|Bumper-mounted turrets are becoming more popular as fire departments realize having personnel sitting on the bumpers with hand lines is not the safest method of fighting fire. Pump and roll pumps are necessary for this type of operation.|
|Monitors mounted on the front bumpers of apparatus can be motorized. (Rosenbauer Photo)|
|Pump and roll apparatus can also work as stop and pump apparatus for hand lines operations.|
|A small fixed monitor is a much better solution to having firefighters sitting or standing on apparatus during pump and roll operations. A bumper monitor permits nozzle performance up to 100 gpm or more. (Rosenbauer Photo)|
|The dangers of pressure fluctuations usually associated with pump and roll operations are eliminated with bumper monitors. (Rosenbauer Photo)|
There are many forms of pump and roll, and not every application can be accomplished efficiently by the same apparatus design. For one apparatus to do all the pump and roll applications, it would be impossibly expensive.
Selecting the pump and roll applications required for departmental needs is the first order of business. To do that, one needs to look at the different applications and what performance requirements are needed for each.
First, there’s the walk-along pump and roll application. As the name implies, the person with the hose walks along with the apparatus. That means the road speed needs to be about 2 mph. Any faster than that and the operation would quickly become a pump and drag as the person at the nozzle would not be able to keep up with the apparatus.
Since this is a handline operation, a low pressure and low flow handline makes the most sense. For most applications, 100 to 120 psi out of the pump, with a 50 to 70 psi nozzle tip pressure will do the trick. Spot grass and brush fires, or washing down a street would be normal applications for this apparatus design.
Keeping the pressure reasonably stable is important. Great fluctuations in pressure will make the handline hard to control and add to operator fatigue.
The other challenge is for the driver to watch the position of the hose and the person with handline. The operator needs to be mindful of his road speed, road hazards and the pumping pressure.
The next type of operation is the walk along pump and move. The operation is similar to the walk along pump and roll, but in this application the apparatus moves from position to position with the pump in gear, but stopping to let the handline operator discharge water.
This procedure allows the driver to focus on driving from place to place at speeds which can be greater than 2 mph without having to control pumping pressure. This method requires communication between the driver and the handline operator.
While not the safest method, there are still plenty of departments that ride on the apparatus during pump and roll operations.
To achieve this kind of application, the handline operator usually sits on top of the hose bed or stands on a walkway or bumper extension. That makes the road speed more flexible with speeds from 5 to 10 mph possible. Even at the higher speed, the nozzle performance is still low, much like the walk along operation.
Travel speed can also be affected by the environment and topography. Chasing a wheat field fire in the Midwest at 20 to 30 mph is common.
The biggest challenge in a pump and ride operation is the safety of the personnel riding on the apparatus exterior. Unfortunately, adding a seat, seatbelts and a roll cage, is no guarantee that a rider won’t be injured or killed.
A much better solution is a fixed small monitor. That permits nozzle performance up to 100 gpm or more, and the pressure fluctuations are less dangerous.
Yet another pump and roll application is the ground sweep system: This setup is for road clearing or focused grass fires.
Two fixed ground nozzles are mounted under the front bumper with the controls located inside the cab.
Road speed is not as important, as there are no personnel to worry about on the bumper or walking along side, meaning speeds up to 15 mph are possible with low flows, 20 to 50 gpm, at the nozzle, with medium pressure, 120 to 150 psi.
A long dormant practice of equipping apparatus with remote-controlled roof and bumper turrets is back. In the 1960s, some fire departments in New England bought Maxim pumpers with pump and roll capabilities and turrets designed particularly for freeway auto fires.
For years, the concept had been all but forgotten, but today, remote-controlled bumper turrets ranging from 100 to 300 gpm are showing up with more frequency, particularly for auto and wildland fires. The most popular set up these days is a 100 gpm monitor with foam capabilities. The addition of foam, besides the obvious benefits of improved direct fire attack capabilities, is the potential to provide Class A exposure protection quickly and efficiently.
Why are bumper turrets back? Perhaps the strongest answer is they are readily available once again. There are good bumper turrets available from TFT, Akron and Elkhart at reasonable prices.
Firefighters have multiple options to create pump and roll apparatus that will provide the exact performance needed. We have Class A and B foam systems to augment the performance and the best part of a pump and roll system with a remote turret is the operator is inside the cab, safe and sound .
There are also lots of options to improve the chassis low-speed capabilities. About 100 gpm at 150 psi is needed to operate the turret and the pressure only needs to be somewhat stable. Fluctuations are not as critical and speeds can range from 5 to 15 mph. That’s a lot faster than the handline operator can travel.
