The Knowledge Bank at The Ohio State University

Ohio State Engineer

Title: The Modern Fire Engine

Creators: Stinson, Karl W.

Issue Date: Nov-1926

Publisher: Ohio State University, College of Engineering

Citation: Ohio State Engineer, vol. 10, no. 1 (November, 1926), 9-10, 24, 41-

43.

URI: http://hdl.handle.net/1811/33832

Appears in

Collections: Ohio State Engineer: Volume 10, no. 1 (November, 1926)

THE OHIO STATE ENGINEER

THE MODERN FIRE ENGINEBy PROF. K. W. STINSON, Department of Mechanical Engineering

HE first fire engines of which we have any knowl-edge were built and operated by the Greeks andRomans about 50 B. C. These pumps were largesyringes and each one required three men to

operate it. This syringe type was followed closely bya double-piston pump mounted on wheels. This pumpwas hand-operated and even today, in many parts ofthe world, outlying districts have nq other means of fireprotection.

About one hundred years ago the first steam-drivenfire engine was built and this was followed by rapiddevelopment of the pump as well as the boiler andengine. The small sizes of these engines were drawnby hand while the larger engines were horse-drawn.

The boilers were fired with coal and were perfectedto such a degree that from 100 to 200 pounds per squareinch could be developed in the boiler in from six toten minutes from the time that the fire was started. Thesteam engine and the pump were usually of the opposed-piston type with a steam piston and a water piston oneach rod. Some of these engines were equipped withflywheels. There were two double-acting steam cylindersand two double-acting water cylinders on the majorityof engines. The piston pump was practically the onlytype of pump used on steam-driven fire engines. Ro-tary pumps, however, were used by at least one concern.

Some twenty years ago, attempts were made to propelthe steam fire engine by its own power. This type ofdrive was not very successful due to a somewhat crudemethod of operation and also to the fact that, unlesssteam was kept in the boiler at all times, the engine couldnot start for the fire for perhaps five minutes after thealarm was received.

Soon the steam fire engines were drawn by gasoline-engine tractors, many of which were mounted on onlytwo wheels, the unit replacing the front wheels of thefire engine. The power was transmitted through the

front wheels, and brakes were mounted on these as wellas on the rear wheels. This is the first application ofbrakes on all four wheels known to the writer. Thebrakes, however, were not applied on all wheels at onetime. This arrangement of brakes caused many seriousaccidents due to faulty operation. If the brakes on thefront wheels were applied suddenly, the wheels wouldlock and cause the machine to skid, while the driverhad absolutely no control over it.

Along with the conversion of the steam fire engineto a self-propelled vehicle came the first of the gasolinefire engines. Several manufacturers were attempting tobuild fire engines with a gasoline engine to operate thepump as well as drive the apparatus on the road. Thegasoline engine and automobile of twenty years ago werenot very dependable when compared to their present-dayperformance. This condition caused the gasoline fireengine to be considered unfavorably in comparison tothe steam-driven. However, the development of alloysteels and the great advance made in automotive designraised the standing of this new type of fire engine untiltoday it has replaced practically all steam fire engines.

The rise of the gasoline fire engine has been a verynoteworthy engineering achievement as the problems en-countered were, in many cases, much different from thoseof the automobile industry, although they might ap-pear at first to be practically the same. The one pointthat is foremost in fire-engine design is dependability,—not the cheapest, but the best,—not the lightest weightpossible, but strength at any cost. Engine proportionsthat were very satisfactory for the automobile were notsuitable for such service. The bearings were too small,the crank shaft was not strong enough, and many otherparts would not stand up under the severe conditionsof operation encountered in fire service. Approximatelythese same conditions were being encountered at thistime in the development of the airplane engine. The

Sectional View of Modern Fire Engine.

10 T H E O H I O S T A T E E N G I N E E R

airplane engine differed from the fire engine in thatweight is one of the primary points to be considered.

