Probably there is no branch of the plumbing industry which constantly presents more difficult situations than hot-water supply and circulation, and the consideration of some of these problems, with the methods applied in their solution, should prove of interest and value.
The matter of expansion for range boilers introduces problems which are sometimes difficult to solve. Under some conditions, for instance, hot water from the boiler will back into the cold-water pipe supplying the boiler, in which event there is great danger of damage to the meter. In overcoming this trouble, recourse has often been made to the use of a check valve on the supply pipe, the action of which would be to prevent expansion of the boiler in this direction. Expansion back into the water mains is the natural and necessary outlet for excessive pressure in direct pressure boilers, and if such a path is not provided, a water front explosion is the common result. The use of check valves in this way is by no means uncommon among careless or ignorant workmen, and the results are often disastrous both to life and to property.
Plate LVIII. Special Problems And Devices In Hot-Water Supply
Special Problems Plate 58.
in Hot Water Supply
Fig. A. To Prevent Backing of Hot Water info Meters.
Fig. C. Detail of Non-by-pass Tee.
If such a course is to be followed, it becomes necessary to use a safety valve in connection with the check valve, although this does not absolutely insure against bad results, as the safety valve may be defective, or may stick and refuse to operate. Under these conditions, the method presented in Fig. A, Plate 58, will be found very useful. It consists in the use of a by-pass around the meter, with two check valves closing in opposite directions, one on the by-pass and the other on the house supply. The latter serves to prevent expansion into the meter, and the check valve on the by-pass prevents any flow to the house through it, but allows expansion to take place back into the water main.
It will be seen that this arrangement allows all water to pass through the meter, while removing the danger to it of damage from a back flow from the boiler.
In the case of boilers supplied from an attic tank, there is no chance of this damage to meters, because of the different nature of the supply connections.
In Fig. B, Plate 58, is shown a method that will be found very effective in thawing frozen service pipes, and also in preventing freezing. As shown, the plan is to encase the service pipe in a second pipe, closing the opening of each end of the casing by a lock-nut working on a running thread, and closing against a packing.
At either end of the casing a tee is used. Into the outer tee a pipe of small size is connected, one branch rising through the street box, and another passing into the cellar through the foundation. By means of steam or hot water, entering through either branch, the pipe may be thawed whenever it freezes, or it may be kept from freezing. The casing is drained through the inner tee, just inside the foundation, and should point downward.
Another problem concerns the trouble experienced in the by-passing under certain conditions, of gas-water-heater connections made into the top of the boiler. In this by-passing, which is not due to the heater itself, cold water draws in and mixes with the hot water at the point where the ordinary tee connection is made. This trouble is overcome by the use of a fitting known as a non-by-pass tee, which is illustrated in cross section by Fig. C, Plate 58. Fig. D shows the fitting connected to a rising line of hot water, and Fig. E to a horizontal line.
Mixing of cold water with hot water may also occur from other causes. For instance, it sometimes happens that the boiler tube is carelessly omitted, or has become so corroded that it breaks off. Either of these things will allow cold water to enter the top of the boiler, and cause either cold or lukewarm water to be drawn at the fixtures.
Another subject not generally well understood is the matter of air-lock on hot-water piping.
Air-lock often prevents flow of hot water to fixtures, and it will generally be found that when such a state exists, it is in connection with a system which has a very low pressure.
If the air pressure is greater than the water pressure, air-lock results, but if the water pressure is the greater, the air-lock will be overcome. The trouble seldom occurs in the case of direct pressure supplies, owing to the fact that they generally are under sufficient pressure to overcome the air. The pressure required to do this amounts to about one pound for each two feet of vertical air-lock, and if there is a back pressure, the amount of it would have to be added. It is a common practice to turn down from the top of the boiler with the hot-water pipe, and it is at the point where the turn is made that air-lock occurs. This can be overcome in the case of the tank-supply system, by taking an expansion pipe from this point, up to and over the tank.
It may also be done by taking a branch supply to some fixture above, from this high point.
Under certain conditions it may sometimes be very convenient to reduce the size of a range boiler without making a change in boilers. This may be done effectively by taking the cold-water connection to the water front out of the side opening of the boiler, instead of from the bottom, and connecting the range flow-pipe at the top. This method has the effect of reducing the size of the boiler to that part of it which is above the side opening. Such a reduction in size might often be of advantage during the warm months, when only the gas water-heater is in use, and economy in the use of gas becomes a matter of importance.
The cold-water connection to the water front, from the side opening of the boiler, as mentioned above, is a good one for another reason. It is preferable to the common connection from the bottom of the boiler, for the reason that when the water is taken from this part of the boiler, it is free of rust and sediment, and in the use of gas water-heaters, this is of special importance, as the presence of sediment will, after-a time, fill the coils and destroy the effectiveness of the heater.