Fire Hydrants and Frost.
To the Board of Water Commissioners, Little Falls, N. Y.:
In view of the discussion in regard to hydrants being frozen, I submit as directed, a description of the method of construction, and means taken to render them serviceable during the winter season.
The hydrants consist of a vertical stand-pipe extending up about three feet out of the ground and running down in the earth to the level of the mains in the street. The hydrant is opened and closed by a slide valve at the bottom, shutting against the pipe leading in from the main. This pipe is called the lateral or hydrant main and is for a six inch hydrant, a six inch pipe, and for the four, a four inch main in diameter. The valve at the bottom is operated by a long rod running up to the top of the hydrant, and water is conveyed into the fire hose through two openings near the top of the hydrant called the fire nozzles.
The hydrants are prevented freezing by having a inch opening at the bottom of the hydrant and below the valve called the drip, which is automatically opened when the hydrant is closed and shut tight by the operation of opening. The plug of the drip is fastened to the long rod and moves in exactly the opposite direction to the valve, in opening and closing as the long rod is turned. There is, therefore, an interval of time as the valve is being opened or closed, when the drip is neither wide open nor closed tight.
In order to allow the water to run away quickly from the hydrant instead of slowly soaking away in the ground, and thus get it below the valve as soon as possible, there is laid a four or six inch drain tile, beginning at the hydrant and running alongside of the lateral or hydrant main out to and alongside the regular street main, for a short distance and in some cases, where it could be done, emptying into the sewers.
The amount of water to be disposed of quickly is the capacity of the hydrant, eight inches in diameter by about eight feet long, and for the four inch, six inches diameter by eight feet.
If the drip and drain are in working order, soon after the hydrant is closed it will be entirely dry below the valve, free from water, and nothing to freeze.
The test, therefore, of a hydrant not being frozen is the fact of the drip being in good working order and the working of the valve. If the valve opens and closes the hydrant is no frozen, and if the water does not respond to the opening of the valve the stoppage is in the main ; that, then is frozen; not the hydrant.
The practice in Little Falls has always been to inspect the hydrants in the spring and fall and see if the drips are in working order, the hydrants dry and the valves in order, and not to open or molest them from fall to spring, for the reason that after winter sets in the water fails to run away in the surtounding ground from the tile drain quickly, due to several reasons, the ground or sub soil is always fairly full of water, and frost prevents rapid drainage. If the hydrants arc frequently inspected, opened and tried during the winter, the drip may become gorged with water, raises the water above and freeze the valve solid, rendering it almost impossible to again get the hydrant in working order during the winter.
The other difficulty is the freezing of the main. It is a self evident proposition that to prevent the mains from freezing they must be placed below the frost line. The depth at which water mains are laid is governed by the probable depth at which frost will penetrate and varies with the climate and each particular locality.
The mains in Little Falls are put down five feet, being at a depth below where frost had never been known to reach in this locality, even by the oldest inhabitants. The fact is the water commissioners and myself were censured by a large number of citizens for the apparent waste of money in going down so deep. It is further apparent that the lateral main leading out from the regular main is a dead end with no circulation and no possibility of creating one. In designing the Little Falls system I had this in mind and always located the hydrants as near the regular mains as possible, reducing the length of lateral to the minimum length possible. If the frost reaches down to the mains this sub-main will of necessity coat inside with ice so that if the frost remains for a long period at this depth under ground, coatings of ice will accumulate in the pipe or main, beginning first at the outer sides of the barrel of the pipe and so continuing until perhaps the main is materially contracted in area or stopped up altogether. After the process starts the work is quite rapid. This process of transferring cold from the surrounding earth is very similar to the crystaline appearance of frost we notice on exposed iron in the atmosphere, the base becoming more solid as the frost advances into the cross section of the pipe and with the main so frozen that no water will pass when the hydrant is open ; the central part is more like snow than ice, and will thaw away and present a small opening for water to flow, if the main is not frozen to solid ice when hot water is applied, providing the valve of the hydrant is open so that the hot water may have access to the ice or snowy crystals in the main. After the water is once started it will cut away the ice formation and if the water is allowed to run long enough it will enlarge the opening until finally the full capacity of the lateral main is reached.
I know of no human authority that can regulate the depth to which frost will penetrate or that is able to gauge an un. usual season or to provide for all contingencies. The past winter has been a phenomenal one, just as the recent fire in Little Kails is a phenomenal loss and damage with a waterworks capable of furnishing twenty streams at once and all under ioo pounds pressure to the square inch and for a reasonably unlimited time, but notwithstanding our calculations the unexpected is sure to happen, and yet, in view of all the inflammable material grouped together so compactly perhaps, we should wonder that the fire was ever stopped where it was. With the headway the fire had acquired at the onset neither human skill nor abundance of water could have made it much less of a fire.
Out of all the hydrants brought into use at the recent fire there was not a single one that was frozen up. In every case the valves moved freely and at once. I myself opened the hydrant at Albany and Mary streets, at the Baptist Church, some six or eight turns and no water. I knew at once that the trouble was in the main and not in the hydrant. I tried hot water, leaving the valve open, but failed. I then made up my mind it was probable there was a film of ice in the lateral mains of the hydrants then in use. I therefore hurried to the valve house and, with assistance, put on temporary heavy pressure of 140 pounds to the square inch from the hydrants in use.
The normal and constant pressure during all the progress of the fire as indicated by the Kdson self recording pressure gauge at the engineer’s office was too pounds to the square inch, except during the time that I added pressure up to 140 pounds to the square inch. In fact the regular pressure carried every day and night is too pounds to the square inch at the hydrants surrounding the fire.
Raising the pressure up to 140 pounds to the square inch was of course a risky thing to do, as perhaps the village hose might not stand the increased pressure and the increased pressure might start a break in some other portion of the water main system. It gave 180 pounds to the square inch on Mill street and all points of the same level, but the fire was so threatening that I judged it was the proper thing to do.
However, while I was absent at the pressure valve house, a most singular performance took place. A big bonfire was built around that portion above ground of the hydrant located at the Baptist Church. The person of person who buit it might just as well have built a fire in Herkimer and expected that to have started the water. But suppose he or they had succeeded in getting the hydrant red hot down to the valve The hydrant is held on in place by a lead joint. If the iron had got red hot there the lead would have melted, the hydrajjt have blown off, leaving a break or opening of six inches for the water to have run to waste. Before I could have shuT off all the several valves required to cut this hydrant out of the system at least an hour would have elapsed. All the streams on ihe lire would have ceased to have any force or pressure or been of any service, and my best judgment is that the fire would in that time, as the fire was then at its height, never have stopped till it reached Sheard’s mill.
I call particular and emphatic attention to this matter in the hopes that it may never be repeated again in Little Kalis.
Resuming the discussion, the fact is, the frost is down to the mains. At the break in the mains on the south side, which occurred Monday morning, I discovered on digging out the main that the frost was down from five feet to five feet six inches, and I suppose this holds true over the town except in some protected localities.
The mains cannot be thawed out with hot water or steam only so far as to get a thread of water through, as the instant the passage is made the cold water comes in from the supply and the good effects of steam or hot water ceases. Steam or hot water could not be forced in against the pressure of the supply unless by some apparatus capable of carrying and maintaining a heavier pressure and volume than that existing in the mains. The pipe is then only a condenser for steam. It is also impracticable to dig up all the mains in the village and get down to the laterals and thaw them out. Very respect fully,
S. E. BABCOCK, Chief Engineer.