In our perfect valve, as we outlined it,
the valve does not move after the port is closed. The exhausting
functions of the valve are very good, giving a quick opening and a
full opening, because this opening occurs when the eccentric is moving
its fastest. The engine also possesses a distinct advantage in having
remarkably small clearance spaces. The length of the steam passage is
very small in comparison with any form of engine, and having but two
ports instead of four, as in the Corliss and four valve type.
In these there must be included in the clearance, that to the exhaust
port as well as the steam port, adding a considerable amount where the
piston comes close to the head. As the engines leave the maker's hand
the engines are provided with a considerable amount of lap to give
plenty of compression, but are, of course, capable of having more
added to increase compression, or some planed off to decrease it.
One of the peculiar things about this engine is the failure to realize
anywhere near boiler pressure, noticeable in every case that has come
under my notice. The considerable lead gives it for an instant, but it
soon falls away, indicating the steam chest pressure only by a peak at
the junction of the admission and steam lines.
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