The Centrifugal Fire Pump Goes “Up-Stage” —And More Power to It, Says the Fire Service
—Photo by Bill Patten
THE ADOPTION OF THE CENTRIFUGAL PUMP for almost universal use on fire fighting equipment has been one of the most interesting and illuminating phases of the development of modern fire apparatus. From the booster-tankers to the heavy duty high-pressure metropolitan pumper and fire boat, the centrifugal serves them all and has proved its merit in long, hard usage.
A centrifugal pump is a high speed device and in its early beginning the impellers had to be quite large in order to obtain sufficient rim speed to develop the required pressures. At the time of its introduction to a somewhat skeptical fire service, the driving engines were of a comparatively slow speed, and 750 rpm was considered a normal range. But over the years, with the improvements in motor design and the trend toward the high speed engine, it was possible to reduce the size of the impellers and with it the over-all bulk of the pump. It is worthy of note that at the same time, the efficiency curve of the centrifugal fire pump has paralleled the upward extending speed curve of the automotive power plant.
The introduction of the pressure-volume type of pump has made possible the raising of the operating pressure ranges to 500 or 600 psi when full volume is not required. Coincidentally, this reduced the required engine speed necessary for the higher pressures to that easily met by the automotive engine. As a net result of all the various progressive developments, the increase of volume obtainable at the higher pressures has led in recent years to a new standard of pump classification. This result is attested by the fact that only a few months ago the NFPA-IAFC Committee on Fire Apparatus voted to drop the old classification of “Class B” entirely and standardize on the “Class A” specifications for future fire pump performance.
—Photo courtesy Solar Aircraft Co.
Fire fighting needs influence progress
Fire fighting methods have both influenced and been influenced by the centrifugal pump. In the days of dependence on the hydrant hose line, it was a common practice for the water department to raise the street water main pressure (not to be confused with high pressure fire mains) to enable firemen to obtain effective streams. With the introduction of the early steamers this practice began to be discarded. Instead, the fire service provided its own working pressure as desired by hooking up pumps. The positive displacement pumps, off-shoots of the steam age, due to their nature, could not make effective use of the pressure at which the water was delivered from a hydrant. However, the centrifugal, as it found its place in the “gasoline era,” could add its capabilities to the pressure received from the mains and, theoretically at least, produce a pressure that would be the sum of the hydrant pressure and the pump pressure. This advantage meant less effort on the part of the driving engine and the pump, with the possibility of longer usable life for both.
As one reviews pump developments, it would appear that the more compact size of the modern pump has resulted in another attribute permitting better use to be made of the chassis space. The earlier pumps, because of their bulk, limited the amount of equipment that could be carried on a given unit. At one time it was thought that the use of more compact pumps would result in smaller apparatus. But the trend has been in just the opposite direction. As smaller space was required for the pump, the fire service began devising new methods of operation and the space obtained has been used for a variety of purposes—to enlarge booster tanks, increase hose loads, or for more compartmentization. At the same time the ease of handling the apparatus while underway has been improved.
The “fast attack” method of fire fighting, so popular today, has primarily been made possible by the progressive operating features of the modern pumper. The use of preconnected lines, with the required piping and valving so necessary for quickly getting into action, is now a common practice. Booster lines have been preconnected since their inception, but have been limited in volume and effectiveness. As larger water tanks were mounted on apparatus—to a great extent made possible by modem pump developments—the use of the IVz inch hose line became more practical and it was quickly pressed into service.
Apparatus design changes follow
The progress in fire fighting methods and pump design has led to many progressive changes in fire apparatus. The modem pumper of today may bear some slight resemblance to its predecessors, but a close look will disclose many differences. At one time, suction connections were found on opposite ends of the pumps. These connections were of a single size to accommodate the hard suction hose carried on the apparatus. Today, front and rear suction connections in addition to the side connections are common, and no one will gainsay their advantages.
The use of previously mentioned preconnected lines, and the more extensive employment of relay operations has brought with it the 2%-inch suction connection equipped with gate valves. Where hydrant supply lines are used in the quick-attack methods, the gated suction connection has eliminated the loss of time associated with attaching heavy adapters.
Discharge gates in the past were seldom found at any location other than on or near the pump panel. With the change in methods, the need for more convenient placement became apparent. Toilay, rear and top discharges are common on mans’ pumpers and all valves for the remote gates are controlled from fire operator’s panel.
Valve design improved
To obtain fire operating speed and ease necessary for the modern conditions it was imperative that control valve action be improved. To meet this situation the quick-action quarter-turn valve has been perfected to a point where anyone can operate it when under pressure. No longer must the pump operator shut down his pump to relieve the pressure when opening a valve. Nor is it necessary to resort to tbe mallet or other “persuader,” (sometimes contrary to standing orders) to open a gate without shutting down.
