Figs. 2,727 and 2,728.—Method of preventing vibration and of supporting pipes. The figures show top and side views of a main header carried in suitable frames fitted with adjustable roller. While the pipe is illustrated as resting on the adjustable rollers, nevertheless the rollers may also be placed at the sides or on top of the pipe to prevent vibration, or in cases where the thrust from a horizontal or vertical branch has to be provided for. This arrangement will take care of the vibration without in any way preventing the free expansion and contraction of the pipe.
Ques. How should the switchboard be located?
Ans. In [fig. 2,720], the switchboard H is mounted against the wall dividing the room A from the room B, and is in line with the machines.
The advantages arising from a switchboard thus installed are, that the switchboard attendant working thereon can obtain at any time an unobstructed view of the performance of each individual machine, and he has in consequence a much better control of them; then, too, while he is engaged at the engines or generators he can also see the measuring instruments on the switchboard, and ascertain approximately the readings upon them.
In cases of emergency it is sometimes necessary for the engineer in charge of a plant to be in several places at the same time in order to prevent an accident, and that this seemingly impossibility may be approximated as nearly as possible, it is essential that the controlling devices be located as closely together as is consistent, and that no moving belt or pulley intervene between them.
These conditions are well satisfied in [fig. 2,720], and owing to the short distances between the generators and the switchboard the drop of voltage in each of the conducting wires between them will be low.
This latter advantage is worthy of notice in a station generating large currents at a low pressure. To offset the advantages just mentioned, the location of the switchboard in line with the machines introduces an element of danger to the switchboard, its apparatus, and the attendant, on account of the possible bursting of a flywheel or other parts of the machines from centrifugal force.
Figs. 2,729 and 2,730.—Points on placing stop valves. The first and most important feature is to ascertain whether the valve will act as a water trap for condensed steam. Fig. 2,729 illustrates a common error in the placing of valves, as this arrangement permits of an accumulation of condensed steam above the valve when closed, and should the engineer be careless and open the valve suddenly, serious results might follow owing to water-hammer. Fig. 2,730 illustrates the correct method of placing the valve. It sometimes occurs, however, that it is not convenient to place the valve as shown in fig. 2,730 and that fig. 2,729 is the only manner in which the valve can be placed. In such cases, the valve should have a drain, and this drain should always be opened before the large valve is opened.