This engine requires small foundation and small space for a unit of given size, the vertical height required being about the same as that of any other type of engine with reciprocating parts in the vertical plane except the vertical tandem, or steeple type, which is much higher. The stresses in these engines are, of course, transmitted with great directness from one piston to the other, and through rigid parts, but there is a prejudice on the part of some engine builders against running these engines at a speed which would bring the inertia effect of their reciprocating parts up to the best point for smooth running and low wear. The exact reason for this disinclination I have never been able to discover, and it is only fair to state that it does not hold with all builders, some of whom build engines of this type to run up to seventy or seventy-five revolutions.

There is no doubt that when run at proper speeds and when built sufficiently strong to withstand vibration, this is a useful, reasonably inexpensive and satisfactory type of engine, capable of giving reliable service for long periods at a stretch, such as is needed in blastfurnace work.

It is, of course, open to the objection which exists with all vertical engines, that supervision, inspection and repairs are much more difficult and expensive than they are with horizontal engines.

The Steeple Type Or Vertical Tandem Cross-Compound

A design of this type of engine built by the Southwark Machine Company is shown in Fig. 97, while nearly all of the prominent builders build this type of engine on demand; the design of valve gear, etc., being different with the different builders, but the general type of construction being the same.

The great objection to this type of engine is its great height with the consequent difficulty of securing adequate inspection and care, and its liability to vibration owing to its height and the elasticity of its small base. It will be seen in the illustration that there are four platforms above the main floor, all of which must be frequently visited for adequate inspection and care of the engine.

It is not to be denied either that these engines are exceedingly difficult of repair. Even where a crane is available, as it should always be in a modern blowing-engine house, there are many parts which it is impossible to reach with the crane without great difficulty, so that this virtually involves partly dismounting the engine for certain repairs. With the limited room available for this work on the platforms it can only be done at a disadvantage, and as a consequence repairs on engines of this type are more difficult, slower, and more expensive than they are on a horizontal engine of the same size.

Fig. 97. Southwark steeple blowing engine-quarter crank compound.

In regard to speed, the engine stands on a relatively small foundation and with its great height excessive vibration is likely to be set up even at very moderate speeds, and this type of engine therefore cannot in general obtain those advantages of high speed which are available to some other types, with consequent loss of efficiency from not having the most desirable resultant diagram of steam, air, and inertia pressures.