The automobile engine is operated most of the timeat from one-quarter to one-half of full throttle opening.In the cases of the airplane engine and the fire engine,the throttle is wide open much of the time. This con-dition of operation necessitates many differences in de-sign and manufacture of fire engines from those em-ployed in the manufacture of automobile and truckengines. It has been necessary for the manufacturers ofgasoline-operated fire engines to carry on much researchand development work in order to overcome the troublesencountered when operating under such extreme condi-

tions. The result has been dependable fire engines,—not trucks, not pleasure cars, but machines built fromthe ground up for a specific job, fire-fighting.

The fire engines of today vary in size from about 400gallons per minute to 1,500 gallons per minute whenpumping at a pressure of 120 pounds per square inch.Some smaller pumps will be found mounted on varioustruck chassis. The fire engines just mentioned requiregasoline engines capable of delivering from 70 horse-power for the smallest size to about 200 horsepower forthe largest. In other words, if six-cylinder engines areconsidered, this means that the engines will range fromabout 3%-inch bore by 5-inch stroke to perhaps 6'Yj.-inchbore and 8-inch stroke. The maximum operating enginespeeds will vary from 2,000 revolutions per minute toabout 900 revolutions per minute. These engines arepractically all larger than those commonly used in au-tomobiles and trucks. At the present time engines whichhave been developed for the bus and rail-car industriesare being adapted to fire service, but not without somevery necessary changes in the details of manufacture.

A fire engine is rated at a certain capacity whenpumping at a pressure of 120 pounds per square inch,

but it must be capable of delivering one-half this vol-ume at 200 pounds per square inch and one-third at 250pounds per square inch. Some fire engines are capableof pumping at pressures of 350 and 400 pounds persquare inch and even higher but will, of course, delivera correspondingly less volume. The National Board ofFire Underwriters, which controls the fire-insurance rates,requires that before a certain make or model of fireengine will be recognized, one fire engine of each modelmust successfully pass an endurance test of twelve hoursunder observation of Underwriter officials. The pumpis operated for a period of six hours at its full ratedcapacity at a pressure of 120 pounds per square inch,three hours at one-half capacity and 200 pounds persquare inch pressure and the final three hours at one-third of its rated capacity and a pressure of 250 poundsper square inch. Besides this test, which is required butonce for each model, each fire engine must undergo asix-hour acceptance test similar to the former test, ex-cept that the time required at each pressure is only halfthat in the official rating test. The fire engine mustundergo these tests at approximately wide-open throttlewithout a serious fault, and be capable of doing thatmuch and more in actual service. It is not an uncom-mon experience for fire engines to be required to oper-ate continuously for from ten to twenty hours.

The steam fire engine brought the piston pump intogreat favor with the fire-fighters all over the world.When the gasoline fire engine was first conceived, it wasquite natural that the piston pump should be assumedby some to be the most suitable type. This pump hasbeen so well adapted to the modern fire engine that itis favored by many today. However, it must be saidthat some of this preference is a result of the perform-ance of this type of pump on the steam fire engine andnot wholly based on the present relative merits of thevarious types. The piston-type fire pump is directlyconnected to the engine and is made up of a pair of two-or three-cylinder pumps one or both of which may beoperated, depending upon whether a high pressure or alarge volume of water is wanted. A fire engine of thistype when operating at a high pressure requires onlyone section of the pump, but if it is necessary to oper-ate at a lower pressure and a much greater volume ofwater, both sections of the pump must be used. Thepump must stop functioning for an instant to permit thisshift.

The piston pump is generally located in front of theengine and is connected to the engine by means of ajaw clutch when the pump is to be operated. This lo-cation of the pump makes connections for the suction

( C o n t i n u e d o n P a g e 2 4 )

24 THE OHIO STATE ENGINEER

THE MODERN FIRE ENGINE(Continued from Page 10)

and discharge hose very accessible and also gives asomewhat striking appearance to the fire engine, as thepump and its large nickel-plated air chamber are mount-ed in front of the engine and radiator.

The most common type of pump used in fire serviceis the rotary-gear. It is much smaller than the pistonpump and, like the centrifugal pump, is located underthe driver's seat. The rotary pump is connected to theengine through a special pump transmission. The needof various delivery pressures requires changeable gearratios for different operating conditions and necessitatesshifting the gears to the proper relation of engine andpump seeds so as to insure maximum delivery at anydesired pressure.

