either mechanical seals or packing.
End suction pumps have a single-eye impeller. Water from the intake flows directly into the single eye of the impeller, and the water is pressurized by the rotation of the impeller. These pumps are available in cast iron or bronze as well as aluminum and, in some special cases, stainless steel. End suction pumps have smaller pump bodies and physical size than a full body pump. The pump interior, or volute, is also smaller, which means less water is in the pump to absorb heat when operating at a low flow. The impeller is designed to flow 1,500 gpm. When operating at a low flow, it can cause recirculation cavitation or an overheat condition if the water is not adequately recirculated. For higher flow requirements, there may be an added inducer at the impeller to promote better water flow. Operators can circulate water to prevent heat issues. In the spec process, include an optional pump overheat protection manager with alarm. Mechanical seals are the only choice for end suction pumps.
An end suction pump has one mechanical seal, which can make maintenance easier. Both end suction pumps and full body pumps meet the National Fire Protection Association (NFPA) requirement for a 10-foot lift at 2,000-foot elevation. When considering adding items to suction inlets like butterfly valves, be sure to discuss this with the OEM’s engineering team.
There can be differences in drafting capability between end suction and full body pumps. Dual-eye impellers can vacate air in the pump body quicker, allowing a quicker vacuum and draft. While end suction pumps can draft, it may take a little longer depending on local conditions and elevations.
PUMP DRIVE
Pump drive types include split shaft, power take-off (PTO), hydraulic, and direct drive. Centrifugal fire pumps typically need some sort of speed increaser to boost impeller speeds. A typical diesel engine application used in a custom or commercial chassis has a governed speed of 2,000 to 2,200 revolutions per minute (rpm). Typical impeller speeds required of a 1,500-gpm single-stage pump can be as high or greater than 4,000 rpm. To accommodate various flow rates, a speed increaser (drive) will boost the speeds from the engine into the pump.
In a split shaft application, the vehicle’s driveline is used to provide power to the vehicle’s rear wheels for forward and reverse operations, and the split shaft is also used to power the fire pump in stationary pump applications. The driveshaft in the vehicle is literally split to power both the pump and the vehicle.
In a PTO application, the pump is powered from a PTO from the vehicle’s transmission. These pumps can pump in stationary applications as well as pump-and-roll applications. If pump-and-roll is needed, ensure the pump can meet the NFPA’s stationary rating requirements as well the pump-and-roll requirements. Gallon and pressure ratings for PTO pumps depend on the available torque capabilities of the PTOs that will be used for each application.
Hydraulically driven pumps require a hydraulic package, including a hydraulic pump, hydraulic motor, and other components, to power the pump. Hydraulically driven pump packages accommodate mobile and stationary pump applications and can accommodate pump mounting outside the standard or more commonly used locations.
Finally, direct drive pumps are for stationary and mobile pumping and are typically packaged with the pump/engine combination being mounted on a flatbed or trailer. The fire pump is directly coupled to an engine using a bellhousing assembly and drive plate integration. Direct drive pumps come in a variety of sizes and flow capabilities from small portable packages to pumps of 4,000 gpm or more.
Always remember to inquire about support from the pump manufacturers you consider and about parts availability. Also, involve pump experts when you are spec’ing pumps. Consider setting up meetings with pump manufacturers to talk through your application. Also consider on-site visits to their facilities. Remember, the pump protects the firefighters at the end of a handline. Proper assessment and careful attention to the pump, its performance needs, and the applications will result in a well-suited fire apparatus to meet the needs and demands of the community it protects.
CHRIS Mc LOONE, editor in chief of Fire Apparatus & Emergency Equipment, is a 30-year veteran of the fire service currently serving as a safety officer and is a former assistant chief with Weldon Fire Company (Glenside, PA). He has served on past apparatus and equipment purchasing committees. He has also held engineering officer positions, where he was responsible for apparatus maintenance and inspection. He has been a writer and an editor for more than 30 years.
