The hot cap and its fins are
the source of the energy for the hot gas inside the engine.
piston is the device that captures that energy and transmits it to
To do so, it must be gas tight and have low
World wide there are billions of pistons in
internal combustion engines.
Surely, the Stirling engineer
can pick and choose from all this proven technology?
the internal combustion (IC) engine piston has far too much friction.
generated by the diesel or petrol engine is colossal. Multiple
piston rings can
be needed to stop the gas from seeping past
the piston. And they must grip the cylinder walls
with friction – to stay gas tight.
differential between top and bottom of the Stirling piston is
hundreds of times smaller than in the IC engine. In the UK
Stirling boats, various solutions have been found.
all work, but some call on specialist skills or materials.
I suggest is that, out of simplicity, we should use proven
technology from yesteryear.
Something like 20,000 Ericsson and Rider Stirling engines were made in the late 1800s.
And a few are still working 150 years later.
They use a
Take a trip to the UK Hereford Water
Works museum. They have two 6ft high Rider engines.
called Hayward Tyler engines because they were made under license
in the UK.
These are workhorses. They were used all day
long, every day. The leather seal works.
We use them
successfully in the boat engines.
The beauty of a leather seal
is that it accommodates imperfect pistons and cylinders.
precision is needed to make perfectly round, matching pistons and
In private workshops, this can be achieved –
but leather makes up for any discrepancy.
How is a
leather cup seal made?
Buy an offcut from a leather
goods market stall trader. Medium thickness.
disc, say 20mm larger than the piston diameter.
the leather in water. It becomes flexible.
Make a mould
to the size of the piston and cut a groove around the top.
groove needs to be say 5 mm from the top.
wet leather over the mould and over the sides, across the
Twist grip a wire around the groove to hold the
leather to shape.
Pull the leather skirt to remove
Leave the leather to dry out overnight.
around the clamping wire to reveal a circular cup seal.
the cup seal with a light oil and make the leather flexible.
a centre hole to allow a bolt to fix the seal to the top of the
Hold the seal down onto the piston with a
washer just smaller than the piston.
This supports the upturn
of the cup seal when in use in the engine.