The final pump and roll commonly utilized is for airport crash rescue operations. This differs greatly from all the other applications looked at because the pump performance is high.
In some applications, the pump and roll power needs are higher than the vehicle acceleration power needs.
Aircraft Crash Scenes
At aircraft crash scenes, water and foam must be deployed within the first 2 minutes and at a far greater throwing distance than normally found at structural, auto, or wildland fires.
For aircraft response apparatus, the pump performance is typically at the 1,500 to 2,000 gpm range at 240 psi. The apparatus still needs to maneuver safely and accurately, even with the engine at higher RPMs.
Once the kind of pump has been decided and the roll performance best suits the department’s needs, it’s time to look at the chassis and its drivability at the road speed range required.
No matter what the pump is doing, if the chassis will not operate efficiently or consistently at a low enough speed, the required pump and roll performance will not be achieved.
To determine the appropriate chassis road speed, the following formula can be used: MPH = (engine RPM X tire rolling radius X .00594)/ Total gear reduction.
In today’s market, most full-size fire apparatus chassis have 11:00 22.5 tires with a 19.4 Rolling Radius.
They also have Allison automatic transmissions with .75 5th gear ratio and a 3.49 1st gear ratio and are geared for 65 to 70 mph top speed
Be mindful of the fact that a 5.6 to a 5.3 rear axle ratio will have a 1st gear total reduction of about 18 to 1.
With an automatic transmission one can drive with both feet, keeping engine speed up and using the brakes to keep road speed down, but that will only work to drop the road speed down by approximately 2 mph.
This two-foot driving, if prolonged, will generate transmission and brake heat, and excessive heat causes damage. It’s not an extended operating option, only a short-term solution at best.
The automatic transmission also has an engagement point which means the apparatus will not move until the engine speed is nearly 900 RPMs.
The other low-speed issue is lack of engine power. At low engine RPMs, there will be little power. Don’t expect much power until the engine reaches 1,000 to 1,200 RPMs.
The road speed will be about 7 to 8 mph at 1,100 RPMs, in 1st gear on the common 4X2 fire apparatus chassis. That’s way too fast for walk along pump and roll application. It’s even a little fast for other pump and roll applications, except when moving from location to location for spot fires and wheat field applications.
There is a solution to that problem. The total gear reduction will need to be increased. To increase the total gear reduction with out lowering the top speed will cost money, one way or another.
The common way to increase the total gear reduction is with a lower 1st gear found in Allison 3500 and 4500EVS transmission. They cost money, but they do drop the 1st gear ratio from 3.49 to a 4.59 and 3.51 to 4.70 on the 4000/4500 transmission. This lower first gear will lower the pump and roll speed by almost 2 mph.
Another way is to install a two-speed transfer case, which is normally provided with a 4×4 cab and chassis. That option gives a two times factor, which translates into a 4 mph typical pump and roll speed. If the lower first gear transmission is added, the speed will be close to the 2 mph point.
Lastly, a two-speed rear axle could be installed – a common ratio spilt would be 5.3/7.9. The two-speed rear axle used with the lower first gear transmission will give a 4 mph operating speed.
Remember, one can scuff off about 2 mph for short durations by driving with two feet – one on the throttle and one on the brake.
When using the move-pump-move technique, the exact road speed is not terribly important. The actual pumping is done after the move is made and the transmission is in neutral. The pump’s total output pressure during vehicle maneuvering is not important.
Once the application has been selected, the appropriate chassis with the low-speed performance required for the application selected, it’s time to look at the pump and its drive system.
Some apparatus with pump and roll capabilities have pumps driven by a separate engine. They can be auxiliary or primary pump systems driven by engines from 10 to 500 hp engines.
Engine-driven pumps for pump and roll capabilities are common on West Coast pumpers, interface and wildland apparatus. Typically, they also have a larger capacity chassis-driven pump.
Apparatus with pumps driven by a separate engine typically have a 21 to 34 hp diesel engine. That kind of pump package is often mounted above the main, apparatus-driven pump system and can easily supply a 1.75-inch line and a booster reel, or a 100 gpm bumper turret.
An engine-driven primary pump system will vary depending on the apparatus mission and its size. On a simple wildland slip-on package, on a pick-up truck, an 18 hp pump package may be perfect.
On an Aircraft Rescue Fire Fighting (ARFF) 8X8 crash truck, the system may have a separate 500 hp engine. In the Midwest, pumpers with 1,000 gpm pumps driven by separate V8 gas engines, are not uncommon. These pumpers provide a full range of fire fighting capacity including chasing down fast moving wheat field fires.
The big advantage of these separate engine-driven pump packages is they provide full and constant pump performance no matter what the truck chassis is doing. Slow, fast or even stopped- the pumping performance is unaffected. This is the most common way to achieve pump and roll.
