Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/9



CHAPTER I.

turbines may be divided into two classes: the impulse or action type, in which a jet of steam or fluid at high velocity impinges on a number of vanes or paddles fixed around the rim of a wheel free to rotate, and the reaction type, more generally known as Hero's Engine or Barker's mill.

Both these types are pretty familiar to us from our childhood's days, in the windows of the toyshop, and no doubt in many cases (the writer's also) formed our first steam model. They are illustrated in figs. 1 and 2, and frequently appear in patent specifications, though, of course, with considerable modification.

In order that the principles on which these machines are designed and for which they depend on their action may be thoroughly understood, the following elementary mechanical considerations are necessary.

A body has both mass and weight. The weight of 5