Where it is necessary to join together two lines of piping, so that the flow of liquid or gas passing through the pipe may be interfered with as little as possible, it is a good plan to make a connecting pipe of the form shown in Fig. 18. This shape of bend gives no abrupt break in the pipe, and maintains the full cross-sectional area throughout its length.

It is most important that the exact shape of the bend should first be set out. This can be done by setting down the distance between the lines of pipes and the length of the bend (18 in. and 30 in. respectively in this case), thus obtaining the points A A. The line A A is now divided into four equal parts, and perpendiculars drawn through the end division points, D D, to meet A C in C. This gives the centres for the curves. If a line, C C, be now drawn, this will determine the points where the two curves of the pipe outline should join together. Each half of the bend is now divided into a convenient number of segments (in this case, four), and the pattern Fig 18 for one segment set out, as explained in connection with Fig. 16.

If for the sake of appearance it is required to run the seams in a line, or to alternate the longitudinal seams, then two patterns will be necessary, one giving the seam on the outer curve, and the other on the inner curve.

In jointing up pipes of this description, some care should be exercised, so as to get the bend without twist, and to the exact shape.