Revolution and Elongation of Fire Hose
In reply to questions asked by a subscriber of FIRE AND WATER ENGINEERING on the construction of 2 1/2-inch double jacket cotton rubber lined hose several answers have been furnished by experts in the manufacture of it. which are given herewith and must prove valuable to our readers who are all interested in the subject:
Fire and Water Engineering, 154 Nassau street, New York City.
To the Editor:
I have noticed in the specifications for the construction of 2 1/2-inch double jacket cotton rubber lined fire hose of some cities that the maximum allowance at 400 pounds pressure per square inch for twist shall be not more than two revolutions, for elongation not more than 54 inches and shall not increase in external diameter more than 1-16 of an inch. If a 50-foot section of hose in an acceptance test exceeded the maximum in any or all of the above what would it indicate? Suppose a section of hose elongated 108 inches instead of 54 inches and met the test in the other respects what would it signify? What difference would there be if the hose had a cemented or loose inner tube?
Fabric Fire Hose Company.
A city like New York, for instance, might be justified in limiting the tendency of fire hose to elongate within 54 inches under test pressure of 400 pounds, only because the hose may be used in conjunction with the special high pressure service carrying working pressure at times of nearly 400 pounds, so that the elongation beyond this might, in a line of hose, cause some inconvenience, but for ordinary service either with the regular steam fire engine or gravity pressure there is no objection whatsoever to the use of hose that will under 400 pounds stretch even double the 54 inches, as the tendency to stretch under normal pressure would be nominal and always within the 54 inches. Of course it is needless for us to say to you that if a section of hose was submitted for test under specifications calling for 54 inches elongation, the section of hose stretched more than this would not meet the specifications. It is a source of regret to the fire department officials of the larger cities that they deem it expedient to limit elongation to 54 inches, as the hose constructed to meet such requirements must necessarily be made larger bulk in the fabric by using middling grade of yarn rather than sea island cotton or grades approximating this standard, because the best cotton is the most elastic and of course the fabric is woven up with the highest grade yarn and the tendency to stretch will be greater. A hose that would stretch 108 inches without twisting more than two turns must be well constructed mechanically and the yarn must be of the very best quality to permit such a stretch under 400 pounds pressure, and come back nearly to its normal length of 50 feet in a test of a single section of hose. This is a remarkable performance and any one using such a hose should have no anxiety whatever but on the contrary be congratulated upon having a hose that would be well nigh everlasting. but we question whether such a high quality hose can be produced with yarn of the present day product. You understand, of course, that the principal objection to so-called extensive elongation is on account of the tendency of such a hose to twist four, five or even six turns, but if this tendency to twist can be resisted as in the example you mention, it is decidedly a very great advantage rather than being objectionable. Such a hose could only be lined, of course, with the very highest grade of rubber tubing. While we have no actual figures with which to demonstrate, we are inclined to believe that it would not be a very great difference between the stretch in the hose with cemented tube or loose tube if the fabric were identically of the same construction and the same quality of yarn. We believe, Mr. Editor, that you probably referred this inquiry to us simply to have your own opinions verified and we have no doubt but that you will confirm our conclusions within your own judgment.
W. T. COLE, President.
The Goodyear Tire & Rubber Company.
The tests given for 2 1/2-inch double jacket cotton rubber lined fire hose in the correspondence from FIRE AND WATER ENGINEERING are Standard Underwriter acceptance tests with the possible exception of the expansion. In my copy of the Underwriters I find no expansion limit, but the 1-16-inch expansion mentioned in the attached letter is given in the Navy specifications. Just why these figures should be set as they are, we have not determined and I do not think it worth while to involve ourselves in a discussion with the Underwriters’ Laboratory in this connection, inasmuch as we are not making any of the hose and have not experimented with it. The twist, elongation and expansion are all objectionable, but must be tolerated to a certain degree and the figures should be set at the lowest limit which can be obtained with good manufacturing practice. I have heard it rumored that hose which elongated too much pulled some firemen from their ladders when the hose burst and the corresponding contraction took place. I cannot confirm this, but it is entirely within the limits of reason. The objection to twisting is based on the probability of the couplings being loosened if the twist is in the wrong direction. We doubt the seriousness of this point in view of the fact that we have taken six lengths of left-hand twist, wrapped hose and coupled them together without wrenches. Four hundred pounds pressure failed to open up the couplings, although the free end was held with a bar so that it could not turn. The distortion of the jacket under pressure puts a corresponding strain on the rubber lining, which does no harm if the lining is of good quality. Regarding the difference between a cemented or loose inner tube, I believe that the adhesion has very little to do with the service of the hose. In fact, I understand that cured tubes have been slipped into cotton jackets with absolutely no adhesion at all and very good results were obtained.
