By Jason Estep
There have been many strides made in firefighting technology in the past 100 years.
At the beginning of the 20th century, firefighting equipment consisted of a steam-powered piston pump pulled to the scene of a fire by a team of horses. Once the apparatus arrived on scene, some type of water source had to be secured to effectively fight the fire. Modern day apparatus have evolved into high-horsepower, high-volume pumping machines that have tremendous advantages over earlier apparatus. However, one thing remains the same: Once arriving on scene, a water source still has to be established to properly extinguish the fire.
Since the majority of the United States is rural, many communities are not blessed with water systems, and if they are, they are often weak systems. Regardless of the reason for a feeble water supply, the fire department is still charged with the responsibility of properly controlling fires within its community. This has caused most fire departments in rural America to depend on streams, ponds, lakes, rivers, etc. to provide water for firefighting operations. The only problem is to get it from the source to the fire. To do this, tanker shuttle operations are set up. A tanker shuttle consists of individual trucks, usually with large tanks, transporting water from point A to point B.
|1 A vacuum tanker can effectively obtain water at the closest source without the need for a fill site pumper and with minimal personnel. (Photo courtesy of Firovac.)|
The flow rate of a tanker shuttle depends on two variables: dump time and fill time. The Insurance Services Office (ISO) formula for travel time in a two-mile shuttle is a constant 35 miles per hour. To increase flow rates, departments began trying to lower the fill and dump time. Lowering the dump rate was easily accomplished by placing 10-inch Newton gravity dumps on trucks. The problem is you cannot dump what you have not first loaded. To decrease fill times, large quantities of personnel, hose, and at least one 1,250-gallon-per-minute (gpm) pumper must be committed to fill a tanker. As a rule of thumb, the fill site pumper will only be operating at 70 percent efficiency. Combine that with the fact that most conventional tankers have only one 2½-inch direct tank fill, and you can see the difficulty in reducing fill times. Now, examine the number of personnel needed to fill the conventional tankers. You must have a fill site pump operator; at least one person per tanker (in a large shuttle) to connect the hoses; one person tending to portable pumps/drafting operations; a driver for each tanker; and, in a large shuttle, more fill site pumpers to reduce wait time.
Next, let’s examine the setup time for a fill site operation. A drafting operation has to be set up, whether it is directly from a water source or from a dump tank being supplied by portable pumps. If portables are used, crews must take time to set them at the water source, stretch the lines, and get the dump tank set. Once the drafting operation is established, personnel must lay out fill lines along with any adapters or appliances needed to fill each tanker in the shuttle. This all has to be done when the attack crews are fighting the fire and needing the water the most: at the beginning. There is no doubt that after everything is set up, with enough personnel and trucks to establish an efficient shuttle, it is usually well into the fire suppression effort. Most of the time our tankers do not meet the needed fire flow of the fire, but the fire burns down to the flow rate provided by our tanker shuttle before it is extinguished.
A Different Type of Tanker
What if there was a tanker that could cut the staffing required at the fill site by more than half, fill itself without a pumper, and offer a flow rate much better than that of an ordinary tanker? Sounds impossible? If a tanker like that was available, it would revolutionize the fire service. This tanker does exist in the form of a vacuum tanker. It works using a very simple, yet efficient, system that requires little maintenance and is easy to operate. Vacuum was introduced to the fire service market in the mid 1980s. Although vacuum had been used for years in the industrial field, it had never been engineered for the fire service. Many companies have tried to use industrial type vacuum units in the fire service but have been unsuccessful because they have not made the necessary changes to get the performance and safety required by the fire service. Innovative fire departments have realized that rapid water movement involves more than dumping quickly. It is a complete system with the ability to rapidly load from the nearest water source, safely transport it, and then quickly evacuate the water from the tank.
|2 The vacuum tanker works well in shallow water, eliminating the need to build a makeshift dam. It can effectively fill at more than three inches over water, and a gulp of air will not cause a loss of prime. (Photos 2-4 by author.)|
As tested, a vacuum tanker can create and maintain flow rates close to the 250 gpm required by ISO by itself. It can self load at approximately 1,000 gpm (usually more with fill rates that can approach more than 1,300 gpm; 1,000 gpm is a safe “average” number for vacuum tankers) and self unload at 1,250 to 1,400 gpm. It can load from available water sources (ponds, creeks, portable tanks, etc.), remote locations through 48 feet of hose or more (limited in a horizontal lay only by the hose carried), and vertical lifts approaching 30 feet. It also has been recognized as a “zero-loss” tanker by ISO, meaning it is not penalized the 10 percent tank capacity like conventional tankers.
The ability of the vacuum tanker to effectively obtain water at the closest source without the need for a fill site pumper and with minimal personnel is a game changer. Too often, the lack of staffing or an available fill site pumper forces fire departments to run back to a hydrant to refill, often passing usable water sources. The vacuum tanker allows you to put your firefighters on the fireground where you need them, not at a fill site. With the fire service facing a shortage of firefighters across the country, shouldn’t we be looking for a better way?