Both the piston and rotary-gear pumps are positivedisplacement and for this reason are desirable when Itis necessary to draft water from a lake, stream or cis-tern. These pumps are equipped with various bypassarrangements and relief valves for regulating and gov-erning the discharge pressure. The piston pump tends togive an intermittent flow of water, but this is partiallyovercome by an air chamber which helps the pump givean approximately uniform delivery. However, thereare very marked pulsations in the hose lines as well asbad vibrations in the fire engine caused by this un-evenness of flow. The displacement in the rotary-gearpump is not uniform during the whole pump revolutionand some produce pulsations as serious as those result-ing from the piston pump. An air chamber is suppliedby some manufacturers to partially correct this trouble.

The centrifugal pump is not of the positive-displace-ment type, but delivers the water by imparting to it ahigh velocity which is changed to pressure as the waterpasses through the pump casing. When a pump of thistype is correctly designed, the flow of water will be freefrom pulsation and the whole fire engine very free fromvibration. The pump is driven through a pair of gearsselected to give the proper speed relation between thepump and the engine. This gear ratio is fixed for alldeliveries and pressures. The variation of pressure isaccomplished by only varying the quantity discharged.An increase in pump pressure is accompanied by aslight increase in the pump and engine speeds. Eventhough the discharge valves were completely closed, thepump would develop a certain pressure dependent uponits speed but would not require any relief valves such asare necessary on positive displacement pumps. When itis necessary to pump water from a stream or othersource, the centrifugal pump cannot deliver water un-til it has first been primed or the? pump and suction pipefilled with water. The manufacturers of fire enginesequipped with centrifugal pumps have overcome thisdifficulty by installing a priming or vacuum pump ofthe positive-displacement type. Although this secondpump and its drive add somewhat to the complication ofthe apparatus, this type of fire engine is capable of de-livering a steady stream and also of priming itself. Theauxiliary priming pump, which operates only whenpriming the fire pump, is capable of many years ofdependable service, while it is not uncommon For ro-tary-gear pumps after years of service to. be* worn so asto render priming practically impossible. Thus thecentrifugal pump has been madei yeryl jdefpendable, v̂jithjAthe addition of a few parts, m i^. iP u m J^g an(^ Pr"$fng|qualities will not deteriorate frorii j^eajr^ !, ! ; -

The centrifugal+pumpl jfire1 |e|ngine|ljiU peeh developed 'primarily in the United Sjtates iby The Seagrave Corpora,-!tion of Columbus, Ohio^ while the pis'toh pump was de-veloped mainly by The Ahrens-Fox Fire Engine Com-pny of Cincinnati, Ohio, and the rotary-gear pump by

the American LaFrance Fire Engine Company of El-mira, N. Y. There are at the present time several otherconcerns building fire engines using one of these typesof pumps. In order to give somewhat in detail the char-acteristics of fire-engine construction as well as themethod of operation, the remainder of this article willbe devoted to the description and operation of a 750-gallon Seagrave centrifugal fire engine.

The streamline appearance of the apparatus is ob-tained largely through the use of an aluminum dash.This casting is heavily ribbed so as to support the bell,searchlight and perhaps a siren as well as side handlesand an instrument box. The frane of the fire engineis built of six-inch structural-steel channels with a trussrod under each side. The wheel base is 160 incheswhile the over-all length is 252 inches. The fire engineis capable of a road speed of more than 55 miles perhour, even though the weight without men or fire hoseis about 10,000 pounds. From 1,000 to 1,500 feet of2%-inch fire hose is carried in the hose body at the rearof the truck, the amount depending upon the size of bodydesired by the various cities.

