This engine, shown in Fig. 95, is built in practically the same design by several of the best builders, and is not, as far as I know, recommended particularly by any of. them. I shall not, therefore, do any injustice to any of these builders when I say that in my judgment this is the poorest type of blowing engine in regular use to-day. A certain measure of accessibility is obtained by the fact that it has no tandem cylinders, but it requires a considerable amount of space, a much larger foundation than a long cross-head engine of the same capacity, and an equal if not greater height, while its running parts are very inaccessible for handling with a crane.

Fig. 05. Vertical quarter crank blowing engine, 42-in. steam, 84 air x 60 stroke.

The principal objection, to it, however, is that it has two complete sets of running gear with their high first cost and maintenance, and that all the energy developed in the steam cylinder has to be transmitted through running parts into the crank-shaft and then from the crank-shaft through another set of running parts into the air cylinder. Taking the mechanical efficiency of a standard steam engine at 90 per cent. and the mechanical efficiency of a crank-driven compressor at the same, we have an efficiency for this engine of 81 per cent. as against 91 to 93 per cent. that may be and is secured in regular practice with the tandem-connected machine.

Fig. 96. Horizontal-vertical cross-compound, 52 in. and 90 in. steam, 90 in. and 90 in. air x 60 stroke blowing engine the Wm. Tod Co.

It is well to remember that this 19 per cent. of friction loss as against 8 per cent. in the other case, represents not only a loss of power but an expenditure of energy for destructive purposes which must reappear in the form of wear of two sets of heavily stressed running gear instead of one set lightly stressed.

This can, in my judgment, mean in the long run only one thing, high maintenance and repair cost, which, coupled to the high first cost of this type of engine with the consequent high fixed charges, all tend to make this an undesirable type from the technical, operating and financial points of view.