Gear Driven Pump - Some
makes of engine were equipped with a displacement pump that were driven
by a gear mounted on the crankshaft, so that the pump operated whenever
the engine rolled over. The geared pump was thought by some to be
better than a crosshead pump in that it could be geared down to a
more advantageous speed, could be made double-acting (thus smoothing
out the pressure surges), and was nearly impossible to get out of
The pump is actually two displacement pumps
that share common inlet and discharge chambers. As the ram works back
and forth in the cylinders, the check valves alternately open and
close, pulling the water from the inlet chamber and forcing it into
the discharge chamber, and thence into the boiler. The discharge line
has a tee in it, with a bypass valve regulating how much water may
pass back into the tank. Closing the valve forces all the water into
the boiler, opening it allows all of the water to return to the tank.
It is considered best to run with an intermediate setting, ideally
one that introduces exactly as much water as the engine is using.
Given the pressures in use, this can be as little as 1/8 of a turn
Like many things on a steamer, the geared
pump is too simple to not work. Barring leaky plumbing and dry tanks,
about the only way they fail is by getting pieces of foreign matter
into the check valves, allowing the water in the cylinder to pass
back into the inlet chamber. You do want to be sure that the line
to the boiler is equipped with a functioning pressure relief valve,
though. If the boiler inlet valve is left closed, the geared pump
is capable of generating hundreds of pounds of pressure, and something
is guaranteed to fail before the load stops the engine. Most often,
the pressure dome on top of the pump ruptures, tossing bits of metal
around, and making a small replica of Old Faithful.
The output of a geared pump is often routed
through a feedwater heater, which transfers some of the heat energy
of the exhaust steam to the incoming water, improving economy and
making the feedwater less likely to cool the boiler.