E. G. KIMMICK,
New Jersey Car Spring and Rubber Company, Inc.
In regard to your letter of the 12th instant, we would say that according to the specifications of fire hose, if any test does not meet the requirements, it would be rejected. As to the reasons for these failures, we would say that it depends on the conditions under which the hose is made and would suggest that the manufacturer get in touch with a technical expert on this subject and have him look over the apparatus and method of manufacture.
N. E. DOWNS,
C C C Fire Hose Company.
The maximum elongation of fire hose is often included in the specifications and the advantages in keeping down the stretch under pressure are as follows: In the first place when a line of fire hose is laid from a hydrant or engine to a fire, say 500 feet long, there is no water in it and if the water is turned on the hose stretches excessively it means that this stretch will be “taken up” in curves or snakes in the line and the result will be that the water will not travel in a straight line to the fire and the water will be retarded by friction and the pressure reduced thereby. This is the main point in our opinion. Another point that also is important is that if a fireman is at the top of a ladder with a 500-ft. line of hose under a working pressure of 125 to 150 pounds and each 50-ft. section stretches excessively, say 30 inches to the section, or a total of 300 inches, and the water is suddenly shut off, or a length of hose bursts somewhere back in the line, the nozzle will immediately be snapped back 300 inches, which is liable to pull the fireman off the ladder, or pull down the whole ladder. Woven fire hose will stretch in spite of the best manufacturing facilities, but the less the stretch the better. As regards the question asked, “Suppose a section of hose elongates 108 inches instead of 54 inches and met the tests in other respects, what would it signify?” This excessive elongation would probably be due to the fact that when the cotton jacket was woven the tensions on the loom were not tight enough and the fabric was loosely woven, which would probably mean loss in strength. If, however, it met the pressure requirements of the tests it would indicate that it was strong enough for the purpose.
The Bi-Lateral Fire Hose Company.
Excessive elongation in fire hose indicates a loose weave. It is necessary that a cotton jacket has a reasonable amount of elasticity, and this is why the knit jacket hose has never proven a success, because it would elongate but a few inches. The reason for this is: in weaving a knit jacket the cord runs lengthwise without much of a curve caused in weaving, and it is like stretching a rope that was straight. In a circular woven hose the warp threads go around, over and under the filling cord. When the pressure is on these naturally draw up tighter and it means the hose will go out some or lengthen. We do not think 54 inches of elongation of any injury, and we think between that and 36 inches is the amount it should elongate under 400 lbs. test pressure. The objections to the elongation of hose are mainly two, the first being that the elongation of a hollow tube means reducing the diameter and the delivery of water. The other is that firemen sometimes get into a position on a roof where it is difficult to stand and then when the water is turned on if the hose pushes forward, it is hard for them to stay where put. It might push them off the roof.
Now, as to the twist in hose, it is known that a single-jacket hose will twist three or four or even five times one way. As a double-jacket hose is composed of two single jackets, it is necessary to weave these jackets to avoid twisting, so that the filling thread will run in opposite directions to each other, then if the two jackets conform perfectly together, there will be approximately no twist. If there is a twist of two or three turns it would indicate that either the outer jacket or the inner jacket is bearing the greater amount of the burden. To illustrate—if the outer burden was too small and the inner jacket would not then share its burden of the pressure. The opposite would be true were the inner jacket too small so that when the pressure was on it would not press sufficiently tight against the outer jacket to make it bear its half of the pressure, then the twist would be caused by the inner jacket. As stated, if the two jackets conform together there will be but little twist, and this is indicative of a perfect weave. The last question, the difference between a tube if it is cemented to a jacket or a loose inner tube, would state that a loose inner tube has been tried and has not been found a success. The reason for this is that the water is forced through one end of the hose and out of the other, the stream of water being always toward the male coupling. The tendency would be in the loose tube to push the tube forward until it obstructed the male coupling. To avoid this, manufacturers of a recent construction have attempted to put on a cloth to prevent this elongation. This cloth will accomplish this purpose, we think, for a year or two, or until it rots, then the same trouble as at first will occur. The tube should be cemented to the jacket securely on the sides.
The Republic Rubber Company.