Many fire engines carry a chemical tank of from 35to 60 gallons capacity and 200 feet of one-inch chem-ical hose for small fires. A solution of bicarbonate ofsoda and water is carried in these tanks together witha closed bottle of sulphuric acid. When the fire isreached, the acid is dumped into the soda solution. Avery high pressure is developed in the tank and is usedto force the solution through the hose to the fire. Dueto the great amount of damage caused by this chemicalsolution, there is a rapidly growing tendency towardthe use of water tanks of 65 to 80 gallons capacity inplace of the chemical tank. This water is pumped bythe regular fire pump through the chemical hose. Thismethod has been found to be very effective on smallfires that have not gained much headway.

A twenty-foot extension ladder and a twelve-foot roofladder are mounted on one side of the fire engine.

The engine used in the Seagrave 750-gallon pumper isa six-cylinder, T-head engine which has the cylinderscast separately and mounted on a Lyhite crankcase. Theengine has a 5%-inch bore and 6^>-inch stroke with apiston displacement of 1,012.7 cubic inches. The S. A. E.rating is 79.3 horsepower while the engine will developabout 150 brake horsepower when operating at 1,700revolutions per minute. The compression ratio is 4.63to 1. Light-weight cast-iron pistons are used with! fourpiston rings on each piston. The connecting rods areI-beam drop forgings and have four bolts in the lowerend. The bearings are 2 it inches in diameter and 2%inches long. The crank shaft is supported on sevenmain bearings of 3-inch diameter. The maximum bear-ing pressure on the connecting-rod bearings is 870 lbs.per square inch while that on the main bearings is 730lbs. per square inch when operating at 1,600 revolutionsper minute. Two cam shafts are used,; each jsuppprtedon four bearings and driven directly from the cj-ank-shaft by a pair of spur gears. The connecting-rod,main and camshaft bearings are all bronze-backed i witha babbitt lining. The main and cam-shaft bearings arereamed to size in the engine crank case. The valves,which are 3% inches in diameter, are operated throughroller-follower tappets and have a lift of A inch. The$tee valve diameter is 2% inches.

f ^ f uel is supplied to the engine through a two-inchurelUr and a! manifold which is Provided: [with jaj ho;t !

that may be usecl at will. :1 , , , j i : ;j j j j II ttjhe electrical isystjenlj is; 12-volt througliotit., : | Thestarting motor connects through a redjuiqtion gear andBendix drive to the flywheel gear. i!he ignition is sup-

(Continued on Page 41)

THE OHIO STATE ENGINEER 25

The pneumatic Paving Breakerdoes the work of 15 hand laborers.

Some years ago, when little boys used to yell"Get a horse" at the hesitant and asthmaticvehicle which was the ancestor of the modernautomobile, the term ditch-digger identifiedthe man who had to perform the hardest laborimaginable. Squads of these workmen wouldbe in the street with their crowbars andhammers, and there was always the sound ofmetal ringing on metal as the ponderous ham-mers descended. The passers-by would wonderthat no hand was crushed in the process.

That was before the development of thePaving Breaker. Work that fifteen men tooka day to perform is now accomplished by oneman. Compressed Air has supplanted theuncertain human muscle, and the ditch-diggeris no longer the man but the machine.

In this instance, as in a hundred others,Ingersoll-Rand Company has enlisted the aid ofCompressed Air in the elimination of wastedtime and effort.

INGERSOLL-RAND COMPANY11 Broadway • • New York City

Offices in principal cities the world over

Ingercoll -Rand

Evolution of theDitch'Digger

THE OHIO STATE ENGINEER 41

THE MODERN FIRE ENGINE(Continued from Page 24)

plied from two independent sources; a distributor andcoil furnish the battery ignition, while a single or two-spark magneto is also provided.

A three-gear oil pump is used to lubricate the engine.This pump delivers two independent streams of oil. Oneof these maintains a supply of oil in troughs under theconnecting rods, while the other forces oil under pres-sure to the main bearings. The connecting rods are pro-vided with scuppers which take up some of the oil fromthe troughs for the connecting-rod bearings and splashoil on the cylinder walls and other bearing surfaces.

