Storage of data on the loss of energy in fittings.

It has already been noted that, for practical pipes, the loss in head in the fittings is usually small compared with that in the pipe. We know that, by the nature of the Moody diagram, the order of accuracy of the figure for  will not be sufficient to justify high accuracy for data on the loss in the fittings or for any unnecessary complexity in the form of any empirical expressions we might devise. It is more important that the data should be stored in a way that fits easily into the total head equation. The most simple system is to express the loss equal to a fraction of the kinetic head, that is to write :-

        loss of head in the fitting = , where  is a coefficient and  is the velocity in the section of pipe in which the loss mainly occurs.

 

Using this system typical values are :-

the loss at entry to a pipe	figure 8-1a	k = 0.5
the loss at exit from a pipe	figure 8-1b	k = 1
the loss at a mitre bend	figure 8-1e	k = 0.5 - 0.75
the loss at a fully open gate valve	figure 8-1f	k = 0.25

 

and in each case the velocity is that in the pipe.

 

Other fittings are not treated in this simple way. The reducer fitting which is used to join pipes of different diameters may be used at an increase in diameter or at a reduction in diameter. The only difference is the direction of flow. The loss will depend on the two diameters as well as the direction of flow. The mitre bend produces a much greater loss than a bend with a large radius, that is, a swept bend and the loss will depend on the diameter of the pipe and the radius of the bend. Clearly expressions that take account of these dimensions will be desirable provided that they are not too complicated to use.