The object of the fire hose specification as we understand it is to provide a safe standard which ordinary manufacturing practice can reach. Experience through many years of manufacturing and testing hose of many different makes led the underwriters to draw up the specification quoted, from the fact that hose which meets or exceeds these requirements proves to give good, consistent service. Therefore, these limits were set so that hose made to these specifications, regardless of where manufactured, would be uniform. This does not mean that hose which does not meet the requirements by a small amount is absolutely worthless, but it simply means that such hose will not, in the long run, give as good service as specification hose. For instance, the idea of the hose twisting under pressure not more than two revolutions is to be sure that it will not be twisted out of the fireman’s hand in service. If it were to twist slightly more than two revolutions there would be no great harm done, but the hose would not be uniform with other lengths bought under the same specification, and would not be worth as much. The increase in external diameter more than one-sixteenth of an inch would indicate a dangerous loosening of the filler, which would be followed by bursting at some time early in the life of the hose. An elongation to 108 inches, or twice the permitted elongation, is impossible to imagine, as the writer has never seen a piece of double-jacket hose elongate even 54 inches. However, there is no doubt but that long before the hose would reach 108 inches elongation it would burst, due to the great spaces between the filler cords. An undue elongation of the hose signifies that the jacket is woven with a loose warp, or the fillers spaced much too far apart. The writer has had no personal experience with hose constructed with a loose inner tube. Theoretically it may seem that there are many advantages in favor of a loose tube. However, practically the loose tube has not worked out especially well. The writer’s best information is that there is friction between the tube and jacket while handling the hose before putting the pressure on, and, furthermore, that this tube, being free, would kink or twist independently of the jacket and thus be injured.
C. W. HARDIN,
Manager Mechanical Sales.
New York Belting & Packing Company.
We have your letter of August 12 relative to specifications for fire hose. The fact of cotton rubber-lined fire hose expanding or elongating more than indicated by specifications would probably indicate that lighter yarns or looser weave was used in weaving the fabric than was intended in the specifications. In regard to the loose inner tube, this is a new patented process which has been brought up recently, and we are not familiar with it.
S. A. COOMBS,
Asst. General Manager.
What an Expert Says.
An expert on jacket fire hose has this to say on the subject: Most specifications for a high grade jacket hose suitable for fire department service require that the pressure test shall be 400 lbs., as your correspondent has it. The twist shall not exceed more than one revolution and the elongation not more than 50 inches. The increase in external diameter of one-sixteenth of an inch is about the minimum. If a 50-foot section of hose, under said test, exceeded 54 inches elongation and made more than one revolution and did not go out in a straight line, we should presume the hose too loosely woven to get the best results. You can see that a man on a ladder, holding a piece of hose which elongated nine feet, would be very apt to be pushed off his perch. Such a strain on the lining, too, would be apt to loosen it from the fabric and stretch it to a breaking point. In my experience I have never seen a length of hose elongate anything like 108 inches under 400 lbs.
Empire Rubber & Tire Company.
Replying to your letter of the 12th inst. under subject of test on fire hose, excessive elongation forces the hose forward and would be very dangerous in some cases. For instance, if firemen were on the edge of a building holding the hose before the pressure was applied, the elongation would endanger the lives of these firemen. This would be especially true if several lengths were used in one line.
J. M. MILLER.
The B. F. Goodrich Rubber Company.
A double-jacket fire hose which, under 400 pounds pressure, will elongate more than 54 inches shows very clearly a weakness in manufacture. In addition to this it is rather cumbersome to handle. To illustrate this statement, it would be hazardous, when operating a three or four hundred foot line of hose on a ladder, to have the pressure released and the hose in turn to contract more than 54 inches. Again, it would be almost impossible to manufacture a hose which would show no elongation under 400 pounds pressure. Another manufacturing weakness would therefore be shown if the hose in question showed no twist or elongation. It is for this reason that certain limits should be prescribed. It has always been our aim to construct fire hose along practical lines in order that we might obtain the maximum strength from the materials used in manufacturing. Regarding the subject of twist, all fire hose couplings are designed with a right hand thread. It is therefore necessary that any twist in the hose take place toward the right, otherwise the hose would uncouple itself. Too great a twist makes the handling of the hose rather cumbersome, as in the case of elongation. A double-jacket fire hose which, under 400 pounds pressure, shows no expansion has no practical value, inasmuch as the slightest overload in pressure will disrupt the hose. It is therefore necessary that a slight degree of expansion be present. Too great an expansion shows a manufacturing weakness, in that the hose would be short-lived. For this reason certain limits of expansion under 400 pounds pressure should be prescribed. Regarding the last sentence in your subscriber’s letter, asking “What difference would there be if the hose had a cemented or loose inner tube?” it has always been our contention that the tube should be securely cemented to the inner jacket for at least the greater part of the surface. This would tend to eliminate any possibility of a loose section of tubing being crowded to the discharge end of the hose while under pressure.
G. R. VAN DUSER.
The recent petition of the men for an increase of $10 monthly for September, October, November and December has been granted by the city council of Newcastle, Pa.