The biggest disadvantage is having the extra engine, its weight, size and added maintains.
Pump and roll capabilities can also be achieved with the chassis pto system. Again, there are primary and auxiliary pump systems in this drive category.
The controlling factor in this drive arrangement is the gear provided inside the truck chassis transmission to power the pto. If it is a small gear, it will have a small pto and a small pump.
If it is a big gear, it can have a big pto and a big pump. All transmission or bell housing ptos have limits lower than the available engine power.
Exceeding these limits, even by small amounts, will lead to a short pto service life and frequent rebuilding. Exceeding the limits by a lot will cause almost certain catastrophic pto failure. The good news is the pump is not normally damaged when a pto fails.
Another limiting factor with ptos is the maximum speed at which they can operate; normally, that’s about 2,500 RPMs.
There are ways to determine how big the pump can be based on the size of the pto. This is where physics rule. The formula that guides it is: Torque foot pounds = (HP X 1714)/ RPM.
The torque limit is dictated by the pto, so the only thing to be chosen is the operating RPM, to determine the available horsepower. Based on the formula, as speed goes up so does the horsepower.
That means operating at 2,500 RPMs will allow one to operate a bigger pump than could be operated at 1,000 RPMs. There’s a catch, because more pto speed means more road speed.
Auxiliary Pto Pumps
The more one looks at it, the more complicated it becomes. Pump and roll can be achieved with a pto drive provided one take into account all the variables, realize that not every combination is going to work correctly and be willing to compromise.
Auxiliary pto pump systems have an advantage in that they usually take less power because they are smaller, normally 100 to 300 gpm.
Lower flows permit the use of pump and pto gearing, which lowers the operating road speed significantly. Since the power required is low, the pto life is normally higher in these types of applications.
If the system is designed properly, it is possible to have 100 gpm at 200 psi at an engine speed of 800 RPMs for pump and roll and, during stationary pumping with the main pump operating at 150 psi, have the auxiliary pump system operating at 600 psi or greater at 100 gpm or greater.
This configuration gives the operator the option to have both normal pressure lines and high-pressure reels or a 1.5-inch, long-distance uphill supply line, operating simultaneously. This may be just the versatility needed during some wildland or interface situations.
A drawback of a pto pump and roll system is the potential of line pressure fluctuations or surges caused by varying engine speeds.
One method to control this is to operate at a higher pressure than normally needed and use flow and pressure reducing valves in the lines.
If you have an auxiliary pump that is putting out 100 gpm at 200 psi at 800 RPMs, there is sufficient pressure to use the flow and pressure reducing valves to maintain steady, constant handline performance.
If the pump is operating at higher RPMs and at lower pressures, the flow and pressure reducing valve may not work well.
Hydrostatic Pump Drives
The other method to control pump output performance is using a hydrostatic pump drive system. These systems vary the hydraulic pumps output to maintain the apparatus pump output. The drawbacks to that system include, high cost set up, consumption of additional power at low engine speeds where power is limited and complicated service issues. Hydrostatic pump drive systems are declining in popularity, but they are still available from several truck builders and many units are in service on the West Coast.
One last option is the primary pump being pto driven and providing pump and roll capabilities. With a normal, single-stage pump, the process is to match the pto to the pump’s National Fire Protection Association (NFPA) rating point performance requirements.
This will determine the pump maximum rated size and the pump gear ratio required for this application.
With that information in hand, one can then calculate the pump and roll input pump speed requirements. That information can then be compared to the slow speed chassis performance to see if it will work.
Sometimes, the problem is an acceptable pump performance level comes at an unacceptable road speed. There are options to solve that problem too. The chassis total gear reduction can be lowered, which would increase the pto output speed at the required road speed.
Another alternative is to add a high-pressure stage to the main pump. The additional pump impellers operate in series, adding output pressure without needing more pto speed.
Yet another option is adding a small auxiliary pump, either a pto or engine-driven model. That eliminates the need to use the main pump for pump and roll applications.
Finally, one can opt for a two-stage pump. Two-stage pumps, when in pressure, will operate at lower flows with higher pressures for a given pto speed.
In some cases, two of the options may be needed to achieve the required performance.
The challenge for either the two-stage pump, or the high-pressure stages added to a main pump, is power consumption. Both setups have low horsepower efficiency at some operating conditions which could exceed the pto capacity, or at least greatly reduce the pto’s life.
What is the best answer? While the process of determining the answer may be complicated, the answer itself is simple. Buy the pump and chassis combination that best meet the department’s needs and budget, without causing reliability problems.
And, don’t forget, help is only as far away as a phone or computer.