Page 32 – Shaft Seal
So
far, this book has been largely about maximising the power output
of the engine.
There
are two other major concerns.
Not losing, or wasting power
anywhere between the engine and the propeller.
Choosing
a hull shape that slides through the water as easily as
possible.
The
first place engine power can be lost, is the point where the shaft
exits the crankcase.
A
pressurised engine needs a seal between the rotating shaft and the
crankcase wall to
retain
the helium gas.
Rotating
shaft seals are nothing new to the engineering world.
Unfortunately the “off the shelf” units are for
the world of far higher power levels
and they can
accommodate far higher levels of friction.
Rather
like the piston ring, the Stirling engineer needs something with
lighter friction.
The
result is shown opposite
An
“O” ring is pinched between the shaft and a cone
shaped housing by a screw cap.
The holder (purple) for the shaft “O”ring has another “O” ring. This static “O” ring prevents
leakage through the screw thread between the purple piece and the pink housing.
The
degree of grip (friction) can be adjusted to just the level
needed.
