Page 40The Kill Tap and Speed Control

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Over the two hundred years since the invention of the Stirling engine, there have been
many and various methods developed to vary the speed of the engine.

Some of them rather complicated.

Philips installed a Stirling in a 25ft cabin cruiser called “Jan de Witt”.
There is even a You Tube
video of it. (Wait till minute 3:22)
It's part 2 of a long video – part one is also very well worth watching
Their method was to vent the pressurised helium to a reservoir and then pump it back to
the engine when required.

It clearly worked, but I would class it as an “engineer’s solution” which involved
“ever more complicated engineering”.

The UK Stirling group have developed a far simpler method.

A pipe, with tap, is used to connect the gas above the piston with the gas below the piston.

When the tap is partially opened, the high pressure which would otherwise be used to push
the piston, is allowed to escape to the crank case. The pressure on the piston is reduced.
The power and speed of the engine is reduced.

When the tap is closed, power is restored immediately.
No need for a pump to rebuild the pressure.

When the tap is fully opened, the pressure above and below the piston is equalised.
There is no force on the piston. The engine stops.

For fine control of the engine speed, a needle valve is needed.