Rubber hose evolved in answer to a challenge for an easier, safer, more reliable and more efficient means of getting a large volume of water on a fire. The first such hose was delivered in 1871 to the Cincinnati Fire Department by the B. F. Goodrich Company. It was made by plying alternate layers of heavy square-woven cotton duck and thin rubber over a rubber tube, with a final layer of rubber covering the fabric.
By modern standards, this rubber fabric hose was stiff and unwieldy but it was gratefully received by firemen who previously had to struggle with leather hose. The old leather hose was made by forming stitched leather hides into a tube and fastening them together with copper rivets. It was stiff, extremely heavy when wet, leaked badly, was difficult to couple, and in cold or freezing weather handled about as easily as iron pipe. The new hose was lighter, waterproof, much easier to couple and much easier to handle in all types of weather and thereby saved a vital element in fire fighting—time.
Rubber-covered, rubber-lined hose was used until the circular woven seamless cotton jacket we know today was introduced and adopted. This new method eliminated the heavy duck plies and rubber cover, and, although not as resistant to abrasion or the elements, permitted equal or greater strength with a marked saving in weight and greatly increased flexibility. This meant hose could be stored easily, compactly, and in greater quantity for industrial protection. Also, more hose could be carried on industrial and municipal apparatus with fewer men required for handling in service. Since the introduction of the woven jacket rubber-lined hose, no other type of construction has been devised which does the job as well.
This does not mean, however, that there have not been great advances in design, weaving techniques, manufacturing techniques, rubber compounding, synthetic fibers and rubbers, and treating of jackets against attack by the elements. Refinements and developments introduced since the inception of circular woven construction include lighter, higher tensile yarns designed for decreased weight with increased flexibility at no sacrifice in strength; flat cure for easier storage; end protection for increased flex life at the couplings; constructions utilizing loose folds reinforced at the edges for improved racking characteristics and performance; improved tubes for better aging and longer life; mildewcides and water-repellant dips for the jackets.
Tube stands long storage
Rubber-lined fire hose, in general, consists of one or more woven fabric seamless jackets into which a rubber tube has been inserted and vulcanized.
The tube is that member which retains the water within the hose. Essential characteristics of fire hose tubes are the absence of defects and pin hole leaks, good aging characteristics and smoothness of surface. Desirable aging characteristics are required to prevent fold or edge cracking and subsequent failure in service. Since the hose is stored during the greater part of its life, this feature is most important.
The compounding of fire hose tubes involves selection of proper ingredients to assure a satisfactory balance of all the desired properties. The first and most important of these selections is that of the basic rubber itself. Twenty-five years ago natural rubber was the only choice possible. However, several man-made rubbers have become commercially available in the years since then. So great has been the acceptance of these man-made rubbers that their nationwide use now exceeds that of natural rubber. Man-made rubbers, whose resistance to ozone, weather, oil and fuels, is far superior to that of natural rubber, are now readily available and have found their rightful place in the manufacture of fire hose.
… its evolution, design, construction and care
Starting with the basic rubber, loading pigments, processing oils, antioxidants, antiozonants, accelerators, and curative ingredients are added to provide the desired physical properties in the finished hose.
Tubes are manufactured by two basic processes—extrusion and calendering. The compounded rubber is extruded from a tube machine in a seamless form to produce a tube, while the calendered tube is made up of a layer of flat sheet which is subsequently hand-lapped to form the tube.
After the tube is formed it is semicured to facilitate handling and to provide the smoothest possible surface in the finished hose. This reduces friction loss caused by passage of water through the hose at high velocity. To adhere the semi-cured tube to the jacket requires the use of a soft uncured backing which is a layer of calendered sheet stock. The backing is applied to the semi-cured tube before its insertion into the jacket. The backing also tends to keep the waterway smooth while the hose is under operating pressure.
The textile jackets have two basic elements—the warp yarns and the filler yarns. Warp yarn is the term given to those ends or yarns that run lengthwise through the jacket; filler yarn is that term which is used to denote those cords which run circumferentially around the jacket. During the weaving operation on circular looms these two yarns are interwoven, with the warp yarns covering the filler yarns. The warp yarns accept the lengthwise component of the internal pressure stresses and the filler yarns accept the circumferential stresses.
Cotton ranks first in usage in the design of fire hose jackets. The new polyester fibers rank second with other man-made fibers such as nylon being used in smaller amounts.
Each fiber has its particular advantages and disadvantages. Cotton has good abrasion resistance; however, it is susceptible to mildew. Mildewcidetreated jackets are available but the hose still must be thoroughly dried after use. The polyester fibers have good chemical resistance, good abrasion resistance, do not mildew even when stored wet, and possess high unit strength. Nylon is used primarily in industrial hose for rack use in factories, mills and offices.
Jackets may be designed with the same fiber for both the warp and filler or they may be designed with one fiber in the warp and another in the filler. A popular hose construction where two fibers are used is “cotton-polyester filled” jackets. The cotton’s bulk in the warp provides excellent abrasion resistance and the polyester filling gives a high burst strength. The overall result is a hose that is more flexible with less weight.
Pressure distortion controlled
The most important characteristic of quality of any fire hose is its pressure behavior as a finished hose. The elongation, warping, twisting, circumferential expansion or any distortion under pressure must be reasonably low to effect desirable performance. Quite naturally the ultimate strength of the jacket is a fundamental requirement of any finished hose.
In weaving, the interlacing of the warp through the filling ends results in a crimp in the warp yarn. The crimp, or bending as the yams go over and under the filling yarn, detracts both from the pressure behavior and the strength of the hose. It is, therefore, desirable to keep the crimp at a minimum. Also, the filling yarns must be placed in the jackets under uniform tension to be sure that each carries its full share of the load and keeps its circumferential expansion to the minimum.
