This type of piston is used in conjunction with a crosshead which takes the
side thrust generated by a crank and con rod mechanism. The familier type
used in most IC engines is called a trunk piston and combines the two roles,
with the extended skirt taking the side thrust.
at the sale I posted about recently, I had the opportunity to look at the first
steam piston I've seen. It was
basically a thick disc of metal with ring grooves. It was a piston, but with no
skirt, so quite different in appearance
to the pistons I usually see.
Now for a display of conspicuous ignorance:
Do most steam engines have this sort of piston?
This leads me to the questions, why do IC engines have piston skirts?
Did early IC engines have skirtless pistons?
i think it's because most steam engines are double acting....they use the
piston in both directions. therefore there needs
to be a packing on the rod end.
they use a 'scotch yoke' (not sure what the uk may call it) to terminate
the connecting rod,
so the piston doesn't rock as an internal combustion engine may.
does this help? my best, sammm
IC engines invariably run at higher speeds and combustion pressures than
those employing hot fog to push them around. The skirt is certainly there to
resist side thrust caused by the varying angle of attack from the
crankpin/connecting rod, but is important in providing somewhere to put
extra rings in the bottom of the skirt.
Radial engines had very short skirt pistons, very little longer than the
gudgeon pin bosses required. I often wondered why.
In answer to my own question -
"Pistons used to have long tail skirts (which sometimes cracked or broke
off). Now most pistons have ?mini-skirts.? Instead of a 2.5? skirt length,
the piston may only have 1.5? skirt. Shorter skirts reduce weight but also
require a tighter fit between the piston and cylinder bore to minimize
piston rocking and noise. Consequently, today?s piston clearances are much
less than before (typically .001? to .0005? or less). Some have a zero
clearance fit or even a slight interference fit (made possible by special
low friction coatings)."
I did know that Bristols were renowned for the close tolerances they
maintained on piston manufacture, so that is probably the best answer ;o))
Thanks Martin, very interesting.