The water cooling system incorporates the conven-tional centrifugal circulating pump. However, whenpumping, this system alone is very inadequate and an

(Continued on Page 43)

42 THE OHIO STATE ENGINEER

OHIO STATE ENGINEER

ARCHITECTURALCERAMIC- CHEMICAL

ELECTRICAL

METALLURGICALCIVIL • MECHAMCAL

MINING .

MANAGING BOARD

W. G. HARDY '27Editor

RAY BIRCH '27Managing Editor

L. P. DOYLE '27Business Manager

H. W. FORSOHNERAdvertising Manager

C. C. KELLERCirculation Manager

EDITORIAL STAFF

E. S. HECK Assistant EditorFRANK DICKERSON _ Assistant EditorW. H. FABER Campus NotesW. H. SCHOTTS Alumni News

L. G. STEWART

BUSINESS STAFF

J. F. GABRIEL Assistant Business ManagerR. V. MUCKLEY Assistant Advertising Manager

LEROY J. DUERRCARL W. RYAN

ADVISORY BOARDDean E. A. Hitchcock Prof. C. T. Morris

Asst. Prof. Sada HarbargerOne representative from each student engineering society

Two Representatives from Engineers' Council

ADVERTISERSAmerican Gas Manufacturers Co.American Sheet and Tin Plate Co.American Steel & Wire Co.Artcraft Printing Co.Automotive AbstractsBailey Meter Co.Block's Floral Co.Brown & SharpThe CandleCast Iron PipeThe Crane Co.Cotner's Pharmacy

Du PontThe Foundation Co.Franklin AsphaltGeneral Electric Co.Hercules Powder Co.Huffman-Wolfe Co.Hennick'sIngersoll-Rand Co.KoehringLehman Co.Lufkin Rule Co.Ohio State LanternLong's College Book Store

Mississippi Wire Glass Co.Mt. Vernon Bridge Co.National Paving Brick Co.Otis Elevator Co.Phillips Printing Co.Rider's Pen ShopRose Marie ShoppeSuperheater CompanyTimken Roller BearingsWestinghouse E. & M. Co.Western Electric Co.J. G. Wilson Co.

THE OHIO STATE ENGINEER 43

(Continued from Page 41)auxiliary cooler is provided through which the waterpasses after leaving the radiator. This auxiliary coolerconsists of many small brass tubes enclosed in a casein such a way that the water passes through half of thetubes to one end of the cooler and then returns throughthe other half. These tubes are surrounded with watercirculated by the fire pump, thus the engine coolingwater is cooled while passing through these tubes. Asmall water line from the fire pump directly to the cool-ing-water system is provided so that the supply may bereplenished or allowed to overflow slowly and thus aidin cooling the engine.

The clutch is a dry single-plate type, enclosed in theflywheel and capable of easy adjustment. The plate isfaced on each side with an asbestos fabric clutch lining.The actuating pressure for the clutch is produced byseveral small helical springs. As the clutch wears,there is a tendency for it to slip and thus require ad-justing. This slipping might not be evident until pump-ing at a fire and then there would be no time availableto adjust the clutch. To guard against such an emerg-ency, a clutch lock is provided which will prevent anyslipping and transmit the power directly to the pump.

The road transmission is built as a unit and is locatednear the rear axle. There are three speeds forward andone reverse and they are obtained through the standardautomobile gear-shift positions. Stub-tooth gears of5-7 pitch with 1%-inch face are used and the shafts aresupported on large ball bearings. The power is trans-mitted to the rear axle through an all-metal type doubleuniversal joint.

A worm-drive rear axle is used with a Hotchkiss-styledrive. The speed reduction in the rear axle is 4% to 1or 5 to 1. Taper roller bearings are used throughoutthe worm-drive rear axle as well as the pivot supportsof the front axle. The brakes are all internal expand-ing and act on the rear-wheel brake drums. Cast-stee.1disc wheels are furnished as specified by the purchaserand are mounted on taper-roller bearings.

Both two-stage and four-stage centrifugal pumps areused in this make of fire engine, the two-stage is theone used in the 750-gallon pumper. All parts of thepump that come in contact with water are made ofbronze. The pump is made up of a large barrel-shapedbody, the two heads, the diffuser rings, and the rotatingparts, which consist of the impellers and shaft. Thebody contains all of the water passages from one im-peller to the next as well as two suction and two dis-charge passages. Each head contains a ball bearingand a packing gland.

