It is not the purpose of this chapter to go extensively into the subject, but to give some of the necessary principles which will be of assistance along these lines. While it is not to be expected that the average workman in the plumbing trade is or can become a skilled draughtsman, the requirements of the times certainly de-maud that the plumber, if he is to make the most of his capabilities, must have a certain practical knowledge of the subject of drawing, as applied to his own trade. It is of inestimable value to the employing plumber and to the foreman on plumbing work, to be able to show intelligibly by means of a pencil sketch, for the benefit, of workmen or customers, methods of connections, etc. Furthermore, in many cities of the country, boards of health now demand sketches of contemplated work, both on new and old construction, to be submitted before issuing a permit to perform the work. Again, in many cities, in order to secure a plumber's license, the applicant must be able to draw the connections for work as indicated by his examiners, and to be able to criticise intelligently drawings of plumbing construction of faulty nature. Journeymen plumbers' unions in many instances also require applicants for admission to pass an examination which includes the making and criticizing of plumbing drawings. These remarks will serve to show some of the reasons why ability to read and make drawings is a necessary part of the plumber's knowledge, and it may be truly stated that the necessity for such knowledge is steadily increasing.
The mechanical, architectural, and engineering draughtsman is compelled to go deeply into the subject, but the rudiments are sufficient as a foundation for the plumber, his greatest difficulty being in executing drawings neatly and in such a manner as to be readily understood.
The plumber really needs to be acquainted with only two views, these being known as the plan view and the elevation.
Experience shows that if he learns to properly distinguish between these two views, the plumber's greatest difficulty as a draughtsman will disappear, and that if he does not thoroughly master this principle, his drawings will in all probability be a confusion of plan and elevation, which it will often be impossible for another person to understand. A perspective view of plumbing connections, which, by the way, is a very difficult drawing to make, should very rarely be used by the plumber, although there is a strong temptation to make use of it.
Every object, if it is to be shown completely by drawings, will require two views, a plan and an elevation, although in showing plumbing work, one view will often, and probably usually show the work with sufficient clearness.
A plan view is a view obtained by looking down upon the object as it stands in its natural position. Thus a cellar plan or floor plan of a house is obtained by viewing the cellar or floor from a point above it. An elevation, on the other hand, is a view obtained by standing away from the object, and looking horizontally at it. Every object such as a house, would have four elevations, front, rear, and two side elevations. For the plumber's use, however, not more than two elevations, front and side, are ever needed, and in a great many cases only one elevation is required by him. He must know what the elevation of the house is, in order to know the distance between floors, the total height, etc., in figuring the amount of piping in vertical lines of pipe. He needs the plan view equally as much, to show him the horizontal lines of piping.
It will be clear then that a full knowledge of the work can be obtained only by means of at least one elevation, and the several plan views of the cellar and floors, and in estimating work, these drawings are always necessary. On the other hand, very often an elevation or a plan, as the case may be, will be sufficient. For instance, in showing the principles of certain work by means of a drawing, very often an elevation will show all that is necessary.
The idea of plan and elevation may be seen by reference to Fig. 335.
The first is a perspective view of a piece of pipe, and the other two views are the plan and elevation of the same piece of pipe.
The perspective view gives as much information concerning the object as the plan and elevation combined, that is, it shows the length, shows that it is cylindrical, and also the inside and outside diameters. On the other hand, the elevation shows only length and width, and gives no idea as to whether the object is square or round. In connection with the elevation, the plan is necessary in order to show that the object is cylindrical instead of square, and that it is a hollow cylinder and not solid. It may be asked, since the perspective in one view gives the entire information, while in the mechanical drawing two views are needed, why it is not better to use perspective views.
Fig. 335. - Perspective and Mechanical Views of an Object.
In the first place, it is very much more difficult and takes more time to make the perspective view of this piece of pipe than to make the two mechanical views. In the second place, in making a perspective view of a complicated system of piping and fixtures, the task would become so much more difficult than the making of the mechanical views, that the person not well versed in such work could not expect to do otherwise than produce a drawing which would be utterly impossible to understand.
Regarding the plan and elevation, it may be stated that if the pipe of Fig. 335 had been a square pipe, the elevation would not have been different, but the plan would have been a hollow square, rather than the circular view shown.