Vacuum Tanker Operation
How does vacuum work? Vacuum works simply by extracting air from a closed container, which causes a negative pressure in the container, allowing water to replace it. This movement of air is caused by a vacuum pump. There are several types of vacuum pumps. They are rotary vane and piston or displacement pumps. There are two rating standards for vacuum pumps in the United States accepted the most. Cubic feet per minute (cfm) is when the displacement capacity of the pump is measured in expanded air at 15 column inches of Mercury. Vacuum degrees are measured in inches of Mercury. As a vacuum pump reduces the atmospheric pressure on top of the calibrated column of Mercury, a measurement can be taken. Standard cubic feet per minute (scfm) is when the displacement capacity of the pump is brought back to normal atmospheric pressure and measured at free air. Make certain that the comparison of pumps is done by the same rating standards. It should be done at 15 inches of Mercury to show a pump’s efficiency at working levels of vacuum. In conjunction, it should be judged for its maximum vacuum capacity. If properly constructed, the vacuum pump will be just one part of a system that allows the vacuum tanker to meet its performance and safety requirements.
Vacuum System Components
Many parts comprise a vacuum system and need to be carefully considered, including the kind of vacuum/pressure pump, the cfm rating, the pump’s efficiency, the pump’s vacuum producing capacity, recovery rate, maintenance requirements, cooling, oiling, warranty, and how the pump is set up. Pump protection (shutoff system) should be effective enough to keep moisture and debris from entering the vacuum pump yet allow for complete filling of the tank. It should be easily serviceable. The power source and drive mechanism should be of a proper size, type, capacity, strength, and construction to provide proper service for the varied conditions of the fire service.
The next major component of a properly constructed vacuum system is the tank. One of the most important things to remember when buying a metal tank of any kind for use in the fire service is that the inside must be coated, regardless of the material and grade of material being used. Marine grade and aircraft grade aluminum corrode just like any other metal. Chlorinated water is highly corrosive. This is what brought on the polypropylene tank revolution in the mid to late 1980s, when many of the major manufacturers had considerable problems with uncoated aluminum and stainless tanks. Tanks for vacuum tankers are steel or aluminum and have been coated to prevent this corrosion.
|3 Often, big water exists, but personnel cannot access it. A vacuum tanker makes it possible to access hard-to-reach water.|
The water tank used for vacuum tankers should be a round structure with dished heads constructed of material strong enough to withstand the vacuum forces placed on it. It should be constructed with the proper material thickness. Aluminum is the most common material used for a vacuum tank. Quarter inch aluminum material is sufficient to handle the vacuum forces when properly constructed. The tank must be properly supported and mounted to reduce road stresses from reaching it. Improper supports and lightweight material have been known to cause problems in the industrial world (especially in aluminum tanks).
Baffling is another major component of a vacuum tank. The baffles inside a vacuum tank should be used to control the movement of water inside the tank and also reinforce the tank against the vacuum force placed on it. Flow rates should not be affected if the baffles are properly constructed. Flat pieces of metal installed inside a vacuum tank to prevent slosh will do little to reinforce the tank and will only partially help in the water swash prevention. One manufacturer has a patented baffle system that exceeds the National Fire Protection Association (NFPA) requirement for tank baffling, reinforces the tank, and drastically reduces water swash.
Since a vacuum tank must be a totally closed system to build vacuum within a tank, a venting system must be added to fill conventionally from a hydrant. Some manufacturers also use a patented internal vent system, which when open will allow the tanker to operate as a conventional tanker if needed. The drawback to this is that, when being used in the conventional way, a vacuum tanker is only as efficient as a conventional – it will cut the normal vacuum tanker flow rates by more than half. To gain the maximum flow rates, the vacuum tanker must be operated from vacuum as much as possible.
In Their Infancy
Although centrifugal fire pumps made the transition from the industrial to fire service market years ago, vacuum tankers are still infants to the fire service. Therefore, it is understandable that departments research them and become familiar with their capabilities. Remember, not all vacuum tankers are created equal, and many have not been adapted to the fire service. Just keep an open mind and let the tankers prove what they can do to increase your flow rates while reducing the amount of staffing and equipment needed to run a tanker shuttle.
|4 Thirty-foot vertical lifts have been achieved, but this can vary with elevation. Just like a centrifugal fire pump, this is dictated by the laws of physics.|
If properly constructed, vacuum tankers can supply more water to a fire with fewer personnel and expense because:
- They load from available water sources and do not have to return to town or a hydrant system to get water.
- Setup time is quick and easy using minimal personnel.
- They eliminate the need for a fill site pumper.
- Self-load times are quick and easy.
- Vacuum tankers can provide more water at the same distance in the same time period as a conventional tanker.
- It pressure unloads all water in the tank quickly, recognized as a “zero loss tanker” by ISO.
JASON ESTEP is chief engineer of the Morrisvale (WV) Volunteer Fire Department with 21 years of service. He has a mechanical engineering degree from Fairmont State University and is currently employed as a senior maintenance planner for a major coal company.