A basic pressure behavior of a woven jacket is a tendency to twist. This twisting tendency results from the effort of the circular woven construction to unwind. Therefore the direction of twist of the finished hose depends directly on the direction in which the jacket is woven. It is a prime requirement of all fire hose that its twist be in the direction to tighten the hose couplings rather than to loosen them. All single and doublejacket hose is designed to meet that requirement.
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In double jackets, inasmuch as the two jackets are made completely independently, the direction of weaving the outer jacket is reversed so that the tendency of the inner jacket to twist will be counteracted to a great degree by the outer jacket. Therefore, the importance of fit between the inner and outer jackets becomes quite obvious. After the jackets are woven and before usage, the inner jacket is inserted into the outer jacket.
If hose is to be treated with an antimildew and water-repellent solution, the jackets are run through dipping tanks where each fiber becomes saturated with the solution. The jackets are then dried at controlled temperatures and are ready for further processing.
Curing the hose
After the component parts are assembled, the semi-cured tube, covered with backing, is inserted into the jackets. Vulcanization is effected by internal steam within the hose tube, forcing it out against the woven jacket. This is accomplished in a multiple-length curing unit. Careful attention is given to keeping the temperature and pressure at constant specified levels. During cure, each length is under individually controlled tension to obtain a low level of elongation in the finished hose when under pressure.
Fire hose can be cured “round” or “flat.” Round cures are produced by introducing internal steam pressure and letting the jacket assume their natural round shape. Flat cures are produced by an initial round cure cycle to insure even flow of the backing into the interstices of the jackets, followed by a final cure cycle with the hose confined in a flattened position between metal plates. The flat cure molds the edges leaving the rubber stress relieved in the flat position in which the hose is normally stored and produces a hose with excellent racking characteristics.
After the final cure, the finished hose is transported to the coupling machines for coupling prior to hydrostatic testing.
The most common coupling for fire hose is the expansion-ring type. The female end has a bowl into which the hose is inserted but the threads are cut into a free-swiveling heavy brass ring. This swiveling thread section provides easy joining of the male and female without twisting the hose. The hose end is anchored in the bowl by’ means of a metal expansion ring which forces the hose wall against the inner surface of the bowl under controlled hydraulic or mechanical pressure. The inner surface of each bowl is serrated to facilitate handling.
Expansion-ring couplings and expansion rings are almost universally made of a brass composition. Its corrosive characteristics, appearance, and ductility are all desirable for this application. There are several types of lugs used on the fittings by which the couplings are tightened—pin lugs, rocker lugs, guard lugs, forestry or slotted lugs. In industrial service the pin lug is generally preferred. Other methods for tightening couplings are spanner holes, long handle and Jones Snap.
There are three basic types of manufacture: casting, forging, and extruding. The forging and extruding processes result in a coupling with a higher tensile strength designed for heavy-duty service but with less ductility than a cast coupling. The finish of couplings can be either a rough cast finish, satin finish, a highly polished finish or chrome-plated. Practically all industrial couplings are of the cast type as the service is not too severe. Forged and extruded couplings are used for the heavier-duty municipal service. There are many different fire hose threads in service and available, but in industrial and municipal applications iron pipe and National Standard are by far the most prevalent.
Expansion ring couplings are reusable; only the expansion ring itself and that part of the hose within the coupling need be replaced when the coupling is reapplied.
Before shipment, each length of fire hose receives a hydrostatic hold test at the designated proof test pressure, depending upon the construction or specification.
While the hose is under this straight pressure test, it is inspected for any signs of leaking or coupling slippage. The inspectors also check twist, elongation, warp and rise. The twist is determined by how many turns the free end of the hose rotates under pressure from 10 psi to the proof pressure. All twists must be in the direction to tighten the couplings. Warp is the amount the hose deviates from a straight line under the proof pressure. Rise is the measure of how far the hose lifts from the test table at the proof pressure.
When required, or at specified intervals for regular production, a “kink” test is performed to detennine the ability of a hose to withstand sudden kinks or bends in service.
Burst control tests are usually run on 3-foot samples. Control tests are also conducted to measure the adhesion of the tube to the jacket and to measure the physical properties of the rubber tube, both aged and unaged.
Proper care of fire hose is important from the standpoint of safety, effectiveness in use, and economy. Since fire hose spends much of its life doing nothing, constant effort must be made to keep it ready for instant use. As new base is received, it should be unpacked immediately and checked for any damage during shipment. It should be recoiled loosely.
Fire hose, like any other rubber product, should be stored in a cool, dry, dark, ventilated area, where it will be protected from abrasion and abuse of nearby traffic and away from accidental spilling and fumes of acids, caustics and other deteriorating agents.
Hose should be cleaned after each use by brushing off dirt or scrubbing with water, and then thoroughly dried in towers, racks or in blower-type dryers.
After it is dried, it should be inspected before being put on the truck. Inspectors should watch for snagged jackets, damage from abrasion, damaged and loose couplings, etc. Damage to the jacket has to be weighed somewhat by experience as to what will affect its serviceability. Damaged couplings must be replaced. Coupling threads should be inspected to insure easy coupling. Nicks in threads can be dressed. Loose couplings should be cut off the hose and recoupled.
Racking hose with as few folds as possible, and reracking to change the position of the folds every month will extend service life. Hose should be tested at 150 psi for single and 250 psi for double jacket, or at any higher pressure used, with the pressure maintained for no less than 5 minutes.