RELIEF VALVES AND SHUT-OFF NOZZLES.
Some of our correspondents have recently been discussing the merits of relief valves for Steam Fire Engines, and while one inclines to favor one kind, others are equally favorable to others. There are several kinds in use—the Prunty, the Shaw, the Mayer, the Orr, the Pallette— and we are not prepared to express a preference for either. So far as we are informed, they do all the work required of them satisfactorily, and that is the main point. It is not necessary for the friends of one to disparage the other; let each concede the merit that belongs to the others, but show better results if possible. The one that does the best work is the one that is wanted. “ The proof of the pudding is in the eating ” is a trite old adage, and to prove that one pudding is good it is not necessary to disparage all other puddings that have been eaten with a satisfied gusto. We are glad to see our correspondents discussing the subject, but beg them to bear in mind the suggestion made above ; do all you can to build up, but don’t try to destroy the good we now have.
One of the most important problems the Firemen of the country now have to contend with is how to save property from destruction by water as well as by fire. Insurance companies and individual propertyowners have learned to their cost that water is quite as destructive an element as fire, and we often read accounts of fires wherein it is stated that the damage by water exceeded the damage by fire. Sometimes it is impossible to avoid this, and frequently where it occurs, the responsibility lies with the owner of the property, who stores a lot of combustible material on his upper floors and valuable goods on the lower ones; when a fire occurs on the top floor, water must be used to extinguish it, and if it flows down upon the goods below, the Firemen should not be held accountable for the damage inflicted. Much has to be left to the judgment of the pipeman. It is his duty to seek out the exact location of the flames and extinguish them with the use of as little water as possible. To enable him to do this, he is generally supplied with a shut-off nozzle, so that he can with a turn or two of the nozzle, shut off the water instantaneously. But this he can not do if the Engine is working and giving him water under a heavy pressure, unless there is an outlet provided for the water somewhere between the pumps of the Engine and the play pipe. The relief valve is intended to supply this outlet. Placed on the Engine and regulated so as to open under slight pressure, when the nozzle is suddenly shut off, the valve opens and permits the water to flow back into the pumps or some other place of discharge. To meet all the requirements of prompt and quick work, there must be perfect harmony between the relief valve and the shut-oft nozzle, otherwise there comes a strain upon the hose that is liable to burst it.
How great this pressure upon the hose is was demonstrated by an experiment made last week by Assistant Chief Shay, of this Department. He placed a gauge at the base of the play-pipe, and, working with a shut-off nozzle open, this gauge indicated a steady pressure of 40 pounds. Cutting off the stream suddenly by giving a quarter turn to the nozzle, the gauge flew around suddenly to 140 pounds. It came upon the hose like the striking of a sudden and tremendous blow, and would have ruptured any but the best of hose. With a different shutoff nozzle, that required three turns to entirely stop the discharge of water, the indicator ran up more slowly, showing a gradual increase of pressure from 60 to 120 pounds. The shock to the hose in the first instance, with a sudden shut-off, was more than hose should be expected to stand, while with the nozzle acting more gradually the shock was comparatively slight. But wherever a shut-off nozzle is used, this back pressure upon the hose must come with more or less severity, depending upon the amount of water-pressure at the Engine and the celerity with which the discharge is interrupted. When the pressure has traveled back from the nozzle through the whole line of hose to the relief valve, if that opens promptly, the pressure on the hose is removed and the danger of its bursting has passed. But if the relief valve does not act promptly, and the Engine continues working, there being no outlet for the water at either the nozzle or the relief valve, the hose must take all the pressure and the pounding that the Engine can give it. Under such circumstances the column of water in the hose becomes a solid, like a wedge seeking to rend it asunder, and every stroke of the Engine is like a blow of a siedge hammer upon it. One of the principal reasons why so much hose is destroyed in the Fire Departments is that proper attention is not paid to the conditions under which it is subjected to pressure. If it is stretched in with kinks and twists in it, it is more liable to burst than if laid straight; every kink forms an obstruction to the flow of water and increases the pressure at that point. It is like placing a dam across a flowing stream, either stopping the water entirely till it overflows its banks, or contracting the current, and thereby increasing its velocity. While relief valves and shut-off nozzles are indispensable to a judicious use of water at fires, they require to be used with intelligence and judgment, or much damage may result. It is a satisfaction, however, to us to see all points of this nature discussed in THE JOURNAL, for it indicates that the Firemen are making a study of their business, and are seeking for the best appliances to enable them to perform their work to the best advantage.