PORTABLE PUMPS FOR FIREFIGHTING
VOLUNTEERS CORNER
THE PORTABLE PUMP is often overlooked as a firefighting pump due in large part to its long set-up time and its relatively limited capacity as compared with a truck-mounted pump. However, it can be extremely useful in fire situations where it is impossible or undesirable to use a truck-mounted pump.
TYPES OF PORTABLE PUMPS
The National Fire Protection Association classifies firefighting pumps in three basic groups. The smallest type is the small-volume, relatively high-pressure pump. It is light and portable and can deliver 15 to 20 gallons per minute at 200 psi net pressure through a oneinch discharge while taking suction through a 1 1/2-inch inlet. It is useful for such situations as brush fires, where limited quantities of water are needed but long hoselavs are required.
The NFPA calls the midsize portable pump a medium-volume, medium-pressure pump, This type provides limited use for small structure fires and can supply 250 feet of 1 1/2-inch hose equipped with a one-half-inch nozzle tip with a good fire stream. It will deliver 60 gallons per minute at 90 psi or 125 gallons at 60 psi. This pump has a 1 1/2-inch discharge and a 2 1/2-inch suction inlet.
The third type of portable pump is the large-volume, relatively low-pressure pump. Pumps of this class are frequently used for filling tanks when a pumper can’t get close to a source of water. They are also useful for pumping out submerged cellars, manholes, and other areas where water has accumulated and contaminants may damage a truck-mounted pump. The pump will deliver 125 gallons at 60 psi or 300 gallons at 20 psi. The discharge is 2 1/2 inches and the intake is 3 inches.
PORTABLE PUMP CHARACTERISTICS
The portable class is generally comprised of centrifugal pumps because they can handle sandy or dirty water with less damage and because increased capacity is obtainable with a reduction in discharge pressure.
Because a pump must be limited in size and weight to be truly portable, it must not weigh more than 175 pounds, nor should it exceed 25 inches in height, length, or width.
Portable pumps are subject to extremely rough use and should be protected by metal framing. Caps should also be provided for suction and dicharge outlets.
Since centrifugal pumps aren’t selfpriming, they must be equipped with a priming device. The exhaust ejection primer system is the most common type used in portable pumps. The operation of the system requires that gas pass through a venturi to create a partial vacuum. This vacuum is used for priming purposes. To prime the pump the exhaust gas is diverted through a venturi. A line from the venturi to the pump permits the air to be exhausted from the pump and suction hose when the valve in the priming line is opened. When the pump is fully primed, water will flow to the injector housing, where it is discharged on the ground.
Traditionally, the fire service has used a four-cycle engine for portable pumping units because these units have proven to be reliable, are easy to start, are less hard on spark plugs, and do not require that oil be premixed with the gasoline as is the case with two-cycle engines. These engines operate on regular fuel and are air-cooled. Parts subject to moisture damage are protected.
The portable pump often must run for a considerable time; its fuel tank should be large enough to sustain operation for at least one hour. The tank must be located where it can be refilled while the pump is running.
SUPPLYING WATER WITH A PORTABLE PUMP
Because a portable pump’s capacity is limited, it must be operated more closely to basic principles of hydraulics than any other pumping apparatus. Minor problems that would go unnoticed with a truck-mounted pump can cause the failure of a portable pumping operation.
Any pumping operation is a simple mathematical equation in which the quantity and pressure of water delivered are the results of the pump’s capacity, a plus (or positive) factor, and minus factors —lift, friction loss, backpressure, and restraints of the hose itself.
The only plus factor in the pumping equation is the pump itself. Portable pumps have a very limited capacity. From a practical standpoint this means that the minus factors must not be excessive or the pump will not be able to deliver even its rated capacity. They must be minimized to the greatest possible extent. Since portable pumps deliver their rated volume and pressure at 10 feet of lift, reducing the distance a pump has to lift will add to the volume of water the pump will deliver.
We often forget that friction loss also occurs in the suction hose. For this reason the suction hose should be kept as short as possible. Friction loss can be reduced even further by using the largest diameter suction hose that can be fitted. Locating the portable pump as close as possible to the water’s edge greatly reduces this minus factor.
Friction loss in the handline is another minus factor. There are two methods of reducing friction loss in hose. If the volume of water passing through a hose is reduced, the energy lost to friction will be reduced. One method of accomplishing this is to Siamese the lines; thus a quantity of water will be split between the two lines. For example, 320 gpm flowing through 100 feet of 2 1/2-inch hose creates 23 psi of friction loss. However, if the lines are siamesed the friction loss is only six psi, which is well within the portable pump’s capacity.
The second way to reduce friction loss is to increase the diameter of the hose. Increasing the diameter of the hose dramatically reduces friction loss. The 320 gpm that created 23 psi friction loss in 2 1/2-inch hose would only create 9 psi loss in 3-inch hose. If hose diameter is further increased to four inches, the friction loss is reduced to only 2 1/4 psi. This would allow almost the full capacity of the pump to be utilized 100 feet from the pump.
Back pressure is another minus factor. This is the weight of the water above the pump. Back pressure will rob a pump of approximately one-half psi for each foot of difference in height between the pump and its outlet.
The length of a hoselay is another minus factor. Friction loss increases with the length of hose the water must travel. Thus the shorter the hoselay, the less friction loss. Often, hose can be stretched a shorter route by laying across ponds and through brush rather than along paths and roads.
The hose itself is often a minus factor. Old hose often increases the friction loss, and kinks form restrictions that require energy to overcome.
Successful portable pump operations depend on two conditions: The pump chosen must actually be capable of delivering water in the quantity and pressure required, and the hose layout must be as free of minus factors as possible. If you are aware of the capabilities, strengths, weaknesses, and limitations of the portable pump, it can be a useful foreground tool.
