This section is from the book "Plumbing Problems", by The Sanitary Engineer. Also available from Amazon: Plumbing Problems, or Questions, Answers and Descriptions Relating to House Drainage and Plumbing.
It frequently happens that the kitchen-boiler must be connected with two or more ranges. Sometimes the reason is that the water-back in a laundry-range must be connected with it for the purpose of getting more hot water on washing days, and again it frequently happens that a winter kitchen is on the first floor of a house, and that the summer kitchen is in an extension or in a basement. This sometimes happens and admits of several combinations. Sometimes they are a matter of choice, but more often of necessity.
When one range is in an upper room above another range in a room below, the diagrams a, b, c, and d illustrate the principles involved in the forms usually met with.
Diagram a is used when a boiler is provided with two side couplings and two bottom couplings, one set for each range. This requires just a little forethought and the knowledge that two water-backs are to be used. The increase in cost is inconsiderable, and it permits of entirely separate connections, which can in no way interfere with each other by influencing the flow of the water in either. From the lower water-back the flow of water will be more rapid than from the upper one, assuming they are alike in size and construction. The reason for this is that the up-take or flow-pipe and its return-pipe is so much longer, perpendicularly, than the same pipes from the upper water-back, that there is a greater relative difference of weight between the up-take and its corresponding return, that this difference increases with the increased lengths of the pipes, but in a very much inversed ratio, but still considerable and very marked to an observing plumber.
This (a) presumably is the most suitable connection for double ranges, but under one condition, at least, an objection has been made to it. It is claimed that should the lower range be in a cold or exposed place, and no fire in it, the water in the water-back and in the pipes leading to and from it will be inert - that is, have no circulation - and that they may freeze. This presumption is reasonable. and a method of securing a circulation from the boiler through them sufficient to prevent freezing is something for thoughtful plumbers to take into consideration.
Figure 116.
In the case of the upper water-back and pipes freezing when the lower one is in use, the danger is not so great. The heat of the boiler is generally sufficient to warm the room beyond the danger of frost, and should the dampers of the stove be closed, so as to prevent a strong draught over the water-back, the danger is reduced to a minimum.
Diagram b shows the method generally followed when there is but one set of couplings on the lower part of the boiler. It is claimed by some that with this arrangement of pipes the water in neither back can freeze so long as one of the ranges is in use. It is claimed, for instance, that should the upper range be in use, the hot water flowing from the back into the boiler will draw the water from the lower back by induction, as it passes over it, thus keeping up a circulation through it from the return-pipe. However, this may be questioned. Of course, one can imagine how the stream of warm water from the upper range flowing over the end of the up-take pipe from the lower one may draw water out of it; but if we look a little further we will also see how the return-current to the water-back in the upper range will also be trying to draw water from the return - pipe to the lower water-back by the very same inductive principle which is applied to the other pipe, and that they may be assumed to balance each other and make abortive any claim that can be put forth for the principle. However, it may be that some accident of construction - some peculiarity of the making of a joint in lead pipe, for instance - may make one of the joints at their junctions a more favorable injector, if we may use the word, than the other, and that by this means the water will move in some one direction, which is just as likely to be drawn up through the return-pipe and into the water-back as passing up through the flow-pipe and into the boiler. As said, in lead pipe this can be assumed as likely to happen, but with brass or iron pipe the conditions of the junctions will be always the same, and positive circulation in the lower water-back without fire cannot be assured.
Diagram d shows a method with which there is some hope of getting a positive circulation of the water through the lower back when the fire is out. It will be noticed that the flow-pipe from the upper back enters the flow-pipe from the lower one some distance below the side coupling of the boiler, and that there are two bottom couplings. The fact of there being two separate return-connections produces the result that there can be no inductive influence from one to the other on the return-flow in either. But, again, the fact of the upper flow-pipe joining the lower one at the level of the upper back makes it reasonable to assume that here an inductive influence may be at work. If instead, as in the diagram (d), the flow-pipe from the lower back entered the flow-pipe from the upper one, as in diagram b, there would appear to be no doubt of an induced circulation through the lower back. As d is now drawn, it is the most favorable for the inducing of a current through the upper back, if the lower range be in operation and the upper one cold.
Figure 117.
Diagram c is a method which is claimed to be positive. The water is passed through the lower back first, then through the upper one, and into the boiler. When the lower range is in use this cannot be other than a positive method. On the other hand, when the upper range only is in use, there is reason to believe this method will not circulate freely under all conditions, and that at its best it will not do as well as separate or branched connections.
 
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