The addition of friction-locking devices to the new valves has brought even greater flexibility to the modern pumper. By means of individual pressure gauges for discharge gates, the operator can now supply a different volume of water to each line as desired. This has resulted in greater efficiency and safety for the hosemen, no mean attributes.
The advent of the quick-action valve has inspired style-conscious apparatus designers to make further attempts to clean up the exterior appearance of the operator’s panel. The easy action of the new valves has allowed flush mounting, or the enclosing of the valve housing back of the panel, with only the coupling and the control handle or rod exposed. Recently one manufacturer introduced the power-controlled valve which, with its push-button operation, may add to this trend. In addition to the artistic values, Hush mounting may also help prevent freezing in cold weather areas.
—Photos courtesy American LaFrance Corp.
—Photo courtesy Waterous Co.
Many pumpers delivered today are equipped with built-in systems for supplying turret nozzles or proportioning foam or water wetting agents. While direct connection of turrets to the pump is not new, a more versatile and efficient arrangement can now be supplied. A pressure gauge is connected to the supply piping and mounted directly above the turret valve control on the operating panel. By measuring the nozzle pressure for the various tips during tests, friction loss in the turret can be determined. A simple chart may be prepared from the pitot readings for future reference. A pump operator can then supply any discharge required for a given operation by referring to the chart and setting his pump to produce the required reading on the gauge.
Proportioning systems, although still somewhat of a mystery to some skeptics, were a logical development in fire control methods. Originally, chemical foam with its separate additional equipment, was the only type of foam agent available. Experiments with mechanical foam liquid and its use by the armed forces during World War II opened a new field which was immediately explored by the civilian fire service. The possibility of quickly getting into action with foam appealed to many chiefs, and it was not long before foam tanks were being installed on apparatus. The same is true of wetting agents. Manufacturers report many departments arc ordering built-in systems, some of which are dual-purpose, permitting the use of either foam or wetting agents.
Development in operating panels and priming
One of the apparently incongruous developments in the associated parts of fire pumps is the operator’s control panel. The earlier antecedent of today’s gasoline-powered products were equipped with a minimum of indicators, levers and gauges. Compared with these venerable models, the modern conception, which in some cases resembles the control panel of an airplane, may be a bit disconcerting to the pump novice. But second consideration will indicate that these operating appendages, if we may use the term, are essential to efficient pump operation. In order to take advantage of the full flexibility of the modem pump, and the accessories available, controls are necessary. By grouping all these controls at a central point within easy sight and reach, the task of the pump operator naturally is simplified. Before the days of remote control, the operator was required to walk around the apparatus to open or close valves, as required. Today, the same results are obtainable more quickly and without the operator leaving his position. Individual gauges tell the operator the conditions of his equipment at a glance, and with all controls near at hand it is a simple matter for him to meet the varying conditions which may be called for by the situation. The future may witness even more radical developments in this field of design.
One of the problems connected with operating centrifugal pumps is priming failure. Many times this failure is traced to an open drain valve and checking the source of the air leak is frequently an irritating and time-consuming task. On the older models of apparatus, drain valves are often found underneath the chassis and add to the operator’s frustration.
Some manufacturers now equip their pumps with a central drain valve, piped to the required locations, and controlled by a single lever on the operating panel. This allows a quick check to be made for possible trouble when beginning draft operations, as well as a positive drain of all points when shutting down.
Power operated controls
One of the minor controversies that is presently raging in the fire pump field revolves around the question of automatic controls. In the past some operators have complained about the multitude of levers required to control a centrifugal pump. In an attempt to overcome this objection and at the same time obtain smoother operation, manufacturers turned to power-assisted controls.
While many of these controls have been in operation for a number of years and have proven themselves in service, a few are recent innovations. Alarmed by what might be a trend to “gadgetry” one Underwriters’ authority cautioned field engineers to be on the lookout for “unnecessary” power controls when conducting acceptance tests. One manufacturer of fire pumps supports this thinking in these words: “We do not believe in (power) controls for their own sake. To our mind, a control becomes a gadget when it does not have a real advantage. Real advantages would be greater reliability, quicker and simpler operation and a reduction in maintenance cost.” On the other side of the controversy this warning is sounded by the chief engineer of one the leading apparatus manufacturers in these words, “The present trend is to more application of power to controls. Some organizations are becoming concerned about the added complication of these controls and are demanding proof of reliability. While these agencies are to be commended for their efforts to protect the fire service, too many restrictions tend to stifle new developments.”