A gear on the pump shaft is in mesh with a gear thatmay be connected to the main drive shaft when the pumpis to be operated. The pump shaft is supported on twoball bearings, one is a deep-groove type while the otheris a double-row combined radial and thrust type. Thisarrangement takes care of any unbalanced end thrust inthe pump. On the opposite side of the pump transmis-sion is the priming pump. This is an eccentric-vanetype of positive displacement pump, and is capable ofpriming the fire pump at lifts of over 25 feet in lessthan a minute.

The pump-transmission gears are 4-pitch, 14% de-gree involute with 2%-inch face. These gears areground after heat treatment to lessen the noise of opera-tion, as they sometimes have pitch-line speeds over4,000 feet per minute. The gears are free when theapparatus is on the road and are connected to the driveshaft by a special type three-jaw clutch. The primingpump is connected, when needed, to the end of thecentrifugal-pump shaft by a second jaw clutch. Thepump and transmission are mounted under the driver's

seat. This assembly and the exhaust pipe are enclosedby sheet-steel walls in order to prevent freezing in thewinter.

The pump is controlled by means of a lever on theright-hand side of the apparatus. When this lever israised, the main clutch is released. With the clutch outthe lever may be pushed sideways to engage the jawclutch that drives the pump transmission. When thelever is lowered, the gears and pump are put in motion.If the pump is to draft water, the priming pump mustbe used, and it is controlled by a latch on the controllever. This latch is pressed down when shifting side-ways to engage the pump transmission. The latch isthen held down until water has been obtained, when it isreleased so that the priming pump may stop. This con-trol system also operates a valve connecting the cen-trifugal pump and the priming pump while priming.Thus with this unified control system, one lever con-trols all operations. There are other levers nearby forcontrolling the fire streams, auxiliary cooler and pres-sure regulator.

Centrifugal fire pumps are made as small as possible,due to the limited space available for installation, buteven then the pumps have maximum efficiencies of 70 to75 per cent. A centrifugal pump is designed to oper-ate at some certain pressure, but, for a fire engine wherethe pressure may vary from 120 to 350 pounds per sq.in., this design pressure is very difficult to determineand is based in a great part on experience. Anothervery important item in centrifugal fire engine construc-tion is the determination of the proper gear ratio be-tween the pump and engine. This ratio must correlatethe variations in engine torque and pump efficiency sothat the maximum volume of water may be obtained atthe various pressures.

The engineering problem in fire engine manufactureis greater than would be expected, due to the numberof models of apparatus produced. For instance, onemanufacturer builds seven sizes of fire engines, whichrequire five sizes of engines. Along with this thereare about ten models of combination cars, service (lad-der) trucks, aerials and water towers. This makes atotal of seventeen models, many of them coming throughthe shop at one time. Besides this, practically all citieshave many special features which they insist must beincorporated in their machines, such as special stylesof bodies and equipment. In fact, anything except theengine, pump, transmission and axles, is subject to therequirements of the various cities. Production meth-ods are applied to the manufacture of the standardunits, but with much difficulty, as the great volume ofspecial work tends to disrupt such routine. Individualshop specifications are required for each fire enginebuilt, that is, they are "custom built."

In present-day production, it is surprising that thecities should insist upon special fire engines,—insist thatthe manufacturer building to suit the various cities, withthe result that the people pay perhaps twenty per centmore for practically the same thing. Why should notthe manufacturers discontinue building special fire ap-paratus? They should, but the writer believes theinitiative must be taken by the cities.

Great development has been made in fire apparatusin the last few years, but, like most other industries,much improvement is still needed. This fact is real-ized when one considers that the annual fire loss in theUnited States is over $500,000,000, and that more than15,000 people lose their lives in fires each year. It isto be hoped that these figures may decrease in futureyears with the aid of improved fire-fighting methodsand more effective fire engines.