High pressure pumps
As changes in methods have occurred, pumps have been adapted to keep pace with the trends. With the introduction of the high pressure method of water fog production, changes in pump design were introduced to accomplish the desired mechanical results. At one time the piston pump had been practically counted out of the pumper apparatus picture, but its return in the high pressure field has been welcomed in many quarters. It has proved to be a capable performer and is giving excellent service. It was a natural development that the centrifugal pump should emerge in several new designs to meet the requirements of the high pressure field.
Some pump manufacturers have added a third stage to their volume pumps and an additional control to give the operator a choice of discharge. Another has designed an entirely new pump that offers a selection of volume, standard pressure ranges or high pressure in a single package.
A third type unit is the small, auxiliary, multistage centrifugal pump designed to be operated from the apparatus power take-off in a similar manner to the piston style. A newcomer is a multistage auxiliary that is capable of supplying highpressure requirements as well as producing volumes necessary at conventional pressures for booster pump service.
These features enable the use of this pump as a booster on apparatus where necessary. In addition to its ability to supply conventional and high-pressure booster lines, it is capable of supplying 1 1/2-inch lines. The pump may be mounted on standard pumpers, squad trucks or ladder trucks for this service. It can also be mounted with a separate engine drive as a skid unit for operation completely independent of the chassis. This feature may appeal to departments which require a pump unit of this nature for grass and grain field fires, or brush fires.
—Photo courtesy The Seagrave Corp.
Due to the nature of high-pressure service, it is very important that certain mechanical protection features be incorporated in the design of the complete pump package. One such automatic feature in the new centrifugals is cooling ot the pump transmission oil. Whenever water Hows through the pump, a portion of it will flow through a cooling coil in the bottom of the transmission case. 1 his action reduces oil oxidation, foaming and loss ot viscosity.
Pressure relief in the high-pressure system is necessary to prevent heat buildup when me nozzles are closed. All systems use relief valves set at the factors tor normal operation. If higher pressure reliet is necessary, a manual adjustment can be made. Some centrifugal pumps provide a small amount ot continuous bypassing as a further precaution. In all ot the pressure-relief systems the by-passing action is trom the discharge of the pump direct to the water tank, rather than to the suction side ot the pump as in the case of conventional volume pumps. This is done to take advantage ot the greater cooling action possible and tends to keep the water within sate limits.
Future looks promising
As history of the fire services discloses, fire apparatus pumps and related accessories have shown a gradual improvement over the years, keeping pace with the advancements in fire methods and manufacturing. The progress has been constant but not spectacular as is typical ot a service where tried and proven performance is necessary.
In recent years however, certain experiments have been carried on in the automotive and pumping fields which may foreshadow important future developments in the fire service.
The use of gas turbine engines for propulsion has been studied and tried out in the automotive and truck fields. With the possibilities of fantastic rpm s from these engines, perhaps the volume pump of the future may be of a size comparable with the present portable. The U. S. Navy already has procured a gas turbinedriven pump measuring about two feet in each dimension complete, which produces a volume of 500 gpm. In this pump the gas turbine speed exceeds 10,000 rpm’s.
Turbine-driven pumps are finding their way into the public fire service. Many predict continued progress will lie made in the entire field of portable pumping equipment beyond the adoption of high speed units. This progress will almost certainly result in devices delivering still greater gallons-per-minute at fewer weight-pounds-per-horsepower. Not only will the forestry service encourage such developments but such pumps will possibly find broader applications in disaster and civilian defense operations.
The extensive exploration being undertaken into the combustion of fire, and its extinguishment by waterfog, fog-foam and wetting agents, cannot help but have repercussions in the field of pumping equipment.
—Photo courtesy Ward LaFrance Truck Corp.
There will undoubtedly be even more important developments in major pumping apparatus. Exploration of the broader application of large-scale pumping units, up to as high as 3,000 gpm, may be expected in concert with the revised and improved strategy of fire attack whereby greater use is made of water supplies nearer the fire.
In the area of auxiliary pumping equipment, we may see the paradox develop whereby pump controls may increase in number, to better govern every single pumping operation, yet there will be greater simplicity and efficiency of operation. Just as today, while practically all motor vehicles are increasing the application of automatic features and this may entail more controls, it cannot be denied that automation does make for simpler and more convenient operation.
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CENTRIFUGAL FIRE PUMP
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Not everyone will agree with the principles of automation as applied to fire department vehicular operation, but neither did many automotive manufacturers and distributors accept it at the outset. Nevertheless, history tells us we seldom, if ever, return to old methods, old principles, once a newer, better way to do things has been well introduced. This has thus far been the experience in pumping progress. So it may prove in the future.